COVER CROP INFLUENCE ON NITROGEN AVAILABILITY, WEED DYNAMICS, AND DRY BEAN (Phaseolus vulgaris L.) CHARACTERISTICS IN AN ORGANIC SYSTEM By Erin Christene Hill A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Crop and Soil Sciences- Doctor of Philosophy 2014   ABSTRACT COVER CROP INFLUENCE ON NITROGEN AVAILABILITY, WEED DYNAMICS, AND DRY BEAN (Phaseolus vulgaris L.) CHARACTERISTICS IN AN ORGANIC SYSTEM By Erin Christene Hill Michigan is the number one producer of organic dry beans in the United States. Commercial pesticides and fertilizers cannot be used in organic systems, therefore it is essential to maximize the potential benefits of cover crops for increasing nutrient availability, weed control, and crop yields. Field experiments were conducted from 2011 to 2013 on Michigan State University research farms (main sites) and at organic grower cooperator farms (satellite sites) to determine the impact of cover crop species on dry bean production, including weed management and nitrogen (N) availability. Cover crops included: medium red clover, oilseed radish, and cereal rye; a no cover control was also included. Within each cover crop treatment there were four bean varieties: ‘Zorro’ and ‘Black Velvet’ black beans and ‘Vista’ and ‘R-99’ (non-nodulating) navy beans. Overall, the commercial dry bean varieties responded to the cover crops similarly and showed few differences among varieties with regard to nodulation, percent N derived from the atmosphere in the grain, grain total N, and yield. The non-nodulating variety ‘R-99’ had less total grain N and yield, showing the benefit of N fixation. Cover crops altered some soil, dry bean, and weed characteristics. Soil inorganic N increased following red clover by as much 34 kg N ha-1 at planting and 55 kg N ha-1 at V2 compared with the no cover crop control; yield was not increased but grain N increased by up to 32% in some site-years. Cereal rye reduced soil inorganic N in some instances and caused early maturity of the beans in two of six site-years. At maximum biomass production (12.8 Mg ha-1), cereal rye reduced dry bean yield, however grain   N was not affected. Oilseed radish occasionally increased inorganic N availability at the V2 dry bean stage, but had no impact on bean maturity, yield, or grain N. Oilseed radish and cereal rye did not impact weed populations or biomass during the dry bean growing season. However, when clover biomass exceeded 5 Mg ha-1, soil inorganic nitrogen was often higher compared with the no cover crop control, which occasionally resulted in increased weed populations and biomass. Weed responses appeared to also be dependent upon fall seed inputs while the cover crop was growing, precipitation during cover crop establishment and the dry bean growing season, and weed seed bank composition. High concentrations of cereal rye residues, with a high C:N ratio, increased giant foxtail and velvetleaf seed persistence by 12 and 6%, respectively, compared with the no cover crop control in one of two years. Red clover, with a low C:N ratio, decreased common lambsquarters seed persistence by 25% in one of two years. Understanding how the C:N ratio and N content of cover crops change during development and impact N release and N cycling after cover crop termination will improve the synchronization of N availability with cash crop needs, improve weed management, and potentially increase crop yield and quality. Enhancing the predictability of cover crop performance and nutrient availability through management recommendations and breeding will encourage cover crop use among growers.     Dedicated to the light of my life, my son Jonah iv   ACKNOWLEDGEMENTS Over the winding course of time it has taken the support of many people to help me complete this degree. First and foremost I would like to thank my major professors, Drs. Christy Sprague and Karen Renner. It is hard to quantify just how much I have learned from you both over the past several years, but I hope that I can live up to the examples you have set for me. Thank you also to Drs. Jim Kelly and Dan Brainard who have always been available to discuss my research both in the office and in the field. Teamwork is what keeps the weed science program at MSU going strong and without the help of our dedicated team this research would not have been possible. Thank you to Gary Powell, a co-worker and friend, who has taught me invaluable lessons about field research; always with a side of laughter. It has been an adventure and a pleasure working with several great graduate students, including: Ryan Holmes, Alicia Spangler, David Powell, Amanda Harden, Victoria Ackroyd, Amanda Goffnett, and Jon Kohrt; thank you all. And last, but certainly not least, I need to thank our army of hard-working undergraduate students (which I lovingly refer to as ‘Minions’): Dave Reif, Mark Dingee, Megan Tomlin, Canton Brissette, Meghan Bonthuis, Amanda Anderson, Dave Houghtaling, Heather, Van Lieu, Cody Tyrrell, Chris Bauer, Chelsey Bonthuis, Matt Reau, Kalvin Canfield, R.J. Lee, Taylor Truckey, Kelly White, Connor Hubbard, and Morgan Cnudde. A project like this, where we grew cover crops and dry beans in as many as 11 locations each summer also required a lot of outside assistance. Thank you to Todd Martin, Dale Mutch, Dean Baas, and Joe Simmons for helping with all things cover crops and for your support at the Kellogg Biological Station. Thank you to Brian Graff, Bill Chase, Gary Zehr, Tom Galecka, and Gary Winchell for all of your assistance at the MSU farms. I am also grateful for the opportunity to collaborate with several organic dry bean producers from around Michigan, including: Richard Stuckey, Mark and Steven Vollmar, Eric Houthhoofd, Kurt Cobb, Don Brockriede, Tom Nelson, Michael and Jon Findlay, and Steve Reinbold. Thank you for providing your expertise. Thank you to Dan Rossman for his help in coordinating the on-farm research. Finally, the glue that holds me together is my family, friends, and my fiancée Roberto. Thank you for all of your love and support over the past 5 years; this and so many things in my life would not be possible without all of you. v   TABLE OF CONTENTS LIST OF TABLES ......................................................................................................................... ix LIST OF FIGURES ....................................................................................................................... xi CHAPTER 1 LITERATURE REVIEW ................................................................................................................1 Worldwide Dry Bean Production and Use Overview ..........................................................1 Growth Habits and Market Classes......................................................................................1 Production Practices in Michigan ........................................................................................2 Nutrient management ...............................................................................................4 Pest management- Insects ........................................................................................4 Pest management- Pathogens ...................................................................................6 Pest management- Weeds ........................................................................................8 Organic Dry Bean Production in the United States .............................................................9 Organic pest management ......................................................................................10 Organic nutrient management ................................................................................11 Cover Crop Overview ........................................................................................................12 Cover crops influence soil composition and structure ...........................................13 Cover crops alter soil moisture ..............................................................................13 Cover crops retain and add nutrients .....................................................................14 Cover crops influence soil biology ........................................................................15 Cover crops alter pest dynamics- Diseases and insects .........................................16 Cover crops alter pest dynamics- Weeds ...............................................................17 Cover Crops for Use in Michigan Dry Bean Systems .......................................................18 Medium red clover .................................................................................................19 Cereal rye ...............................................................................................................21 Oilseed radish.........................................................................................................23 APPENDICES ...................................................................................................................26 APPENDIX A- CHAPTER 1 TABLE ..................................................................27 APPENDIX B- METHODS OF STUDYING NITROGEN FIXATION AND MEASURING SOIL INORGANIC NITROGEN .................................................28 LITERATURE CITED ......................................................................................................35 CHAPTER 2 COVER CROP IMPACT ON NITROGEN AVAILABILITY AND DRY BEAN CHARACTERISTICS IN AN ORGANIC SYSTEM ...................................................................50 Abstract ..............................................................................................................................50 Introduction ........................................................................................................................52 Materials and methods .......................................................................................................56 Cover crop quantity and quality .............................................................................58 Cover crop influence on soil moisture at dry bean planting ..................................59 Cover crop influence on soil nitrogen availability .................................................59 vi   Soil extraction ............................................................................................59 Cation and anion exchange resin strips ......................................................60 Relative chlorophyll readings ....................................................................60 Dry bean variety and cover crop influence on dry bean attributes ........................61 Statistical analysis ..................................................................................................62 Results and Discussion ......................................................................................................63 Cover crop quantity and quality .............................................................................63 Biomass ......................................................................................................63 Winter weed biomass .................................................................................65 Nitrogen content.........................................................................................66 C:N ratios ...................................................................................................67 Cover crop influence on soil moisture at dry bean planting ..................................68 Cover crop influence on soil nitrogen availability .................................................69 Soil extraction ............................................................................................69 Resin strips .................................................................................................73 Relative chlorophyll readings ....................................................................75 Dry bean variety and cover crop influence on dry bean attributes ........................76 Populations .................................................................................................76 Root nodules and nitrogen fixation ............................................................78 Maturity......................................................................................................79 Yield...........................................................................................................80 Grain N content ..........................................................................................82 Conclusions ........................................................................................................................82 Acknowledgements ............................................................................................................86 APPENDICES ...................................................................................................................87 APPENDIX C- CHAPTER 2 TABLES AND FIGURES .....................................88 APPENDIX D- CHAPTER 2 ANALYSIS OF VARIANCE FOR SUBPLOT VARIABLES AT THE MAIN SITES.................................................................118 LITERATURE CITED ....................................................................................................119 CHAPTER 3 COVER CROP IMPACT ON WEED DYNAMICS IN AN ORGANIC DRY BEAN SYSTEM ......................................................................................................................................129 Abstract ............................................................................................................................129 Introduction ......................................................................................................................130 Materials and Methods .....................................................................................................135 Cover crop quantity and quality ...........................................................................137 Weed seed banks ..................................................................................................138 Weed population and biomass .............................................................................139 Weed seed mortality ............................................................................................139 Statistical analysis ................................................................................................141 Results and Discussion ....................................................................................................141 Cover crop influence on weeds at cover crop termination ..................................142 Weed seed banks ..................................................................................................144 Cover crop effects on weed population and biomass after termination ...............144 Weed seed mortality ............................................................................................150 vii   Weed seed mortality over time ................................................................150 Cover crop impact on weed seed mortality..............................................152 Conclusions ......................................................................................................................153 Acknowledgements ..........................................................................................................155 APPENDICES .................................................................................................................156 APPENDIX E- CHAPTER 3 TABLES AND FIGURES ...................................157 APPENDIX F- CHAPTER 3 ANALYSIS OF VARIANCE FOR SUBPLOT VARIABLES AT THE MAIN SITES.................................................................181 APPENDIX G- WESTERN BEAN CUTWORM TRENDS IN ORGANIC DRY BEAN IN MICHIGAN FROM 2011-2013 AND POTENTIAL MANAGEMENT WITH PYGANIC® (1 YEAR) ............................................................................182 APPENDIX H- ON-FARM TRIAL REFLECTIONS 2010-2013 ......................190 LITERATURE CITED ....................................................................................................216 viii   LIST OF TABLES Table 1.01. Dry bean production in 2013 by market class with the top three producing states (data pooled from USDA-NASS 2014b). ......................................................................................27 Table 2.01. Soil composition at each main and satellite site-year. ................................................88 Table 2.02. Monthly precipitation and the 30-yr averages for the main sites, 2011 – spring 2014................................................................................................................................................90 Table 2.03. Cover crop parameters describing quantity and quality just prior to winter-kill (i.e. oilseed radish) or at termination (i.e. medium red clover and cereal rye) and soil moisture as impacted by cover crop for each main site-year from 2011 to 2013. ............................................91 Table 2.04. Correlation coefficients (R) for cover crop, soil, and dry bean parameters combined across all site-years from 2011 to 2013. ........................................................................................93 Table 2.05. Cover crop parameters describing quantity and quality just prior to winter-kill (i.e. oilseed radish) or at termination (i.e. medium red clover and cereal rye) for each satellite siteyear.................................................................................................................................................95 Table 2.06. Total soil inorganic Nitrogen available throughout the dry bean growing season at the satellite sites from 2011 to 2013. Values are based on soil extractions. ..................................98 Table 2.07. Dry bean relative chlorophyll readings, populations, yield, and nitrogen derived from the atmosphere (NDFA) via fixation as influenced by bean variety for each main site-year. .....101 Table 2.08. Dry bean relative chlorophyll readings, populations, and yield as influenced by bean variety for each satellite site-year from 2011 to 2013. ................................................................103 Table 2.09. Dry bean relative chlorophyll readings, populations, yield, and nitrogen derived from the atmosphere (NDFA) via fixation as influenced by cover crop for each main site-year from 2011 to 2013. ...............................................................................................................................106 Table 2.10. Dry bean relative chlorophyll readings, populations, and dry bean yield as influenced by cover crop for each satellite site-year from 2011 to 2013. .....................................................108 Table D.01. Analysis of variance p-values for relative chlorophyll content and dry bean parameters measured at the subplot level ...................................................................................118 Table 3.01. Cover crop planting date and field operations for cover crop termination and seed bed preparation prior to dry bean planting at the main sites. .......................................................157 ix   Table 3.02. Cover crop planting date and field operations for cover crop termination and seed bed preparation prior to dry bean planting at the satellite sites. ..................................................159 Table 3.03. Monthly precipitation and the 30-yr averages for the main sites, 2011 – spring 2014..............................................................................................................................................162 Table 3.04. Weed management operations at the main sites during the dry bean growing season from 2011 to 2013. .......................................................................................................................163 Table 3.05. Weed management operations at the satellite sites during the dry bean growing season from 2011 to 2013. ...........................................................................................................164 Table 3.06. Summary of cover crop biomass, nitrogen content, C:N ratio and influence on soil nitrogen at the main sites from 2011 to 2013. .............................................................................167 Table 3.07. Summary of cover crop biomass, nitrogen content, and influence on soil nitrogen at the satellite sites from 2011 to 2013. ...........................................................................................169 Table 3.08. Correlation coefficients (R) for cover crop, soil, and dry bean parameters combined across all site-years from 2011 to 2013. ......................................................................................172 Table 3.09. Estimates of initial germinable weed seed bank for the main and satellite sites from 2011 through 2013. ......................................................................................................................174 Table 3.10. Weed populations and biomass recorded at bean stage V2 as influenced by cover crop at the main sites from 2011 to 2013. Values are averaged over all four dry bean varieties. .......................................................................................................................................175 Table 3.11. Weed populations and biomass recorded at bean stage R1 as influenced by cover crop at the main sites from 2011 to 2013. Values are averaged over all four dry bean varieties. .......................................................................................................................................177 Table 3.12. Weed seed mortality over time for 2012 and 2013. Values are averaged across cover crop treatments (i.e. red clover, cereal rye, and no cover crop control treatments). ....................179 Table 3.13. Weed seed mortality as influenced by cover crop in 2012 and 2013. Values are averaged across all pull times (i.e. 0 to 12 months after cover crop incorporation). ...................179 Table F.01. Analysis of variance p-values for weed parameters measured at the subplot level .181 Table G.01. Western bean cutworm pheromone trap catches in Michigan organic dry bean fields from 2011-2013. ..........................................................................................................................187 x   LIST OF FIGURES Figure 2.01. Cropping sequence at the main and satellite research sites. Cover crops were interseeded into or planted following a small grain in the season preceding the dry edible bean crop. Oilseed radish winter-killed and red clover and cereal rye were terminated using primary tillage in the spring before dry bean planting. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. For interpretation of the references to color in this and all figures, the reader is referred to the electronic version of this dissertation ............................111 Figure 2.02. Total inorganic nitrogen in the top 20 cm of soil (nitrate + ammonium) as influenced by preceding cover crop for each main site-year, as measured by soil extraction. Fall samples were collected in November of the previous year while cover crops were present, all other samples times are listed in relation to dry bean stage. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. Within each sampling time different letters represent differences as determined by Fisher’s protected LSD (P ≤ 0.05); NS= not significant.....................................................................................................................................112 Figure 2.03. Total inorganic nitrogen in soil (nitrate + ammonium) as influenced by preceding cover crop for each main site-year, as measured by cation and anion exchange resin strips. The xaxis reflects weeks after dry bean planting, with dry bean stages noted below; H= harvest. Inorganic soil nitrogen units are two dimensional as they are based on the surface area of the resin strips and reflect daily exposure during the two weeks the strips were buried in the field. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. Within each sampling time different letters represent differences as determined by Fisher’s protected LSD (P ≤ 0.05); NS= not significant............................................................................113 Figure 2.04. Dry bean root nodules as influenced by preceding cover crop at V2 (2nd trifoliate, ~3 weeks after planting) and R1 (first flower, ~6 weeks after planting) combine across 2011 and 2012. Root nodules were not counted in 2013. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. Within each sampling time different letters represent differences as determined by Fisher’s protected LSD (P ≤ 0.05); NS= not significant.....................................................................................................................................114 Figure 2.05. Dry bean root nodules numbers as influenced by variety at V2 (2nd trifoliate, ~3 weeks after planting) and R1 (first flower, ~6 weeks after planting) for 2011 and 2012. Root nodules were not counted in 2013. Black Velvet and Zorro are both black bean varieties; Vista is a navy bean variety. All nodule counts were conducted on the same day at each location; V2 and R1 timings were based on the average stages for all varieties and cover crop treatments as some slight variations occasionally occurred. Within each sampling time different letters represent differences as determined by Fisher’s protected LSD (P ≤ 0.05); NS= not significant...............115 Figure 2.06. Dry bean grain nitrogen content at harvest as influenced by variety. Black Velvet and Zorro are both black bean varieties, Vista and R99 are navy bean varieties. R99 does not xi   produce nodules for nitrogen fixation. Within each site-year different letters represent differences as determined by Fisher’s protected LSD (P ≤ 0.05); NS= not significant. ................................116 Figure 2.07. Main site dry bean grain nitrogen content at harvest as influenced by the preceding cover crop. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. Within each year different letters represent differences as determined by Fisher’s protected LSD (P ≤ 0.05); NS= not significant............................................................................117 Figure 3.01. Cropping sequence at the main and satellite research sites. Cover crops were interseeded into or planted following a small grain in the season preceding the dry edible bean crop. Red clover and cereal rye were terminated using primary tillage in the spring before dry bean planting. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. ..............................................................................................................................180 Figure G.01. Western bean cutworm pheromone trap using a standard gallon milk jug with windows cut out and anti-freeze in the reservoir. ........................................................................188 Figure G.02. Black and navy bean yield responses to PyGanic® application timings. Error bars represent the standard error. .........................................................................................................188 Figure G.03. Percent of total pods harvested exhibiting damage due to feeding by western bean cutworm. Error bars represent the standard error. .......................................................................189 Figure H.01. Introductory flyer presented to potential grower cooperators at the beginning of the project; one page printed front and back......................................................................................198 Figure H.02. Methods outlined for growers and provided in their three-ring binders. ...............200 Figure H.03. Organic dry bean production systems field trial recording form, provided to growers in their annual three-ring binder.....................................................................................205 Figure H.04. Two sample postcards sent as a supplemental reminders during the season. This form of communication was received positively and helped keep field operations and data collection aligned. ........................................................................................................................215 xii   CHAPTER 1 LITERATURE REVIEW Worldwide Dry Bean Production and Use Overview Dry edible beans (Phaseolus vulgaris L.), or common beans, are one of the most widely consumed grain legumes in the world because of their wide growing range and nutrient value (Broughton et al. 2003). Dry beans can be grown in tropical, subtropical, and temperate regions of the world (Schwartz et al. 2004). Dry beans are a rich source of dietary proteins, vitamins, and minerals; with 20 to 25% of bean seed weight being protein. Beans contribute to more than 20% of the protein intake per capita in several of the world’s poorest countries, such as Burundi, Rwanda, Uganda, and Kenya (Broughton et al. 2003). The top producing dry bean countries in the world are Brazil, Mexico, and the United States of America, with production increasing in China (Akibode and Maredia 2012). Dry beans are grown in the northern regions and at higher elevations in the western region of the United States (Kelly and Cichy 2013). Dry beans produced in the western regions (approximately 40% of total production) are grown under irrigation, whereas the northern regions are largely rain fed. The top producing states based on hectares harvested in 2013 were: North Dakota (33%), Michigan (13%), and Idaho (9%) (USDA-NASS 2014a). Of the dry beans produced in the US, over one third are exported (FAOSTAT 2014). Growth Habits and Market Classes 1      Within the dry bean species there are four different growth habits, and many different market classes. The four possible growth habits of dry beans include:  Type I- determinate, bush habit  Type II- upright, indeterminate, short vine habit  Type III- prostrate, indeterminate, semi-vine type habit  Type IV- climbers, indeterminate vine In North America, the commercially grown varieties all fall into the type I, II, or II (Singh 1982). Both large and small seeded beans are grown within the US. In 2013, production of pinto, navy/white, black, and great northern bean ranked the highest based on hectares harvested (USDA-NASS 2014b). Often regions specialize in the production of certain market classes (Table 1.01). Michigan is the 2nd highest producer of navy bean and the 1st highest producer of black beans in the country. Type II navy beans were originally derived from black beans using chemical mutagenesis, and therefore these two classes of dry beans are both genetically and architecturally very similar (Prakken 1934, Kelly 2001), resulting in similar production practices. Production Practices in Michigan Dry beans are a short-season crop, with maturity being reached typically within or before 100 days after planting. Michigan typically receives 84 cm of rainfall annually in the dry bean growing region (26 year average for Caro, MI State Climatologist Office 2014). Forty-three cm of that precipitation comes between June and October, the typical growing season for dry beans, 2      and therefore the majority of dry bean production in the state is not irrigated. During this time period, typical temperatures range from 10 C (low in October) to 28 C (high in July). Row spacing varies based on production equipment and typically ranges from 35 to 76 cm. Larger space between the planted rows historically allowed for weed control via cultivation and also accommodated a two-pass harvest system, in which plants were first windrowed and then harvested with a pick up head on a combine (Holmes 2012). Advancements in herbicides available for season-long weed control, newer varieties that are more upright and narrow, and a movement towards direct harvest (one-pass) have resulted in more producers moving to narrower row widths, with most now between 35 and 55 cm (Kelly and Cichy 2013). Planting populations are dependent on market class, with navy and black bean populations targeting 262,000 seeds ha-1 in 76 cm rows. Holmes (2012) found that varying planting populations from 196,500 to 327,000 plant ha-1 in black bean did not ultimately impact yield. Yield components responsible for the compensation were increased number of pods per plant and number of seeds per pod. In 2013, average yields for navy and black beans in Michigan were 2,400 and 2,100 kg ha-1, respectively (USDA-NASS 2014b). Michigan’s largest export market for black beans is Mexico (MI Bean Commission 2014). Other export markets for black beans and other market classes include the UK, Ireland, Italy, Spain, and Portugal. 3      Nutrient management In Michigan, maintenance amounts of potassium and phosphorus are recommended at 36 kg ha-1 K2O and 27 kg ha-1 P2O5, dependent upon soil tests (Warncke et al. 2009). It is typical for producers to apply 45 kg ha-1 of N or more at planting because N fixation can vary based on variety (Heilig 2010) and exogenous N sources are beneficial during dry bean vegetative and reproductive growth (George and Singleton 1992). Higher N rates of 54 kg ha-1 are recommended if beans are grown in narrow rows, or under irrigation (Warncke et al. 2009). Excess N is discouraged as it can create a dense canopy which can favor white mold (Sclerotinia sclerotiorum (Lib.) de Bary) and delay plant maturity. Maturity can also be delayed and yields can be reduced if soils are deficient in zinc, particularly if sugar beet is the preceding crop (Warncke et al. 2009). Fertilizers are often applied to dry beans before planting (preplant incorporated) or are placed 5 cm below the row and to the side; additional N can be applied two weeks after planting as a sidedress treatment (Warncke et al. 2009). Pest management- Insects The most common insect problems in Michigan dry beans include: potato leaf hopper (Empoasca fabae Harris), Mexican bean beetle (Epilachna varivestis Mulsant), seedcorn maggot (Delia platura Meigen) (DiFonzo 2006), and a more recent addition, western bean cutworm (Striacosta albicosta, Smith) (DiFonzo 2010a). Potato leaf hopper (PLH) is the most prevalent insect problem in dry beans, moving in on storm fronts from warmer climates where it is capable of overwintering (DiFonzo 2009). PLH sucks sap out of the dry bean leaves and as a result turns them yellow, usually beginning at leaf tips; a condition which is commonly referred to as 4      “hopperburn”. Scouting PLH is important as the appearance of hopperburn may already indicate yield loss. The threshold level for PLH is 0.5 plant-1 at VC, and 1 plant-1 more for each trifoliate. Mexican bean beetle is an example of an occasional pest. The adult beetles can overwinter in Michigan in crop residue or in wooded areas nearby. Both the larvae and adults chew on dry bean leaves and under heavy infestations can result in total defoliation. The threshold for treatment is 25% foliar damage or more. There are several insecticide products registered for PLH and Mexican bean beetle control in dry bean in Michigan. Seedcorn maggot can be problematic for dry beans if there is a lot of fresh organic matter decaying in the field prior to planting or if soils are cool and wet (DiFonzo 2009). Adults lay their eggs in decaying organic matter and the maggots feed on the germinating seeds. Though seedcorn maggot can be managed through cultural practices, insecticidal seed treatments can also be used. Western bean cutworm (WBC) is a new pest to Michigan, first appearing in traps in 2006 (DiFonzo 2010a; Chludzinski 2013). WBC uses both corn and dry bean as a host plant, with corn being the preferred host. WBC can overwinter in the soil as pre-pupa. Adults emerge in July and lay their eggs on the upper leaves of corn or the underside of dry bean leaves. In dry bean, the emerging larvae feed on leaves, blossoms, pods, and developing seeds. Larval feeding can increase the percentage of defective beans, based on weight, which translates into greater cleaning costs for producers. Larval feeding can also allow for pathogen infection. In 2013, Chludzinski observed that two or more WBC egg masses per 1.5 m and two or more larvae per 0.3 m of row resulted in dry bean damage of up to 6.1% and 0.8%, respectively. Damage of 2% or greater is considered to cause an economic loss (Blickenstaff 1979; Mahrt 1987; Michel et al. 2010; Chludzinski 2013). Egg masses and larvae are difficult to scout in dry bean due to their 5      size and therefore pheromone traps are often used to track peak moth flight, as there is only one generation per year (Michel et al. 2010). Pod injury is usually found within 3 weeks of peak flight; therefore trap counts and pod scouting are important to consider together (Michel et al. 2010). Flight threshold values are still being developed for Michigan, as the previously established western thresholds appear to be too high. The onset of WBC feeding is typically outside that in which seed treatments or insecticides applied at planting will last, therefore postemergence applications of pyrethroids are recommended at the onset of pod feeding (DiFonzo 2010b). Pest management- Pathogens Common disease concerns in Michigan dry beans include common bacterial blight (Xanthomonas axonopodis pv. phaseoli Smith) and halo blight (Psuedomonas syringae pv. phaseolicola Burk.), white mold, and root rots (Fusarium solani sp. phaseoli Burk., Rhizoctonia solani Kuhn, and Pythium spp.). There are also more minor concerns with bean common mosaic virus (BCMV), angular leaf spot (Psuedocercospera griseola Sacc.), rust (Uromyces appendiculatus), and anthracnose (Colletotrichum lindemuthianum Sacc. & Magnus) (AgBioResearch 2014). Bacterial blight usually occurs through natural leaf openings or as a secondary problem following foliar damage. The first signs of common blight are water soaked spots on the undersides of leaves that turn brown with often yellow borders. Pods can also become infected and under warm conditions common blight can spread from plant to plant. The bacteria can overwinter in crop debris and can also be seed borne, therefore control methods include: rotation with non-host crops and utilization of certified seed, bactericidal seed treatment, 6      such as streptomycin, or planting of resistant varieties (Schwartz et al. 2004; DiFonzo et al. 2006). White mold over winters in Michigan as sclerotia in the soil and can infect a large number of crop and weed species (AgBioResearch 2014). Infections in dry beans most commonly occur when conditions are cool and wet at the time of flowering (Esker et al. 2011). The fungus enters the plant through the senescing flower and infects the stem, at which point all tissue above that portion of the stem dies. The first signs of infection are water-soaked stem lesions, which become bleached and stringy over time and eventually have white cottony mycelial growth. Crop rotation with non-host plants can reduce the number of sclerotia present in the soil over time. However, due to the number of host crop and weed species, more effective cultural measures aim to reduce humidity beneath the canopy through changes in plant population, row spacing, fertility management, and planting date (Schwartz et al. 2004; DiFonzo et al. 2006). If needed, timely chemical applications can be effective in controlling white mold so long as the spray can penetrate the canopy to reach the flowers. Root rot can be caused by several different fungi and fungi-like pathogens, such as the Oomycetes. With the fungi (Fusarium solani sp. phaseoli Burk. and Rhizoctonia solani Kuhn), symptoms first appear as lesions on the root and may not appear as yellowing, stunting, or plant death until much later in the growing season (Schwartz et al. 2004; DiFonzo et al. 2006). These fungal diseases are favored under wet soil conditions, high planting densities, high amounts of decaying organic matter, and when plants have been wounded and there is a clear entry point. The fungal pathogens can be managed through using certified seed and resistant varieties when 7      available, planting seed when soils are warm and moist and favor rapid germination, avoiding potential root injury through close cultivation, and rotating fields to non-host crops. In the case of the Pythium spp., (i.e. Oomycetes), whole bean seedlings turn yellow and die quickly, resulting in gaps in the dry bean row. Pythium spp. infection is favored by wet, compacted soils. Pythium spp. can be managed through crop rotation, improved soil drainage, seed treatments, and fungicide applications. Pest management- Weeds Weed management is one of the highest costs in field crop production. Potential yield losses in dry beans in the absence of weed management can reach over 80% (Blackshaw and Esau 1991, Malik et al. 1993; Woolley et al. 1993; Chikoye et al. 1995; Wall 1995; Burnside et al. 1998; Blackshaw et al. 2000; Holmes 2012), depending on the weed species composition and density. To avoid yield loss, the critical period for weed control in navy beans occurs between V2 and R1 (Woolley et al. 1993; Burnside et al. 1998). In the past, producers relied heavily on mechanical control to manage weeds, however advancements in herbicides labeled for use in dry beans along with the general move away from in-season soil disturbance, prompted by the rise in herbicideresistant crop use [i.e. corn (Zea mays L.), soybean (Glycine max (L.) Merr.), sugar beet (Beta vulgaris L.)], have resulted in many producers relying solely on chemical weed control. Typical recommendations for optimal weed control include the use of a preplant incorporated or a preemergence herbicide followed by a postemergence treatment to control escaped weeds (Blackshaw et al. 2000; Holmes and Sprague 2013). Besides yield loss, the pFSchresence of weeds can also reduce dry bean quality. For example, Solanaceous weeds that have berries can 8      stain lighter colored dry bean seeds, reducing their market value (Burgert et al. 1973; Schwartz et al. 2004). The most common problematic weeds in Michigan dry bean production systems are annual broadleaves, including: common lambsquarters (Chenopodium album L.), pigweed species (Amaranthus powellii S. Wats. and A. retroflexus L.), common ragweed (Ambrosia artemisiifolia), and velevetleaf (Abutilon theophrasti L.). Of the annual grasses, the foxtail species [Setaria faberi Herrm., S. pumila (Poir.) Beauv., and S. viridis (L.) Beauv.] are the most prevalent across the state. Perennial and biennial weeds are not commonly found in dry bean fields, but occasionally there are infestations of perennial sowthistle (Sonchus arvense), Canada thistle [Cirsium arvense (L.) Scop.], and quackgrass [Elymus repens (L.) Gould]. Organic Dry Bean Production in the United States Demand for organically produced dry beans has been on the rise in recent years both within the US and abroad. The only survey of organic agriculture in the U.S. was conducted in 2007 at which time Michigan was the top organic dry bean producing state, comprising 39% of the hectares harvested (USDA-NASS 2008). Average organic dry bean yields in Michigan in 2007 were 1,700 kg ha-1, compared with 1,800 kg ha-1 for conventionally produced beans that same year (USDA-NASS 2014c). Heilig and Kelly (2012) found that average organic dry bean yields were depressed by nearly 20% when compared with conventionally produced beans. Yield differences varied with genotype, however overall dry beans that performed better in conventional systems also performed better in organic systems. Producing a quality dry bean crop without the use of synthetic amendments and pesticides presents unique challenges for 9      organic growers, especially when it comes to bean variety selection, pest management (i.e. insects, diseases and weeds), and soil fertility. Organic pest management Common insect and disease problems are first and foremost managed through the cultural practices mentioned above. In the event of outbreaks, there are materials approved by the Organic Materials Review Institute (OMRI) that can be applied. All such materials are naturally derived; examples include: copper and PyGanic® (McLaughlin Gormley King Company, Minneapolis, MN). Copper has many uses in organic systems, but probably is most commonly utilized as a fungicide, for instance controlling downy mildew (Plasmopara viticola) in vineyards (Mackie et al. 2013). Pyrethrins derived from chrysanthemums are the active ingredient in PyGanic, which is used as a broad-spectrum insecticide. Pyrethrins are also used in conventional systems, though they are synthetically derived, and therefore not suitable for use in organic systems. PyGanic has no residual activity, meaning it may need to be applied multiple times to control outbreaks of detrimental insects, whereas synthetic pyrethrins can have some residual activity depending on additives included (Rife 1976). Weed management in organic systems, including dry beans, can be particularly difficult as producers must rely on cultural and mechanical means. Cultural practices that can increase the manageability of weeds in organic systems include: crop rotation, delayed planting, stale seed bed approaches, and the inclusion of cover crops. For mechanical control, tined weeding and rotary hoeing are the most common method of early-season weed management as propane flaming damages dry beans causing stand loss and delayed maturity (Taylor et al. 2012). Tined 10      weeders are generally used before crop emergence to disturb small weed seedlings that are sprouting above the crop seeds in the soil profile (Martens and Martens 2005). This process is sometimes referred to as “blind cultivation.” Many different tine shapes and sizes are available and their orientations and spacing can be adjusted as appropriate for the situation. Rotary hoes have been around since the mid-1800s and were widely used starting in the early 1900s (Peters et al. 1959). They are popular implements for early-season weed control in organic systems because of their efficiency in uprooting small weeds, while leaving small, well-rooted crop plants intact. Once dry beans are too large to rotary hoe without damage, intra-row cultivation is utilized until canopy closure. Increasing fuel and hand labor costs, coupled with a concern for losing soil carbon by frequent tillage to manage weeds, have caused organic growers to seek more efficient and profitable ways to control weeds. Areas of interest in the North Central region have included changing fertilization practices (DiTomaso 1995; Sweeney et al. 2008), and timing propane flaming and rotary hoeing based on environmental cues (Taylor et al. 2012). Organic nutrient management Options for amending the soil to improve fertility for dry bean production is more limited in organic compared with conventional systems, particularly when it comes to nitrogen. Organic producers in Michigan generally apply manure and/or compost to fields in the fall, with application rates dependent on the material. The two largest caveats to utilizing these resources are a) transportation costs, as most come from off farm locations (MI organic growers, personal communications 2012) and b) the potential to introduce new pest problems. As an example of the latter point, Palmer amaranth (Amaranthus palmeri L.) arrived in Michigan around 2010 as a result of manure applications from dairy cattle fed infested feed from southern states where 11      Palmer amaranth is prevalent (Sprague, personal communication 2011). A third option for supplying nutrients, in particular nitrogen, to organic dry bean fields is the use of leguminous cover crops (i.e. green manures). Cover Crop Overview Cover crops are not harvested like a cash crop, but instead the biomass produced is utilized to improve or maintain the agricultural ecosystem in which they are grown. Cover crops have been used since the early days of agriculture to reduce soil erosion, improve soil fertility and health, and to help manage pests. Advances to agriculture over the past 70 years, including a shift to monoculture cropping, reduced crop rotation lengths, the availability of synthetic fertilizers and a broad range of pesticides, and the introduction of genetically modified crops have all reduced the use of cover crops (Doran and Smith 1987; Doran and Smith 1991). These advances however have led to new concerns regarding soil erosion, decreased productivity of soil (related to soil fertility and health changes), nutrient leaching and runoff, shifts in weed populations including the rise of herbicide resistant weeds, and an increase in insects and plant pathogens. For these reasons, the benefits of cover crops are being re-visited and fine-tuned to improve agronomic sustainability for the future. Currently, cover crops are planted on approximately 1.8 million hectares of grain and oilseed production land in the U.S.; 2% of the total (USDA-NASS 2014d). This number is expected to increase as producer interest grows and the number of cost share programs rises in an effort to mitigate surface water pollution. Producers have indicated that their goals in using cover crops are to reduce soil compaction and erosion, scavenge nitrogen, and provide weed control (CTIC 12      and NCR-SARE 2013). In the Midwest, cover crops are utilized most frequently between corn and soybeans (57% of respondents), between soybeans and corn (54%) and following a small grain (43%) (CTIC and NCR-SARE 2013). The biggest challenges producers face with utilizing cover crops are: establishment, time/labor/management requirements, species selection, cover crop seed costs, planting and management costs, cover crops using too much soil moisture, seed availability, and danger of the cover crop becoming a weed in subsequent crops. Cover crops can alter the soil environment through changes in organic matter, structure, biology, water infiltration and retention, as well as erosion prevention, all of which are interrelated. Cover crops influence soil composition and structure Cover crops can alter the composition and structure of soil through changes in organic matter and aggregation. Several cover crops such as crimson clover (Trifolium incarnatum L.), rye (Secale cereale L.), hairy vetch (Vicia villosa Roth), etc. increase and alter the composition of soil organic matter in the top layer of soil, particularly in no-till systems (Reicosky et al. 1995; Reicosky and Forcella 1998; Sainju et al. 2002; Reddy et al. 2003; Steenwerth and Belina 2008). Alterations to soil structure, such as a decrease in compaction associated with oilseed radish (Raphanus sativus L.) (Williams and Weil 2004; Horton 2013), have been noted in some instances. Conflicting results have been reported on the effect of cover crops on soil aggregation, with some observing no effect (Schutter and Dick 2002; Lehrsch and Gallian 2010), while others report an increase in aggregation (Dapaah and Vyn 1998). Cover crops alter soil moisture 13      Increased water infiltration and retention (Lehrsch and Gallian 2010; Dapaah and Vyn 1998; Reicosky et al. 1995) along with reduced erosion (Derpsch et al. 1986) are important benefits of cover crops. Cover crops may be planted to mitigate surface water pollution (Dabney et al. 2010). Cover crops growing in the spring act as a mulch and high biomass producers, such as rye, can maintain higher levels of soil moisture for the subsequent cash crop compared with no cover crop treatments (Daniel et al. 1999; Teasdale and Mohler 1993). In Stillwater, Maine, the incorporation of red clover (Trifolium pretense L.) and compost increased soil water content relative to the unamended treatment by a minimum of 2% in 5 to 62 days following incorporation (Conklin et al. 2002). In Ontario, Canada, wet aggregate stability was improved through the use of over-wintering cover crops such as red clover and ryegrass (Lolium multiflorum Lam.) (Dapaah and Vyn 1998), which could translate into increased soil water holding capacity. One of the primary concerns for growers considering cover crop use however, is the potential for reduced soil moisture for crops planted following cover crops (CTIC and NCR-SARE 2013), especially in areas where moisture is more limited. In northern California, McGuire et al. (1998) found that incorporation of a mixture of woollypod vetch (Vicia villosa Roth subsp. Varia) and field pea (Pisium sativum L.) reduced soil moisture in a dry year by up to 6.6 cm in the top 90 cm of the soil profile compared with fallow. In central California, Stivers and Shennan (1991) reported decreased soil moisture by up to 2.0 cm in the top 24 cm of soil in winter legume cover crops compared with a fallow glyphosate treatment. Cover crops retain and add nutrients Soil fertility, and specifically N availability, is impacted by the use of cover crops (Dabney et al. 2010). Some cover crops act as nutrient scavengers, uptaking and then releasing nutrients back 14      into the soil (Sainju et al. 1998; O’Reilly et al. 2012). Leguminous cover crops can increase soil N through fixation (Ladd et al. 1986; Stivers and Shennan 1991; Sainju and Singh 2001). The magnitude and timeframe over which cover crops alter soil inorganic N is dependent on many factors, including environment and climate, soil characteristics (soil composition), cover crop characteristics (composition and growth stage), and management practices (crop rotation, tillage, etc.) (Doran and Smith 1991; Wagger et al. 1998; Dabney et al. 2010). Cover crops influence soil biology Changes to abiotic soil environment directly impact soil biota both at micro- and macroscopic levels (Harris et al. 1994; Teasdale 1998; Schutter and Dick 2002; Ferris et al. 2004; Gallandt 2006; Reeleder et al. 2006; Carrera et al. 2007). The magnitude to which cover crops impact the soil environment is directly related to the amount of biomass produced by the cover crop and biomass composition (Sarrantonio 2007; DuPont et al. 2009; Magdoff and Van Es 2009; Gruver et al. 2010; De Cauwer et al. 2011; Goméz et al. 2013). As an example, both crimson clover and rye increased fungal and bacterial populations compared with no cover crop, with microbial populations following clover being higher than rye (Reddy et al. 2003). Cover crops, grasses, legumes, and mixtures, increase total nematode abundance (DuPont et al. 2009). Legume and legume-grass mixtures of cover crops increase the abundance of bacterial and fungal feeding nematodes associated with N mineralization compared with a grass-only cover crop and a fallow treatment. Predator and omnivorous nematodes were not impacted by cover crops. Cover crops with mid-range C:N ratios (e.g. legume-grass mixtures) may allow for steady N mineralization and avoid losses due to leaching following rapid N mineralization compared with lower C:N ratio cover crops (e.g. legumes alone) (DuPont et al. 2009). 15      Cover crops alter pest dynamics- Diseases and insects Cover crops have the ability to influence diseases and insects in both positive and negative ways. The biological activity of the soil can be increased through soil organic matter additions introduced with cover crops. Soils with highly active and diverse soil fauna reduce pest pressure compared with soils with lower activity (Clark 2007). Cover crops can also attract beneficial organisms such as predator and parasitoid insects and diseases, especially when they remain undisturbed or are utilized in reduced tillage systems. Some cover crops can also act as trap crops. Trap crops attract detrimental insects and deter them from attacking the cash crop. An example of this is oilseed radish, which can act as a trap crop for the sugar beet cyst nematode (Heterodera schachtii Schm., BCN). Radish induces the hatching of BCN eggs in the soil (Peterka et al. 2004). The BCN larvae then enter the roots of the radish but the radish prevents further development of the larvae into adults. Recent research at Michigan State University has shown that this interaction between oilseed radish and BCN depends on the radish variety/brand utilized, with some being highly effective, such as ‘Defender’, ‘Tajuna’, and ‘FumaRad’, and others showing a reduced trap cropping effect on BCN, such as ‘GroundHog’, ‘PileDriver’, and ‘Intermezzo’ (Fred Warner personal communication, 2014). Cover crops that overwinter, or are planted in the spring before a cash crop, have the potential to increase disease and insect problems in the cash crop. Seedcorn maggot adults oviposite eggs into fields where cover crops were tilled into the soil (Hammond and Cooper 1993). Shortly after, maggots hatch and start feeding on plant material, including seeds, cotyledons and plumules of germinating cash crop seeds. Maggot development is determined by growing degree 16      days and once the maggots pupate they no longer feed. Waiting two to three weeks after cover crop incorporation greatly reduces the potential of crop loss from seedcorn maggot because the crop is not planted at the time of maggot feeding (Hammond and Cooper 1993). Cover crops alter pest dynamics- Weeds Cover crops have the potential to influence weed competition in cropping systems in a number of ways, including direct competition, allelopathy, and alterations to the soil environment (Dyck and Liebman 1994; Creamer et al. 1996; Conklin et al. 2002; Snapp et al. 2005). Direct competition with weeds occurs from the time of cover crop emergence through termination and may result in reduced inputs to the weed seed bank, and therefore less weed pressure in the following cash crop (Teasdale 1998; Ross et al. 2001; Gallandt 2006). Allelopathy refers to biochemical interactions among plants and most commonly focuses on negative interactions. Allelochemicals, or compounds which become allelopathic through microbial degradation, have been identified in several cover crop species, and detailed accounts of the allelopathic impact of cover crop on weeds have been published in the literature (Hill 2006; Kelton et al. 2012). Until recently, studies on cover crop allelopathy have mainly focused on laboratory assays of extracted chemicals (Hill et al. 2006; Dhima et al. 2006; Alder and Chase 2007; Hill et al. 2007; Farooq et al. 2011) because it is difficult to discern the impact of allelopathy from direct competition and physical and light interference in the field. In 2012, a protocol was released to demonstrate allelopathy in the field for well characterized allelochemicals, such as the bezoxazinoids found in cereal rye (Teasdale et al. 2012; Rice et al. 2012). Any suppression of weed emergence or growth from allelochemicals is usually short17      lived (Kruidhof et al. 2009) and would occur at the time of cover crop termination. Suppression via rye allelochemicals does not exceed 30 days after rye termination (Clark 2007). Lastly, and perhaps most importantly, weeds may be impacted by alterations to the soil environment as a result of growing cover crops. These alterations include: physical and light barriers to weed emergence due to cover crop surface residue (Teasdale 1996, 1998; Blum et al. 1997), changes in soil nutrient and moisture availability (Teasdale 1998), and soil biology both within the soil matrix and at the surface (Teasdale 1998, Gallandt 2006). Cover crops that increase nitrogen availability could stimulate the germination and growth of some weed species (Blackshaw et al. 2003; Sweeney et al. 2008; Shem-Tov et al. 2005). It is also important to mention that cover crops themselves can become weed problems in the following cash crop if seed is produced. This has been observed for several species, including buckwheat (Fagopyrum esculentum Moench), oilseed radish, and hairy vetch (Clark 2007; O’Reilly et al. 2011). Cover Crops for Use in Michigan Dry Bean Systems Medium red clover and cereal rye are popular cover crops among Midwest producers because they can be planted early in the spring and late in the fall, respectively, making them easier to fit into rotations that include long-season row crops. Typically medium red clover is interseeded into or planted following a small grain the year before corn is planted. Cereal rye is most often planted between corn and soybean or dry bean. The seed of these two cover crops is readily available and relatively inexpensive, which enhances their popularity. Oilseed radish is a newer 18      cover crop of interest over the past 15 years. Row crop producers are still experimenting how best to incorporate this cover crop into their rotations. All three of these cover crops scavenge and reduce soil inorganic N during the fall and winter months (Hoyt and Mikkelsen 1991; Sainju et al. 1998; Baggs et al. 2000; Vyn et al. 2000; Weinert et al. 2002; Williams and Weil 2004; O’Reilly et al. 2012). Following is a discussion on how these three cover crop species impact soil fertility and weed populations in cash crops the following season. Medium red clover When interseeded into winter wheat, medium red clover germinates in early spring and grows slowly while the wheat tillers and completes its growing cycle. After grain harvest, the clover accumulates more leaf and stem biomass and flowers. Medium red clover can be terminated in the fall or spring to provide carbon and nutrients to the soil, including nitrogen. Medium red clover is one of two types of red clover; the other is mammoth red clover. Medium (i.e. doublecut) is the more common and is different from mammoth (i.e. single-cut) in that it performs better when frost-seeded into wheat and grows back more rapidly after cutting for forage (USDA-NRCS 2002; Knorek and Staton 1996; Duiker and Curran 2007; Clark 2007). Both of these red clovers are short-lived perennials and differ from crimson clover and white clover (Trifolium repens). Crimson clover is a larger seeded annual species that can reseed itself (Cavigelli et al. 1998). It can be advantageous as a cover crop because of its tolerance of shade and potential to grow rapidly in cool weather, however it can winterkill in Michigan (Clark 2007). Crimson clover does not tolerate frost seeding into a small grain like the red clovers. White clover is low growing perennial that tolerates mowing and grazing (Clark 2007). White 19      clover is more likely to be used as an interseeded species with vegetables, fruit, trees, or in pastures. Corn is often planted following a medium red clover cover crop to utilize the available nitrogen from the incorporated cover crop (Magdoff and Van Es 2009). When comparing the introduction of a clover cover crop for one season with long-term clover use within the rotation, the full N benefit to corn was realized within the first year; a long term clover stand did not have an additive effect on soil N (Gentry et al. 2013). Furthermore, one season of clover increases residual soil inorganic N for at least two years following incorporation, compared with synthetic N (Harris et al. 1994). Several researchers have shown greater corn nitrogen uptake and/or yield following a clover cover crop compared with no cover (Dapaah and Vyn 1998; Gentry et al. 2013; Torbert and Reeves 1991; Vyn et al. 2000). More detailed studies have been conducted on N release from crimson clover (Wilson and Hargrove 1986; Wagger 1989). In a bagged residue study conducted in Georgia, 60% of the nitrogen from crimson clover was released into the soil by four weeks after moldboard plowing (Wilson and Hargrove, 1986). By 16 weeks, 69% had been released, showing that 31% of the nitrogen accrued in the crimson clover biomass remained and was not immediately available to the following cash crop. The magnitude and duration of N release from clovers may be slower in Michigan, where temperatures are cooler and there is less precipitation during the growing season. Cooler soil temperatures reduced N release from alfalfa pellets, blood meal, and chicken manure in laboratory incubation studies (Agehara and Warncke 2005). Reduced precipitation 20      resulted in 28% more N retention in crimson clover residue 16 weeks after soil incorporation compared with a year with normal precipitation (Wagger 1989). Medium red clover planted as an intercrop into a cereal crop has the potential to increase summer annual weed seed inputs into the seed bank, particularly foxtail species, compared with corn and soybean portions of a crop rotation (Heggenstaller and Liebman 2006). This is especially true when the establishment of the cereal or clover is slow, allowing weeds access to light and moisture (Miksky et al. 2010). Different clover species vary in their ability to actively compete with weeds (den Hollander et al. 2007). Increases in soil inorganic N increase the germination of some weed species (Blackshaw et al. 2003; Sweeney et al. 2008; Shem-Tov et al. 2005), however increased summer annual weeds in a cash crop following red clover have not been reported. Fisk et al. (2001) found no impact of red clover on summer annual weed density in three of four site-years in a no-till system where herbicides were used and corn was the following crop (Fisk et al. 2001). In the other site-year, red clover was shown to reduce weed density compared with the no cover control. Red clover has been shown to reduce root growth of the weed wild mustard (Sinapsis arvensis L.) up to twelve days after clover incorporation (Ohno et al. 1999; Conklin et al. 2002), however the potential allelopathic properties of this cover crop and other ways in which it influences weed dynamics in the following cash crop has not been widely studied. Cereal rye Rye is a well-known nutrient scavenger and reduces nitrogen losses in the fall and winter months (Sainju et al. 1998; Baggs et al. 2000; Vyn et al. 2000; O’Reilly et al. 2012; Weinert et al. 2002; 21      Hoyt and Mikkelssen 1991). The release of N from rye residue is dependent on its physical characteristics and chemical composition at the time of termination (Wagger et al. 1998). The C:N ratio is one of the components most highly correlated with decomposition and N release in N-limited soils. C:N ratios of 25:1 or less led to net N mineralization (Clark et al. 1997; Kuo and Jellum 2002), while higher ratios led to N immobilization. As rye grows and matures in the spring, the C:N ratio increases and can quickly exceed 25:1 (Wagger 1989; Clark et al. 1994). Immobilization of N by rye has occurred in numerous studies, particularly when rye is nearing the reproductive phase and/or biomass is high (Wyland et al. 1995; Clark 2007; Ruffo et al. 2004). Producers target rye termination at heights of 46 cm or less to avoid N immobilization (Clark 2007). The impact of rye on crop yields has been variable, with some crops, such as corn, suffering due to N immobilization (Torbert and Reeeves 1991), while other crops such as potato (Solanum tuberosum L.) benefited from having rye in the rotation (Larkin et al. 2010). Soybean yield is generally not influenced by a rye cover crop (Reddy 2001; Reddy et al. 2003; Sawyer et al. 2012). Rye can reduce the growth of fall weeds through competition (Kruidhof et al. 2008). Rye also has well characterized allelochemical compounds that can impact weed growth following termination, as previously mentioned (Hill 2006; Clark 2007; Teasdale et al. 2012; Rice et al. 2012). In the field, rye reduced and enhanced weed density and biomass in cash crops planted following termination in previous studies, depending on whether or not herbicides were used and the tillage system (Reddy 2001; Reddy et al. 2003; Peachy et al. 2004). Though rye has not been specifically studied, high soil C:N ratios, or the addition of high C:N plant material to the soil, has been found to increase weed seed persistence (Davis et al. 2005, 2006; Shem-Tov et al. 22      2005; Davis 2007). It has been suggested that increased persistence is the result of reduced microbial activity due to N limitations (Davis et al. 2006). The impact of medium red clover on weed seed persistence has not been reported. Oilseed radish Oilseed radish and forage radish are both subspecies of Raphanus sativus, var. oleiformis and longipinnatus, respectively (Weil et al. 2006; Jacobs 2012). Sometimes they can be distinguished by their root architecture, as oilseed radish has a somewhat branched root compared with forage radish. The distinction is not likely important however as the two can cross-pollinate and most characteristics and management recommendations are the same. Therefore, the two subspecies shall be referred to in this literature review as “oilseed radish”. Oilseed radish has piqued the interest of producers due to its rapid shoot and root growth during the late summer and early fall, potential to alleviate soil compaction, and potential for pest suppression (Clark 2007; Williams and Weil 2004). Oilseed radish is typically planted in latesummer in the northern climates of the U.S. and does not survive the winter when temperatures drop below -4 C, thus requiring no management in the spring. Oilseed radish is known to scavenge nitrogen (Clark 2007; Jackson et al. 1993; Stivers-Young 1998; Dean and Weil 2009; Vyn et al. 2000; Horton 2013). Vyn et al. (2000) found that oilseed radish fall plowed following a killing frost, had 2.9 mg NO3-N kgsoil-1 more N at the time of pre-sidedress sampling than the no cover crop treatment, equating to a 20% increase in concentration, in one of two locations in Ontario, Canada. In Indiana, undisturbed oilseed radish plots were found to have increased soil nitrate availability in the spring in the six weeks leading up to corn planting in May, with 23      concentrations being highest directly next to the tuber holes. The weather that year was unseasonably warm in the late winter and dry in the spring and summer, meaning residue breakdown and nitrogen mineralization occurred earlier and nitrate was not leached from the system as quickly as would be expected in a typical year (Horton 2013). Outside of these reports, little is known about nitrogen release and mineralization from oilseed radish during the winter and subsequent growing season. Corn and soybean crops generally show no yield response to oilseed radish compared with no cover (Vyn et al. 2000; Williams and Weil 2004), however in Ontario, Canada, corn yield increased following oilseed radish compared with no cover crop in two of three years (Dapaah and Vyn 1998). In Indiana corn yield was improved by radish compared with no cover crop at one of four research sites in 2012, a year limited by precipitation (Horton 2013). Oilseed radish (4 to 7 Mg ha-1) reduced the weed density of the summer annual weed common lambsquarters and the winter annual weeds common chickweed (Stellaria media L.) and annual bluegrass (Poa annua L.) in the fall in the Netherlands due to early light interception, but differences in weed establishment in the spring were not observed (Kruidhof et al. 2008). A similar trend with regard to the influence of radish on fall and spring weeds was observed in Canada (O’Reilly et al. 2011). In the U.S. however, oilseed radish reduced spring weed densities compared with no cover (Weil and Kremen 2007; Wang et al. 2008). In Michigan specifically, radish (6.2 Mg ha-1) reduced redroot pigweed (Amaranthus retroflexus L.) density and biomass in the subsequent late-April planted onion crop on muck soil 2 and 2.5 months after planting (Wang et al. 2008). The proposed primary mechanism of weed suppression is fall competition 24      with winter and summer annual weeds (Wang et al. 2008; O’Reilly et al. 2011; Lawley et al. 2012). Wang et al. (2008) showed reduced total weed seed banks in the spring following fall Brassica cover crops compared with a no cover crop control. Though extensive work has been done on the biologically inhibitory properties of glucosinolates found in Brassicaceae species, limited research has been done on the allelopathic potential of oilseed radish, with one study showing inhibitory effects on the germination and growth of the weed downy brome (Bromus techtorum L.) (Machado 2007). The observations reported above for medium red clover, cereal rye, and oilseed radish are of limited scope and leave many questions remaining with regard to utilizing these cover crops before organic dry beans. Dry beans are planted later than sugar beets, corn or soybeans, and therefore overwintering cover crops can be terminated later in the spring. Delaying the termination of overwintering cover crops would mean warmer soil and air temperatures which could alter decomposition rates and the timing of nitrogen mineralization. Decomposition and N mineralization rates would also be different for oilseed radish, as the length of time between winter-kill and dry bean planting would be longer than sugar beets, corn, or soybean by 30 days or more. Few studies have been published on the influence of cover crops on soil moisture, nitrogen availability to dry bean, or bean growth and yield (Shrestha et al. 2002; Haramoto and Gallandt 2005). 25      APPENDICES 26      APPENDIX A CHAPTER 1 TABLE Table 1.01. Dry bean production in 2013 by market class for the top three producing states (data pooled from USDA-NASS 2014b). 1st 2nd 3rd Market class ─state─ ──Mg── ─state─ Pinto ND 216,000 NE 53,000 ID 27,000 Navy ND 59,000 MI 57,000 MN 31,000 Black MI 66,000 ND 25,000 MN 13,000 Great northern NE 56,000 WY 5,000 ND 4,000 Dark red kidney MN 28,000 WI 4,000 NY 2,000 Light red kidney MN 14,000 NE 8,000 MI 6,000 Small red MI 13,000 ID 9,000 ND 1,000 Pink ID 8,000 ND 6,000 MN 5,000 Cranberry MI 2,000 CA 500 27      ──Mg── ─state─ - ──Mg── - APPENDIX B METHODS OF STUDYING NITROGEN FIXATION AND MEASURING SOIL INORGANIC NITROGEN Like soybeans (Glycine max L.), dry beans are a legume capable of fixing atmospheric nitrogen (N), however the efficiency of the two species is very different (Piha and Munns 1987; George and Singleton 1992). Methods of quantifying fixation The most popular methods used to quantify N fixation include: N difference, isotope dilution, and natural abundance. All of these methods require the use of a reference plant that does not fix nitrogen. The reference plant could be a different species or a non-nodulating or uninoculated plant of the same species. In dry bean there are two nodulation mutants which were formed by mutagenesis of the navy bean ‘OAC Rico’ using ethyl-methane sulfonate (Park and Buttery 1992). R69 forms small, ineffective nodules and R99 does not form nodules at all in the presence of Rhizobium spp. Difference method Using the difference method, N derived from fixation is determined by the following equation: [Eq. 1] 28      where NDFA represents the nitrogen derived from the atmosphere via fixation and the two N terms represent total N content per unit of biomass. This method is less technical to calculate than the methods that follow and is reliable when soil N is very low. This calculation assumes that the uptake of N from the soil is similar between the fixing plant and the reference plant, and therefore may not be suitable when an appropriate reference cannot be used. This is not a good method for distinguishing differences when available soil N is high as it may mask contributions from atmospheric fixation. Isotope dilution method In the isotope dilution method, a 15N labeled source of synthetic N is utilized along with a reference plant, as mentioned above. The equation used to determine N fixed using isotope dilution is as follows (Fried and Middelboe 1977; Kagabo 1986): 1 % % ∗ [Eq. 2] The benefits to this method are that the amount of N taken up by the reference plant does not have to be the same as the fixing plant because it is calculated based on percentage. Also, the application rate of 15N is much higher than that which naturally occurs, and therefore there is no need to account for that in the equation. The isotope dilution method can be problematic because labeled materials are costly and it is difficult to uniformly distribute the labeled N. Natural abundance method 29      The natural abundance method has come to light as mass spectrometry has advanced. This method is based on the assumption that the percent of naturally occurring 15N in the atmosphere is lower than in the soil. Utilization of the natural abundance method in the field requires a baseline calculation of the percentage of N in the atmosphere that is 15N (i.e. δ 15Natmosphere) (ACIAR 2007). This must be done in the greenhouse in the absence of soil N and is species and variety specific (James Heilig, personal communication, 2014). The equation to calculate NDFA using the natural abundance method is as follows: [Eq. 3] The benefits of this method are that no additional N needs to be added and therefore the experimental size is not limited. The initial greenhouse work needed could be a deterrent to using this method and there is also a concern that fractionation may result in an underestimate of NDFA. Dry bean versus soybean fixation In a greenhouse experiment, Piha and Minns (1987) explored the relative fixation capabilities using a modified version of the difference method described above. An inoculated soybean, ‘Evan’, and dry bean ‘Puebla 152’ were the “fixers” and un-inoculated plants of these species were the “reference” plants. In this modified experiment, only the reference plants received exogenous N, therefore the equation to determine efficiency was as follows: 30      % ∗ 100 [Eq. 4] In both dry bean and soybean total nodule weight increased over time. In dry beans the increase was associated more with increased nodule number, whereas in soybean the increase was more associated with increased nodule size. In the absence of soil N, soybean accrued 43% the quantity of shoot N through fixation compared with the reference plant at 0 to 28 days after planting; 96% was acquired 28 to 42 days after planting. The black bean only accrued 28% and 68% for those same time periods. It is important to point out that Puebla 152 is currently used in dry bean breeding programs for its relatively high fixation capabilities within the species (Heilig 2010), so the efficiency of commercially available dry beans is likely even lower. For both species fixation increased over time, however soybean was more efficient than dry bean throughout its lifecycle. To further understand the differences between these two species in the field, the isotope dilution method [Eq. 3] was utilized with 15N (George and Singleton 1992). The N fixing plants were soybean ‘Clark’ and dry bean ‘Brazil 2’ and the reference plants used were a non-nodulating soybean isoline of ‘Clark’ and uninoculated dry bean ‘Brazil 2’. They concluded that by physiological maturity, soybean had 69% NDFA and dry bean had only 16% NDFA, when a minimal amount of N fertilizer was supplied (9 kg ha-1). Dry beans were more dependent on N assimilation from the soil than from fixation. Soil-applied N was found to have the most beneficial effect on N accumulation when applied before full bloom (R2) for both species. This study and others have found that increasing soil inorganic N rates are detrimental to fixation, 31      nodule number, and nodule mass (Allos and Bartholomew 1955; Beard and Hoover 1971; Graham 1981; Tsai et al. 1993). Though dry beans accumulated more total N by R2 than soybeans, the reverse was true at maturity. Yields were similar across species (N fixing plants) but differences in total accumulated N at maturity occurred because soybean seed contains more N than dry bean seed. Nitrogen fixation capacities vary among dry bean varieties (Heilig 2010) and breeding work is currently underway at Michigan State University to improve fixation in commercially available varieties. Methods for determining soil inorganic N availability There are several methods for quantitatively or qualitatively measuring the amount of inorganic N available in the soil for plant uptake. The most widely used method is soil extraction, however ion exchange resin and chlorophyll meters can also be used. Soil extraction Chemical soil extractions to determine the availability of plant nutrients have been used for many decades (Tisdale and Nelson 1975). These tests, along with knowledge of crop specific requirements for growth, are used to make fertilizer recommendations around the world. To get a representative sample for soil extraction, samples are generally collected using a probe to collect a small core, to the depth of the plow layer, from several points across the area of interest. All subsamples are combined, homogenized, and air dried prior to grinding and extraction to 32      determine nitrate and ammonium levels. Timing of soil sample collection is dependent on the goals of testing. Cation and anion exchange resin strips Ion exchange resin membranes have been used to study N availability in agricultural soils for 20 years (Subler et al. 1995; Qian and Schoenau 2001). Ion exchange resin membranes are said to closely mimic root uptake of nutrients (Qian and Schoenau 1995). Typically resin membranes can remain in place for up to one month, allowing for continuous measurements of N availability. Upon removal, new membranes can be put in place to continue measuring soil inorganic N. This ability to continually monitor soil N gives resin membranes an advantage over soil extractions, which only reflect N availability at a single point in time. A potential disadvantage to the use of resin membranes is the small soil area being utilized by the resin strip, and at low soil moisture N uptake may be reduced due to decreased contact between the resin surface and the soil solution (Johnson et al. 2005). Relative chlorophyll readings The amount of chlorophyll in plant leaves reflects the nutrient status of the plant. Researchers have documented an increase in plant chlorophyll as soil inorganic N increased (Piekkielek and Fox 1992; Blackmer and Schepers 1995). It is on this principle that the idea of non-destructively measuring leaf reflectance and chlorophyll content to determine nitrogen status was born. The main advantage in measuring chlorophyll content versus using soil extraction is the reduced amount of time required for feedback. Relative chlorophyll readings from devices such as a Minolta SPAD meter are instantaneous, whereas turnaround time for a soil extraction can take 33      days to weeks. The disadvantage of utilizing relative chlorophyll content is that there are variations in chlorophyll content among plant hybrids and varieties, such as corn (Schepers et al. 1992) potato (Minotti et al. 1994), and tomato (Sandoval-Villa et al. 2000). These differences then require the use of reference strips, because no one single value represents optimal N availability for all hybrids and varieties within a species. Reference strips are strips of the same hybrid or variety, planted in the same field, which receive high rates of fertilizer so nitrogen needs are met. The readings obtained in the reference strip can then be used to determine if N needs to be added to the larger portion of the field. 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Pages 247-270 in Hatfield JL, Buhler DD, Stewart BA, eds. Integrated weed and soil management. Chelsea, MI: Ann Arbor Press Teasdale JR, Ride CP, Cai G, Magnum RW (2012) Expression of allelopathy in the soil environment: soil concentration and activity of benzoxazinoid compounds released by rye cover crop residue. Plant Ecol 213:1893-1905 Tisdale SL, Nelson WL (1975). Soil fertility and fertilizers. 3rd edn. New York, NY: Macmillan Publishing Co., Inc. 694 p 47      Torbert HA, Reeves DW (1991) Benefits of a winter legume cover crop to corn: Rotation versus fixed-nitrogen effects. Pages 99-100 in Cover crops for clean water. Jackson, TN: Soil and Water Conservation Society Tsai SM, Bonetti R, Agbala SM, Rossetto R (1993) Minimizing the effect of mineral nitrogen on biological nitrogen fixation in common bean by increasing nutrient levels. Plant Soil 152:131-138 United States Department of Agriculture-National Agriculture Statistic Service (USDA-NASS). 2008. Organic Survey: Table 7. Organic field crops harvested from certified and exempt organic farms. Available at: http://www.agcensus.usda.gov/Publications/2007/Online_Highlights/Organics/organics_1_0 7.pdf Accessed September 22, 2014 United States Department of Agriculture-National Agriculture Statistic Service (USDA-NASS) (2014a) Crop production: 2013 Summary. Available at: http://usda01.library.cornell.edu/usda/current/CropProdSu/CropProdSu-01-10-2014.pdf Accessed August 29, 2014 United States Department of Agriculture-National Agriculture Statistic Service (USDA-NASS) (2014d) 2012 United States Summary and State Data. Volume 1. Geographic Area Series. Part 51. Available at: http://www.agcensus.usda.gov/Publications/2012/Full_Report/Volume_1,_Chapter_1_US/us v1.txt Accessed May 5, 2014 United States Department of Agriculture- National Agriculture Statistics Service (USDA-NASS) (2014b) National statistics for beans. Available at: http://www.nass.usda.gov/Statistics_by_Subject/ Accessed September 10, 2014 United States Department of Agriculture-National Agriculture Statistic Service (USDA- NASS) (2014c) Quick stats. Available at: http://quickstats.nass.usda.gov/ Accessed September 22, 2014 United States Department of Agriculture-Natural Resources Conservation Service Plant Materials Program (USDA-NRCS) (2002) Plant fact sheet: Red clover (Trifolium pretense L.). Available at: http://plants.usda.gov/factsheet/pdf/fs_trpr2.pdf Accessed September 18, 2014 Vyn TJ, Faber JG, Janovicek KJ, Beauchamp EG (2000) Cover crop effects on nitrogen availability to corn following wheat. Agron J 92:915-924 48      Wagger MG (1989) Time of desiccation effects on plant composition and subsequent nitrogen release from several winter annual cover crops. Agron J 81:236-241 Wagger MG, Cabrera ML, Rannells NN (1998) Nitrogen and carbon cycling in relation to cover crop residue quality. Soil and Water Cons 53:214-218 Wall DA (1995) Bentazon tank-mixtures for improved redroot pigweed (Amaranthus retroflexus) and common lambsquarters (Chenopodium album) control in navy bean (Phaseolus vulgaris) Weed Technol 9:610-616 Wang G, Ngouajio M, Warncke DD (2008) Nutrient cycling, weed suppression and onion yield following brassica and sorghum sudangrass cover crops. Hort Technol 18:68-74 Warncke D, Dahl J, Jacobs L (2009) Nutrient recommendations for field crops in Michigan, Bulletin E2904. East Lansing, MI: Michigan State University Extension. 35 p Weil RR, White C, Lawley Y (2006) Forage radish: New multi-purpose cover crop for the MidAtlantic, Fact sheet 824. College Park, MD: Univ of Maryland Cooperative Extension. 8 p Weil R, Kremen A (2007) Perspective: Thinking across and beyond disciplines to make cover crops pay. J Sci Food Agric 87:551-557 Weinert TL, Pan WL, Moneymaker MR, Santo GS, Stevens RG (2002) Nitrogen recycling by nonleguminous winter cover crops to reduce leaching in potato rotations. Agron J 94:365372 Williams SM, Weil RR (2004) Cover crop root channels may alleviate soil compaction effects on soybean crop. Soil Sci Soc Am J 68:1403-1409 Wilson DO, Hargrove WL (1986) Release of nitrogen from crimson clover residue under two tillage systems. Am J 50:1251-1254 Woolley BL, Michaels TW, Hall MR, and Swanton CJ (1993) The critical period of weed control in white bean (Phaseolus vulgaris). Weed Sci 41:180-184 Wyland LJ, Jackson LE, Schulbach KF (1995) Soil-plant nitrogen dynamics following incorporation of a mature rye cover crop in a lettuce production system. J Agric Sci 124:1725 49      CHAPTER 2 COVER CROP IMPACT ON NITROGEN AVAILABILITY AND DRY BEAN CHARACTERISTICS IN AN ORGANIC SYSTEM Abstract Michigan is the number one producer of organic dry beans in the United States. Commercial pesticides and fertilizers cannot be used in organic systems, therefore cover crops could play an important role in increasing nutrient availability and ultimately crop yield. The objective of this research was to determine the influence of red clover, cereal rye, and oilseed radish cover crops on soil moisture, soil inorganic nitrogen (N), and dry bean growth and yield in an organic system. To meet this goal, 24 site-years of field data were collected on Michigan State University research farms and at organic grower cooperator farms in Michigan between 2011 and 2013. The cover crops studied included: medium red clover, oilseed radish, and cereal rye; a no cover crop control was also included. Within each cover crop treatment there were four bean varieties: ‘Zorro’ and ‘Black Velvet’ black beans and ‘Vista’ and ‘R-99’ (non-nodulating) navy beans. Cover crop biomass, N content, and carbon to nitrogen ratio (C:N) were recorded at peak production. Cover crop impact on soil moisture was measured at the time of dry bean planting. Soil inorganic N availability was monitored during the dry bean growing season using soil extractions, ion exchange resin strips, and a chlorophyll meter. Dry bean nodules were counted and grain N and the percentage of N derived from the atmosphere (%NDFA) in the grain were determined at harvest. Dry bean maturity, final population, and yield were also recorded. Overall, the commercial dry bean varieties responded to the cover crops similarly and showed few differences among varieties with regard to nodulation, percent N derived from the 50      atmosphere in the grain, grain total N, and yield. The non-nodulating variety ‘R99’ had less total grain N and yield, showing the benefit of N fixation. Soil moisture in the upper 2.5 cm was greater following red clover and cereal rye compared with the no cover control 50% or more of the time; for the other main site-years and following oilseed radish, soil moisture was not altered. Soil inorganic N often increased following red clover by as much 34 kg N ha-1 at planting and 55 kg N ha-1 at V2 compared with the no cover crop control, resulting in increased relative chlorophyll content in bean leaves, decreased nodulation at R1, delayed maturity, and greater grain N in some site-years; dry bean population and yield however were not affected. Cereal rye reduced soil inorganic N in some site-years, and caused early maturity of the beans. At maximum biomass production (12.8 Mg ha-1), rye reduced dry bean yield, however grain N was not affected. Oilseed radish occasionally increased inorganic N availability and bean populations at the V2 dry bean stage, but had no impact on nodule numbers, chlorophyll readings, maturity, yield, or grain N. No differences in %NDFA were detected following the cover crop treatments. Cover crop C:N ratio was the most consistent factor influencing inorganic N availability. Within the range of C:N ratios observed for oilseed radish, cereal rye, and the no cover control treatments, there was a negative correlation between C:N ratio and soil inorganic N availability at the time of dry bean planting; the higher C:N ratios within each of these treatments, the more likely N was immobilized. Conversely for clover, there was a positive correlation between the C:N ratio and soil inorganic N availability at the time of dry bean planting; lower C:N ratios result in more N available. Cover crop management to manipulate biomass and C:N ratios to advantage dry beans is dependent on the goals of the producer and the cover crop species. Understanding N release and N cycling in cover crop systems will continue to be important to 51      synchronize N availability with cash crop needs to improve crop yield and quality. Overall, in 24 site-years, cover crops had no detectable effect on dry bean yields in 21 of 24 cases, and reduced yields in 3 of 24 cases compared with the no cover crop control. Although thoughtful management can reduce the risk of yield loss, farmer adoption of these cover crops will depend on demonstration of potential benefits including nutrient scavenging, reduced N leaching during the winter months, increased soil organic matter, and improved water infiltration. Introduction Dry edible beans (Phaseolus vulgaris L.) are grown in several regions of the United States. The top producing states based on hectares harvested in 2013 were: North Dakota (33%), Michigan (13%), and Idaho (9%) (USDA-NASS 2014a). Michigan is the 2nd highest producer of navy beans and the highest producer of black beans in the country (USDA-NASS 2014b). Under conventional dry bean production, producers typically treat seeds with insecticides and/or fungicides and both pre- and post-emergence herbicides are used to control weeds. Furthermore, though dry beans are a legume, 45 kg ha-1 of nitrogen (N) or more is applied at planting as N fixation is not as efficient in dry beans as in other legumes, such as soybean (Piha and Munns 1987; George and Singleton 1992). Demand for organically produced dry beans has been on the rise in recent years both within the US and abroad. The only survey of organic agriculture in the U.S. was conducted in 2007 at which time Michigan was the top organic dry bean producing state, comprising 39% of the hectares harvested (USDA-NASS 2008). Producing a quality dry bean crop without the use of synthetic amendments and pesticides presents unique challenges for organic growers, especially 52      when it comes to soil fertility, pest management (i.e. insects, diseases and weeds), and bean variety selection. Cover crops are one possible solution to address soil fertility and some pest management issues in the production of organic dry beans. Cover crops can impact soil fertility, specifically N availability, through nutrient scavenging (Sainju et al. 1998; O’Reilly et al. 2012) and N fixation by leguminous cover crops (Ladd et al. 1986; Stivers and Shennan 1991; Sainju and Singh 2001). The magnitude and timeframe over which cover crops alter soil inorganic N is dependent on many factors, including environment and climate, soil characteristics (soil composition), cover crop characteristics (composition and growth stage), and management practices (crop rotation, tillage, etc.) (Doran and Smith 1991; Wagger et al. 1998; Dabney et al. 2010). Medium red clover (Trifolium pratense L.) and cereal rye (Secale cereale L.) are popular cover crops among Midwest producers because they can be planted early in the spring and late in the fall, respectively, making them easier to fit into rotations that include long-season row crops. Typically medium red clover is interseeded into, or planted following, a small grain the year before corn (Zea mays L.) is planted. Cereal rye is most often planted between corn and soybeans (Glycine max (L.) Merr.) or dry beans. The seed of these two cover crops is readily available and relatively inexpensive, which enhances their popularity. Oilseed radish (Raphanus sativus L.) has been a newer cover crop of interest over the past 15 years. Row crop producers are still experimenting with how to best integrate this cover crop into their rotations. All three of these cover crops scavenge and reduce soil inorganic N during the fall and winter months (Hoyt and 53      Mikkelsen 1991; Sainju et al. 1998; Baggs et al. 2000; Vyn et al. 2000; Weinert et al. 2002; Williams and Weil 2004; O’Reilly et al. 2012). Corn is often planted following a red clover cover crop to utilize available N (Magdoff and Van Es 2009). Several researchers have shown greater corn nitrogen uptake and/or yield following a clover cover crop compared with no cover (Dapaah and Vyn 1998; Gentry et al. 2013; Torbert and Reeves 1991; Vyn et al. 2000). One season of clover increased residual soil inorganic N for at least two years following incorporation compared with synthetic N (Harris et al. 1994); a long term clover stand did not have an additive effect on soil N compared with a single season of red clover planted as a cover crop (Gentry et al. 2013). Rye is a well-known nutrient scavenger and reduces nitrogen losses in the fall and winter months (Sainju et al. 1998; Baggs et al. 2000; Vyn et al. 2000; O’Reilly et al. 2012; Weinert et al. 2002; Hoyt and Mikkelssen 1991). The release of N from rye residue is dependent on its physical characteristics and chemical composition at the time of termination (Wagger et al. 1998). The C:N ratio is one of the components most highly correlated with decomposition and N release in N-limited soils. C:N ratios of 25:1 or less lead to net N mineralization (Clark et al. 1997; Kuo and Jellum 2002), while higher ratios lead to N immobilization. As rye grows and matures in the spring, the C:N ratio increases and can quickly exceed 25:1 (Wagger 1989; Clark et al. 1994). The impact of rye on crop yields has been variable, with some crops, such as corn, suffering due to N immobilization (Torbert and Reeves 1991). Corn uptake of N mineralized from rye is low compared with N uptake from crimson clover (Ranells and Wagger 1997). Other crops such as potato (Solanum tuberosum L.) have benefited from having rye in the rotation (Larkin et al. 54      2010). Soybean yield is generally not influenced by a rye cover crop (Reddy 2001; Reddy et al. 2003; Sawyer et al. 2012). Oilseed radish has piqued the interest of producers due to its rapid shoot and root growth during the late summer and early fall, potential to alleviate soil compaction, and potential for pest suppression (Clark 2007; Williams and Weil 2004). Oilseed radish is typically planted in latesummer in the northern climates of the U.S. and does not survive the winter when temperatures drop below -4 C, thus requiring no management in the spring. Oilseed radish is known to scavenge nitrogen (Clark 2007; Jackson et al. 1993; Stivers-Young 1998; Dean and Weil 2009; Vyn et al. 2000; Horton 2013), however research on N release and mineralization following oilseed radish winter-kill is limited (Vyn et al. 2000; Horton 2013). Corn and soybean crops generally show no yield response to oilseed radish compared with no cover (Vyn et al. 2000; Williams and Weil 2004). However in corn, yield increased following oilseed radish compared with no cover in two of three years in an Ontario study (Dapaah and Vyn 1998). Corn yield was also improved at one of four research sites in Indiana in 2012 (Horton 2013). Previous research has focused on corn and potato yield following incorporation of medium red clover, cereal rye, and oilseed radish cover crops, and many questions remain with regard to utilizing these covers before organic dry beans. Dry beans are planted later than sugar beets, corn, and soybean, and therefore overwintering cover crops can be terminated later in the spring. Delaying the termination of overwintering cover crops would mean warmer soil and air temperatures which could alter decomposition rates and the timing of nitrogen mineralization. Decomposition and N mineralization rates would differ for oilseed radish, as the length of time 55      between winter-kill and dry bean planting would be at least 30 days longer compared with sugar beets, corn, or soybean. Few studies have been published on the influence of cover crops on nitrogen availability to dry bean, and dry bean growth and yield (Shrestha et al. 2002). The objective of this research was to determine the influence of red clover, cereal rye, and oilseed radish cover crops on soil moisture, soil inorganic N, and dry bean growth and yield in organic dry bean production systems. Materials and Methods The two main sites for this research were located on organically certified or transitional ground at Michigan State University (MSU) research farms for three years (2011-2013). The MSU campus locations were in Lansing, MI at the Horticultural Teaching and Research Center (42.67⁰N, 84.48⁰W) (2011 and 2012) and the Agronomy Farm (42.71⁰N, 84.47⁰W) (2013). The other location was at the Kellogg Biological Station (KBS) (42.40⁰N, 85.38⁰W) in Hickory Corners, MI. Soil types at these locations were loam or clay loam, with soil organic matter ranging from 2.0 to 4.0% (Table 2.01). Additional satellite sites were located throughout Michigan on certified organic farms in cooperation with growers. Soil types at these satellite sites ranged from sandy loam to clay loam soils with organic matter averaging 3.1%, excluding two sites in Sandusky, MI (Table 2.01). Over the three year period there were a total of 18 siteyears of data collected at satellite locations located at Alma, Caro, Columbiaville, Millington, and Sandusky, MI. At each site, a split plot design was used with three to four replications. The main plot factor was cover crop species and the subplot factor was dry bean variety. At the main sites there were four 56      cover crop treatments: medium red clover, oilseed radish, cereal rye, and no cover. All cover crops were planted into or after the harvest of a small grain in the calendar year preceding dry bean planting (Figure 2.01). Medium red clover ‘Marathon’ was frost seeded (11 kg ha-1) into the small grain usually around March, with the exception of 2011 MSU when red clover was seeded in August of 2010. Following the harvest of the small grain, Groundhog ™ oilseed radish (Ampac Seed Company, Tangent, OR) was planted (12 kg ha-1) in mid-August and cereal rye ‘Wheeler’ was planted (100-125 kg ha-1) in mid-September. At the main sites, the sub-plot factor consisted of four dry bean varieties, two each in two classes. Black bean varieties included ‘Zorro’ (Kelly et al. 2009) and ‘Black Velvet’ and navy bean varieties included ‘Vista’ and a non-nodulating line ‘R99’ (Park and Buttery 1992). Each cover crop plot at the main sites was 12.2 m wide and a minimum of 15.2 m long. During the dry bean season, four 3 m wide bean subplots were planted within each main cover crop plot. Each subplot consisted of four rows of one dry bean variety at 76 cm spacing. At the satellite sites there were two cover crop treatments: one of the cover crops (i.e. medium red clover, oilseed radish, or cereal rye) and a no cover crop control. Clover (seven site-years) and rye (five site-years) varieties were chosen based on what the growers were already using on their farms, typically ‘variety not stated’. GroundHog™ oilseed radish was provided to growers interested in oilseed radish (six site-years). Cover crop planting times and rates were more variable at satellite sites than at the main sites. At the satellite sites the subplot factor consisted of two dry bean varieties, ‘Zorro’ black bean and ‘Vista’ navy bean. Plot dimensions at the satellite sites were based on the grower’s equipment size, with minimum plot lengths of 30.5 m. Most 57      growers planted rows at a 76 cm spacing, however three sites planted at 56 cm spacing. Target bean planting populations ranged from 262,000 to 296,000 seeds ha-1 for both main and satellite site locations. No external N sources were added to fields in this study. In general, the red clover and cereal rye cover crops were terminated using a primary tillage tool (e.g. chisel plow). All oilseed radish and no cover control plots also received primary tillage in the spring. After cover crop termination, all field activities were performed uniformly across all treatments at each location (e.g. seedbed preparation, mechanical weed control measures, etc.). Precipitation data was collected at the main sites by utilizing Michigan State University’s Enviro-weather online database (MSU Enviroweather 2014) for the main site locations (Table 2.02). Cover crop quantity and quality Cover crop measurements included percent cover, height, dry biomass, C:N ratio, and N content of the plant tissue. Measurements were taken at the time of peak production, which occurred in mid- to late-November for oilseed radish, prior to winter-kill, and in spring at the time of incorporation for clover, rye, and no cover. Percent cover was determined using line-transects (Laflen et al. 1981) laid diagonally across the main cover crop plots, 15 m (main sites) or 30 m (satellite sites). Counts of cover crop, weed, or no vegetation were taken along transects at 50 and 100 points at 30 cm spacing, for the main and satellite sites, respectively. Two 0.25 m2 quadrats of whole plant material (shoots + roots) were collected for each cover crop plot. Samples were separated into cover crop and weed material and were then dried at 66 C for 7 d and weighed. The C:N ratios and N content of the tissue were determined by grinding dried 58      biomass samples using a Christy Mill (Suffolk, United Kingdom) fitted with a ≤ 2 mm sieve and sending 2 g samples to Midwest Laboratories, Inc. (Omaha, NE) for total carbon and nitrogen analysis. Cover crop influence on soil moisture at dry bean planting Soil moisture was measured in each cover crop treatment at the time of dry bean planting at the main sites (2012 and 2013). A Field Scout TDR 300 Soil Moisture Meter (Spectrum Technologies, Inc., Aurora, IL) with prongs set at planting depth (2.5 cm) was used to measure 20 points within each plot. Cover crop influence on soil nitrogen availability Three methods for quantitatively or qualitatively measuring the amount of inorganic N available in the soil for plant uptake were used in this research. Soil extraction. Eight to ten soil cores were pulled in the fall and at five times during the dry bean growing season (at planting, V2, R1, R5, and harvest) to a depth of 20 cm in each cover crop plot. Samples were homogenized within each plot, dried at room temperature, and ground in a Wiley mill (Thomas Scientific, Swedesboro, NJ) fitted with a 1 mm sieve. After grinding, samples were extracted with 1 M KCl and filtered through #2 Whatman filter paper (GE Healthcare Bio-Science, Pittsburg, PA). Extracts were sent to the Michigan State University Soil and Plant Nutrient Laboratory to determine NH4-N and NO3-N concentrations via the ammonium-salicylate and cadmium reduction methods, respectively, using a Lachat rapid flow injection autoanalyzer (Hach Co., Loveland, CO) (Mulvaney 1996). 59      Cation and anion exchange resin strips. Ion exchange resin membranes have been used to study N availability in agricultural soils for 20 years and reportedly mimic root uptake of nutrients (Subler et al. 1995; Qian and Schoenau 1995, 2001). The ability to continually monitor soil N gives resin membranes an advantage over soil extractions, which only reflect N availability at a single point in time; however the area of soil included in the test is much more limited. A protocol adapted from the Kellogg Biological Station was utilized for this experiment (Jasrotia and McSwiney 2008). Two cation and two anion ion exchange resin strips (GE Water and Process Technologies, Minnetonka, MN), measuring 2.5 by 10.1 cm were inserted into the soil using a putty knife directly into the dry bean rows of the two center dry bean plots within each cover crop. Each resin strip sampled the top 10.1 cm of the soil profile. Strips were buried so that no portions were exposed above the soil surface to minimize rodent feeding. Resin strips were replaced every two weeks throughout the growing season for a total of eight sampling times. Following removal, soil was washed away using distilled water and all four strips from a given cover crop plot were combined and stored in plastic 7.6 by 17.8 cm Whirl-Pak bags (Nasco, Fort Atkinson, WI) at 4 C until extraction. At the time of extraction, 25 ml per strip of 1 M KCl solution were added to the Whirl-Paks. The Whirl-Paks were sealed and shaken at 60 rpm for one h, after which the extracts were filtered through #2 Whatman filter paper and sent for analysis as described above for the soil extracts. Relative chlorophyll readings. Researchers have documented an increase in plant chlorophyll as soil inorganic N increased (Piekkielek and Fox 1992; Blackmer and Schepers 1995). Therefore, relative chlorophyll readings were taken at the V2, R1, and R5 bean stages using a 60      Minolta SPAD-502 chlorophyll meter (Spectrum Technologies, Inc., Aurora, IL). Ten plants per plot were sampled at each stage by placing the meter on the center leaflet of the uppermost, fully expanded trifoliate. Readings for a chlorophyll meter are all relative within a given site and variety. Higher numbers indicating higher chlorophyll content and imply that soil inorganic N is higher. Dry bean variety and cover crop influence on dry bean attributes Dry bean measurements included: plant density, root nodule number, relative chlorophyll readings, yield and at the main sites only, maturity, grain N content, and percent N derived from fixation. Plant densities were recorded at V2 and at the time of harvest by counting the number of plants in 4.6 m (main sites and V2 satellite sites) or 9.1 m (harvest satellite sites) of two rows. Root nodules were counted on five plants per plot in 2011 and 2012 at V2 and R1. Peak fixation has been reported to occur between 28 to 42 days or more after planting, depending on temperature fluctuations (Graham 1979). Bean top growth was removed at the base of the plant with pruners. Roots were then collected by placing a Miltona PowerStroke cup cutter (Maple Grove, MN) over the cut stem and removing a cylinder of soil 10.5 cm in diameter by 20 cm deep. Roots were then removed from the soil cores, rinsed with water, and the number of nodules were counted. Bean maturity was visually assessed one to two times per growing season at the main site locations only. Early ratings were taken 85-90 days after planting (DAP), whereas late ratings were taken 100-105 DAP. The scale ranged from 1 to 5; with 1 representing fully defoliated dry bean plants that were ready for harvest and 5 representing plants that were almost entirely green with all leaves still attached. At the time of harvest, whole plants were pulled by hand (4.6 m of two rows at main sites and 9.1 m of two rows at satellite sites) and an Almaco 61      stationary thresher (Nevada, IA) was used to separate the beans from the other plant material. Secondary cleaning of the samples was done using a Vac-A-Way seed cleaner (Hance Corp. Westerville, OH) to remove dirt, debris, and malformed or underdeveloped beans. Cleaned samples were weighed and grain moisture recorded using a Grain Analysis Computer 2100 Agri (Dickey-John Corp. Auburn, IL). Yields were calculated by adjusting to 18% moisture. Cleaned beans were then dried to remove all moisture, ground using the Christy Mill with ≤ 2 mm sieve, packed in tins and sent to the University of California at Davis Stable Isotope Laboratory for analysis of total N content and δ15N. The percentage of N derived from the atmosphere (%NDFA) was determined using the following formula (Shearer and Kohl 1986; Ramaekers et al. 2013) %NDFA δ15N δ15N δ15N B 100 where B is the δ15N value of the N2 fixing bean grown in the greenhouse in the absence of soil N. A B value of -3.62 was used for both the ‘Zorro’ and ‘Black Velvet’ black bean varieties and a value of -3.29 was used for the ‘Vista’ navy bean variety based on prior greenhouse work performed by the Michigan State University Dry Bean Breeding Laboratory (James Heilig, personal communication 2014). Statistical analysis All data sets were analyzed in SAS 9.3 using the MIXED procedure. All cover crop parameters, soil moisture, soil N extractions, and resin strip extractions were measured at the main plot level, 62      therefore cover crop, year, and location was treated as fixed effects and replication was treated as a random effect. Dry bean populations, root nodulation, maturity, yield, grain N, and %NDFA data were taken at the subplot level, therefore cover crop, bean variety, year, and location were treated as fixed effects and replication was treated as a random effect. Variance assumptions were checked using the UNIVARIATE procedure. Mean separation was conducted using Fisher’s Protected LSD (P≤0.05). Variations in management and weather led to many interactions among locations, years, and measurement timings, therefore within each main effect (i.e. cover crop and dry bean variety) site-years and timings are presented separately. The exceptions were root nodulation, which was combined across main site-years (2011 and 2012, root nodulation was not recorded in 2013) and total bean grain N, which was combined across main site locations for each of the three years. The influence of the cover crop treatments on soil inorganic N and relative chlorophyll content were compared at each sample time, and not over time, for all methods. Pearson’s correlation coefficients were used to assess linear correlations among cover crop, soil, and dry bean properties across all site-years for each cover crop treatment using the CORR procedure in SAS. Results and Discussion Cover crop quantity and quality Biomass. Timely planting of cover crops, either within (red clover) or following (oilseed radish, rye) a small grain crop, resulted in substantial cover crop biomass (> 4 Mg ha-1) at the main sites in most years. 63      Clover dry biomass ranged from 2.3 to 11.6 Mg ha-1 over the six main site-years, with additional weed biomass of 0 to 1.3 Mg ha-1 (Table 2.03). The 2011 MSU site-year had the least clover biomass, 2.3 MG ha-1 because the cover crop was established in mid-August, whereas all other main site-years had clover established by interseeding into the small grain crop in the spring. Typical aboveground biomass production for red clover ranges from 4.5 to 9 Mg/ha (Clark 2007). Red clover biomass in the present study included root biomass, making the range of biomass production observed slightly higher by comparison, with the exception of the late established location, 2011 MSU. Percent cover of the red clover cover crops at the main sites ranged from 84 to 100% at the time of incorporation in the spring. Oilseed radish biomass in late fall (i.e. two to three months after planting) ranged from 2.9 to 6.1 Mg ha-1 in five of the main site-years; the N content of the biomass was 33 to 164 kg ha-1 (Table 2.03). At 2011 MSU, oilseed radish had extremely low biomass (0.8 Mg ha-1) and N content (10 kg ha-1) due to competition from volunteer oats (Avena sativa L.) (67% of the cover and 6.1 Mg ha-1 dry biomass in the fall, data not presented). By spring, volunteer oats were not a component of the weed samples because of winter-kill in northern climates. In the southeastern USA where oilseed radish can overwinter, Schomberg et al. (2006) recorded aboveground oilseed radish biomass of up to 6.2 Mg ha-1 and more consistent N content, ranging from 75 to 95 kg N ha-1. In our study, at peak oilseed radish biomass, ground cover ranged from 21 to 74% for oilseed radish. Oilseed radish biomass and percent cover can vary based on the time of seeding, as well 64      as differences in fall growing conditions and residual soil N available at the time of oilseed radish seeding (Jablonski 2007), which was not measured in our research. Cereal rye biomass ranged from 7.9 to 12.8 Mg ha-1 at the main sites, similar to other studies (Clark 2007; Reeves 1994; Schomberg 2006); although our biomass for 2011 MSU is higher than any previously reported observations. Our target incorporation height for rye was 46 cm; however spring precipitation often made it difficult to terminate rye at this stage with a chisel plow. This was particularly true for three of the main site-years (2011 MSU, 2012 KBS, 2013 MSU), where termination was not possible until rye heights were greater than 70 cm, which resulted in biomass accumulations greater than 11 Mg ha-1. To prevent further growth, the 2011 MSU and 2012 KBS plots were mowed and then incorporated with a chisel plow once the soil dried sufficiently. Percent cover of the rye cover crops at the main sites ranged from 80 to 100% at the time of incorporation in the spring. Weed biomass within the rye cover crop was negligible in all main site-years. Winter weed biomass. The weed biomass present in the spring in all cover crop treatments was comprised of a variety of species based on year and location. The most commonly observed weeds in the spring included winter annuals such as common chickweed (Stellaria media L.), field pennycress (Thlaspi arvense L.), mayweed chamomile (Anthemis cotula L.), annual bluegrass (Poa annua), and henbit (Lamium amplexicaule L.) and occasionally volunteer wheat. Weed biomass in the no cover control treatments ranged from 1.5 to 7.1 Mg ha-1. Volunteer 65      wheat was the dominant species in the high biomass site-year, 2011 KBS. Percent weed cover in the no cover control treatments ranged from 59 to 95%. In general, there was more total plant (cover + weed) biomass produced when a cover crop was planted, compared with the no cover control (Table 2.03). Cereal rye produced more total biomass than oilseed radish in all main site-years, with the exception of 2011 KBS. Red clover total biomass was equal to or greater than rye in four of six site-years and greater than oilseed radish in two of six site-years. Nitrogen content. Cover crop nitrogen content was positively correlated with cover crop and total biomass for all cover crop treatments and also for the weed biomass in the no cover control when analyzed across all site-years (Table 2.04). Red clover interseeded into a small grain cover crop in early spring contained more potentially mineralizable N within its biomass than oilseed radish, cereal rye, or the no cover control; values ranged from 115 to 232 kg ha-1 at the main sites (Table 2.03). Rye and oilseed radish had higher N content than the weeds found in the no cover control in two of six site-years. Nitrogen content for those treatments were 33 to 164 kg ha-1 for oilseed radish, 42 to 136 kg ha-1 for rye, and 18 to 53 kg ha-1 for the weeds in the no cover control (Table 2.03). Schomberg et al. (2006) recorded more consistent aboveground oilseed radish N content, ranging from 75 to 95 kg N ha-1. Our results for rye are similar to other researchers (Clark 2007; Reeves 1994; Schomberg 2006), although our highest N content, 136 kg N ha-1, is higher than any previously reported observations. 66      C:N ratios. C:N ratio was positively correlated with cover crop biomass in the three cover crop treatments and weed biomass in the no cover control (Table 2.04). The C:N ratios of clover ranged from 15:1 to 18:1 and were consistently lower than cereal rye, the weeds in the no cover control, and occasionally lower than oilseed radish (Table 2.03). The C:N ratio of oilseed radish was variable, with values ranging from 14:1 to 31:1. Schomberg et al. (2006) also observed varying oilseed radish C:N ratios from 14:1 to 29:1 over a three year period, though these values were for aboveground material only. The C:N ratios of the rye biomass ranged from 26:1 to 52:1 and were higher than clover, oilseed radish and the weeds in the no cover control in five of six site-years (Table 2.03). These C:N ratios are similar to what others have observed (Reeves 1994; Clark et al. 1997; NRCS 2011). For all of these cover crops, the variability in C:N values by siteyear could be the result of differences in development and relative plant component composition (i.e. leaves, stems, roots) at the time of incorporation (Müller et al. 1988; Quemada and Cabrera 1995; Clark et al. 1997; Schomberg et al. 2006; NRCS 2011). For the weeds in the no cover control, C:N ratios ranged from 22:1 to 29:1. To date, C:N ratios of winter annual weed species have not been reported in the literature. Of the 18 satellite sites, only seven produced biomass that was within the ranges of the main sites and only six had biomass containing similar levels of N (Table 2.05). Unlike the main sites, growers were not always able to interseed clover into a small grain or plant oilseed radish immediately following small grain harvest at the satellite sites. This and other production considerations often resulted in later cover crop planting dates compared with the main sites, greatly reducing biomass production and N content, two factors which were positively correlated for all cover crop treatments (Table 2.04). The C:N ratios were also lower overall for the satellite 67      sites compared with the main sites because of delayed cover crop planting and reduced plant development at the time of winter kill (oilseed radish) or tillage (red clover or rye). At most satellite sites there was no weed biomass present in the no cover control treatments due to delayed cover crop planting (and thus later fall tillage operations). Information collected from the satellite sites offer insight into correlations among cover crop, soil N, and dry bean properties when pooling across all site-years, despite showing few differences within a site-year. Cover crop influence on soil moisture at dry bean planting Cover crops have the potential to increase, decrease, or have no effect on soil moisture (Stivers and Shennan 1991; Teasdale and Mohler 1993; Dapaah and Vyn 1998; McGuire et al. 1998; Daniel et al. 1999; Conklin et al. 2002). In this study, the overwintering cover crops, red clover and rye, increased soil moisture in the surface 2.5 cm at planting in three and two of the four main site-years where soil moisture was measured, respectively (Table 2.03). Soil moisture at this depth did not differ between the oilseed radish and no cover control treatments in three of four site-years. No reduction in soil moisture at the time of dry bean planting occurred in our research in any site-year, in spite of lower than normal precipitation in 2012 (Table 2.02). Cover crops growing in the spring act as a mulch and high biomass producers, such as rye, can maintain higher levels of soil moisture for the subsequent cash crop compared with no cover control treatments (Teasdale and Mohler 1993; Daniel et al. 1999). In Stillwater, Maine, the incorporation of red clover and compost increased soil water content relative to the unamended treatment by a minimum of 2% in the 5 to 62 days following incorporation (Conklin et al. 2002). In Ontario, Canada, wet aggregate stability was improved through the use of over-wintering 68      cover crops such as red clover and ryegrass (Lolium multiflorum Lam.) (Dapaah and Vyn 1998), which could translate into increased soil water holding capacity. One of the primary concerns for growers considering cover crop use however, is the potential for reduced soil moisture for crops planted following cover crops (FJensen and NCR-SARE 2013), especially in areas where moisture is more limited. In California, winter legume cover crops reduced soil moisture compared with fallow, glyphosate treatments (Stivers and Shennan 1991). In this study, we measured moisture only in the top 2.5 cm of soil. Though growers have been primarily concerned with how cover crops impact soil moisture at the time of crop planting future studies should consider measuring impact of cover crops on soil moisture throughout the season at varying depths of the root zone. Cover crop influence on soil nitrogen availability Soil extraction. Soil nitrate was always greater than ammonium, with an average of four times more nitrate than ammonium (data not presented), which concurs with previous research (Sweeney et al. 2008; Spangler et al. 2014). Phaseolus vulgaris can utilize both forms of nitrogen (Guo et al. 2007); therefore soil N availability will be presented as total inorganic N, combining nitrate and ammonium. Soil inorganic N in November was lower in the oilseed radish treatments compared with the no cover control in four of six main site-years (Figure 2.02). Rye and clover also had less inorganic N in November compared with the no cover control in two of six site-years. When clover was planted late in the summer (2011 MSU), fall soil inorganic N was greater in the clover compared with the no cover control, suggesting that the small clover scavenged less N than the weeds in the no cover control. In previous research, red clover, rye, and oilseed radish cover crops, reduced soil inorganic N during the fall and winter months (Hoyt 69      and Mikkelsen 1991; Sainju et al. 1998; Baggs et al. 2000; Vyn et al. 2000; Weinert et al. 2002; Williams and Weil 2004; O’Reilly et al. 2012). During the dry bean growing season, cover crop differences in soil inorganic N compared with the no cover control were most prevalent at the time of dry bean planting (i.e. two to four weeks after cover crop incorporation), V2 (i.e. five to eight weeks after incorporation), and R1 (i.e. eight to eleven weeks after incorporation) (Figure 2.02). The V2 stage (late-June to early-July) was generally associated with the highest soil inorganic N levels in the no cover control. Despite differences in soil organic matter of up to 2% among KBS and MSU locations each year, soil inorganic N availability at V2 in the no cover control treatments only differed by 3 to 14 kg ha-1. Red clover increased total available N at the time of dry bean planting (June) in all site-years and in four of five site-years at V2 compared with other treatments (2011 MSU is excluded because clover was planted late in the summer) (Figure 2.02). Soil inorganic N increased by 13 to 34 kg N ha-1 at planting and 14 to 55 kg N ha-1 at V2, compared with the no cover control. During the latter part of the growing season (R1 through harvest), clover treatments had greater soil inorganic N compared with the no cover control in some site-years. Soil inorganic N at the time of dry bean planting was positively correlated with red clover C:N ratio and N content. These two attributes and red clover biomass were also positively correlated with soil inorganic N at V2. Seasonal fluctuations in soil inorganic N are related to soil moisture, soil temperature, microbial populations, and soil organic matter (Harmsen and Van Schreven 1955), all factors which 70      influence the decomposition and N mineralization of cover crop residues as well. A clover cover crop can increase soil inorganic N for multiple growing seasons (Harris et al. 1994). In a bagged residue study conducted in Georgia, 60% of the N from crimson clover had been released into the soil by four weeks after moldboard plowing (Wilson and Hargrove 1986). By 16 weeks, 69% had been released, showing that 31% of the N accrued in the clover biomass remained and was not immediately available to the following cash crop. The magnitude and duration of N release from clover may be slower in Michigan than in Georgia because temperatures are cooler and there is less precipitation during the growing season. Cooler soil temperatures reduced N release from alfalfa pellets, blood meal, and chicken manure under laboratory incubation (Agehara and Warncke 2005). Also, reduced precipitation resulted in 28% more N retention in crimson clover residue after 16 weeks compared with a year with normal precipitation (Wagger 1989). Soil inorganic N averaged 13 kg N ha-1 greater in the oilseed radish treatment in two of six main site-years compared with no cover control at V2 and was greater than rye in five of six site-years (Figure 2.02). Soil inorganic N at V2 was positively correlated with oilseed radish N content prior to winterkill (Table 2.04). A similar observation was made by Vyn et al. (2000) at one of two Ontario, Canada locations when oilseed radish was planted preceding corn. Oilseed radish fall plowed following a killing frost, had 2.9 mg NO3-N (kgsoil)-1 more N at the time of presidedress sampling than the no cover control, equating to a 20% increase in concentration. In Indiana, undisturbed oilseed radish plots were found to have increased soil nitrate availability in the spring in the six weeks leading up to corn planting in May, with concentrations being highest directly next to the root holes. The weather that year was unseasonably warm in the late winter 71      and dry in the spring and summer, meaning residue breakdown and N mineralization occurred earlier and nitrate was not leached from the system as quickly as would be expected in a typical year (Horton 2013). Rye reduced soil inorganic N at the time of dry bean planting in two of six site-years, at V2 in three of six site-years, and at R1 in one of six site-years, compared with the no cover control (Figure 2.02). The average N reduction was 13 kg N ha-1 at planting and 15 kg N ha-1 at V2 in those site-years. Rye biomass, C:N ratio, and N content were all negatively correlated with soil inorganic N at the time of planting (Table 2.04). Immobilization of N by rye has been observed in numerous studies, particularly when rye is nearing the reproductive phase and/or biomass is high (Wyland et al. 1995; Ruffo et al. 2004; Clark 2007). The reason N was immobilized in some site-years and not others is not immediately clear. Rye biomass, N content (except 2011 MSU), and C:N values (except 2012 KBS) were also similar (Table 2.03). Soil composition, soil organic matter, and precipitation were variable among the site-years, however they do not appear to explain the incidence of N immobilization (Tables 2.01 and 2.02). Soil moisture in the rye plots was higher in 2012 and 2013 at MSU at the time of dry bean planting compared with KBS, however other studies have found net soil N mineralization and residue decay to be positively correlated with soil moisture (Myers et al. 1982; Andrén et al. 1992). Spring weed biomass was negatively correlated with soil inorganic N at the time of dry bean planting for red clover, radish and the no cover control and at V2 for the red clover and the no 72      cover control (Table 2.04). This appears to be related to the C:N ratio of the weeds, as it is also negatively correlated with N availability in the no cover control. The satellite sites had fewer differences in total available N in the soil compared with the main sites (Table 2.06). In Caro in 2011, more N was available to dry beans following clover at the time of planting and at R1. This site produced 6.0 Mg ha-1 of clover biomass, second only to the Sandusky clover satellite site in 2012 (Table 2.05). However the Sandusky site did not show differences in total available N, perhaps due to droughty conditions at that location in 2012 reducing N leaching and resulting in high inorganic levels over both the red clover and no cover treatments. Few of the sampling times at the oilseed radish satellite sites showed differences in soil inorganic N when comparing oilseed radish with the no cover control (3 of 29) (Table 2.06). At Alma in 2011, soil inorganic N was greater following oilseed radish compared with the no cover control at V2. Conversely, soil inorganic N was lower at two sampling times, 2012 Alma R1 and 2012 Millington planting, following oilseed radish compared with the no cover control. A large rye cover crop (10.7 Mg ha-1) reduced available N at the V2 stage of dry bean development at Caro in 2012 (Table 2.05), however at other site-years when rye biomass ranged from 1.0 to 1.9 Mg ha-1, soil inorganic N was not different from the no cover control. Resin strips. Soil inorganic N measurements with resin strips were more variable compared with extracted soil cores measurements. Though general trends in inorganic N availability were similar among the two methods, the resin strips only detected differences among the cover crop treatments at eight of the 30 common sample times, compared with 21 differences detected by 73      the soil extractions (Figures 2.02 and 2.03). An increase in soil inorganic nitrogen following red clover compared with the no cover control was found by both the extracted soil samples and the resin strips 63% of the time when the two methods concurrently detected differences. The relationship of soil inorganic N among oilseed radish and cereal rye compared with each other, red clover, and no cover was variable among the two sampling methods. Reduced sample size, fluctuations in soil moisture, and positioning are most likely responsible for the variability seen when using the resin strips. The resin strips were placed at two points within a cover crop plot and may not be as representative of the whole plot as the eight to ten points sampled and pooled for soil extraction. Also, low soil moisture can reduce N uptake by ion exchange resin membranes, due to decreased contact between the resin surface and the soil solution (Johnson et al. 2005). As soil moisture fluctuates throughout the growing season (not measured) the resin strips N adsorption may be reduced compared with soil extractions, especially in a dry year, like 2012. Finally, due to cultivation in this organic system, the resin strips were placed directly in the bean row, where N was likely depleted by the growing dry bean roots. Soil samples on the other hand were collected between the rows to avoid damaging plants. To investigate the suspected N depletion in the root zone, soil cores were collected and extracted both within and between the row at KBS and MSU in 2012 and 2013. More inorganic N was found in the between row samples for most sampling times (V2 to harvest) at 2012 MSU, 2013 KBS, and 2013 MSU (data not shown). Inorganic N was 18 to 48% lower within the dry bean row compared with between the rows. At 2012 KBS differences in N among the in- and between-row sampling locations did not vary and differences in soil inorganic N in cover crop 74      treatments occurred at five of eight sampling times using the resin strips (Figure 2.03). Increasing the number of resin strips in the field may decrease variability; however, it would be difficult to change their placement in an organic system due to regular soil disturbances used to manage weeds. Destructive dry bean sampling for N content throughout the growing season for comparisons with resin strip and soil extractions may further our understanding of which sampling system is more appropriate for studying N dynamics in this organic system. Relative chlorophyll readings. Relative chlorophyll readings were usually highest during the vegetative growth phase (V2) compared with the reproductive phases (R1 and R5) of dry beans in 2012 and 2013 (Tables 2.07 and 2.08). Sandoval-Villa et al. (2000) attributed this trend in tomato to the shift in the location of the N sink to the flowers and developing fruit. Black Velvet black bean usually had higher chlorophyll readings compared with the non-nodulating navy bean R99 at the main sites (Table 2.07, Appendix D Table D.01). However, at the satellite sites, there were several instances where chlorophyll readings were higher for the Vista navy bean compared with the Zorro black bean (Table 2.08). Differences in chlorophyll readings among plant hybrids and varieties have been observed for other crops, such as corn (Schepers et al. 1992) potato (Minotti et al. 1994), and tomato (Sandoval-Villa et al. 2000). Schepers et al. (1992) attributed chlorophyll differences among corn hybrids to genetic differences in greenness. Dry beans planted following frost-seeded red clover had higher relative chlorophyll content compared with the no cover control at V2 in three of the five site-years (Table 2.09, Appendix D Table D.01); soil inorganic N was higher in four of five site-years according to V2 soil extractions. Previous researchers have documented an increase in plant chlorophyll as soil 75      inorganic N increased (Piekkielek and Fox 1992; Blackmer and Schepers 1995). Reduced chlorophyll readings were not observed following a rye cover crop relative to the no cover control, even when reduced N availability was detected in the soil extractions (Table 2.09). Satellite site measurements rarely showed differences in relative dry bean chlorophyll content between the cover crop and no cover crop treatment, regardless of cover crop biomass (Table 2.10). The lack of bean relative chlorophyll response at the satellite sites when compared with the main sites is possibly due to high micro-site variability across these much larger scale sites. The same number of samples were taken at the main sites as the satellite sites, in spite of differences in scale. Again, future studies should consider destructive tissue analysis at various bean stages for more sensitive measures of N status. Chlorophyll measurements lagged behind destructive assays in sugar beet and did not detect differences above a threshold N content (Sexton and Carroll 2002). Dry bean variety and cover crop influence on dry bean attributes Populations. One or both of the black bean varieties always had higher populations compared with both navy bean varieties at the main sites at harvest (Table 2.07, Appendix D Table D.01). In 12 of the 17 satellite site-years, Zorro black bean populations were higher than the navy bean Vista (Table 2.08). Germination was above 90% for all varieties in all years of the study based on laboratory tests (data not shown). Field observations indicated a higher incidence of “bald heads”, or damage to the cotyledons or growing point just after emergence, for navy beans compared with the black beans. Typically bald heads are thought to be associated with internal damage to the seed (Robinson 1975), but damage may also be caused by emergence through a rough seedbed or crusted soil. 76      Dry bean populations at V2 and harvest were seldom impacted by cover crop treatment (Table 2.09, Appendix D Table D.01). In 2011 higher populations at the V2 growth stage were observed at both KBS and MSU following an oilseed radish cover crop (data not shown). At the time of bean harvest populations at KBS remained higher, with approximately 44,000 more plants ha-1 (32% higher) following oilseed radish compared with the no cover control (Table 2.09). In 2012 at the time of harvest at KBS, the dry bean population following rye was 57% greater than the no cover control, possibly because of increased moisture at the time of planting in the rye treatment compared with all other treatments (Table 2.03). At the satellite sites, dry bean populations were reduced twice by cover crop treatments (Table 2.10). Red clover reduced dry bean populations by 20% in 2012 Sandusky, possibly due to dry weather early in the growing season. At 2013 Caro the rye cover crop was incorporated only one day prior to dry bean planting, and seedcorn maggot reduced the dry bean population by 57% compared with the no cover control. Waiting 2.5-3 weeks after cover crop incorporation greatly reduced the incidence of soybean injury by seedcorn maggot (Hammond and Cooper 1993). Dry bean populations at harvest were correlated with the biomass of cover crops and weeds. When pooled across all main and satellite site-years, populations were negatively correlated with cover crop biomass production for oilseed radish and cereal rye (Table 2.04). In contrast, dry bean populations at harvest were positively correlated with weed biomass in the no cover control. Red clover showed no correlation between these two parameters. The negative correlation between rye and oilseed radish biomass and crop establishment may have been due to interference with planting or emergence where residue is abundant or due to changes in fungal or 77      insect pathogens that may influence emergence. A positive correlation between dry bean populations at harvest and weed biomass is more difficult to explain, but one possibility is that more than one factor outside of spring weed biomass plays a role, such as edaphic soil conditions; reminding us that correlation does not imply causation. Root nodules and nitrogen fixation. Data were combined across years as there were no interactions with the main effects of cover crop and dry bean variety. Differences in nodule numbers based on dry bean variety or prior cover crop were not observed at the satellite sites (data not shown). At the main sites, Black Velvet had more nodules at V2 compared with the other two nodulating varieties, Zorro and Vista (Figure 2.05); no differences were observed at R1. Previous greenhouse research at Michigan State University has shown differences in nodulation among dry bean varieties and breeding lines, although Black Velvet was not included (Heilig 2010). The percentage of N derived from the atmosphere (% NDFA) among the three bean varieties differed only at 2013 MSU (Table 2.07); Vista derived more grain N from the atmosphere (28%) than Black Velvet and Zorro (average 22%). Dry beans are not as efficient at N fixation as soybeans (Piha and Minns 1987; George and Singleton 1992) and the capacity for N fixation by variety (Heilig 2010) and the availability of soil inorganic N for dry bean uptake are critical in organic production systems. There was no difference in dry bean nodule counts at V2 at the main sites (Figure 2.04), but by R1 beans planted following clover had 58% fewer nodules [8 nodules (5 plants)-1] than the other treatments [average 19 nodules (5 plants)-1]. The presence of inorganic N in the soil, either from 78      direct fertilization or from residual N applied to previous crops has been reported to reduce symbiotic fixation of N by dry beans (Graham 1981) and other leguminous cash crops (Harper and Cooper 1971; Groat and Vance 1981). Applications of synthetic N sources may reduce nodule weight and hemoglobin content (Harper and Cooper 1971; Hardarson and Danso 1993) or fixation-related enzyme activity (Groat and Vance 1981; Hardarson and Danso 1993), and therefore nodule number is not likely the best assessment of fixation responses to soil N. We did not measure nodule mass or activity. We did not detect any differences in % NDFA in the bean grain (Table 2.09), with the exception of Black Velvet at 2011 KBS where beans following oilseed radish had a higher % NDFA than red clover and cereal rye. Lack of detectable difference in %NDFA was due in part to high variability in this response. In dry beans and soybeans, NDFA makes up a higher proportion of N found in pods and seeds than N derived from the soil or mobilized from other plant tissue (Zapata et al. 1987; Kumarasinghe et al. 1992), so differences in % NDFA in the other plant tissues would not be expected either, even though soil N following clover was usually greater than the other treatments. Maturity. Average days to maturation are established for dry bean varieties upon their release to the public. Our visual maturity evaluations supported the expected differences in maturity, with the order of maturation earliest to latest maturing: Zorro > Vista = R99 > Black Velvet. Dry bean maturity (main sites only) was only occasionally influenced by cover crop. Dry beans following rye and red clover were more mature and less mature, respectively, than those following the no cover treatment at the early evaluation time at 2012 KBS for the Black Velvet, 79      Vista, and R99 varieties, the late evaluation times for all varieties at 2012 KBS, and the late evaluation at 2011 MSU (data not shown). In N stressed environments, mobile forms of N translocate out of leaf tissue as the N concentration gradient in the phloem is lowered. If the N concentration in the leaf is lowered to the point that protein synthesis is inhibited, premature senescence can be triggered (Streeter 1978; Hill 1980), which we suspect was the case where dry beans matured early following rye. In contrast, increasing rates of soil N delay maturity in dry beans (Buttery et al. 1987; Blaylock 1995), as well as many other crops such as rapeseed (Brassica napus L.) (Ozer 2003), cotton (Gossypium hirsutum L.) (McConnell et al. 1993), and pepper (Capsicum annum L.) (O’Sullivan 1979). Delays in dry bean maturity following red clover can be a concern in northern climates if a freeze would prematurely terminate grain development (Blaylock 1995). Yield. In three of six main site-years, the non-nodulating R99 yielded significantly less than the other varieties, showing the advantage of nodulation and N fixation (Table 2.07, Appendix D Table D.01). Yield reductions in those site-years ranged from 15 to 36%. In the other three siteyears no advantage to N fixation was observed (i.e R99 yielded similarly to the other three varieties). In 2012, this may be explained in part by drought, which is known to reduce the efficiency of N fixation (Graham 1981). However, it is unclear why no differences occurred at 2011 MSU. Yields of Black Velvet, Zorro, and Vista were similar at the main sites. At the satellite locations, yields were similar among Zorro and Vista in 14 of the 17 site-years (Table 2.08). Vista dry beans compensated for reduced populations by producing greater yield per plant, an effect which has been previously reported (Holmes 2012). Holmes reported similar black bean yields across three plant populations, ranging from 196,500 to 327,000 plants ha-1. Yield 80      components responsible for the compensation were: a) increased number of pods per plant and b) increased number of seeds per pod (Holmes 2012). In most cases, the previous cover crop did not influence final dry bean yield (Table 2.09). In only one instance, 2011 MSU, the rye treatment reduced yield compared with the other cover crops and no cover treatment. As previously mentioned this was the site-year where rye produced 12.8 Mg ha-1 of biomass, levels of inorganic N available at planting and V2 were reduced, and beans matured faster when compared with the other cover crop treatments. Two satellite site-years showed reduced dry bean yields following a cover crop compared with the no cover treatment: 2012 Sandusky (clover) and 2013 Caro (rye). Possible reasons include high clover biomass and dry conditions at 2012 Sandusky and seedcorn maggot at 2013 Caro. The lack of cover crop influence on dry bean yield concurs with other yield comparison studies of other cash crops in the absence of fertilizer (Baggs et al. 2000; Sainju and Singh 2001; Sainju et al. 2002). Though the influence of red clover on yield of a legume cash crop has not been previously reported, rye and oilseed radish have shown no effect on soybean yield (Reddy 2001; Reddy et al. 2003; Williams and Weil 2004). In corn, Torbert et al. (1996) observed that 3-4 Mg ha-1 rye biomass reduced corn biomass and yield compared with no cover crop, which they attributed to N immobilization. Since dry beans derive a higher proportion of N from soil inorganic N compared with soybeans (George and Singleton 1992), but requires less N than corn, it is not a surprise that N immobilization following a robust rye cover crop reduces dry bean yield. Rye was the only cover crop treatment to show any correlations between biomass 81      produced, C:N ratio, or N content and yield when pooled across site-years; all correlations were negative (Table 2.04). Grain N content. In three of six main site-years the non-nodulating bean R99 had 15 to 24% lower grain N content than nodulating navy bean, Vista (Figure 2.06). Zorro had reduced grain N content compared with Black Velvet and Vista in two and three of six site-years, respectively. This reduction does not appear to be attributed to reduced nodulation or population or yield differences, however many of the chlorophyll readings for these site-years were lower for Zorro compared with Black Velvet and/or Vista (Table 2.07). Perhaps varietal differences or lower N uptake was responsible for reduced N content of Zorro grain. Dry beans following a red clover cover crop had greater N content in the grain compared with oilseed radish, rye, and no cover when locations were combined in two of three years (Figure 2.07). Grain N content following clover was 32 and 9% greater compared with no cover crop for 2012 and 2013, respectively. Grain N content was positively correlated with red clover biomass, N content, and soil inorganic N availability at V2 (Table 2.04). Previous studies have shown that increased fertilizer N availability, applied either at the time of pea (Pisum sativum L.) planting or at the flat pod stage, increased N recovery in the seed (Jensen 1986), suggesting that the increased N availability following a clover cover crop would increase the final N content of the dry bean seed produced, even with a higher percentage of N coming from NDFA (Kumarasinghe et al. 1992). Conclusions 82      Cover crops altered the soil environment during the dry bean growing season by changing soil moisture at planting and by influencing soil inorganic N throughout the growing season. Dry bean populations, relative chlorophyll content, days to maturity, and grain N were also occasionally influenced by the preceding cover crop. Soil inorganic N often increased following clover compared with the no cover crop control, resulting in some instances in increased chlorophyll content in bean leaves and greater grain N; yield however was not affected. Rye cover crops reduced soil inorganic N in some instances, and caused early maturity of the beans. At maximum biomass production, rye reduced dry bean yield. Oilseed radish occasionally increased inorganic N availability and populations at the V2 dry bean stage, but had no impact on nodule numbers, % NDFA, relative chlorophyll readings, maturity, yield, or grain N. Cover crop C:N ratio was the most consistent factor influencing inorganic N availability. The C:N ratios of rye were consistently greater than 25:1 at the time of incorporation at the main sites, favoring N immobilization (Table 2.03). Oilseed radish and the no cover control had C:N ratios greater than 25:1 in one site-year each. Within the range of C:N ratios observed for cereal rye, oilseed radish, and the no cover control treatments, there was a negative correlation between C:N ratio and soil inorganic N availability at the time of dry bean planting; the higher C:N ratios within each of these treatments, the more likely N was immobilized (Table 2.04). Conversely for clover, the maximum C:N ratio observed was 18:1 and there was a positive correlation between the C:N ratio and soil inorganic N availability at the time of dry bean planting (Tables 2.03 and 2.04). Overall, low C:N ratios result in more N available. Cover crop management to manipulate biomass and C:N ratios to advantage dry beans is dependent on the goals of the producer and the 83      cover crop species. Cover crop C:N ratio and occasionally soil moisture at dry bean planting, influenced dry bean populations, maturity, and grain N content (Table 2.04). Cover crop management to manipulate biomass and C:N ratios to the advantage of the dry beans that follow is dependent on the goals of the producer and the cover crop species. For example, as greater N content (i.e. protein) of beans becomes important to human health, growing a large clover crop by frost-seeding and incorporating two to three weeks before dry bean planting may be desirable. If a grower is interested in a cover crop such as rye, there is a potential risk of N immobilization during the bean growing season or seedcorn maggot if bean planting is too close to rye incorporation. However, a farmer may want the benefits of rye, including N scavenging in the fall and winter months, soil erosion reduction, building of soil organic matter, etc. Therefore, rye management will be important and may include planting the rye later in the fall, and incorporating rye earlier in the spring, likely a month or more before dry bean planting. Information on oilseed radish and soil inorganic N is limited; however earlier planting of oilseed radish in early to mid-August will enhance weed suppression in the fall and result in more radish biomass for N mineralization in the spring. This research placed dry beans in rotation after a small grain to increase the opportunities for cover crop planting. This is not a typical rotation for Michigan. Dry edible beans are more likely to be planted following corn and therefore integration of the cover crops studied, except for rye, may be more difficult. Clover and oilseed radish have been successfully interseeded into corn without a yield penalty, which in an organic system could be done at the time of final cultivation (Wall et al. 1991; Taylor et al. 2008). Organic producers typically disc or chisel plow corn 84      stubble in the fall to break down residues over the winter months that might interfere with cultivation the following year (MI organic growers, personal communication 2011). This practice may be a hindrance to the use of clover between corn and dry beans. Overall, in our 24 site-years, cover crops had no detectable effect on dry bean yield in 21 cases and reduced yields in three cases compared with the no cover crop control. Although there are several potential benefits of cover crops including N scavenging in the fall and winter months, N availability to the cash crop the following spring, soil moisture retention, and increased grain N, some of which were detected in our research, none resulted in a direct dry bean yield increase. However, it important to point out that our study examined the impacts of cover crops over the course of one growing season, whereas long-term benefits and concerns with the use of cover crops within a crop rotation should also be considered and require further investigation. Potential long-term benefits include increases to soil organic matter, changes to soil biology, changes to soil tilth and aggregation, altered weed seed banks, etc. Nonetheless, for growers to adopt cover crops, efforts to minimize short-term risks are needed. In the current study we found that red clover and cereal rye's impact on N availability was dependent on cover crop biomass (also C:N ratio and N content) and management. Oilseed radish did not increase soil inorganic N compared with the no cover control although a few others have reported increased N availability to cash crops. Understanding N release and N cycling in cover crop systems is important to synchronize N availability with cash crop needs to improve crop yield and quality. Furthermore, some of the potential detriments of the cover crops studied might be overcome through breeding efforts focused on increasing manageability. For 85      example, reducing the spring growth rate of rye may allow for more timely incorporation. Enhancing the predictability of cover crop performance through management recommendations and breeding will encourage use among growers. Acknowledgements Funding for this research was provided by the United States Department of Agriculture- National Institute of Food and Agriculture- Organic Research and Extension Initiative (Project #: 201051300-21224). This work would not have been possible without the technical support of Gary Powell and Todd Martin and several Michigan organic dry bean producers who helped conduct research with us on their farms. Thank you to Richard Stuckey, Mark and Steven Vollmar, Eric Houthhoofd, Kurt Cobb, Don Brockreide, Tom Nelson, Michael and Jon Findlay, and Steve Reinbold. 86      APPENDICES 87      APPENDIX C CHAPTER 2 TABLES AND FIGURES Table 2.01. Soil composition at each main and satellite site-year. Year 2011 Site type Cover † crop Main All Satellite Clover Radish Rye 2012 Main All Satellite Clover Radish Rye Location‡ KBS MSU Alma Caro Sandusky Alma Caro Millington Caro-A Caro-B Columbiaville KBS MSU Sandusky Alma Millington Caro Sand Silt ─────────────%───────────── 36.2 42.1 21.7 26.2 39.1 34.7 64.2 14.1 21.7 48.2 22.1 29.7 37.3 32.0 30.7 44.2 28.1 27.7 38.2 26.1 35.7 58.9 22.0 19.1 38.2 26.1 35.7 46.2 27.1 26.7 62.3 19.4 18.3 50.7 32.7 44.7 52.7 58.7 56.7 34.0 46.0 30.9 26.0 21.9 22.0 88      Clay 15.3 21.3 24.4 21.3 19.4 21.3 Soil type Organic matter loam clay loam sandy clay loam sandy clay loam clay loam clay loam clay loam sandy loam clay loam sandy clay loam sandy loam ──%── 2.3 3.9 3.9 2.3 8.8 2.7 3.0 4.2 3.0 2.4 3.5 loam loam loam sandy clay loam sandy loam sandy clay loam 2.0 4.0 6.4 2.3 3.7 2.5 Table 2.01 (cont’d) Year Site type Cover † crop 2013 Main All Satellite Clover Radish Rye Location‡ Sand Silt Clay Soil type Organic matter KBS MSU Alma Columbiaville Sandusky Alma Caro 48.7 48.7 63.7 66.7 54.7 63.7 52.7 35.1 30.9 19.9 19.1 27.1 19.9 23.0 16.2 20.4 16.4 14.2 18.2 16.4 24.3 loam loam sandy loam sandy loam sandy loam sandy loam sandy clay loam 2.1 2.6 2.5 4.0 3.5 2.5 2.8 † Clover= medium red clover, radish= oilseed radish, rye= cereal rye. ‡ KBS- Kellogg Biological Station, Hickory Corners, MI. MSU- Michigan State University Horticulture Teaching and Research Center (2011 and 2012) and Agronomy Farm (2013), Lansing, MI. 89      Table 2.02. Monthly precipitation and the 30-yr averages for the main sites, 2011 – spring 2014. KBS†‡ Month Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. MSU 30 year average ─────────────mm────────────── 27.2 68.1 50.5 54.6 69.1 36.1 188.5 50.3 0.0 73.4 94.5 28.7 65.3 58.4 132.8 91.2 159.5 90.9 121.7 74.2 33.5 127.8 99.1 197.3 25.6 37.4 107.9 100.8 148.8 131.3 40.4 76.0 97.8 17.5 95.2 75.2 126.5 106.7 66.3 79.0 39.6 19.3 119.1 47.8 94.0 142.0 55.1 87.9 54.1 109.2 13.7 86.4 47.7 63.0 52.1 68.8 2010 2011 2012 30 year average ─────────────mm────────────── 7.9 38.1 69.1 42.4 18.8 25.7 23.4 36.8 66.0 63.0 16.8 43.2 135.1 53.1 165.1 73.4 151.9 72.9 83.8 83.8 44.4 28.4 114.6 83.6 178.1 63.7 55.6 82.0 34.0 63.5 49.3 109.7 83.3 92.0 67.0 59.4 17.8 92.5 34.3 73.7 96.3 118.4 68.6 50.0 75.9 8.4 68.8 13.7 53.8 31.8 43.2 2013 2010 2011 2012 2013 † Monthly precipitation data were collected from the Michigan State University Enviro-weather database (MSU Enviroweather 2014). Thirty year average data were collected from the Michigan State Climatologist’s office (MI Climatologist 2014) ‡ KBS- Kellogg Biological Station, Hickory Corners, MI. MSU- Michigan State University Horticulture Teaching and Research Center and Agronomy Farm, Lansing, MI. 90      Table 2.03. Cover crop parameters describing quantity and quality just prior to winter-kill (i.e. oilseed radish) or at termination (i.e. medium red clover and cereal rye) and soil moisture as impacted by cover crop for each main site-year from 2011 to 2013. Dry weight Incorporation Ground Height Year Location Cover date cover Cover § Total Weed crop ──%── ─cm─ ──────Mg ha-1──────  2011 KBS Clover 19 Mar. 2010 1 June 2011 95 37 7.1 0.4 7.6 Radish 16 Aug. 2010 4.5 2.2 6.7 Rye 14 Sept. 2010 13 May 2011ǁ 89 57 9.7 0.0 9.7 No cover 1 June 2011 95 0.0 7.1 7.1 ƺ NS LSD † 2012 ‡ Planting date kg ha-1 153.9 53.8 53.2 52.5 32.8 15.1 31.0 28.4 23.9 1.0 Soil moisture at bean planting ───%─── - MSU Clover 17 Aug. 2010 3 June 2011 Radish 17 Aug. 2010 Rye 10 Sept. 2010 3 June 2011ǁ No cover 3 June 2011 LSD 83 100 64 29 92 - 2.3 6.1 12.8 0.0 1.3 0.9 0.0 3.4 3.6 7.0 12.8 3.4 2.4 44.4 164.2 135.5 33.6 34.7 17.6 14.3 26.3 23.3 3.4 - KBS Clover 1 Apr. 2011 30 May 2012 Radish 23 Aug. 2011 Rye 21 Sept. 2011 10 May 2012ǁ No cover 30 May 2012 LSD 100 74 100 65 125 - 10.3 4.5 12.0 0 0.0 2.3 0.0 4.2 10.3 6.8 12.0 4.2 1.8 195.8 60.9 65.9 43.3 30.2 17.7 23.9 51.6 29.3 4.6 3.2 3.1 4.3 2.4 0.6 MSU Clover 9 June 2011 24 May 2012 Radish 6 Sept. 2011 Rye 11 Oct. 2011 27 Apr. 2012 No cover 24 May 2012 LSD 98 21 80 59 65 46 - 11.6 0.8 7.9 0 0.0 2.8 0.0 1.9 11.6 3.6 7.9 1.9 2.0 231.8 10.0 42.0 24.1 30.7 17.0 18.1 30.3 26.7 4.8 7.4 7.3 6.6 6.2 NS 91      Cover crop/ weedƪ N C:N content Table 2.03 (cont’d) Incorporation Ground Height date cover Cover § Total Weed crop ──%── ─cm─ ──────Mg ha-1────── Clover 14 Mar. 2012 4 June 2013 84 66 8.6 0.8 9.4 Radish 12 Sept. 2012 65 5.2 2.4 7.6 Rye 12 Sept. 2012 13 May 2013 84 67 10.5 0.0 10.5 No cover 13 May 2013 85 0 1.5 1.5 LSD 2.1 Cover crop/ weedƪ N C:N content kg ha-1 114.7 17.1 68.0 23.3 60.0 30.9 17.5 22.8 41.1 4.1 Clover 19 Mar. 2012 20 May 2013 Radish 20 Aug. 2012 Rye 17 Sept. 2012 9 May 2013 No cover 9 May 2013 LSD 6.4 5.2 11.8 1.9 2.8 144.9 32.5 72.6 22.1 36.1 16.6 24.5 29.3 22.3 3.4 3.1 2.2 3.2 1.8 52.1 28.4 38.2 16.2 2.8 3.1 4.1 5.5 Year Location† Cover‡ 2013 KBS 2013 MSU LSD, comparing site-years † ‡ § ƪ ƺ ǁ  Dry weight Planting date 88 56 90 74 38 71 - Clover Radish Rye No cover 0.6 2.3 0.0 1.9 ───%─── 1.0 0.1 0.4 0.1 0.5 14.9 13.4 16.1 12.3 2.2 KBS- Kellogg Biological Station, Hickory Corners, MI. MSU- Michigan State University Horticulture Teaching and Research Center (2011 and 2012) and Agronomy Farm (2013), Lansing, MI. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. Weed biomass was taken during the spring at the time of cover crop incorporation, even for oilseed radish, which winterkilled. For clover, radish, and rye the N content and C:N represent the cover crop biomass alone; for the no cover treatment, the nitrogen content is for the weed biomass collected in the spring. Fisher’s protected LSD (P ≤ 0.05). NS= not significant. Rye was mowed prior to incorporation in a few instances on the following dates: 2011 KBS- 13 May 2011 same day as incorporation; 2011 MSU- 12 May 2011; 2012 KBS- 8 May 2012. 92      5.7 2.9 11.8 0 Soil moisture at bean planting Table 2.04. Correlation coefficients (R) for cover crop, soil, and dry bean parameters combined across all site-years from 2011 to 2013†. Cover crop/weed parameters Weed Total C:N N biomass biomass ratio content Cover crop‡ Clover Radish Cover crop/weed Cover crop biomass Weed biomass Total biomass C:N ratio Cover crop N content Soil inorganic N Planting V2 Dry bean Population Yield Grain N Cover crop/weed Cover crop biomass Weed biomass Total biomass C:N ratio Cover crop N content Soil inorganic N Planting V2 Dry bean Population Yield -0.47*** 0.23*** 0.62*** 0.38*** 0.88*** 0.66*** 0.40*** 0.01*** 0.37*** 0.39*** 0.61*** 0.60*** 0.90*** -0.51*** 0.46*** 0.32*** 0.84*** 0.00*** 0.94*** -0.07*** 93      Soil inorganic N Planting V2 Dry bean parameters Population Yield Grain N 0.30*** 0.49*** -0.53*** -0.46*** -0.21*** -0.01*** 0.43*** -0.03*** 0.45*** 0.63*** 0.08*** 0.01*** 0.13*** 0.28*** 0.01*** -0.03*** 0.04*** -0.05*** 0.14*** -0.09*** 0.58*** -0.39*** 0.55*** 0.36*** 0.54*** 0.90*** -0.06*** -0.16*** 0.12*** 0.03*** 0.53*** 0.69*** 0.53*** -0.50*** -0.55*** -0.10*** 0.24*** -0.39*** -0.12*** -0.27*** 0.12*** -0.46*** -0.12*** 0.21*** 0.44*** -0.33*** -0.27*** -0.40*** -0.52*** -0.03*** 0.18*** 0.30*** 0.29*** 0.07*** 0.25*** 0.10*** 0.00*** 0.11*** 0.24*** -0.05*** 0.72*** 0.43*** 0.25*** 0.29*** 0.43*** 0.35*** 0.09*** 0.50*** -0.53*** 0.00*** Table 2.04 (cont’d) Cover crop‡ Rye No cover † ‡ ƪ ƺ Cover crop/weed Cover crop biomass Weed biomassƪ Total biomassƪ C:N ratio Cover crop N content Soil inorganic N Planting V2 Dry bean Population Yield Cover crop/weed Cover crop biomassƺ Weed biomass Total biomassƺ C:N ratio Weed N content Soil inorganic N Planting V2 Dry bean Population Yield Cover crop/weed parameters Weed Total C:N N biomass biomass ratio content . . . . . . 0.62*** . . . 0.66*** . 0.82*** . . 0.30*** . 0.72*** . 0.44*** Planting V2 Dry bean parameters Population Yield Grain N -0.69*** 0.05*** . . . . -0.51*** 0.01*** -0.63*** -0.07*** -0.47*** . . -0.19*** -0.34*** -0.38*** . . -0.38*** -0.35*** 0.16*** . . 0.23*** 0.22*** 0.20*** 0.15*** -0.12*** 0.37*** 0.37*** -0.24*** -0.33*** 0.51*** 0.37*** -0.49*** . . *** -0.29 -0.25*** . . -0.47*** -0.23*** -0.24*** -0.19*** . 0.21*** . -0.11*** 0.07*** . 0.32*** . 0.12*** 0.08*** . 0.19*** . 0.24*** 0.27*** 0.85*** -0.06*** -0.17*** 0.17*** 0.13*** -0.17*** -0.15*** 0.53*** -0.41*** -0.41*** Correlation significant at * P ≤0.05, ** P ≤0.001, *** P ≤0.0001 Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. Weeds present at the time of rye incorporation were negligible, therefore no correlations that included weed or total biomas could be calculated. No cover crop was present in the no cover control treatments, therefore no correlations that included cover crop or total biomass could be calculated. 94      Soil inorganic N Table 2.05. Cover crop parameters describing quantity and quality just prior to winter-kill (i.e. oilseed radish) or at termination (i.e. medium red clover and cereal rye) for each satellite site-year. Planting date Incorporation date Cover crop/weed § Cover† Clover 2011 Alma ───%─── ─────Mg ha-1───── kg ha-1 Clover 5 Sept. 2010 18 May 2011 1.2 9.6 10.8 17.4 No cover 18 May 2011 0.0 14.1 14.1 65.1 16.5 30.1 Caro Clover 17 Mar. 2010 18 May 2011 No cover 18 May 2011 82 0 6.0 0.0 0.0 0.0 6.0 0.0 130.0 - 13.0 - Sandusky Clover 3 Sept. 2010 No cover - 9 June 2011 9 June 2011 94 0 1.0 0.0 6.9 0.5 7.9 0.5 29.8 11.1 13.1 13.8 2012 Sandusky Clover 18 June 2011 24 May 2012 No cover 24 May 2012 78 0 4.4 0.0 0.2 0.0 4.6 0.0 128.8 - 12.9 - 2013 Alma Clover 11 Mar. 2011 15 May 2013 No cover 15 May 2013 - 9.1 0.0 0.0 0.0 9.1 0.0 150.7 - 15.2 - Cover ‡ Total crop Weed N content C:N Columbiaville Clover 30 Mar. 2013 No cover - 5 June 2013 5 June 2013 45 0 1.0 0.0 2.6 0.0. 3.6 0.0 15.2 - 110.7 - Sandusky 6 June 2013 6 June 2013 48 0 1.4 0.0 1.0 1.2 2.5 1.2 31.3 19.4 14.1 15.0 Clover 5 Sept. 2012 No cover - 95      Ground cover Dry weight Cover Year Location crop Table 2.05 (cont’d) Cover Year Location crop Radish 2011 Alma Cover† Planting date Incorporation date Dry weight Cover ‡ Total crop Weed Cover crop/weed § N C:N content ───%─── ─────Mg ha-1───── kg ha-1 Radish 24 Aug. 2010 50 2.0 1.8 3.9 31.0 No cover 9 May 2011 0 0.0 6.7 6.7 125.8 20.4 11.4 Caro Radish 30 Sept. 2010 No cover 4 June 2011 - 0.2 0.0 0.0 0.0 0.2 0.0 7.0 - 8.7 - Millington Radish 10 Sept. 2010 No cover 19 May 2011 - 2.5 0.0 0.5 0.0 3.0 0.0 81.4 - 10.6 - Radish 2 Sept. 2011 No cover 11 Apr. 2012 50 0 1.6 0.0 0.1 0.1 1.7 0.1 30.6 - 16.2 - Radish 21 Sept. 2011 No cover 25 May 2012 43 0 0.6 0.0 0.0 0.0 0.6 0.0 13.3 - 12.2 - Radish 24 Aug. 2012 No cover 15 May 2013 87 0 4.8 0.0 0.0 0.0 4.8 0.0 95.2 - 14.4 - 2012 Alma Millington 2013 Alma 96      Ground cover Table 2.05 (cont’d) Cover Year Location crop Rye 2011 Caro-A Caro-B Cover† Planting date Incorporation date Ground cover Dry weight Cover ‡ Total crop Weed Cover crop/weed § N C:N content ───%─── ─────Mg ha-1───── kg ha-1 Rye 3 Nov. 2010 10 May 2011 44 1.9 0.0 1.9 17.1 No cover 10 May 2011 0 0.0 0.0 0.0 - 16.1 - Rye 3 Nov. 2010 18 May 2011 No cover 18 May 2011 48 0 1.4 0.0 0.0 0.0 1.4 0.0 11.1 - 21.4 - 9 May 2011 9 May 2011 35 0 1.0 0.0 0.0 0.0 1.0 0.0 9.5 - 17.0 - 2012 Caro Rye 4 Nov. 2011 19 May 2012 No cover 19 May 2012 67 0 10.7 0.0 0.0 0.0 10.7 0.0 61.5 - 27.4 - 2013 Caro Rye 6 Nov. 2012 13 June 2013ƪ No cover 13 June 2013 23 0 0.8 0.0 0.0 0.0 0.8 0.0 12.0 - 14.7 - Columbiaville Rye 11 Nov 2010 No cover - † Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. ‡ Weed biomass was taken during the spring at the time of cover crop incorporation, even for oilseed radish, which winterkilled. § For clover, radish, and rye the N content and C:N represent the cover crop biomass alone; for the no cover treatment, the nitrogen figures are for the weed biomass collected in the spring. ƪ The sample date for the rye in 2013 at Caro was May 17, so since it was nearly a month prior to incorporation, these ground cover, height, and biomass data are underestimates of what was actually present. 97      Table 2.06. Total soil inorganic Nitrogen available throughout the dry bean growing season at the satellite sites from 2011 to 2013. Values are based on soil extractions. Cover Year Location crop Cover crop treatment† Total soil inorganic N Planting V2 R1 R5 Harvest -1 Clover 2011 Alma Clover No cover LSD‡ ─────────────────kg ha ────────────────── 23.5 30.2 31.6 17.9 15.6 31.0 33.0 32.2 17.9 17.6 NS NS NS NS NS Caro Clover No cover LSD 87.2 68.8 8.8 112.3 76.3 NS 66.9 47.8 18.4 28.9 22.2 NS 37.7 28.9 NS Sandusky Clover No cover LSD 30.0 34.3 NS 47.5 71.1 NS 55.1 72.7 NS 59.1 75.2 NS 51.8 48.5 NS 2012 Sandusky Clover No cover LSD 63.8 105.8 NS 100.1 118.5 NS 134.6 109.0 NS 87.8 63.5 NS 50.2 55.0 NS 2013 Alma Clover No cover LSD 44.9 45.0 NS 54.4 50.8 NS 52.9 54.0 NS 52.2 51.6 NS 36.8 42.9 NS - 37.8 39.0 NS 33.7 33.1 NS 23.0 23.4 NS 25.0 23.4 NS 45.5 48.7 NS 51.2 43.6 NS 41.6 37.2 NS 16.5 15.2 NS 26.8 23.2 NS Columbiaville Clover No cover LSD Sandusky Clover No cover LSD 98      Table 2.06 (cont’d) Cover Year Location crop Cover crop treatment† Total soil inorganic N Planting V2 R1 R5 Harvest ─────────────────kg ha-1────────────────── 47.4 53.2 35.8 24.0 21.8 39.1 42.9 30.9 27.8 17.5 NS 4.3 NS NS NS Radish 2011 Alma Radish No cover LSD Caro Radish No cover LSD 39.8 37.1 NS 37.0 36.0 NS 35.8 36.9 NS 23.5 21.3 NS 18.4 20.9 NS Millington Radish No cover LSD 69.4 70.2 NS 108.5 102.2 NS 44.7 44.8 NS 27.3 27.1 NS 16.0 17.3 NS Radish No cover LSD 44.7 50.6 NS 58.3 55.1 NS 50.2 40.0 NS 22.1 27.0 3.76 37.7 36.6 NS Radish No cover LSD 50.6 57.5 4.2 60.0 64.9 NS 54.5 36.2 NS 20.6 17.1 NS - Radish No cover LSD 36.3 45.0 NS 48.8 50.8 NS 48.5 54.0 NS 46.4 51.6 NS 38.6 42.9 NS 2012 Alma Millington 2013 Alma 99      Table 2.06 (cont’d) Cover Year Location crop Cover crop treatment† Total soil inorganic N Planting V2 R1 R5 Harvest -1 Rye ─────────────────kg ha ────────────────── 42.3 39.2 39.9 20.9 20.8 41.3 35.4 37.8 19.8 20.8 NS NS NS NS NS 2011 Caro-A Rye No cover LSD Caro-B Rye No cover LSD 32.7 30.7 NS 47.5 37.2 NS 42.3 31.1 NS 15.8 12.7 NS 19.4 18.1 NS Columbiaville Rye No cover LSD 41.7 35.1 NS 35.6 35.1 NS 41.4 45.7 NS 23.8 18.2 4.6 22.6 23.5 NS 2012 Caro Rye No cover LSD 26.6 40.1 NS 37.9 46.8 7.9 26.2 29.6 NS 18.5 20.3 NS 23.4 23.2 NS 2013 Caro Rye No cover LSD 30.4 40.5 NS 37.3 45.9 NS 37.4 39.6 NS 26.3 29.0 NS 18.1 25.4 NS † Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. ‡ Fisher’s protected LSD (P ≤ 0.05). NS= not significant. 100      Table 2.07. Dry bean relative chlorophyll readings, populations, yield, and nitrogen derived from the atmosphere (NDFA) via fixation as influenced by bean variety for each main site-year. Relative chlorophyll readings§ Year Location† Bean variety‡ NDFAƺ Populationƪ Yield V2 2011 KBS MSU 2012 KBS MSU Black Velvet Zorro Vista R99 R1 R5 LSDǁ 41.7 36.5 38.7 38.0 0.7 42.7 40.6 41.9 40.3 * 43.1 38.8 39.8 36.6 * Black Velvet Zorro Vista R99 LSD 41.0 36.4 41.8 37.9 0.7 39.6 36.2 38.0 36.5 0.8 43.5 40.3 42.5 40.9 1.1 214,172 240,899 186,549 181,616 14,224 2.5 2.2 2.1 2.0 0.2 10.9 8.2 8.8 Black Velvet Zorro Vista R99 LSD 46.3 41.6 43.7 42.7 0.8 40.1 36.5 40.3 39.2 0.9 27.9 42.0 33.8 35.4 * 202,692 170,854 141,615 144,485 20,623 1.6 1.6 1.6 1.6 NS 3.6 2.8 2.6 Black Velvet Zorro Vista R99 LSD 42.7 39.1 40.7 39.2 1.0 39.7 38.4 38.8 35.4 1.1 36.4 27.2 26.6 26.6 * 219,822 189,239 190,495 197,221 12,095 2.3 2.2 2.2 2.0 NS 7.6 3.3 6.9 NS 101      plants ha-1  Mg ha-1  ───%───  12.7 126,757 3.0 5.4 193,126 3.1 8.8 137,520 3.1 167,655 2.6 14,326 0.2 * NS NS Table 2.07 (cont’d) Relative chlorophyll Year Location† Bean variety‡ readings§ Populationƪ V2 R1 R5 2013 KBS Black Velvet Zorro Vista R99 LSD 45.5 39.8 42.6 39.5 0.9 40.3 37.9 39.0 37.9 * 35.6 35.3 38.4 32.5 1.1 2013 MSU Black Velvet Zorro Vista R99 LSD 43.3 39.5 40.7 40.4 1.0 41.1 37.5 40.3 38.0 * 40.4 38.5 41.8 35.5 * † Yield plants ha-1 Mg ha-1 219,942 2.4 214,112 2.6 149,708 2.3 150,964 2.0 18,079 0.3 195,305 209,059 173,299 195,305 16,994 2.9 3.1 3.1 2.0 0.4 NDFAƺ ───%─── 17.3 15.4 15.9 NS 21.4 22.8 28.0 5.0 KBS- Kellogg Biological Station, Hickory Corners, MI. MSU- Michigan State University Horticulture Teaching and Research Center (2011 and 2012) and Agronomy Farm (2013), Lansing, MI. ‡ Black Velvet and Zorro are both black bean varieties, Vista is a navy bean varieties. §  Relative chlorophyll readings were taken using a Minolta SPAD-502 chlorophyll meter (Spectrum Technologies, Inc., Aurora, IL). Chlorophyll meter readings are all relative within a given site and variety and have no units. Higher numbers indicate higher chlorophyll content and imply that soil inorganic N is higher. ƪ  Populations as measured at the time of dry bean harvest.  ƺ  NDFA= Nitrogen derived from the atmosphere, as determined by the natural abundance method. Values are averaged across varieties, excluding the non-nodulating ‘R99’. ǁ Fisher’s protected LSD (P ≤ 0.05). NS= not significant. * There was an interaction between the main effects cover crop and dry bean variety. 102      Table 2.08. Dry bean relative chlorophyll readings, populations, and yield as influenced by bean variety for each satellite site-year from 2011 to 2013. Relative chlorophyll Cover Bean readings§ Year Location Yield Populationƪ crop† variety‡ V2 R1 R5 Clover 2011 Alma Zorro Vista LSDƺ 31.1 34.4 * 42.1 42.5 NS 38.2 37.6 NS Caro Zorro Vista LSD 42.9 43.2 * 38.0 39.1 * 42.4 41.1 NS 245,515 171,751 14,271 Sandusky Zorro Vista LSD 34.7 37.1 1.9 42.3 44.1 1.3 43.0 45.0 NS - 2012 Sandusky Zorro Vista LSD 42.7 44.6 1.1 35.6 38.4 1.2 31.6 31.3 NS 122,602 155,338 19,486 2.2 2.2 NS 2013 Alma Zorro Vista LSD 38.0 41.0 1.8 39.6 43.6 1.8 39.4 43.3 2.1 228,553 126,924 13,246 2.0 2.0 NS Columbiaville Zorro Vista LSD 35.7 39.2 1.5 33.4 37.8 1.5 39.1 41.5 * 262,280 133,383 22,889 1.8 1.6 NS Sandusky 38.7 41.3 2.5 37.4 40.1 1.1 41.3 42.5 NS 170,967 102,078 22,476 3.2 2.8 0.3 Zorro Vista LSD 103      ─plants ha-1─  Mg ha-1  288,158 3.5 236,656 3.1 16,600 * 3.3 3.1 NS - Table 2.08 (cont’d) Cover crop† Radish Year Location Bean variety‡ Relative chlorophyll readings§ V2 R1 R5 Yield ─plants ha-1─ Mg ha-1 236,925 2.3 196,929 2.1 14,540 NS 2011 Alma Zorro Vista LSD 43.5 46.0 1.4 36.3 36.0 NS 38.8 41.4 1.5 Caro Zorro Vista LSD 42.3 41.7 NS 40.5 42.1 1.3 41.3 43.0 1.3 310,819 216,210 24,174 2.5 2.4 NS Millington Zorro Vista LSD 39.8 42.1 1.2 37.6 39.7 1.3 34.8 37.4 2.4 292,166 216,031 23,963 3.1 2.9 0.2 Zorro Vista LSD 38.9 42.1 1.3 39.7 41.0 NS - 115,965 162,692 16,235 0.7 0.8 NS Zorro Vista LSD 38.4 40.9 1.3 37.1 37.0 NS 20.1 20.2 NS - Zorro Vista LSD 37.7 40.7 1.4 39.3 43.7 1.9 39.6 42.3 2.0 232,859 132,934 20,598 2012 Alma Millington 2013 Alma 104      Populationƪ - 1.8 1.9 NS Table 2.08 (cont’d) Cover crop† Rye † Year Location Bean variety‡ Relative chlorophyll readings§ V2 R1 R5 Populationƪ Yield ─plants ha-1─ Mg ha-1 261,048 3.5 185,361 3.0 * * 2011 Caro-A Zorro Vista LSD 40.4 44.7 1.4 43.5 44.5 0.9 43.1 42.8 NS Caro-B Zorro Vista LSD 43.5 46.5 1.1 39.1 38.6 NS 41.0 42.5 NS 242,212 224,841 NS 2.3 2.3 NS Columbiaville Zorro Vista LSD 36.9 39.9 2.1 38.5 39.6 NS 36.9 39.9 1.8 295,036 145,007 36,505 2.0 1.7 NS 2012 Caro Zorro Vista LSD 38.7 41.3 1.6 38.5 39.1 NS 12.8 18.7 2.3 140,001 148,970 NS 1.1 1.3 NS 2013 Caro Zorro Vista LSD 36.4 37.5 NS 40.5 41.0 NS 41.6 44.5 1.6 80,370 52,115 11,415 0.9 1.1 * Clover= medium red clover, radish= oilseed radish, rye= cereal rye. ‡ Black Velvet and Zorro are both black bean varieties, Vista is a navy bean varieties. §  Relative chlorophyll readings were taken using a Minolta SPAD-502 chlorophyll meter (Spectrum Technologies, Inc., Aurora, IL). Chlorophyll meter readings are all relative within a given site and variety and have no units. Higher numbers indicate higher chlorophyll content and imply that soil inorganic N is higher. ƪ  Populations as measured at the time of dry bean harvest. ƺ  Fisher’s protected LSD (P ≤ 0.05). NS= not significant.  * There was an interaction between the main effects cover crop and dry bean variety. 105      Table 2.09. Dry bean relative chlorophyll readings, populations, yield, and nitrogen derived from the atmosphere (NDFA) via fixation as influenced by cover crop for each main site-year from 2011 to 2013. Relative chlorophyll Cover readings§ Year Location† Yield Populationƪ NDFAƺ ‡ crop V2 R1 R5 2011 KBS MSU 2012 KBS MSU Clover Radish Rye No cover LSDǁ 39.8 37.6 39.2 38.3 1.0 41.9 41.5 41.2 41.0 * 41.2 38.8 39.5 38.8 * Clover Radish Rye No cover LSD 40.4 38.9 38.2 39.5 1.5 39.4 37.8 35.7 37.5 1.8 42.7 41.5 41.5 41.4 NS 198,567 219,105 205,203 200,360 NS 2.3 2.7 1.5 2.2 0.6 1.2 17.3 9.0 Clover Radish Rye No cover LSD 43.8 44.0 43.1 43.5 NS 38.7 40.9 38.2 38.3 1.4 43.7 39.2 21.1 35.2 * 138,835 160,808 217,580 138,835 24,611 1.4 1.9 1.6 1.6 NS 6.0 2.3 3.0 Clover Radish Rye No cover LSD 42.2 39.7 39.8 40.2 1.3 38.8 38.1 36.5 38.9 NS 34.4 27.5 25.3 29.6 * 191,930 200,091 205,652 199,105 NS 2.1 2.3 1.8 2.5 NS 4.1 4.9 6.0 8.8 NS 106      ─plants ha-1─ ─Mg ha-1─  ───%─── 5.6 162,273 3.2 9.2 179,613 3.0 8.2 147,326 2.7 12.8 135,846 3.0 27,083 NS * 9.7 NS 0.5 NS Table 2.09 (cont’d) Year Location† 2013 † Cover crop‡ Relative chlorophyll readings§ V2 R1 R5 KBS Clover Radish Rye No cover LSD 42.2 41.6 41.7 41.8 NS 38.6 38.6 37.7 38.1 * 34.7 36.2 35.7 35.1 NS MSU Clover Radish Rye No cover LSD 42.1 41.1 39.8 40.8 1.2 40.3 39.3 38.6 38.8 * 39.5 39.2 39.9 37.7 * Populationƪ Yield NDFAƺ ─plants ha-1─ ─Mg ha-1─ ───%─── 11.8 177,836 2.8 15.9 174,906 2.3 16.7 186,403 2.2 20.4 186,902 2.1 NS NS NS 189,923 196,262 191,358 200,209 NS 2.8 3.0 2.4 2.9 NS 21.4 22.3 33.7 19.0 NS KBS- Kellogg Biological Station, Hickory Corners, MI. MSU- Michigan State University Horticulture Teaching and Research Center (2011 and 2012) and Agronomy Farm (2013), Lansing, MI. ‡ Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. §  Relative chlorophyll readings were taken using a Minolta SPAD-502 chlorophyll meter (Spectrum Technologies, Inc., Aurora, IL). Chlorophyll meter readings are all relative within a given site and variety and have no units. Higher numbers indicate higher chlorophyll content and imply that soil inorganic N is higher. ƪ  Populations as measured at the time of dry bean harvest.  ƺ  NDFA= Nitrogen derived from the atmosphere, as determined by the natural abundance method. Values are averaged across varieties, excluding the non-nodulating ‘R99’. ǁ Fisher’s protected LSD (P ≤ 0.05). NS= not significant.  * There was an interaction between the main effects cover crop and dry bean variety. 107      Table 2.10. Dry bean relative chlorophyll readings, populations, and dry bean yield as influenced by cover crop for each satellite site-year from 2011 to 2013. Relative chlorophyll Cover Cover crop readings‡ Yield Year Location Population§ crop † treatment V2 R1 R5 Clover 2011 Alma Clover No cover LSD 32.9 32.7 NS 42.8 41.8 NS ─plants ha-1─  ─Mg ha-1─ 38.5 250,889 3.2 37.3 269,298 3.5 NS NS NS Caro Clover No cover LSD 43.5 42.6 NS 39.0 38.1 NS 42.9 40.6 NS 202,577 214,688 NS 3.3 3.1 NS Sandusky Clover No cover LSD 36.7 35.1 NS 43.1 43.4 NS 44.4 43.6 NS - - 2012 Sandusky Clover No cover LSD 45.6 41.7 1.7 37.3 36.8 NS 33.9 29.0 NS 123,947 153,992 25,344 1.7 2.6 0.6 2013 Alma Clover No cover LSD 40.0 39.1 NS 41.5 41.8 NS 41.3 41.4 NS 175,452 180,026 NS 2.0 2.0 NS Columbiaville Clover No cover LSD 37.3 37.5 NS 35.4 35.8 NS 40.1 40.4 NS 190,880 204,783 NS 1.8 1.6 NS Sandusky 40.5 39.5 NS 38.9 38.7 NS 41.6 42.1 NS 134,280 138,765 NS 3.0 3.0 NS Clover No cover LSD 108      Table 2.10 (cont’d) Cover Year Location crop Relative chlorophyll Cover crop readings‡ treatment† V2 R1 R5 Population§ Yield Radish 2011 Alma Radish No cover LSD 41.0 39.3 NS 37.7 34.5 3.1 ─plants ha-1─ ─Mg ha-1─ 44.4 221,501 2.4 45.1 212,354 2.0 NS NS NS Caro Radish No cover LSD 42.2 41.9 NS 41.0 41.5 NS 41.5 42.7 NS 260,600 266,429 NS 2.4 2.6 NS Millington Radish No cover LSD 41.0 40.7 NS 38.5 38.8 NS 35.9 36.1 NS 260,151 248,045 NS 3.2 2.8 NS Radish No cover LSD 40.8 40.2 NS 40.9 39.8 NS - 143,858 185,767 NS 0.8 0.8 NS Radish No cover LSD 39.9 39.4 NS 37.0 37.1 NS 19.6 20.6 NS - - Radish No cover LSD 39.3 39.1 NS 41.3 41.8 NS 40.5 41.4 NS 183,708 176,801 NS 1.7 2.0 NS 2012 Alma Millington 2013 Alma 109      Table 2.10 (cont’d) Cover Year Location crop Rye † Relative chlorophyll Cover crop readings‡ treatment† V2 R1 R5 Population§ Yield 2011 Caro-A Rye No cover LSD 41.5 43.6 1.8 43.9 44.0 NS ─plants ha-1─ ─Mg ha-1─ 42.2 228,137 3.2 43.7 218,272 3.3 NS NS NS Caro-B Rye No cover LSD 44.8 45.2 NS 39.0 38.7 NS 41.9 41.5 NS 239,521 227,532 NS 2.3 2.4 NS Columbiaville Rye No cover LSD 39.0 37.8 NS 39.2 38.9 NS 38.3 39.3 NS 222,128 217,914 NS 1.8 1.9 NS 2012 Caro Rye No cover LSD 39.4 40.6 NS 39.1 38.6 NS 16.0 15.5 NS 148,163 140,808 NS 1.3 1.1 NS 2013 Caro Rye No cover LSD 37.1 36.9 NS 40.6 41.0 NS 44.0 42.2 NS 39,647 92,839 16,791 0.7 1.3 * Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. ‡  Relative chlorophyll readings were taken using a Minolta SPAD-502 chlorophyll meter (Spectrum Technologies, Inc., Aurora, IL). Chlorophyll meter readings are all relative within a given site and variety and have no units. Higher numbers indicate higher chlorophyll content and imply that soil inorganic N is higher. §  Populations as measured at the time of dry bean harvest. ƪ Fisher’s protected LSD (P ≤ 0.05). NS= not significant.  * There was an interaction between the main effects cover crop and dry bean variety. 110      Figure 2.01. Cropping sequence at the main and satellite research sites. Cover crops were interseeded into or planted following a small grain in the season preceding the dry edible bean crop. Oilseed radish winter-killed and red clover and cereal rye were terminated using primary tillage in the spring before dry bean planting. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. For interpretation of the references to color in this and all figures, the reader is referred to the electronic version of this dissertation. 111      2011 KBS 2011 MSU 2012 KBS 2012 MSU 2013 KBS 2013 MSU Figure 2.02. Total inorganic nitrogen in the top 20 cm of soil (nitrate + ammonium) as influenced by preceding cover crop for each main site-year, as measured by soil extraction. Fall samples were collected in November of the previous year while cover crops were present, all other samples times are listed in relation to dry bean stage. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. Within each sampling time different letters represent differences as determined by Fisher’s protected LSD (P ≤ 0.05); NS= not significant. 112      2011 KBS 2011 MSU     2012 KBS 2012 MSU 2013 KBS 2013 MSU   Figure 2.03. Total inorganic nitrogen in soil (nitrate + ammonium) as influenced by preceding cover crop for each main site-year, as measured by cation and anion exchange resin strips. The x-axis reflects weeks after dry bean planting, with dry bean stages noted below; H= harvest. Inorganic soil nitrogen units are two dimensional as they are based on the surface area of the resin strips and reflect daily exposure during the two weeks the strips were buried in the field. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. Within each sampling time different letters represent differences as determined by Fisher’s protected LSD (P ≤ 0.05); NS= not significant. 113      Figure 2.04. Dry bean root nodules as influenced by preceding cover crop at V2 (2nd trifoliate, ~3 weeks after planting) and R1 (first flower, ~6 weeks after planting) combine across 2011 and 2012. Root nodules were not counted in 2013. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. Within each sampling time different letters represent differences as determined by Fisher’s protected LSD (P ≤ 0.05); NS= not significant. 114      Figure 2.05. Dry bean root nodules numbers as influenced by variety at V2 (2nd trifoliate, ~3 weeks after planting) and R1 (first flower, ~6 weeks after planting) for 2011 and 2012. Root nodules were not counted in 2013. Black Velvet and Zorro are both black bean varieties; Vista is a navy bean variety. All nodule counts were conducted on the same day at each location; V2 and R1 timings were based on the average stages for all varieties and cover crop treatments as some slight variations occasionally occurred. Within each sampling time different letters represent differences as determined by Fisher’s protected LSD (P ≤ 0.05); NS= not significant. 115      Figure 2.06. Dry bean grain nitrogen content at harvest as influenced by variety. Black Velvet and Zorro are both black bean varieties, Vista and R99 are navy bean varieties. R99 does not produce nodules for nitrogen fixation. Within each site-year different letters represent differences as determined by Fisher’s protected LSD (P ≤ 0.05); NS= not significant. 116      Figure 2.07. Main site dry bean grain nitrogen content at harvest as influenced by the preceding cover crop. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. Within each year different letters represent differences as determined by Fisher’s protected LSD (P ≤ 0.05); NS= not significant. 117    APPENDIX D CHAPTER 2 ANALYSIS OF VARIANCE FOR SUBPLOT VARIABLES AT THE MAIN SITES Table D.01. Analysis of variance p-values for relative chlorophyll content and dry bean parameters measured at the subplot level. Year Location† Main effect Relative chlorophyll content Dry bean population V2 R1 R5 Cover crop <0.0001 0.0593 0.0001 Variety <0.0001 <0.0001 <0.0001 Cover*variety 0.2285 0.0165 0.0012 V2 0.0131 <0.0001 0.6667 MSU Cover crop <0.0001 <0.0001 0.0453 Variety <0.0001 <0.0001 <0.0001 Cover*variety 0.3977 0.1123 0.1005 0.0351 <0.0001 0.4623 0.1283 0.0108 <0.0001 <0.0001 0.7312 0.3618 2012 KBS Cover crop 0.1648 <0.0001 <0.0001 Variety <0.0001 <0.0001 <0.0001 Cover*variety 0.9256 0.2743 0.0046 <0.0001 <0.0001 0.0009 <0.0001 <0.0001 0.3364 0.0716 0.7564 0.5662 MSU Cover crop <0.0001 <0.0001 <0.0001 Variety <0.0001 <0.0001 <0.0001 Cover*variety 0.9296 0.3606 0.0022 0.3657 0.0079 0.4353 0.3967 <0.0001 0.6264 0.0222 0.0957 0.4028 2013 KBS Cover crop 0.5200 0.0409 0.0431 Variety <0.0001 <0.0001 <0.0001 Cover*variety 0.4667 0.0168 0.3373 0.4573 <0.0001 0.1406 0.6597 <0.0001 0.7540 0.1061 0.0011 0.6260 MSU Cover crop <0.0001 0.0002 0.0050 Variety <0.0001 <0.0001 <0.0001 Cover*variety 0.2834 0.0209 0.0017 0.8629 0.0002 0.3214 2011 KBS Harvest 0.0289 <0.0001 0.5263 Yield 0.3690 0.0007 0.4676 0.6092 0.1312 0.0017 <0.0001 0.4192 0.3913 † KBS- Kellogg Biological Station, Hickory Corners, MI. 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J Agric Sci 124:1725 127    Zapata, F, Danso SKA, Hardarson G, Fried M (1987) Time course of nitrogen fixation in fieldgrown soybean using nitrogen-15 methodology. Agron J 79:172-176 128    CHAPTER 3 COVER CROP IMPACT ON WEED DYNAMICS IN AN ORGANIC DRY BEAN SYSTEM Abstract Cover crops have the potential to enhance crop rotations by increasing crop diversity and maintaining or improving ecosystem quality when cash crops are not present. When dry beans are part of a rotation, their later planting date (mid-June, Michigan) allows more time for spring growth of cover crops compared with earlier planted cash crops such as corn and soybean. The objectives of this study were to assess the influence of cover crops on 1) weed dynamics in subsequent organic dry beans and on 2) weed seed mortality. A total of 24 site-years of field data were collected on Michigan State University research farms and at organic grower cooperator farms in Michigan between 2011 and 2013. The cover crops studied included: medium red clover, oilseed radish, and cereal rye; a no cover crop control treatment was also included. Weed populations and biomass within the bean rows were sampled at both the V2 and R1 stages of bean development for all site-years. For the seed mortality study, mesh bags containing sand and weed seeds of common lambsquarters, giant foxtail, or velvetleaf were buried into red clover, cereal rye, and no cover control treatments at one location in 2012 and 2013. Upon cover crop incorporation, bags were excavated, cover crops were added, and the amended bags were reburied. Bags were retrieved at 0, 1, 2, 4, 6, and 12 months after cover crop incorporation (MAI) to examine weed seed mortality over time. Oilseed radish and cereal rye did not impact weed populations or biomass present during the dry bean growing season. When red clover biomass exceeded 5 Mg ha-1, soil inorganic nitrogen was often higher than the no cover crop control treatment, which occasionally resulted in increased weed populations and biomass. Weed 129    responses also appeared to be dependent upon seed inputs in the fall while the cover crop was growing, precipitation during cover crop establishment and the dry bean growing season, weed seed bank composition, and weed seed distribution as influenced by tillage. High concentrations of cereal rye residue increased giant foxtail and velvetleaf seed persistence compared with the no cover crop control in one of two years. Red clover decreased the persistence of common lambsquarters seed in one of two years. Understanding how cover crops impact fall weed seed inputs and how cover crop C:N ratios impact soil inorganic N availability during the growing season will improve weed management and synchronize N release with cash crop demands. Introduction Currently, cover crops are planted on approximately 1.8 million hectares of grain and oilseed production land in the U.S.; 2% of the total (USDA-NASS 2014a). This number is expected to increase as producer interest grows and the number of cost share programs rise in an effort to mitigate surface water pollution. Producers have indicated that their goals in using cover crops are to reduce soil compaction and erosion, scavenge nitrogen, and provide weed control (CTIC and NCR-SARE 2013).The weed control provided by cover crops is of particular interest to organic producers who cannot use genetically modified crop technologies or synthetic herbicides. Organic dry beans (Phaseolus vulgaris L.) are typically planted between early and mid-June in Michigan and harvested in late-September or October. This short season crop increases the time between winter-kill of a cover crop and dry bean planting, and expands the options for termination dates of overwintering cover crops. Including dry beans in the crop rotation also provides the opportunity to plant cover crops in early to late fall following harvest. 130    Cover crops have the potential to influence weed competition in cropping systems in a number of ways, including direct competition, allelopathy, and alterations to the soil environment (Dyck and Liebman 1994; Creamer et al. 1996; Fisk et al. 2001; Conklin et al. 2002; Snapp et al. 2005). Direct competition with weeds occurs from the time of cover crop emergence through termination and may result in reduced inputs to the weed seed bank, and therefore fewer weeds in the following cash crop (Teasdale 1998; Ross et al. 2001; Gallandt 2006). Allelopathy refers to biochemical interactions among plants and most commonly focuses on negative interactions. Allelochemicals, or compounds which become allelopathic through microbial degradation, have been identified in several cover crop species, and detailed accounts of the allelopathic impact of cover crops on weeds have been published in the literature (Hill 2006; Kelton et al. 2012). Any suppression of weed emergence or growth from allelochemicals is usually short-lived (Kruidhof et al. 2009) and would occur at the time of cover crop termination. Lastly, and perhaps most importantly, weeds may be impacted by alterations to the soil environment as a result of growing cover crops. These alterations include: physical and light barriers to weed emergence due to cover crop surface residue (Teasdale 1996, 1998; Blum et al. 1997), changes in soil nutrient and moisture availability (Teasdale 1998) and soil biology both within the soil matrix and at the surface (Teasdale 1998, Gallandt 2006). Cover crops that increase nitrogen availability could stimulate the germination and growth of some weed species (Blackshaw et al. 2003; Sweeney et al. 2008; Shem-Tov et al. 2005). Medium red clover (Trifolium pretense L.) and cereal rye (Secale cereale L.) are popular cover crops among Midwest producers because they can be planted early in the spring and late in the fall, respectively, making them easier to fit into rotations that include long-season row crops. 131    Typically medium red clover is interseeded into or planted following a small grain the year before corn (Zea mays L.) is planted. Cereal rye is most often planted between corn and soybeans (Glycine max (L.) Merr.) or dry beans. The seed of these two cover crops is readily available and relatively inexpensive, which enhances their popularity. Oilseed radish is a newer cover crop of interest, with use rising over the past 15 years. Row crop producers are still experimenting with how to best incorporate oilseed radish into their rotations. All three of these cover crop species have the potential to impact weed dynamics in the cash crops planted the following season. Medium red clover planted as an intercrop into a cereal crop has the potential to increase summer annual weed seed inputs into the seed bank, particularly foxtail species (Setaria spp.), compared with corn and soybean portions of a crop rotation (Heggenstaller and Liebman 2006). This is especially true when the establishment of the cereal or clover is slow, allowing weeds access to light and moisture (Mirsky et al. 2010). Increases in soil inorganic N increase the germination of some weed species (Blackshaw et al. 2003; Sweeney et al. 2008; Shem-Tov et al. 2005), however increased summer annual weeds in a cash crop following red clover have not been reported. In part this may be due to increased rates of seed predation or decay associated with red clover. For example, Davis and Liebman (2003) showed higher predation rates of giant foxtail (Setaria faberi L.) in wheat interseeded with red clover compared to wheat alone both before and after wheat harvest. Red clover has been shown to reduce root growth of the weed wild mustard (Sinapsis arvensis L.) up to twelve days after clover incorporation (Ohno et al. 1999; Conklin et al. 2002), however the potential allelopathic properties of this cover crop and other influences on weed dynamics in the following cash crop has not been widely studied. 132    Rye can reduce the growth of weeds in the fall through competition (Kruidhof et al. 2008). Rye also has well characterized allelochemicals that can impact weed growth following termination (Putnam 1986; Hill 2006; Clark 2007; Teasdale et al. 2012; Rice et al. 2012). Conflicting findings have been reported for the impact of rye on weeds during the growth of the subsequent cash crop, with some reporting reduced weed pressure and others reporting no influence (Reddy 2001; Reddy et al. 2003; Peachey et al. 2004). Oilseed radish has the potential to reduce weed populations in the fall due to rapid growth and light interception (Kruidhof et al. 2008; O’Reilly et al. 2011), however the impact on weed populations in the spring have been mixed with some reporting suppression (Weil and Kremen 2007; Wang et al. 2008) and others reporting no impact (Kruidhof et al. 2008; O’Reilly et al. 2011). The proposed primary mechanism of weed suppression of oilseed radish is fall competition with winter and summer annual weeds (Wang et al. 2008; O’Reilly et al. 2011; Lawley et al. 2012). Wang et al. (2008) showed reduced total weed seed banks in the spring following fall Brassica cover crops compared with a no cover crop control. Though extensive work has been done on the biologically inhibitory properties of glucosinolates found in Brassicaceae species, limited research has been done on the allelopathic potential of oilseed radish, with only one study showing inhibitory effects on the germination and growth of the weed downy brome (Bromus techtorum L.) (Machado 2007). Cover crops have the ability to influence weed seed persistence (Davis et al. 2005, 2006; ShemTov et al. 2005; Davis 2007), though red clover, cereal rye, and oilseed radish have not been specifically studied. Possible mechanisms responsible for changes in weed seed persistence 133    include the stimulation of microbial activity (Mendes et al. 1999) and the fatal germination of weed seeds. When organic amendments are incorporated into the soil a surge in the populations of fungi, nematodes, and other soil microbes have been observed (Chung et al. 1988; Fennimore and Jackson 2003; Manici et al. 2004; Mohler et al. 2012). Several microbial agents have been associated with the decay of weed seeds (Kremer 1993; Fennimore and Jackson 2003), and soil microbial biomass and weed seed mortality have been positively correlated (Fennimore and Jackson 2003). Secondly, organic inputs with relatively low C:N ratios increase soil inorganic N and could thus stimulate fatal germination of weed seeds buried below the emergence zone. Organic inputs with high C:N ratio inputs, such as compost, have been shown to reduce weed populations and seed banks (Fennimore and Jackson 2003; De Cauwer et al. 2011) and, conversely, increase weed seed persistence (Davis et al. 2005, 2006; Shem-Tov et al. 2005; Davis 2007). Overall, the response of weed species to organic inputs appears to be species specific (Menalled et al. 2005; Ullrich et al. 2011) due to factors such as seed coat thickness and chemical composition as well as germination and growth responses to N (Kremer 1993; Davis et al. 2005, 2006; De Cauwer et al. 2011). The objectives of this research were to determine how red clover, cereal rye, and oilseed radish influence weed communities in organic dry bean systems. We hypothesized that the nitrogen fixing ability of red clover, in combination with its relatively low C:N ratio, would increase nitrogen availability in the soil and therefore increase weed emergence, populations and biomass compared with the no cover control. We also predicted that cereal rye would potentially reduce weed populations and biomass due to N immobilization. However, we hypothesized oilseed radish to have no impact on weed communities in a cash crop planted so late in the spring 134    following winter kill of radish. With regard to weed seed mortality, we expected the responses to be dependent on both the cover crop species and weed species, with red clover increasing weed seed mortality and cereal rye decreasing mortality; oilseed radish was not included in this portion of the study. Materials and Methods The two main sites for this research were located on organically certified or transitional ground at Michigan State University research farms for three years (2011-2013). The MSU campus locations were in Lansing, MI at the Horticultural Teaching and Research Center (42.67⁰N, 84.48⁰W) (2011 and 2012) and the Agronomy Farm (42.71⁰N, 84.47⁰W) (2013). The other location was at the Kellogg Biological Station (KBS) (42.40⁰N, 85.38⁰W) in Hickory Corners, MI. Soil types at these locations were loam or clay loam, with soil organic matter averaging 2.8%. Additional satellite sites were located throughout Michigan on certified organic farms in cooperation with growers. Soil types at these satellite sites ranged from sandy loam to clay loam soils with organic matter averaging 3.1%, excluding two sites in Sandusky, MI where soil organic matter was higher. Over the three year period there were a total of 18 site-years of data collected at satellite locations in Alma, Caro, Columbiaville, Millington, and Sandusky, MI. At each site, a split plot design was used with three to four replications. The main plot factor was cover crop and the subplot factor was dry bean variety. At the main sites there were four cover crop treatments: medium red clover, oilseed radish, cereal rye, and no cover. All cover crops were planted into or after the harvest of a small grain in the calendar year preceding dry bean planting (Figure 3.01). Medium red clover ‘Marathon’ was frost seeded (11 kg ha-1) into the 135    small grain usually around March, with the exception of MSU 2011 when red clover was seeded in August of 2010. Following the harvest of the small grain, Groundhog™ oilseed radish (Ampac Seed Company, Tangent, OR) was planted (12 kg ha-1) in mid-August and cereal rye ‘Wheeler’ was planted (100-125 kg ha-1) in mid-September. At the main sites, the sub-plot factor consisted of four dry bean varieties, two each in two classes. Black bean varieties included ‘Zorro’ and ‘Black Velvet’ and navy bean varieties included ‘Vista’ and a non-nodulating line ‘R99’ (Park and Buttery 1992). Each cover crop plot at the main sites was 12.2 m wide and a minimum of 15.2 m long. During the dry bean season, four 3 m wide bean subplots were planted within each main cover crop plot. Each subplot consisted of four rows of one dry bean variety at a 76 cm spacing. At the satellite sites there were two cover crop treatments: one of the cover crops (i.e. medium red clover, oilseed radish, or cereal rye) and a no cover crop control. Clover (seven site-years) and rye (five site-years) varieties were chosen based on what the growers were already using on their farms, typically ‘variety not stated’. GroundHog™ oilseed radish was provided to growers interested in oilseed radish (six site-years). Cover crop planting times were more variable at satellite sites than at the main sites (Table 3.01). At the satellite sites the subplot factor consisted of two dry bean varieties, ‘Zorro’ black beans and ‘Vista’ navy beans. Plot dimensions at the satellite sites were based on the grower’s equipment size, with minimum plot lengths of 30.5 m. Most growers planted rows at a 76 cm spacing, however three sites planted at 56 cm spacing. Target bean planting populations ranged from 262,000 to 296,000 seeds ha-1 for both main and satellite site locations. No external N sources were added to fields in this study. In general, the 136    red clover and cereal rye cover crops were terminated using a primary tillage tool followed by a field cultivator. All oilseed radish and no cover control plots also received primary tillage in the spring. Tables 3.01 and 3.02 describe tillage and seedbed preparation for the main and satellite sites, respectively. After dry bean planting, all weed management was uniform across all treatments at each location; activities are outlined in Tables 3.04 and 3.05 for the main and satellite sites, respectively. Precipitation data was collected at the main sites by utilizing Michigan State University’s Enviro-weather online database (MSU Enviroweather 2014) for the main site locations (Table 3.03). Cover crop quantity and quality Cover crop measurements included percent cover, height, dry biomass, C:N ratio, and N content of the plant tissue. Parameters were all measured at the time of peak production, which occurred in mid- to late-November prior to winter-kill of oilseed radish, and in spring at the time of incorporation for red clover, rye, and no cover. Percent cover was determined using linetransects (Laflen et al. 1981) laid diagonally across the main cover crop plots, 15 m (main sites) or 30 m (satellite sites). Incidents of cover crop, weed, or no vegetation were recorded along transects at 50 and 100 points at 30 cm spacing, for the main and satellite sites, respectively. Two 0.25 m2 quadrats of whole plant material (shoots + roots) were collected for each cover crop plot. Samples were separated into cover crop and weed material and were then dried at 66 C for 7 d and weighed. The C:N ratios and N content of the tissue were determined by grinding dried biomass samples using a Christy Mill (Suffolk, United Kingdom) fitted with a ≤ 2 mm sieve and 137    sending 2 g samples to Midwest Laboratories, Inc. (Omaha, NE) for total carbon and nitrogen analysis. Plant available nitrogen in the soil was measured throughout the dry bean growing season (at planting, V2, R1) by pulling eight to ten soil cores to a depth of 20 cm in each cover crop plot. Samples were homogenized within each plot, dried at room temperature, and ground in a Wiley mill (Thomas Scientific, Swedesboro, NJ) fitted with a 1 mm sieve. After grinding, samples were extracted with 1 M KCl and filtered through #2 Whatman filter paper (GE Healthcare BioScience, Pittsburg, PA). Extracts were sent to the Michigan State University Soil and Plant Nutrient Laboratory to determine NH4-N and NO3-N concentrations via the ammoniumsalicylate and cadmium reduction methods, respectively, using a Lachat rapid flow injection autoanalyzer (Hach Co., Loveland, CO) (Mulvaney 1996). Weed seed banks To determine initial weed pressure among the research sites, the weed seed bank was estimated using a method similar to Forcella (1992). In 2012 and 2013, 10 to 12 soil samples were collected across each site (i.e. across all treatments and replications) the spring prior to dry bean planting at each site using a Miltona PowerStroke cup cutter (Maple Grove, MN) set to a 15 cm depth (for a total of approximately 18 L of soil). After the samples were collected they were mixed, spread out, and allowed to dry in a greenhouse. After drying, 0.95 L of soil was spread on top of a soilless potting media (Suremix Perlite, Michigan Grower Products, Inc., Galesburg, MI) in flats measuring 26 by 53 cm; there were three subsamples were planted for each site-year. Flats were placed outside under irrigation during the early summer and weeds were identified, 138    counted, and removed weekly until emergence ceased. In 2011, soil samples were not collected until the time of dry bean harvest, and samples were grown in the greenhouse during the fall and winter months. Weed population and biomass Weed population and biomass were measured at V2 and R1 in each dry bean variety subplot in each site-year. At V2, beans have two fully expanded trifoliates and it is around this stage that many growers switch from more vigorous cultivation tools, such as a tined weeder or rotary hoe, to an implement targeting inter-row cultivation only (Tables 3.04 and 3.05). At R1, dry beans first begin to flower and plants are often too large for mechanical cultivation to continue and hand labor may be utilized. At each sampling time, three 0.1 m2 quadrats (15 cm wide by 76 cm long) were placed directly over one of the center dry bean rows, weed were counted by species, and all above-ground weed biomass was harvested together. Weed biomass was dried at 66 C and weighed after 7 days. The bean rows sampled were alternated between the V2 and R1 sample timings to avoid sampling the same area twice. Weed seed mortality To determine the influence of cover crops on weed seed decay, an experiment was conducted in 2012 and 2013 at the MSU research sites. The cover crop treatments assessed were medium red clover, cereal rye, and no cover. Fresh seed of common lambsquarters (Chenopodium album L.), giant foxtail, and velvetleaf (Abutilon theophrasti L.) were collected from the MSU and KBS farms in the early fall of each year. Initial viability of the seed lots was determined through tetrazolium chloride testing (Peters 2000). Two hundred weed seeds were buried with 100 g of 139    white silica sand in no-seeum mesh bags (Outdoor Wilderness Fabrics, Nampa, ID), 10 by 10 cm. Bags were buried in the cover crop plots in the fall at a depth of 15 cm. Burial at this time exposed seeds to seasonal fluctuations in temperature and soil moisture and any cover crop root leachates. Enough bags were buried to allow for six removal times at 0, 1, 2, 4, 6, and 12 months after cover crop incorporation (MAI), with four replications for each weed species and removal time combination. In the spring, all bags were excavated immediately prior to cover crop incorporation. One set of bags was analyzed for overwinter seed mortality (0 MAI), while the other sets of seed bags were mixed with a high rate of the cover crop biomass (fresh, chopped shoot and root material, equivalent to 6.2 g of dry biomass per bag) and placed in new mesh bags. Cover crop biomass added to the mesh bags was based on the assumptions that: a) 600 g m2 dry cover crop biomass can be produced by clover and rye, b) cover crops can be uniformly incorporated into the soil profile, and c) a 15 cm furrow slice of soil weighs approximately 18,700 tons. A more typical quantity of dry biomass added to 100 g of sand in each bag would have been 0.3 g; however we considered uniform cover crop incorporation to be unlikely, and we were interested in mimicking activity at microsites with high concentrations of cover crop. Samples in the no cover treatment were also repackaged in new mesh bags. All repackaged seed bags were buried for temporary storage adjacent to the study site in the same field to allow for soil preparation and planting of the dry bean crop; the out-of-plot storage period lasted up to one month. Immediately after dry bean planting, the seed bags were returned to their respective cover crop plots and buried individually to a depth of 15 cm using the cup cutter, mentioned above. Bags were placed in the dry bean row to avoid damage due to cultivation; bean plants emerging adjacent to the seed bags were terminated at VC. At each removal time, bags were excavated and air dried in the laboratory. Samples were then sieved and sorted by hand to separate seeds from 140    the sand and organic debris. Intact seeds retrieved were counted and viability was determined using a combination of germination (dark, 25 C) (Hill et al. 2014) and tetrazolium chloride testing. Seed mortality percentages were calculated as follows: % ∗% ∗% # ∗ 100 [Eq.1] Statistical analysis All data sets were analyzed in SAS 9.3 using the MIXED procedure. All cover crop parameters, soil N extractions, and weed seed mortality were measured at the main plot level, therefore cover crop, year, and location were treated as fixed effects and replication was treated as a random effect. Weed population and biomass data were taken at the subplot level, therefore dry bean variety was also treated as a fixed effect for these analyses. Weed population and biomass data were averaged over the three subsamples in each subplot. Variance assumptions were checked using the UNIVARIATE procedure. Mean separation was conducted using Fisher’s Protected LSD (P≤0.05). Variations in management and weather led to many interactions among locations, years, and measurement timings, therefore within each fixed effect site-years and timings are presented separately. For weed parameters measured at the subplot level, interactions between cover crop and dry bean variety were rare; therefore main effects of cover crop and bean variety are presented and discussed separately. Pearson’s correlation coefficients were used to assess linear correlations among cover crop and soil properties and weed populations and biomass across all site-years for each cover crop treatment using the CORR procedure in SAS. Results and Discussion 141    Cover crop influence on weeds at cover crop termination Full details on cover crop production and its influence on soil inorganic N and dry bean yield and characteristics can be found in the previous chapter. To summarize, the main sites had more cover crop biomass than the satellite sites due to earlier cover crop planting in most years (Tables 3.06 and 3.07). Cover crop C:N ratio was positively correlated with biomass production for each of the cover crops studied (i.e. the more biomass produced, the greater the C:N ratio) when pooling across all site-years (Table 3.08). C:N ratio was the most consistent factor correlated with soil inorganic N availability. The C:N ratios of oilseed radish, cereal rye, and the weeds in the no cover control were negatively correlated with soil inorganic N at the time of dry bean planting (Table 3.08). Maximum C:N ratios observed for these treatments were 31:1, 52:1, and 29:1, respectively (Table 3.06). C:N ratios of 25:1 or greater lead to N immobilization (Clark et al. 1997; Kuo and Jellum 2002). Conversely for red clover, a positive correlation was observed between C:N ratio and soil inorganic N at the time of dry bean planting (Tables 3.08); higher C:N ratios in clover resulted in higher N availability. The maximum C:N ratio observed for clover was 18:1 (Table 3.06). The lower C:N ratios and smaller range of ratios for red clover compared with the other treatments is likely responsible for this positive correlation. The C:N ratio of red clover would never approach 25:1 because of its capacity to produce N through fixation. Unlike the main sites, growers were not always able to plant cover crops following a small grain at the satellite sites. This and other production considerations often resulted in later cover crop planting dates compared with the main sites, which greatly reduced biomass production and N 142    content. Average C:N ratios were also lower overall at the satellite sites compared with the main sites because of reduced biomass (Tables 3.06 and 3.07). Weed species present at the time of cover crop incorporation in the spring varied by year and location. The most commonly observed weeds included the winter annuals: common chickweed (Stellaria media L.), field pennycress (Thlaspi arvense L.), mayweed chamomile (Anthemis cotula L.), annual bluegrass (Poa annua), and henbit (Lamium amplexicaule L.) and occasionally volunteer wheat (Triticum aestivum L.). Weed groundcover and biomass in the no cover control treatments at the main sites ranged from 59 to 95% and 1.5 to 7.1 Mg ha-1, respectively (data not shown, Table 3.06). Volunteer wheat was the dominant species in the high biomass site-year, 2011 KBS. The average percent groundcover for red clover and cereal rye stands prior to incorporation was 91% (data not shown) at the main sites, with little to no weed biomass (Table 3.06). Oilseed radish however, only covered 21 to 74% of the ground prior to winter-kill, with weeds covering 0 to 67% of ground in the fall. The 2012 MSU site-year had the lowest oilseed radish biomass and highest weed biomass production due to fall competition with volunteer oat (Avena sativa L.). By spring, weed ground cover in the oilseed radish plots ranged from 32 to 92%. In three of the six main site-years, spring weed biomass following oilseed radish was similar to the no cover control. Rye and clover cover crops generally had very little weed biomass in the spring at the satellite locations (Table 3.07), similar to the main sites. However, when red clover production at the satellite sites was less than 4 Mg ha-1 weed biomass often exceeded clover biomass at the time of incorporation. Farmer cooperators usually cultivated early in the spring (Table 3.02) to remove 143    weed biomass in the winter-killed oilseed radish and no cover control treatments, therefore there was usually no weed biomass recorded in these plots. Also, delayed cover crop planting, and thus fall tillage, is another reason why spring weed biomass in the no cover control treatments was minimal at the satellite sites compared with the main sites. Weed seed banks The quantity of readily germinable seeds in the weed seed banks at the time of dry bean planting across all field sites ranged from 2 to over 130 million seeds ha furrow slice-1 (Table 3.09). Summer annual broadleaf weed emergence was greater than that of summer annual grasses at most sites, and perennial and biennial weed emergence was sporadic. Common lambsquarters was the most common weed species, occurring at 25 of the 26 sites with populations of 0.6 to 64 million germinable seeds ha furrow slice-1. Other broadleaf species, from most to least common were pigweed species (Amaranthus powellii S. Wats. and A. retroflexus L.), common ragweed (Ambrosia artemisiifolia L.), velvetleaf, and common purslane (Porculaca oleracea L.). The most prominent annual grass species were foxtails (Setaria faberi Herrm. and S. pumila (Poir.) Roemer & J.A. Schultes) and large crabgrass (Digitaria sanguinalis (L.) Scop.). Cover crop effects on weed population and biomass after termination Weed populations and biomass were not influenced by dry bean variety in this study, with the exception of 2011 KBS where there was an interaction among cover crop treatment and dry bean variety for both parameters (Appendix F, Table F.01). Therefore, varieties are pooled for the remaining analyses and interactions for 2011 KBS are indicated within the tables. There was no difference in weed populations or biomass following rye compared with the no cover crop 144    control treatment at the main or satellite sites (Tables 3.10 and 3.11), with one exception: 2011 MSU, where all cover crop treatments reduced the total weed population at R1 relative to the no cover control (Table 3.11). These results concur with Reddy (2001) and Peachey et al. (2004) where rye usually had no impact on weeds compared with a no cover control in no-till soybeans and no-till and conventionally tilled sweet corn, respectively. Though there was only one instance where rye had an impact on weed dynamics in our research, pooling across all site-years showed negative correlations between rye C:N ratio and N content and weed population at both V2 and R1 and weed biomass at R1(Table 3.08). In a later publication by Reddy et al. (2003), rye reduced weed populations and biomass in the following soybean crop compared with no cover. Cover crop biomass was not reported in these references so it is unclear if the differences in the results are biomass related. Similar to our results with cereal rye, there were no differences in weed populations or biomass following oilseed radish compared with the no cover control treatment at the main or satellite sites (Tables 3.10 and 3.11) with one exception: 2011 MSU. However, we found negative correlations between oilseed radish biomass and weed population and biomass at R1 (Table 3.08) when combining the data for all site-years that included oilseed radish. This implies that the greater the oilseed radish biomass production prior to winterkill, the lower the weed population and biomass at R1, however it is unclear why there would be such a delayed response. In the Netherlands, oilseed radish (4 to 7 Mg ha-1) reduced the weed population of the summer annual weed common lambsquarters and the winter annual weeds common chickweed (Stellaria media L.) and annual bluegrass (Poa annua L.) in the fall due to early light interception, but differences in weed establishment in the spring were not observed (Kruidhof et al. 2008); a similar trend was 145    observed in Canada (O’Reilly et al. 2011). Other studies in the U.S. however contradict our findings. Weil and Kremen (2007) and Wang et al. (2008) reported fewer spring weeds in plots following oilseed radish compared with no cover (Weil and Kremen 2007; Wang et al. 2008). In Michigan specifically, oilseed radish (6.2 Mg ha-1) reduced redroot pigweed (Amaranthus retroflexus L.) populations and biomass in the subsequent late-April planted onion crop on muck soil two and two and a half months after planting (Wang et al. 2008). The difference in results in these studies may be due to differences in production systems including tillage, soil type, herbicide use, cash crop planting date, etc. No differences in weed population or biomass were observed between red clover and the no cover control treatment at the satellite sites (data not shown). However, weed populations were greater in dry beans planted following red clover compared with the no cover control in three of six main site-years at V2 and in five of six main site-years at R1 (Tables 3.10 and 3.11). Weed biomass was greater following red clover in two of six main site-years (i.e. 2012 and 2013 MSU) at V2 and R1 compared with the no cover control (Tables 3.10 and 3.11). Red clover N content was positively correlated with weed population at V2 and both N content and red clover biomass were positively correlated with weed population at R1 when looking at all red clover site-years (Table 3.08), which supports the hypothesis that weed species respond positively to nitrogen. Other possible reasons that weed pressure following red clover might have been higher are related to the reduced tillage in this treatment compared with oilseed radish, cereal rye, and the no cover control treatments and the potential for increased fall weed seed production. In previous Michigan research, red clover did not increase summer annual weed populations or biomass in three of four site-years 45-60 days after terminating the cover crop (late-June to early-July) (Fisk 146    et al. 2001). Differences in the weed response to clover between this study and our study may be the result of vastly different production practices. The Fisk et al. (2001) study was no-till, herbicides were applied, and the following crop was corn, which is a better competitor for inorganic soil N than dry beans. Yearly differences in precipitation during the cover crop establishment year and in the dry bean year may be an important factor influencing the availability of N to the subsequent bean crop and to weeds associated with both the cover and cash crops. At 2012 MSU, red clover established well and grew in a year with normal precipitation (2011, Table 3.03), producing abundant biomass (Table 3.06). Red clover was then incorporated in the spring of a dry year (2012); rainfall was 66, 22, 41, and 36% below the 30-yr averages for June, July, August, and September, respectively, possibly slowing cover crop degradation and nitrogen losses (Table 3.03). Twenty-six to 50% more nitrogen was available following red clover compared with no cover at the time of dry bean planting, V2, and R1 in 2012 (Table 3.06). The weed seed bank at this site was very high, with 27 million seeds ha furrow slice-1 of germinable common lambsquarters (Table 3.09). Common lambsquarters is known to thrive (i.e. increased population and/or biomass) in nitrogen rich environments (Williams and Harper 1965; Wilson and Tilman 1995; Blackshaw et al. 2003, 2004; Sweeney et al. 2008). Also, common lambsquarters seeds on the soil surface are less sensitive to reduced soil moisture than other summer annual species (Weaver et al. 1988). At 35% available soil moisture, 67% of common lambsquarters seeds germinated compared with an average of 43% for Powell amaranth, green foxtail (Setaria viridis (L.) Beauv.), and eastern black nightshade (Solanum ptychanthum Dunal). It appears that at 2012 147    MSU the combination of high nitrogen conditions following clover and water-stress may have contributed to the increased common lambsquarters emergence and growth. In contrast, no differences in weed population or biomass occurred among the cover crop treatments at 2012 KBS even though soil inorganic N was greater in the red clover compared with the no-cover crop treatment early in the growing season (Table 3.06) and conditions at dry bean planting and in the first sixty days of the growing season were dry (Table 3.03). Furthermore, 2012 KBS had only 9 million common lambsquarters seeds ha furrow slice-1, three-fold less than 2012 MSU. The decreased common lambsquarters seed bank may have contributed to the lack of red clover influencing weed dynamics at 2012 KBS. At 2013 MSU, red clover was established in a dry year (2012) and incorporated in a year of average precipitation (2013) (Table 3.03). Red clover biomass production and N content were therefore lower compared with the previous year (Table 3.06). This trend towards reduced cover crop quantity and quality following reduced precipitation during establishment has occurred with other leguminous species (Serraj et al. 1999; Zahran 1999; Pimratch et al. 2008). Despite the reduced clover production at MSU, weed populations and biomass were still higher compared with the no cover control at V2 and R1 (Tables 3.10 and 3.11); weed populations and biomass did not differ by cover crop treatment at 2013 KBS. Soil inorganic N was higher following red clover at the time of dry bean planting at both sites, however this did not persist at V2 and R1 at 2013 KBS. Drought conditions during the establishment of the 2013 KBS red clover (i.e. 2012) were more severe than at MSU, with rainfall at 66, 67, 59, 30, and 67% below the 30-yr averages for May, June, July, August, and September, respectively (Table 3.03). It is possible that at 2013 148    KBS the decreased N contribution of clover due to drought in 2012, combined with more normal decomposition rates and nitrate leaching in 2013, were the reasons for the differences observed in weed biomass response to red clover compared with the no cover treatment at the two research sites. The seed bank at 2013 KBS indicated the potential for high common lambsquarters pressure, 39 million germinable seeds ha furrow slice-1, but the actual emergence measured was very low, with less than one plant 10 m row-1 recorded in any treatment. Annual grasses, specifically giant foxtail, accounted for 77 and 88% of the total weed populations observed at V2 and R1, respectively, in the red clover plots at 2013 MSU (Tables 3.10 and 3.11). At KBS annual grasses made up 63 and 66% of the total weed populations at V2 and R1, respectively, in the red clover plots. The germination and/or biomass of foxtail species have been shown to respond positively (Schreiber and Orwick 1978), negatively (Wilson and Tilman 1995; Anderson et al. 1998; Sweeney et al. 2008), or not at all (Fawcett and Slife 1978) to increasing applications of synthetic nitrogen fertilizers. In previous cover crop research, spring tillage of red clover before corn reduced giant foxtail seed emergence and delayed the time to 50% emergence compared with red clover tilled in the fall (Davis and Liebman 2003). Increased giant foxtail emergence in red clover plots in our research may have resulted from increased foxtail seed inputs in the fall of 2012 in a less vigorous clover stand. Rates of foxtail seedling survival have been shown to be higher in the cereal plus legume intercropped portions of rotations compared with the corn and soybean portions of the rotation (Heggenstaller and Liebman 2006). Mirsky et al. (2010) documented increases in foxtail inputs to the seed bank following a red clover cover crop in three of four site-years due to poor establishment of the companion oat cash crop and slow initial growth of the clover. Furthermore, the soil in the 149    clover plots in the present study remained undisturbed from the time of frost-seeding until May of the subsequent year when the clover was incorporated prior to dry bean planting. Conversely, the oilseed radish, rye, and no cover treatments all experienced soil disturbance with a chisel plow and one or two passes with a soil finisher in July and/or August, following small grain harvest. These disturbances were made to prepare the seedbed for cover crop planting and killed any weeds present at the time, reducing new weed seed bank inputs in these treatment areas, unlike the red clover areas which were left undisturbed. These disturbances also may have led to different vertical distributions of the weed seeds in the soil profile, and hence differences in emergence that were unrelated to N or seed rain. Weed seed mortality There was no interaction between the time of seed bag retrieval and cover crop treatment; therefore main effects are presented separately. There was however a significant interaction between the main effects and year, thus years are presented separately within each main effect. Part of that interaction occurred because we were unable to recover the 6 MAI bags in 2013 due to the extended period of snow cover (2013-2014). Weed seed mortality over time. Over the course of this two year experiment the overwinter weed seed mortality (0 MAI), before cover crops were incorporated and added to the seed bags, ranged from 9 to 47% for common lambsquarters and velvetleaf, and from 22 to 72% for giant foxtail (Table 3.12). In a two-year regional study on weed seed persistence, the average overwinter mortality (October through April) of common lambsquarters, giant foxtail, and velvetleaf was 26, 28, and 24% and maximum observed mortality was 95, 95, and 92%, 150    respectively (Davis et al. 2005). The 2013 giant foxtail seed was collected at KBS during 2012, when precipitation was low (Table 3.03), suggesting that the growing conditions of the maternal plants may have impacted overwinter seed mortality. This supports the findings of others where variation in giant foxtail mortality was influenced by maternal environment (Kegode and Pearce 1998; Schutte et al. 2008). The influence of maternal moisture availability on giant foxtail seed development and persistence has not been studied, however in oats, water-stress of maternal plants shortened the period of dormancy in the progeny (Sawhney and Naylor 1982), which under the conditions of our study may have led to fatal germination. In contrast, the 2013 velvetleaf seed had reduced overwinter mortality compared with 2012, confirming that maternal effects are species specific (Schutte et al. 2008). The primary dormancy of velvetleaf lasted longer when maternal plants grow in warm and dry conditions (Cardina and Sparrow 1997). An alternative explanation for our observations may be that giant foxtail was more sensitive to overwinter or spring storage conditions or potential pathogen exposure in 2012-2013, increasing the mortality of giant foxtail, but not common lambsquarters and velvetleaf. Seed mortality of all species, with the exception of 2013 velvetleaf, increased 12 to 40% 1 MAI compared with 0 MAI (Table 3.12). The lack of an interaction between cover crop and retrieval time may indicate that soil disturbance was more likely the cause of increased fatal germination. If the cover crop amendment increased seed mortality we would have expected a retrieval time by cover crop interaction for 1 MAI since no cover crop amendment was added to the no cover control bags. When bags were retrieved and repackaged, with or without cover crop residue, seeds experienced disturbance not all that different from tillage. The germination of common lambsquarters is positively influenced by exposure to light (Henson 1970), and tillage in late- 151    May in Minnesota, even in the dark, increased populations of common lambsquarters, velvetleaf, and giant foxtail (Buhler 1997). Proposed reasons for increased weed seed germination following tillage in the absence of light included seed scarification, changes in soil temperature, moisture, and gas exchange, and altered distribution of the seeds within the soil profile. Beyond 1 MAI, weed seed mortality continued to increase, more so in 2012 than 2013 in spite of spring flooding in 2013 as mentioned above (Table 3.12). Common lambsquarters seed mortality increased between 1 MAI and 4 and 12 MAI for 2012 and 2013, respectively. Giant foxtail mortality increased between 1 MAI and 6 MAI in 2012, but not in 2013. Velvetleaf seed mortality increased between 1 MAI and 12 MAI in 2012, but not in 2013. Maximum mortality rates observed for common lambsquarters, giant foxtail, and velvetleaf were 74, 100, and 49%, respectively. Cover crop impact on weed seed mortality. When pooled across sampling times, there were no weed seed mortality differences between the clover and no cover control treatments in 2012 for any of the weed species examined. However, in 2013 red clover increased the mortality of common lambsquarters by an average of 25% compared with rye and the no cover control (Table 3.13). In contrast, rye increased persistence of velvetleaf and giant foxtail seed, by up to 12 and 6%, respectively in 2012 compared with the no cover control. No effect of rye was observed in 2013, however mortality for giant foxtail mortality was very high (91%) and velvetleaf mortality was low (8%), both quite different from 2012. In a similar study we conducted in Michigan, Palmer amaranth (Amaranthus palmerii L.) seeds showed no mortality response to rye residue compared with a no amendment control; rye residue was added at a rate of 0.3 g seed bag-1, 152    simulating more typical exposure rates versus our concentrated microsite rate (i.e. 6.2 g seed bag-1) (Powell 2014). This implies that cover crop biomass may play a role in microbial activity and weed seed mortality. The clover C:N ratio averaged 17:1 in this study and in both years soil inorganic N increased following red clover compared with the no cover control (Table 3.06). The rye C:N ratio for this portion of the experiment averaged 30:1. Additions of high C:N plant material to the soil has increased weed seed persistence in other studies (Davis et al. 2005, 2006; Shem-Tov et al. 2005; Davis 2007), possibly because of N limitations that reduce microbial activity (Davis et al. 2006). Mohler et al. (2012) attributed differences in weed seedling emergence following the incorporation of another legume, pea (Pisium sativum L.), to the increase in pathogenic fungi attack on the weed seeds and seedlings. Abiotic and biotic differences in the soil environment may both be important factors contributing to the observed changes in seed mortality. Conclusions Cereal rye did not impact weed populations or biomass, contrary to our hypothesis. Oilseed radish did not impact weed populations or biomass, supporting our hypothesis. Frost-seeded red clover resulted in higher weed populations in four of five site-years and higher weed biomass in two of five site-years, supporting our hypothesis. One explanation for this may have been stimulation of germination and growth of weeds from red-clover derived N; when clover biomass accumulation exceeded 5 Mg ha-1, the quantity of plant available N in the soil was often higher than the no cover treatment. The increased N availability from the clover cover crops did not improve dry bean yields. To reduce the risk of red clover increasing weed pressure, we would suggest terminating the clover prior to biomass reaching 5 Mg ha-1 in the spring. In 153    addition to N availability, precipitation in the cover crop and cash crop years, weed seed inputs in the fall, weed seed bank composition, and differences in seed rain and seed distribution resulting from fewer tillage passes in clover treatments may have contributed to whether or not weeds were problematic following red clover. Future work should focus on differences among cover crops with regard to these factors. Were clover planted preceding a cash crop that is a better N competitor than dry beans, perhaps increased weed pressure would not be an issue. For example, red clover killed the day before corn planting resulted in N mineralization in sync with corn demands, similar to fertilizer N (Stute and Posner 1995; Dabney et al. 2010), which may leave less N for weeds to scavenge. With regard to weed seed mortality, the bagged method used here made it difficult to tease apart the impact of cover crop amendment and tillage. Future studies might consider having a no cover crop, no-till control treatment where bags are left undisturbed until their respective retrieval time. The comparisons between the tilled and no-tilled no cover control treatments would help determine what percentage of seed mortality is due to tillage, which could be extrapolated to bags receiving cover crop amendments. Despite this limitation, high concentrations of high C:N residue, such as cereal rye, showed the potential to increase weed seed persistence. Though this scenario is unlikely to have an impact on a large scale, it is one more reason to avoid letting a rye cover crop C:N ratio escalate (i.e. terminating when the rye is large and nearing maturity), in addition to avoiding N immobilization for the subsequent cash crop. Though we hypothesized that the low C:N ratio of red clover residue would increase weed seed mortality, this was only observed in one instance, but may warrant further investigation. Efforts to study the impact of oilseed radish on weed seed mortality should be pursued in the future, but would require a 154    slightly different methodology to be relevant for a winter-killed cover crop; perhaps placing known quantities of residue over seed bags in the fall. Acknowledgements Funding for this research was provided by the United States Department of Agriculture- National Institute of Food and Agriculture- Organic Research and Extension Initiative (Project #: 201051300-21224). We would like to acknowledge the Northeast Regional Association Project NE1047: Ecological bases for weed management in sustainable cropping systems participants for collaborating on the weed seed decay portions of this work. Finally, this work would not have been possible without the technical support of Gary Powell and Todd Martin and several Michigan organic dry bean producers who helped conduct research with us on their farms. Thank you to Richard Stuckey, Mark and Steven Vollmar, Eric Houthhoofd, Kurt Cobb, Don Brockreide, Tom Nelson, Michael and Jon Findlay, and Steve Reinbold. 155    APPENDICES 156    APPENDIX E CHAPTER 3 TABLES AND FIGURES Table 3.01. Cover crop planting date and field operations for cover crop termination and seed bed preparation prior to dry bean planting at the main sites. Bean Cover crop control/seed bed preparations§ Cover crop † ‡ planting Year Location Cover crop Field planting date Mower Chisel plow Disk Cultipacker date† cultivator ─────────days before planting───────── 2011 KBS Clover 3/19/10 14(2x) 4(2x) Radish 8/16/10 14(2x) 1 6/17/11 Rye 9/14/10 35 35 No cover 35 MSU 2012 KBS MSU Clover Radish Rye No cover 8/17/10 8/17/10 9/10/10 - 39 39 17 17 17 17 - 11(2x) 5(2x) 0 5 6/20/11 Clover Radish Rye No cover 4/1/11 8/23/11 9/21/11 - 41 - 19(2x) 19 39 19 7 0 18 6 6/18/12 Clover Radish Rye No cover 6/9/11 9/6/11 10/11/11 - - 19 19 49(2x) 19 - 6 0 - 6/12/12 157    Table 3.01 (cont’d) † ‡ Year Location Cover crop 2013 KBS MSU Cover crop planting date Clover Radish Rye No cover 3/14/12 9/12/12 9/12/12 - Clover Radish 3/19/12 8/20/12 Rye No cover Cover crop control/seed bed preparations§ Field Mower Chisel plow Disk Cultipacker cultivator ─────────days before planting───────── 20 42 5(2x) 42 2 42 - 9/17/12 - - - 31 42 42 31 42 13 0 - 6/24/12 6/20/12 † KBS= Kellogg Biological Station in Hickory Corners, MI and MSU= the Michigan State University Horticulture Teaching and Research Center (2011 and 2012) and the Michigan State University Agronomy Farm (2013). ‡ Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. § Field operations (i.e. field cultivation, soil finishing, cultipacking, and dry bean planting) were performed uniformly and at the same time across the entire study. 158    - Bean planting date† Table 3.02. Cover crop planting date and field operations for cover crop termination and seed bed preparation prior to dry bean planting at the satellite sites. Location Cover crop planting date Cover crop control/seed bed preparations† MP CP DK FC CR ───days before planting─── Cover crop Year Clover 2011 Alma 9/5/10 27 - 22 1 1 6/14/11 Caro 3/17/10 42 - - 39(2x) 0 39(2x) 6/29/11 Sandusky 9/3/10 - - 9(2x) 4 1 4 1 6/18/11 2012 Sandusky 6/18/10 - - 27 7 2 27 7 2 6/20/12 2013 Alma 3/11/11 43 14 41 0(x) - 6/25/13 Columbiaville 3/30/13 Sandusky 9/5/12 159    6/20/13 Information not available 13 - - 0(2x) Bean planting date 0(2x) 6/19/13 Table 3.02 (cont’d) Cover crop planting date Cover crop control/seed bed preparations† MP CP DK FC CR ───days before planting─── 52 52 9 24 24 1 15 15 Cover crop Year Location Radish 2011 Alma 8/24/10 Caro 9/3/10 34 - - 0(2x) - 6/4/11 Millington 9/10/10 - 43 25 14 2 - 7/1/11 64 26 7 2 1 64 6/14/12 - - 6/15/12 0(2x) - 6/25/13 2012 Alma Millington 2013 Alma 9/2/11 - 9/21/11 - 8/24/12 - 160    - 21 0(2x) 1 - 41 Bean planting date 6/30/11 Table 3.02 (cont’d) Cover crop control/seed bed preparations† MP CP DK FC CR ───days before planting─── 34 7 0 Cover crop Year Location Cover crop planting date Rye 2011 Caro-A 11/3/10 Caro-B 11/3/10 42 - - 14 0 14 6/29/11 Columbiaville 11/11/10 - - - 29 18 3 - 6/7/11 2012 Caro 11/4/11 - - 26 0 - - 6/14/12 2013 Caro 11/6/12 1 - - 0 - 6/14/13 † MP= Moldboard plow; CP= chisel plow; DK=disk, FC= field cultivator, CR= Cultipacker. 161    Bean planting date 6/13/11 Table 3.03. Monthly precipitation† and the 30-yr averages for the main sites, 2011 – spring 2014. KBS‡ Month Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. MSU 30 year average ─────────────mm────────────── 27.2 68.1 50.5 74.9 54.6 69.1 36.1 188.5 60.5 50.3 73.4 94.5 28.7 52.1 65.3 132.8 91.2 159.5 58.9 90.9 74.2 33.5 127.8 80.5 99.1 25.6 37.4 107.9 100.8 131.3 40.4 76.0 97.8 95.2 75.2 126.5 106.7 79.0 39.6 19.3 119.1 94.0 142.0 55.1 87.9 109.2 13.7 113.0 86.4 63.0 52.1 64.2 68.8 2011 2012 2013 30 year average ─────────────mm────────────── 7.9 38.1 69.1 14.2 42.4 18.8 25.7 23.4 13.0 36.8 66.0 63.0 16.8 18.5 43.2 135.1 53.1 165.1 20.6 73.4 151.9 72.9 83.8 73.7 83.8 44.4 28.4 114.6 83.6 178.1 63.7 55.6 82.0 63.5 49.3 109.7 83.3 67.0 59.4 17.8 92.5 73.7 96.3 118.4 68.6 75.9 8.4 55.4 68.8 53.8 31.8 26.2 43.2 2014 2011 2012 2013 2014 † Monthly precipitation data were collected from the Michigan State University Enviro-weather database (MSU Enviroweather 2014). Thirty year average data were collected from the Michigan State Climatologist’s office (MI Climatologist 2014). ‡ KBS- Kellogg Biological Station, Hickory Corners, MI. MSU- Michigan State University Horticulture Teaching and Research Center and Agronomy Farm, Lansing, MI. 162    Table 3.04. Weed management operations at the main sites during the dry bean growing season from 2011 to 2013. Bean Weed management Total Year Location† planting operations Tined weeder Rotary hoe Intra-row cultivator Hand weed date ───────────days after planting‡─────────── 3 10(2x) 32 14 2011 KBS 6/17/11 MSU 6/20/11 2 17 29 - 3 2012 KBS 6/18/12 - 17(2x) 23 32 - 4 MSU 6/12/12 - - 27 43 56 3 - 6 - 5 2013 KBS 6/24/12 - 7(2x) 17 MSU 6/20/12 - 11 18 † KBS- Kellogg Biological Station, Hickory Corners, MI. MSU- Michigan State University Horticulture Teaching and Research Center (2011 and 2012) and Agronomy Farm (2013), Lansing, MI. ‡ Days after planting listed in red indicate the operation took place before the dry bean stage V2. Blue color indicates the operation took place after V2, but before R1. 163    21 32 42 28 32 40 5 Table 3.05. Weed management operations at the satellite sites during the dry bean growing season from 2011 to 2013. Dry bean Weed management † Cover crop Year Location Total operations planting date TW RH IRC TM HW ────days before planting‡──── Clover 2011 2012 2013 Alma 6/14/11 - 7 12 57 - - 3 Caro 6/29/11 2 - 13 - - 2 - 58 8 - 79 6 - 41 7 - 4 Sandusky 6/18/11 - 10 13 17 Sandusky 6/20/12 - 3 - 8 14 18 Alma 6/25/13 Columbiaville 6/20/13 Sandusky Information not available 6/19/13 - 164    19 22 26 39 15 20 27 40 23 24 60 5 12 18 31 - - Table 3.05 (cont’d) Cover crop Radish Year 2011 Location Dry bean planting date TW ────days before planting‡──── 3 15 10 20 46 13 32 Total operations Alma 6/30/11 Caro 6/4/11 - 10 25 46 - 67 4 Millington 7/1/11 11 - 19 32 - 32 58 5 6/14/12 - 7 11 14 25 30 - 54 6 6/15/12 34 43 - 20 - - 3 - 8 14 18 23 24 60 - 42 7 2012 Alma Millington§ 2013 Alma 6/25/13 165    Weed management † RH IRC TM HW 7 Table 3.05 (cont’d) Cover crop Year Location Dry bean planting date TW Weed management † RH IRC TM HW Total operations ────days before planting‡──── Rye 2011 Caro-A 6/13/11 2 18 19 42 - 61 5 Caro-B 6/29/11 2 - 13 - - 2 6/7/11 1 3 - 13 23 69 100 - 6 - 61 7 - 26 67 8 Columbiaville 2012 Caro 6/14/12 2 5 2013 Caro 6/14/13 3 7 10 † TW= tined weeder; RH= rotary how; IRC=intra-row cultivator; TM=tall mower, similar to old-fashioned sugar beet weeder; HW=hand weeded. ‡ Days after planting listed in red indicate the operation took place before the dry bean stage V2. Blue indicates the operation took place after V2, but before R1. Black indicates the operation took place after R1. § This site was not harvested and thus weed management operations ended early. 166    14 25 39 54 19 31 38 Table 3.06. Summary of cover crop biomass, nitrogen content, C:N ratio and influence on soil nitrogen at the main sites from 2011 to 2013. Cover Dry weight Soil inorganic nitrogen N C:N † crop Year Cover Location ratio Total Planting V2 R1 contentƪ Weed§ ‡ crop treatment 2011 2012 ─────Mg ha-1──── 7.1 0.4 7.6 4.5 2.2 6.7 9.7 0.0 9.7 0.0 7.1 7.1 NS kg ha-1 153.9 53.8 53.2 52.5 32.8 15.1 31.0 28.4 23.9 1.0 KBS Clover Radish Rye No cover LSDƺ MSU Clover Radish Rye No cover LSD 2.3 6.1 12.8 0.0 1.3 0.9 0.0 3.4 3.6 7.0 12.8 3.4 2.4 44.4 164.2 135.5 33.6 34.7 17.6 14.3 26.3 23.3 3.4 35.2 43.3 22.2 42.0 13.4 56.9 71.8 39.4 58.7 14.3 39.3 38.8 26.1 33.2 9.9 KBS Clover Radish Rye No cover LSD 10.3 4.5 12.0 0 0.0 2.3 0.0 4.2 10.3 6.8 12.0 4.2 1.8 195.8 60.9 65.9 43.3 30.2 17.7 23.9 51.6 29.3 4.6 63.4 33.0 29.2 29.9 4.0 98.7 59.0 39.9 43.6 12.2 68.5 39.0 21.8 35.6 10.4 MSU Clover Radish Rye No cover LSD 11.6 0.8 7.9 0 0.0 2.8 0.0 1.9 11.6 3.6 7.9 1.9 2.0 231.8 10.0 42.0 24.1 30.7 17.0 18.1 30.3 26.7 4.8 47.7 22.8 24.6 25.8 7.5 74.1 42.0 37.0 46.3 4.6 57.0 31.9 25.3 28.8 12.1 167    ─────kg ha-1───── 49.3 82.2 76.6 38.0 66.4 54.0 35.1 70.4 55.4 36.3 53.8 63.0 4.4 NS NS Table 3.06 (cont’d) Year 2013 † Location Cover crop treatment‡ KBS Clover Radish Rye No cover LSD MSU Clover Radish Rye No cover LSD Dry weight Total N contentƪ ─────Mg ha-1──── 8.6 0.8 9.4 5.2 2.4 7.6 10.5 0.0 10.5 0 1.5 1.5 2.1 kg ha-1 114.7 68.0 60.0 17.5 41.1 17.1 23.3 30.9 22.8 4.1 5.7 2.9 11.8 0 144.9 32.5 72.6 22.1 36.1 16.6 24.5 29.3 22.3 3.4 Cover crop Weed§ 0.6 2.3 0.0 1.9 6.4 5.2 11.8 1.9 2.8 Soil inorganic nitrogen Planting V2 R1 ─────kg ha-1───── 46.1 68.6 53.5 30.0 50.9 50.3 23.0 41.9 39.4 25.4 39.7 41.8 13.2 NS NS 45.1 30.9 22.7 29.3 3.8 67.3 53.9 37.5 53.5 10.4 48.4 35.8 29.1 36.8 10.6 † KBS- Kellogg Biological Station, Hickory Corners, MI. MSU- Michigan State University Horticulture Teaching and Research Center (2011 and 2012) and Agronomy Farm (2013), Lansing, MI. ‡ Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. § Weed biomass was taken during the spring at the time of cover crop incorporation, even for oilseed radish, which winterkilled. ƪ For clover, radish, and rye the N content and C:N represent the cover crop biomass alone; for the no cover treatment, the nitrogen content is for the weed biomass collected in the spring. ƺ Fisher’s protected LSD (P ≤ 0.05). 168    C:N ratio Table 3.07. Summary of cover crop biomass, nitrogen content, and influence on soil nitrogen at the satellite sites from 2011 to 2013. Cover Dry weight Total available nitrogen N Cover C:N crop Year Location Cover crop Total V2 R1 content§ ratio Planting Weed‡ † crop treatment ─────Mg ha-1───── 1.2 9.6 10.8 0.0 14.1 14.1 ──────kg ha-1────── 23.5 30.2 31.6 31.0 33.0 32.2 NS NS NS Clover 2011 Alma Clover No cover LSDƪ Caro Clover No cover LSD 6.0 0.0 0.0 0.0 6.0 0.0 130.0 13.0 - 87.2 68.8 8.8 112.3 76.3 NS 66.9 47.8 18.4 Sandusky Clover No cover LSD 1.0 0.0 6.9 0.5 7.9 0.5 29.8 13.1 11.1 13.8 30.0 34.3 NS 47.5 71.1 NS 55.1 72.7 NS 2012 Sandusky Clover No cover LSD 4.4 0.0 0.2 0.0 4.6 0.0 128.8 12.9 - 63.8 105.8 NS 100.1 118.5 NS 134.6 109.0 NS 2013 Alma Clover No cover LSD 9.1 0.0 0.0 0.0 9.1 0.0 150.7 15.2 - 44.9 45.0 NS 54.4 50.8 NS 52.9 54.0 NS Columbiaville Clover No cover LSD 1.0 0.0 2.6 0.0. 3.6 0.0 15.2 11.7 - - 37.8 39.0 NS 33.7 33.1 NS Sandusky 1.4 0.0 1.0 1.2 2.5 1.2 31.3 14.1 19.4 15.1 45.5 48.7 NS 51.2 43.6 NS 41.6 37.2 NS Clover No cover LSD 169    kg ha-1 17.4 16.5 65.1 30.1 Table 3.07 (cont’d) Cover crop Year Location Dry weight Cover crop Cover Weed‡ † crop treatment ─────Mg ha-1───── 2.0 1.8 3.9 0.0 6.7 6.7 Radish 2011 Alma Radish No cover LSD Caro Radish No cover LSD 0.2 0.0 0.0 0.0 0.2 0.0 Millington Radish No cover LSD 2.5 0.0 0.5 0.0 Radish No cover LSD 1.6 0.0 Radish No cover LSD Radish No cover LSD 2012 Alma Millington 2013 Alma C:N ratio kg ha-1 31.0 20.4 125.8 11.4 7.0 - Total available nitrogen Planting V2 R1 ──────kg ha-1────── 47.4 53.2 35.8 39.1 42.9 30.9 NS 4.3 NS 8.7 - 39.8 37.1 NS 37.0 36.0 NS 35.8 36.9 NS 3.0 0.0 81.4 10.6 - 69.4 70.2 NS 108.5 102.2 NS 44.7 44.8 NS 0.1 0.1 1.7 0.1 30.6 16.2 - 44.7 50.6 NS 58.3 55.1 NS 50.2 40.0 NS 0.6 0.0 0.0 0.0 0.6 0.0 13.3 12.2 - 50.6 57.5 4.2 60.0 64.9 NS 54.5 36.2 NS 4.8 0.0 0.0 0.0 4.8 0.0 95.2 14.4 - 36.3 45.0 NS 48.8 50.8 NS 48.5 54.0 NS 170    Total N content§ Table 3.07 (cont’d) Cover crop Rye Year Location Dry weight Cover crop Cover Weed‡ † crop treatment ─────Mg ha-1───── 1.9 0.0 1.9 0.0 0.0 0.0 C:N ratio kg ha-1 17.1 16.1 - Total available nitrogen Planting V2 R1 ──────kg ha-1────── 42.3 39.2 39.9 41.3 35.4 37.8 NS NS NS 2011 Caro-A Rye No cover LSD Caro-B Rye No cover LSD 1.4 0.0 0.0 0.0 1.4 0.0 11.1 21.5 - 32.7 30.7 NS 47.5 37.2 NS 42.3 31.1 NS Columbiaville Rye No cover LSD 1.0 0.0 0.0 0.0 1.0 0.0 9.5 17.0 - 41.7 35.1 NS 35.6 35.1 NS 41.4 45.7 NS 2012 Caro Rye No cover LSD 10.7 0.0 0.0 0.0 10.7 0.0 61.5 27.4 - 26.6 40.1 NS 37.9 46.8 7.9 26.2 29.6 NS 2013 Caro Rye No cover LSD 0.8 0.0 0.0 0.0 0.8 0.0 12.0 14.7 - 30.4 40.5 NS 37.3 45.9 NS 37.4 39.6 NS † Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. ‡ Weed biomass was taken during the spring at the time of cover crop incorporation, even for oilseed radish, which winterkilled. § For clover, radish, and rye the N content and C:N represent the cover crop biomass alone; for the no cover treatment, the nitrogen figures are for the weed biomass collected in the spring. ƪ Fisher’s protected LSD (P ≤ 0.05). 171    Total N content§ Table 3.08. Correlation coefficients (R) for cover crop, soil, and dry bean parameters combined across all site-years from 2011 to 2013†. Cover crop/weed parameters Cover Weed Total C:N crop N biomass biomass ratio content Cover crop‡ Clover Radish Cover crop/weed Cover crop biomass Weed biomass Total biomass C:N ratio Cover crop N content Soil inorganic N Planting V2 Weed Seed bank V2 Population Biomass R1 Population Cover crop/weed Cover crop biomass Weed biomass Total biomass C:N ratio Cover crop N content Soil in organic N Planting V2 Weed Seed bank V2 Biomass Population R1 Biomass Population -0.47*** 0.23*** 0.62*** 0.40*** 0.38*** 0.01*** 0.37*** 0.88*** 0.39*** 0.66*** 0.61*** 0.60*** 0.90*** -0.51*** 0.46*** 0.32*** 0.84*** 0.00*** 0.94*** -0.07*** 172    Soil inorganic N Planting V2 Weed parameters V2 R1 Population Biomass Population Biomass 0.30*** 0.49*** -0.53*** -0.46*** -0.21*** -0.01*** 0.43*** -0.03*** 0.45*** 0.63*** 0.23*** 0.24*** 0.47*** 0.15*** 0.33*** -0.19*** -0.04*** -0.18*** -0.04*** -0.16*** 0.35*** 0.13*** 0.49*** 0.27*** 0.40*** -0.14*** -0.04*** -0.22*** -0.01*** -0.14*** 0.90*** -0.17*** 0.01*** -0.16*** -0.26*** -0.16*** 0.03*** -0.09*** -0.15*** 0.06*** 0.18*** 0.03*** -0.08*** 0.73*** 0.04*** 0.03*** -0.08*** 0.40*** 0.14*** -0.10*** 0.24*** -0.39*** -0.12*** -0.27*** 0.12*** -0.46*** -0.12*** 0.21*** 0.44*** -0.26*** -0.22*** -0.30*** -0.17*** -0.21*** -0.12*** -0.18*** -0.18*** -0.27*** 0.02*** -0.42*** -0.35*** -0.52*** -0.41*** -0.29*** -0.32*** -0.33*** -0.43*** -0.44*** -0.16*** 0.72*** 0.13*** -0.02*** 0.36*** 0.31*** 0.33*** -0.02*** 0.28*** 0.07*** -0.10*** 0.18*** 0.63*** -0.12*** 0.95*** 0.95*** -0.08*** 0.79*** 0.84*** 0.91*** Table 3.08 (cont’d) Cover crop/weed parameters Cover Weed Total C:N crop N biomass biomass ratio content Cover crop‡ Rye No cover † ‡ Cover crop/weed Cover crop biomass Weed biomass Total biomass C:N ratio Cover crop N content Soil inorganic N Planting V2 Weed Seed bank V2 Population Biomass R1 Population Cover crop/weed Cover crop biomass Weed biomass Total biomass C:N ratio Weed N content Soil inorganic N Planting V2 Weed Seed bank V2 Population Biomass R1 Population . . . . . 0.62*** . . . 0.66*** . 0.82*** . . 0.30*** . 0.72*** . 0.44*** Planting V2 Weed parameters V2 R1 Population Biomass Population Biomass -0.69*** 0.05*** . . . . -0.51*** 0.01*** -0.63*** -0.07*** -0.53*** . . -0.44*** -0.42*** -0.29*** . . -0.26*** -0.26*** -0.73*** . . -0.56*** -0.53*** -0.53*** . . -0.48*** -0.37*** 0.21*** 0.63*** -0.15*** 0.11*** -0.04*** 0.56*** -0.27*** 0.52*** -0.12*** 0.06*** 0.35*** 0.14*** -0.01*** 0.76*** 0.06*** 0.19*** 0.82*** 0.03*** 0.73*** . . -0.29*** -0.25*** . . -0.47*** -0.23*** -0.24*** -0.19*** . -0.09*** . -0.18*** -0.11*** . -0.15*** . -0.06*** -0.12*** . -0.08*** . -0.15*** -0.14*** . -0.02*** . -0.11*** -0.15*** 0.85*** 0.00*** -0.08*** 0.07*** -0.05*** 0.01*** 0.06*** 0.07*** -0.06*** -0.11*** 0.13*** 0.08*** -0.10*** 0.71*** 0.08*** 0.12*** 0.39*** 0.50*** 0.46*** Correlation significant at * P ≤0.05, ** P ≤0.001, *** P ≤0.0001 Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. 173    Soil inorganic N Table 3.09. Estimates of initial germinable weed seed bank for the main and satellite sites from 2011 through 2013. Year 2011§ Cover crop(s)† All Clover Radish Rye 2012 All Clover Radish Rye 2013 All Clover Radish Rye Summer annuals Location KBS MSU Alma Caro Sandusky Alma Caro Millington Caro-Aƪ Caro-Bƪ Columbiaville Perennials and Grasses TOTAL Broadleaves‡ biennials ABUTH AMAsp AMBEL CHEAL POROL Total ──────────────────million weed seeds ha furrow slice-1────────────────── 0.6 0.0 0.0 4.8 27.0 45.7 52.9 13.2 111.9 0.0 4.2 0.6 15.0 4.2 64.4 31.3 19.9 15.0 0.6 3.0 0.0 22.9 0.0 105.9 52.9 3.6 22.9 0.0 0.0 0.0 12.0 0.6 12.6 24.1 0.6 37.3 4.2 15.6 0.0 18.0 0.6 93.8 1.8 7.2 102.9 0.0 3.0 0.0 7.8 0.0 27.1 0.0 7.8 34.9 1.2 1.2 0.0 2.4 0.0 6.6 0.0 0.0 2.4 0.0 22.8 0.6 13.2 0.6 87.8 4.2 33.1 125.1 0.0 2.4 0.0 8.4 0.0 11.4 6.6 0.0 18.0 1.2 1.8 0.0 1.8 0.0 4.8 51.1 0.0 55.9 4.2 2.4 0.0 30.7 0.0 38.5 18.0 1.8 58.4 KBS MSU Sandusky Alma Millington Caro 0.0 0.0 1.8 0.0 0.6 0.0 1.2 0.6 22.3 1.2 1.2 1.2 0.6 1.2 0.0 0.0 1.2 0.6 9.0 26.5 12.0 0.6 5.4 8.4 3.0 3.6 0.0 0.6 0.0 0.0 13.8 31.9 52.9 6.0 8.4 10.2 12.0 3.0 0.6 4.2 9.0 4.8 0.6 0.0 0.0 0.0 9.0 0.0 26.5 34.9 53.5 10.2 26.5 15.0 KBS MSU Alma Columbiaville Sandusky Alma Caroƪ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.8 0.6 0.6 1.2 25.9 0.6 18.6 1.2 0.0 0.0 7.8 1.2 0.0 0.6 39.1 0.0 1.8 33.7 6.6 1.8 64.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 112.5 8.4 3.6 90.8 64.4 3.6 100.5 12.6 4.8 0.0 40.3 2.4 0.0 10.2 5.4 0.0 0.0 0.6 0.0 0.0 1.8 130.5 13.2 3.6 131.7 66.8 3.6 112.5 † KBS- Kellogg Biological Station, Hickory Corners, MI. MSU- Michigan State University Horticulture Teaching and Research Center and Agronomy Farm, Lansing, MI. ‡ Bayer codes: ABUTH= velvetleaf, AMAsp= Powell amaranth and redroot pigweed, AMBEL= common ragweed, CHEAL= common lambsquarters, POROL= common purslane. Total includes the five summer annual broadleaf weeds listed, plus any other summer annual broadleaf weed species present. Estimates from 2011 were collected in September at the end of the dry bean growing season and grown and counted in the greenhouse during the winter months. In 2012 and 2013 were collected in June at the time of dry bean planting and were grown outside during the summer. Dry beans at these sites were planted at 56 cm row spacing, which is in contrast to all other sites which were planted at 76 cm row spacing. § ƪ 174    Table 3.10. Weed populations and biomass recorded at bean stage V2 as influenced by cover crop at the main sites from 2011 to 2013. Values are averaged over all four dry bean varieties. Weed population Summer annuals Perennials Cover Year Location† Weed biomass ‡ and TOTAL crop Broadleaves§ Grasses biennials CHEAL Total 2011 2012 KBS Clover Radish Rye No cover LSDƺ ───────────plants (10 m row-1)ƪ─────────── 1.1 1.5 53.6 7.3 62.7 1.8 3.3 5.5 2.6 12.4 0.7 2.2 0.0 2.5 5.1 3.3 5.8 4.4 8.8 18.9 NS NS NS *A *B *C MSU Clover Radish Rye No cover LSD 0.5 0.3 0.5 1.1 NS 0.8 1.6 1.6 0.6 NS 1.6 0.0 0.0 0.0 NS 1.1 0 0 0.3 NS 3.8 0.6 1.6 1.9 NS 0.4 0.0 0.1 0.6 NS KBS Clover Radish Rye No cover LSD 25.6 5.8 0.6 7.1 NS 35.3 12.0 1.6 13.7 NS 35.3 45.9 6.0 42.9 NS 0.0 0.0 0.0 1.0 NS 70.5 59.3 7.9 57.7 NS 1.9 3.5 0.7 2.6 NS MSU Clover Radish Rye No cover LSD 95.4 4.6 3.3 3.6 51.6 121.1 15.0 10.9 19.1 59.2 6.8 0.8 1.1 0.6 NS 0.0 0.0 0.0 0.8 NS 127.9 15.9 12.0 20.5 51.5 2.2 0.2 0.2 0.4 1.2 175    g (10 m row-1) 3.5 0.5 0.3 2.4 Table 3.10 (cont’d) Year 2013 † Location† Cover crop‡ KBS Clover Radish Rye No cover LSD MSU Clover Radish Rye No cover LSD Weed population Summer annuals Perennials and Broadleaves§ Grasses biennials CHEAL Total TOTAL ───────────plants (10 m row-1)ƪ─────────── 0.0 2.5 6.0 1.0 9.6 0.0 2.7 2.2 0.0 5.2 0.6 4.1 1.1 0.0 5.2 0.0 3.3 1.1 0.0 4.4 NS NS 4.2 NS NS 0.0 0.0 0.4 0.0 NS 5.5 1.5 1.1 1.8 NS 16.4 2.2 1.5 0.4 NS 1.1 0.4 0.0 0.4 NS 22.6 4.7 2.9 2.6 13.8 Weed biomass g (10 m row-1) 0.8 0.8 0.7 0.6 NS 3.1 0.3 0.1 0.3 1.6 KBS- Kellogg Biological Station, Hickory Corners, MI. MSU- Michigan State University Horticulture Teaching and Research Center (2011 and 2012) and Agronomy Farm (2013), Lansing, MI. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. ‡ § CHEAL= common lambsquarters, Total= common lambsquarters, plus any other summer annual broadleaf weed species present. ƪ The plants (10 m row)-1 measurement is 15 cm in width. Plant populations and biomass were only recorded within the row as most interrow weeds were effectively removed via cultivation. ƺ Fisher’s protected LSD (P ≤ 0.05). * Cover crop*Dry bean variety interaction: Vista and Zorro show red clover to be significantly higher, Black Velvet and R99 do not *B Cover crop* dry bean variety interaction: Vista and Zorro show red clover to be significantly higher than no cover and rye, Black Velvet and R99 show no significant differences C * Cover crop*dry bean variety interaction: R99 shows red clover to be significantly higher, other varieties are NS A 176    Table 3.11. Weed populations and biomass recorded at bean stage R1 as influenced by cover crop at the main sites from 2011 to 2013. Values are averaged over all four dry bean varieties. Weed population Summer annuals Perennials Cover Weed biomass † and TOTAL Year Location ‡ § Grasses crop Broadleaves biennials CHEAL Total 2011 2012 ───────────plants (10 m row-1) ƪ─────────── 0.0 0.0 20.7 1.0 21.9 0.4 2.2 1.1 0.0 3.3 0.7 0.7 1.0 0.0 1.8 0.4 0.3 0.7 0.0 1.1 A NS NS NS * *B KBS Clover Radish Rye No cover LSDƺ MSU Clover Radish Rye No cover LSD 0.8 0.8 2.5 4.9 NS 1.6 1.6 2.7 8.5 NS 0.0 0.0 0.0 0.3 NS 0 0 1.1 0.3 NS 1.6 1.6 3.8 9.0 5.3 10.1 43.0 35.5 57.6 NS KBS Clover Radish Rye No cover LSD 2.2 0.5 0.3 0.5 NS 5.2 1.6 1.4 2.2 NS 41.0 14.2 2.2 16.7 NS 0.0 0.0 0.0 0.0 - 46.2 15.9 3.6 18.9 26.7 157.6 43.9 20.1 78.3 NS MSU Clover Radish Rye No cover LSD 66.2 2.5 3.0 1.9 37.1 90.8 8.5 12.6 13.4 51.1 2.7 1.1 0.8 1.1 NS 1.3 0.5 0.0 0.0 NS 94.9 13.4 10.1 14.5 52.0 173.0 23.2 39.2 35.9 112.1 177    g (10 m row-1) 28.9 31.0 7.9 2.6 NS Table 3.11 (cont’d) Year 2013 † ‡ Location† Cover crop‡ KBS Clover Radish Rye No cover LSD MSU Clover Radish Rye No cover LSD Weed population Summer annuals Perennials § and Broadleaves Grasses biennials CHEAL Total TOTAL ───────────plants (10 m row-1) ƪ─────────── 0.8 6.3 12.6 0.0 18.8 0.0 2.2 3.3 0.0 5.5 0.3 2.2 1.6 0.0 4.9 0.8 3.8 1.6 0.0 6.0 NS NS NS NS 0.0 0.0 0.0 0.0 - 2.5 0.7 1.5 0.4 NS 20.0 2.2 1.5 1.1 NS 0.0 0.0 0.4 0.0 - 22.6 2.9 3.3 1.5 14.2 Weed biomass g (10 m row-1) 22.5 6.3 13.9 7.5 NS 36.5 3.8 2.8 1.5 26.5 KBS- Kellogg Biological Station, Hickory Corners, MI. MSU- Michigan State University Horticulture Teaching and Research Center (2011 and 2012) and Agronomy Farm (2013), Lansing, MI. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. § CHEAL= common lambsquarters, Total= common lambsquarters, plus any other summer annual broadleaf weed species present. ƪ The plants (10 m row)-1 measurement is 15 cm in width. Plant populations and biomass were only recorded within the row as most interrow weeds were effectively removed via cultivation. ƺ Fisher’s protected LSD (P ≤ 0.05). Cover crop*Dry bean variety interaction: R99 shows a significant difference with red clover being higher than all other cover crop treatments, all other dry bean varieties show no difference among cover crop treatments *B Cover crop* dry bean variety interaction: R99 shows a significant difference with red clover being higher than all other cover crop treatments, all other dry bean varieties show no difference among cover crop treatments *A 178    Table 3.12. Weed seed mortality over time for 2012 and 2013. Values are averaged across cover crop treatments (i.e. red clover, cereal rye, and no cover crop control treatments). Weed species Year Time Common Giant foxtail Velvetleaf lambsquarters ──────── Percent mortality (%) ──────── ──MAI†── 2012 0 1 2 4 6 12 LSD‡ 47 59 59 74 69 60 10 21 71 78 79 83 87 9 23 40 44 49 47 48 8 2013 0 1 2 4 6 12 LSD 20 34 44 46 66 12 72 93 95 97 100 10 9 5 10 10 7 NS † MAI= months after cover crop incorporation ‡ Fisher’s protected LSD (P ≤ 0.05). Table 3.13. Weed seed mortality as influenced by cover crop in 2012 and 2013. Values are averaged across all pull times (i.e. 0 to 12 months after cover crop incorporation). Weed species † Year Common Cover crop Giant foxtail Velvetleaf lambsquarters ─────── Percent mortality (%) ─────── 2012 No cover 62 73 43 Clover 65 75 47 Rye 57 61 36 ‡ NS 10 6 LSD 2013 No cover Clover Rye LSD 36 58 31 9 96 86 92 NS 6 9 9 NS † Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. ‡ Fisher’s protected LSD (P ≤ 0.05). 179    Figure 3.01. Cropping sequence at the main and satellite research sites. Cover crops were interseeded into or planted following a small grain in the season preceding the dry edible bean crop. Red clover and cereal rye were terminated using primary tillage in the spring before dry bean planting. Clover= medium red clover, radish= oilseed radish, rye= cereal rye, no cover= weedy control. 180    APPENDIX F CHAPTER 3 ANALYSIS OF VARIANCE FOR SUBPLOT VARIABLES AT THE MAIN SITES Table F.01. Analysis of variance p-values for weed parameters measured at the subplot level. Weed parameters Total population Biomass V2 R1 V2 R1 Cover crop 0.0246 0.1064 0.0427 0.4899 Variety 0.0149 0.0231 0.0801 0.0516 Cover*variety <0.0001 0.0172 0.0010 0.3862 Year Location† Main effect 2011 KBS MSU Cover crop Variety Cover*variety 0.5981 0.0381 0.4398 0.2293 0.6149 0.8594 0.6048 0.3315 0.4529 0.0968 0.4591 0.6716 2012 KBS Cover crop Variety Cover*variety 0.1474 0.0316 0.5188 0.0681 0.7021 0.8124 0.4613 0.2154 0.1793 0.0284 0.6189 0.5441 MSU Cover crop Variety Cover*variety 0.0016 0.0130 0.5942 0.6579 0.9977 0.7974 0.0128 0.0444 0.1256 0.6559 0.4108 0.5123 2013 KBS Cover crop Variety Cover*variety 0.3699 0.1232 0.2373 0.1144 0.2021 0.4952 0.9826 0.4026 0.5221 0.0717 0.0860 0.2236 MSU Cover crop Variety Cover*variety 0.0328 0.0305 0.8831 0.4153 0.8991 0.2694 0.0095 0.0473 0.5978 0.5305 0.5822 0.4567 † KBS- Kellogg Biological Station, Hickory Corners, MI. MSU- Michigan State University Horticulture Teaching and Research Center (2011 and 2012) and Agronomy Farm (2013), Lansing, MI. 181      APPENDIX G WESTERN BEAN CUTWORM TRENDS IN ORGANIC DRY BEAN IN MICHIGAN FROM 2011-2013 AND POTENTIAL MANAGEMENT WITH PYGANIC® (1 YEAR) Introduction Demand for organically produced dry beans has been on the rise in recent years both within the U.S. and abroad. The only survey of organic agriculture in the U.S. was conducted in 2007 at which time Michigan was the top organic dry bean producing state, comprising 39% of the hectares harvested (USDA-NASS 2008). Average organic dry bean yields in Michigan in 2007 averaged 1,700 kg ha-1, compared with 1,800 kg ha-1 for conventionally produced beans that same year (USDA-NASS 2014b). Producing a quality dry bean crop without the use of synthetic amendments and pesticides presents unique challenges for organic growers, especially when it comes to pest management (i.e. insects, diseases and weeds). The most common insect problems in Michigan dry beans include: potato leaf hopper (Empoasca fabae Harris), Mexican bean beetle (Epilachna varivestis Mulsant), seedcorn maggot (Delia platura Meigen) (DiFonzo 2006), and the more recent addition, western bean cutworm (Striacosta albicosta, Smith) (DiFonzo 2010a). Western bean cutworm (WBC) first appeared in Michigan traps in 2006 (DiFonzo 2010a; Chludzinski 2013). WBC uses both corn and dry bean as host plants, with corn being the preference. WBC can overwinter in the soil as pre-pupa. Adults emerge in July and lay their eggs on the upper leaves of corn or the underside of dry bean leaves. In dry bean, the emerging larvae feed on leaves, blossoms, pods, and developing seeds. Larval feeding can increase the percentage of defective beans, which translates into greater 182      cleaning costs for producers. Larval feeding can also allow for pathogen infection. In 2013, Chludzinski observed that 2 or more WBC egg masses per 1.5 m and 2 or more larvae per 0.3 m of row resulted in dry bean damage of up to 6.1% and 0.8%, respectively. Damage of 2% or greater is considered to cause an economic loss (Blickenstaff 1979; Mahrt 1987; Michel et al. 2010; Chludzinski 2013). Egg masses and larvae are difficult to scout in dry bean due to their size and therefore pheromone traps are often used to track peak moth flight, as there is only one generation per year (Michel et al. 2010). Pod injury is usually found within 3 weeks of peak flight; therefore trap counts and pod scouting are important to consider together (Michel et al. 2010). WBC flight threshold values are still being developed for Michigan, as the previously established western thresholds appear to be too high. The onset of WBC feeding is typically outside that in which seed treatments or insecticides applied at planting will last, therefore postemergence applications of pyrethroids are recommended at the onset of pod feeding in conventionally produced dry bean systems (DiFonzo 2010b). Pyrethroid insecticides used in conventional systems are synthetically derived, and therefore not suitable for use in organic systems. Common insect problems in organic dry bean systems are first and foremost managed through the cultural practices, such as crop rotation and altered planting dates. In the event of outbreaks, there are materials approved by the Organic Materials Review Institute (OMRI) that can be applied; all such materials are naturally derived. PyGanic® (McLaughlin Gormley King Company, Minneapolis, MN) is an OMRI approved broad spectrum insecticide which contains pyrethrins derived from chrysanthemums. PyGanic has no residual activity, meaning it may need to be applied multiple times to control outbreaks of detrimental insects, whereas synthetic 183      pyrethrins can have some residual activity depending on the additives included (Rife 1976). Currently, there are no management recommendations for WBC in organic dry bean. The objectives of this research were to determine if PyGanic is effective at controlling WBC and if so, to establish the most effective application timing to avoid yield and quality losses to organic dry bean. Materials and Methods Western bean cutworm traps were set up at each of the Michigan State University main sites and on-farm cooperator satellite sites over the course of the three year study (Chapters 2 and 3), for a total of 26 site-years. Traps consisted of a standard gallon milk jug with windows cut out, and a WBC-specific pheromone (Great Lakes IPM, Vestaburg, MI) hung under the cap (Figure G.01). Milk jugs were secured to a metal post at least 1.2 m above ground level. Male moths were attracted to the pheromone and then fell into the anti-freeze filled reservoir at the bottom of the jug and died. The traps at our locations were a part of a state-wide network managed by the laboratory group of Dr. Christina Difonzo, Michigan State University Entomologist. Weekly to bi-weekly counts were used to monitor WBC distribution across the state, with full details and results available in the M.S. thesis of Ms. Megan Chludzinski (2013). These counts were also used to infer peak larval feeding pressure at each of our sites, as oviposition by females occurs two to four days following flight/emergence (Blickenstaff 1979; Dorhout and Rice 2008; Chludzinski 2013) and larva hatch five to seven days later (Seymour et al. 2004). In the event that a bi-weekly count exceeded 200 moths, a sub-experiment was conducted to meet our above listed objectives. The sub-experiment consisted of three treatments: 1) PyGanic 184      (392 g a.i. ha-1) applied at seven days after peak flight, 2) PyGanic (392 g a.i. ha-1) applied at the first sign of pod feeding, and 3) an untreated control. The sub-experiment was conducted on both the ‘Zorro’ black bean and ‘Vista’ navy bean subplots in the no cover crop treatment, with four replications. At harvest, whole plants were pulled by hand (3 m of two rows) and an Almaco stationary thresher (Nevada, IA) was used to separate the beans from the other plant material. Secondary cleaning of the samples was done using a Vac-A-Way seed cleaner (Hance Corp. Westerville, OH) to remove dirt, debris, and malformed or underdeveloped beans. Cleaned samples were weighed and grain moisture recorded using a Grain Analysis Computer 2100 Agri (Dickey-John Corp. Auburn, IL). Yields were calculated by adjusting to 18% moisture. An additional 3 m of a single row of dry bean plants was collected and analyzed in the laboratory to determine the number of WBC damaged pods and the total number of pods. Yield and damage data were analyzed in SAS 9.3 using the MIXED procedure. Variance assumptions were checked using the UNIVARIATE procedure. Mean separation was conducted using Fisher’s Protected LSD (p≤0.05). Results and Discussion During the three years that WBC was monitored via pheromone trapping, 2011 had the highest number of total males caught from June through August, averaging 170 total males captured (Table G.01). In 2012 and 2013, the average total males captured dropped to 8 and 20, respectively. Across the state-wide WBC trapping network, 2012 showed a reduced number of moths captured compared with the previous three years (Chludzinski 2013); 2013 data were not 185      reported. Due to low WBC numbers, WBC sub-experiments were not conducted in 2012 and 2013. In 2011, however, the Alma-A location exceeded the 200 moth threshold with 231 moths caught during the latter part of July and was the site-year with the highest total number of moths captured, 467, during the three year study (Figure G.01). The initial PyGanic application following this peak flight was made on August 4, 2011. A small amount of pod feeding was observed on August 15, therefore the second application of PyGanic was made on August 16, 2011. Dry beans at this location were harvested on October 24, 2011. Average yields for this location were 3,800 and 3,100 kg ha-1 for the Zorro black bean and Vista navy bean, respectively. Neither application of PyGanic altered dry bean yield for either Zorro or Vista compared with the untreated control (Figure G.02). Less than 1% of pods were damaged by WBC feeding, regardless of PyGanic treatment or bean variety (Figure G.03); no differences were observed between the treatment timings and the untreated control. The threshold for WBC captured in pheromone traps in the western portion of the United States is 700 total moths captured from the beginning of emergence through peak flight (Mahrt et al. 1987). It is speculated that these threshold levels in the Midwest could be lower due to increased egg and larvae survival in the more humid environment (Michel et al. 2010), which is why we looked at a two week capture of 200 moths or more. Based on our single year of results, it appears that a season total of 467 moths is below that which would result in significant levels of pod injury (≤ 2%). Should the WBC population in Michigan see a 186      resurgence, this project should be attempted again when WBC pressure is higher to truly test the efficacy of PyGanic and determine the optimal application timing. Table G.01. Western bean cutworm pheromone trap catches in Michigan organic dry bean fields from 2011-2013. June July August Year Site type Location Total 1-15 16-30 1-15 16-31 1-15 16-31 ─────────────────# Male moths───────────────── 2011 Main KBS 15 96 78 66 255 MSU 10 16 19 25 70 Satellite Alma-A 7 231 229 0 467 Alma-B 5 157 187 21 370 Caro-A 2 16 15 17 71 Caro-B 1 31 83 64 179 Caro-C 2 35 18 58 113 Caro-D 3 6 17 17 43 Columbiaville 10 86 59 16 171 Millington 3 17 16 0 36 Sandusky 5 43 28 16 92 2012 Main KBS MSU Satellite Alma-B Caro-A Millington Sandusky 0 0 0 0 0 9 0 0 0 0 1 12 0 0 0 0 0 4 1 10 0 0 3 0 1 0 0 1 3 0 0 0 0 4 0 25 2 10 0 5 7 2013 Main - - 0 0 0 0 0 0 1 0 0 1 3 10 6 0 57 0 2 0 2 3 18 0 6 10 9 3 75 1 11 20 KBS MSU Satellite Alma-B Caro-A Columbiaville Sandusky 187      Figure G.01. Western bean cutworm pheromone trap using a standard gallon milk jug with windows cut out and anti-freeze in the reservoir. 4500 4000 7 days after peak flight @ pod damage Untreated Yield (kg ha-1) 3500 3000 2500 2000 1500 1000 500 0 Zorro black bean Vista navy bean Figure G.02. Black and navy bean yield responses to PyGanic® application timings. Error bars represent the standard error. 188      7 days after peak flight @ pod feeding Untreated 1.8 Damaged pods (% of total) 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 Zorro black bean Vista navy bean Figure G.03. Percent of total pods harvested exhibiting damage due to feeding by western bean cutworm. Error bars represent the standard error. 189      APPENDIX H ON-FARM TRIAL REFLECTIONS 2010-2013 Introduction Input from growers and on-farm research are increasingly required in requests for applications from granting entities. On-farm trials are also attractive as a local, low-cost method for collecting data for extension and agribusiness personnel (Koenig et al. 2000). During the course of our United States Department of Agriculture- National Institute of Food and Agriculture- Organic Research and Extension Initiative (USDA-NIFA-OREI) project, we worked with Michigan organic dry bean growers to test our hypotheses on how cover crops impact soil inorganic nitrogen, weeds, and dry bean characteristics and yield in an organic dry bean system. We worked with nine growers, for a total of 20 site-years, with a range of four to nine locations each season. Locations included: Alma, Caro, Columbiaville, Millington, and Sandusky, MI. The duration of each site-year was from the time of cover crop planting (spring, summer, or fall) in year one through the harvest of dry beans planted in year two. Process Locating cooperators Michigan has no formal networks of growers to target for on-farm research work, particularly for organic research. However, we were fortunate enough to have an extension educator who had worked extensively with the organic community in Michigan for around 20 years, Mr. Dan Rossman. His connections and positive relationship with these growers was why we felt it critical to include him as one of the principle investigators on the grant proposal. After receiving 190      notice in July of 2010 that our proposal had received funding, Mr. Rossman found two growers in his local county, Gratiot, who agreed to participate. He also advised me to attend a MSU soybean variety trial field tour in Caro, MI (July 2010) and the Michigan Thumb Organic meeting (August 2010) in Brown City, MI to scout out more potential collaborators. During the tour and meeting I was able to introduce the project and speak with several potentially interested grower. At that time I gave them a one-page, two-sided handout that quickly outlined the project, the land needed, the responsibilities of both the grower and MSU (i.e. me) with regard to supplying seed, field activities, and data collection, and had my contact information (Figure H.01). Follow up phone calls with the people I spoke with gave us a total of nine growers to work with for the initial 2010-2011 season. Division of labor As previously mentioned, I felt it was important to be upfront with the responsibilities of both the grower and MSU, which can be seen in Figure H.01. The goal was to make the effort on the part of the grower fit into their usual routines as much as possible. If the project was located within or near a field of dry beans, then in-season operations like pest management (i.e. cultivation and OMRI-approved pesticide applications) would not be any different in the experimental portion of the field. What was different and required more time however was cover crop management, because there were cover cropped and no cover crop areas, and planting, because two dry bean varieties were studied. Because the growers were doing the field maintenance and we were collecting the data, communication was critical. 191      Communicating with cooperators Weekly to bi-weekly contact with the growers was important during the dry bean season to appropriately time our data collection and to avoid any misunderstandings. When first discussing the project with the nine growers I asked how they preferred to be contacted. Though communications via the telephone were most often requested it became clear that one form of communication would not suit all. Within this groups some of the growers that participated were very technologically savvy and preferred text messaging or email communications, while others did not have cellular phones and preferred written communications via traditional mail. Personal service contracts. In order to pay the growers for their efforts, each year they had to complete a personal service contract with the University. These contracts were sent through the mail by the accounting personnel within the Department of Plant, Soil and Microbial Sciences. Contracts were returned either through the mail of through fax. Informational and record keeping binder. Each year I provided the growers with a three-ring binder. Within the binder there were several sections to try to keep things running smoothly and encourage uniformity across locations. The first section was “Methods”. Within this section the objectives of the research were clearly outlined as well as the methods for site setup, cover crop planting, cover crop management, dry bean planting, dry bean management, and dry bean harvest (Figure H.02). The second section called “Calendar” had a blank calendar covering months from the time of cover crop planting through dry bean harvest for recording of field operations. The third section was called “Forms.” This section was probably the most critical for the growers to fill out because it detailed information about the field history, field operations, 192      and equipment used (Figure H.03). Many of the ideas I got for creating this form came from forms I received from the Practical Farmers of Iowa (practicalfarmers.org) while collecting data from on-farm trials in Iowa, a project funded through USDA- Sustainable Agriculture Research and Education (SARE). Though this information might not be important to know every day during the season, it is very important to know when making comparisons across sites and years during the final analysis of the results at the end of the experiment. To show exactly how I wanted the form to be filled out, I placed a sample form that I had filled out in the front pocket of the binder. The first pages of the form were information that I wanted early in the season, so during the final dry bean year, 2013, I stapled those three pages to a self-addressed stamped envelope and placed it with the welcome letter in the front of the binder. The return rate of these forms in this year was the best of the three years and it was the most effortless. The fourth section was labeled “Observations” and contained blank notebook paper in the event the grower wanted to add anything. The final section was called “Other” and was where I placed all the documentations regarding the seed sources that is required for organic certifiers. At the end of the dry bean growing season binders were either collected directly from the grower or a selfaddressed stamped envelope was sent. Copies of the documents were returned to growers for their file in the event that I needed to call them with questions. Reminders. Though we visited each research site at least biweekly, we did not meet with growers during each visit. Also, it was cumbersome to call up to nine growers with reminders every week or two, so the use of supplemental reminders was helpful. Since not everyone could communicate through electronic means, I sent postcards from late 2011-2013. The postcards were always colored green and could easily be read on the way from the mailbox back to the 193      house (Figure H.04). Each postcard had a maximum of three bulleted points and always contained my contact information so that it did not have to be looked up in the event of questions. Outcomes Positive outcomes I would consider these 20 site-years of data collection on-farm to have been successful. The information we gathered has been useful for making recommendations regarding the use of cover crops before dry beans, both organic and conventional, and when pooled with the data collected from our MSU research farms has helped find correlations between cover crop quantity and quality and soil inorganic N and dry bean characteristics. Overall these collaborations proved to be mutually beneficial, and some of the benefits to both parties are outlined below. MSU benefits of on-farm organic dry bean trials.  Built positive relationships  Grower network helped boost field day attendance  Growers taught researchers about organic production, markets, and other information not easily accessible  Growers are interested in continuing to collaborate with MSU to conduct on-farm research  Growers indicated future research needs 194      MI grower benefits from on-farm organic dry bean trials.  Gained knowledge on how cover crops impact dry beans in the local growing region  Learned how cover crops and navy beans perform on their own farms  Built positive relationships with MSU  Some growers appreciated having MSU on-site to ask other production questions (e.g. disease identification)  MSU listened to further research needs of Michigan organic growers Pitfalls and lessons Though we made our best effort, no research project is without pitfalls. Though some pitfalls are unavoidable, the lessons learned could help improve on-farm research in the future. Communication.  It was often necessary to follow up with growers to get the personal service contracts returned to the University, this was not particularly problematic but I believe adding another communication source was confusing.  Within the binder, most growers did not use the calendar, but instead used their own preexisting record keeping and then transferred information to the forms provided.  At the end of the field trial recording form (Figure H.03), there are open ended questions regarding what they learned from the study, what they would do differently, what research is needed in the future. These questions were rarely answered. In the future a post-harvest interview with the growers may yield better results as it seemed growers 195      were more likely to answer these questions or express future research needs in person throughout the season as opposed to writing them down.  Getting binders returned at the end of the dry bean season often required reminders. Field operations.  The design of this project (i.e. placing cover crops in or following a small grain, and before dry beans) did not fit many growers’ rotations, which lead to delayed planting of the cover crops and reduced cover crop biomass production, often resulting in few differences compared with the no cover crop control treatment.  Growers did not want to plant navy beans for two reasons: 1) there is not a good market for navy beans, black beans dominate the MI organic marketplace and 2) they were fearful of mixing navy beans in with black beans at harvest.  Research sites located near the farmstead or other dry beans resulted in fewer management issues (e.g. timelier weed management operations).  Occasionally fields were hand-weeded before collecting my final weed data. I believe this stems from the short notice on the availability of weeding crews, but as the years progressed I was better about sending reminders about this issue out on the postcards and incidents seemed to decrease. Conclusions Overall the benefits of conducting a portion of this research on-farms with growers greatly outweighed any issues that arose. In addition to all of the data collected, it helped expand my educational experience beyond what can be learned in the classroom. With the lessons I have 196      learned I think that small improvements to the strategies we use to conduct on-farm research could create an even better experience. 197      Organic Dry Bean Production Systems    Objectives:  1. Identify dry bean varieties that are best suited for organic production, including nitrogen  demand and nitrogen fixation through nodulation, the ability to tolerate prolonged mechanical  weed management, and dry bean production and seed yield in cover crop systems.  2. Measure soil nitrogen availability in dry beans planted in rotation following cover crops.   3. Determine if cover crops prior to dry beans influence weed emergence and growth and  mechanical weed management.   4. Evaluate key insects pests in organic dry bean production as influenced by variety and cover  crops prior to planting.    Sites:   Horticulture Teaching and Research Center‐ Student Organic Farm   Kellogg Biological Station   Six on‐farm grower locations    Cover crops to be studied (growers choose one + no cover, all will be planted at the MSU sites):  1. Medium red clover  2. Oilseed radish  3. Rye  4. No cover    Bean varieties to be studied:  1. ‘Zorro’ black bean  2. ‘Jaguar’ black bean (MSU sites only)  3. ‘Vista’ navy bean  4. ‘R99’ navy bean (MSU sites only)            Figure H.01. Introductory flyer presented to potential grower cooperators at the beginning of the project; one page printed front and back.     198      Figure H.01 (cont’d)  Possible field layout for on‐farm sites:  Cover No Cover Rep 4 Vista Zorro Zorro Vista Rep 3 Rep 2 Rep 1     Grower responsibilities:   Fill out personal service contract with Crop and Soil Science accountant Debbie Williams   Cover crop planting and management (Summer/Fall 2010)   Dry bean planting in coordination with Erin Taylor (Summer 2011)   Weed and pest management in the dry beans   Help scout for insect issues   Record comments for the cover crop versus no cover crop with regard to tillage, seedbed  preparation, and pest management issues (these comments are of great value to other growers)     MSU responsibilities:    Compensate growers $1000/trial year (in two installments)   Supply dry bean seed   Take all research measurements (nitrogen samples, weed densities, etc.)   Hand harvest a subsample of the plot area   Produce an extension bulletin with our findings at the conclusion of this study    Contact Information:  Erin Taylor  Research Associate/Ph.D. student  (517) 355‐0271 ext.1222 (Lab)  (810) 397‐7163 (Cell)  hiller12@msu.edu (Email)      199      Organic Dry Bean Production Systems    Contact Information:  Erin Taylor  Research Associate/Ph.D. student  (810) 397‐7163 (Cell)  (517) 355‐0271 ext.1222 (Lab)  hiller12@msu.edu (Email)    Objectives:  5. Identify black and navy dry bean varieties that are best suited for organic production.  6. Measure soil nitrogen availability for dry beans planted in rotation following cover crops.   7. Determine if cover crops prior to dry beans influence weed emergence, growth and mechanical  management.   8. Evaluate key insect pests in organic dry bean production as influenced by variety and cover  crops prior to planting.    Research site setup  Select a site that will both fit in with your rotation and also be representative of your farm. Do not place  the study in an area that stays wet or really dry in comparison to the rest of the field, etc. You will be  responsible for planting the cover crop and dry beans. You will also be responsible for managing the  weeds and other pests within the beans. Your site will be custom sized to fit your equipment. As you  look at the figure with the possible site layout (pg. 2) you will see that we need…     Total dimensions (varies based on equipment and area)  o Four passes that are the width of your planter   o A minimum of 800 feet in length is preferred  Half of the research site seeded to a cover crop the year before the dry beans are planted  o One pass of black beans ‘Zorro’ the following summer  o One pass of navy beans ‘Vista’ the following summer  The other half was be left with no cover  o One pass of black beans ‘Zorro’ the following summer  o One pass of navy beans ‘Vista’ the following summer   This will allow us to make comparisons between cover and no cover for each bean variety. We will also  compare the two varieties within a cover or no cover setting.    Figure H.02. Methods outlined for growers and provided in their three-ring binders.  200      Figure H.02 (cont’d)  Possible research site layout within a large field:    Rep 1 Rep 2 ‘Vista’ nvy Rep 3 ‘Vista’ nvy Rep 4 ‘Zorro’ blk ‘Zorro’ blk At least 800’   The orientation of the dry bean strips can vary based on your fields, your equipment, your  surrounding crop, etc.     Cover Crop Planting  Please record information regarding your cover crop planting in the Forms section.    Cover Crop  Optimal Planting Time  Planting Rate  Clover, Medium red, VNS  March‐April (frost‐seeded)  14 lbs/A  Oilseed radish, Ground Hog  August  11 lbs/A  Rye, VNS  September‐November  90 lbs/A  *VNS= variety not stated  **If your planting time or rate does not match the recommendations in this table, write your current  practices on the forms.    Clover      At the time of frost seeding be sure to leave the “no cover” half of the research site without  clover.   See planting times and rates above.     201      Figure H.02 (cont’d)  Oilseed radish      The research site should be worked (tilled) prior to planting oilseed radish (both the cover and  no cover areas).   Drill (or broadcast) the cover crop at the rates stated above.   Oilseed radish is only being planted in half of the research site.    Rye     The research site should be worked (tilled) prior to planting rye (both the cover and no cover  areas).   Drill (or broadcast) the cover crop at the rates stated above.   Rye is only being planted in half of the research site.      Cover Crop Management  Please record information regarding the management of your cover crop in the Forms section.   Clover      If weeds become prevalent in your clover, mow to reduce weed seed production.  Before plowing the clover, please verify with Erin Taylor at MSU that the biomass and other  necessary cover crop measurements have been taken.  In mid‐May the clover will be chisel plowed and field cultivated again two weeks later, just prior  to planting dry beans.   If your usual practices for killing clover differ from this make note of your methods and proceed  as you usually would.  Oilseed radish         If weeds become prevalent in your oilseed radish or rye, please contact Erin Taylor.  Before the oilseed radish winter‐kills, MSU will take biomass samples and other related  measurements.  In the spring, this area can be cultivated when weeds reach 6 inches in height. It can also be  lightly tilled immediately prior to planting the dry beans.   If your usual practices for managing ground following an oilseed radish cover crop differ from  this make note of your methods and proceed as you usually would.    202      Figure H.02 (cont’d)  Rye      Before plowing the rye, please verify with Erin Taylor at MSU that the biomass and other  necessary cover crop measurements have been taken.  The rye will need to be chisel plowed in the spring when it reaches 10‐12 inches in height in mid‐ May.  This ground will need to be tilled again two weeks later and immediately prior to dry bean  planting.   If your usual practices for killing rye differ from this make note of your methods and proceed as  you usually would.  No cover      Weeds will very likely be growing in your no cover area(s). Mow as necessary to reduce weed  seed production.  In the spring prior to dry bean planting apply the same tillage and cultivation practices to this  area that you did for your cover crop area.   If spring chisel plowing is a concern for your soils please contact Erin Taylor.     Dry Bean Planting       MSU will provide the black and navy bean seed for planting in your on‐farm trial.   The same seed must be used across all sites to eliminate variability.   We will not be treating the seed with commercial rhizobium inoculate this year due to lack of  availability.   The dry beans will be planted in early to mid‐June and harvested at maturity (usually  September).   The beans will be seeded at a rate of 120,000 seeds/acre. This rate is 20% higher than is  conventionally recommended to account for crop removal by mechanical weed control  measures.     Dry Bean Management  Weeds  Manage weeds within the research site as you usually would for dry beans. Manage all areas of the  research site the same so we can make comparisons.  Please keep records for when you apply control  methods on the Forms section. Note that if hand labor is utilized we would like to know how much time  was required to weed each strip if possible.   203      Figure H.02 (cont’d)  Other pests    Please manage insect and disease issues as you usually would for dry beans. Again, please  manage the entire research site in the same manner and keep records of your control methods  in the Forms section.  We are particularly interested in Western Bean Cutworm and intend to place a pheromone trap  for this insect near the research site at each farm.   Fertilizers and other inputs    DO NOT apply any fertilizers, manures, composts, or other inputs that contain nitrogen during  the study (one of the focuses of this trial is comparing the nitrogen contribution of the cover  crop)  Record all fertilizer, soil amendment and other input applications in the Forms section.     Dry Bean Harvest       MSU will harvest four areas from each dry bean strip (2 rows by 60 feet long).   The remaining beans can be harvested after MSU has harvested their areas.   Please contact Erin Taylor to arrange a harvest date when beans are near maturity.      204      Michigan State University Field Trial Recording Form, 2012‐2013  ORGANIC DRY BEAN PRODUTION SYSTEMS     Cooperator name:  _______________________________________________________________   Treatments:  1‐ _________________________  2‐ _________________________  3‐ _________________________    PHYSICAL DESCRIPTION  County: ___________________________  Township: ___________________________________   Nearest crossroads: ______________________________________________________________   Soil types represented:  ___________________________________________________________     ROTATION, FIELD HISTORY:  Year  Crop (s)  Cover crop(s)  Comments  2008        2009        2010        2011        2012          How many years has this field been managed organically? _______________________________   Figure H.03. Organic dry bean production systems field trial recording form, provided to growers in their annual three-ring binder. 205      Figure H.03 (cont’d)  Is this field certified organic? _______________________________________________________   If so, in what year was it certified?  __________________________________________________   Also, what is the certifying agency? __________________________________________________   If not, are you planning to certify? When?  ____________________________________________   PRE‐PLANT (Cover crop for experiment)  Was the ground tilled before planting the cover crop?   YES   NO  If yes, what date(s)?  _______________________________________________________    What equipment was used? _________________________________________________   What was the tractor speed? ________________________________________________   What depth of soil was tilled?  _______________________________________________   Was the no‐cover treatment tilled?   YES   NO  If yes, what date(s)?  _______________________________________________________    What equipment was used? _________________________________________________   What was the tractor speed? ________________________________________________   What depth of soil was tilled?  _______________________________________________     COVER CROP PLANTING  Date:   _________________________________________________________________________     Soil conditions at planting:   ________________________________________________________   Seeding rate: ____________________________________________________________________   Planter/drill /broadcaster type, size, and spacing: ______________________________________   Comments:   ____________________________________________________________________     ______________________________________________________________________________   206        Figure H.03 (cont’d)  COVER CROP MANAGEMENT  Where any weed control measures necessary in the cover crop or no cover area? If so, please   describe.  ______________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________   Date of cover crop kill: ____________________________________________________________   Method(s) of kill:  ________________________________________________________________   If tilled, what equipment was used? ___________________________________________    To what soil depth?   _______________________________________________________   If more than one pass was required, how many did it take?  ______________________________   Comments:   ____________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________   PRE‐PLANT (Dry beans)  Was the ground tilled or worked before planting the beans?   YES   NO    If yes, what date(s)?  _______________________________________________________   What equipment was used? _________________________________________________   What was the tractor speed?  ________________________________________________   What depth of soil was tilled/worked?  ________________________________________   Was the no‐cover treatment tilled at this same time?   YES   NO  If there was more than one ground preparation made, what was the sequence?  _____________     ______________________________________________________________________________   207      Figure H.03 (cont’d)  Comments: _____________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________   DRY BEAN PLANTING  Date: __________________________________________________________________________   Soil conditions at planting:   ________________________________________________________   Seeding rate: ____________________________________________________________________   Seeding depth: __________________________________________________________________   Planter type, size, and spacing: _____________________________________________________   Was there any residue from the cover crop present at planting?  __________________________   Comments (please include any planter issues, etc.):  ____________________________________     ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     WEED MANAGEMENT  Date  Type of weeder  Dominate weed species  App. weed height(s)                                                  208      Figure H.03 (cont’d)  Rotary hoe  Type: __________________________________________________________________________   Width: ____________________________  Tractor HP: __________________________________   Speed(s): _______________________________________________________________________   Comments: _____________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     Tined weeder  Type: __________________________________________________________________________   Width: ____________________________  Tractor HP: __________________________________   Speed(s): _______________________________________________________________________   Comments: _____________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     Cultivator  Type: __________________________________________________________________________   Number of rows: ____________________  Tractor HP: __________________________________   Speed(s): _______________________________________________________________________   Comments: _____________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________   209        Figure H.03 (cont’d)  Other  Type(s): ________________________________________________________________________   Width/ # of rows: ___________________  Tractor HP:  __________________________________   Speed(s): _______________________________________________________________________   Comments:   ____________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     Hand labor  Cover/no cover  Bean variety  Time required to weed  Cover  Black ‘Zorro’    Cover  Navy ‘Vista’    No cover  Black ‘Zorro’    No cover  Navy ‘Vista’      Comments: _____________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________         210        Figure H.03 (cont’d)  Pest Management (other than weeds)   (Please do not apply manure, compost, or other nitrogen containing fertilizers to the trial site)  Date  Rate  Cost/Acre    Product/Management  strategy                          Comments:   ____________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     FERTILIZERS and OTHER INPUTS (from fall 2011‐fall 2012)  (Please do not apply manure, compost, or other nitrogen containing fertilizers to the trial site)  Date  Type  Rate  Cost/Acre                            Comments:   ____________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________       211      Figure H.03 (cont’d)  FIELD MAP (Optional)  A quick sketch is fine.      212      Figure H.03 (cont’d)  LEARNING OPPORTUNITY  POST‐TRIAL  What did you learn from this trial?    ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     What would you do differently in the future?    ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     What differences will this trial make to your farming practices?    ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     What additional questions did this trial raise?    ______________________________________________________________________________   213      Figure H.03 (cont’d)    ______________________________________________________________________________     ______________________________________________________________________________   What needs/questions of organic growers should be addressed by future University research?     ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     Any other post‐trial thoughts?    ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________     ______________________________________________________________________________       214      Figure H.04. Two sample postcards sent as a supplemental reminders during the season. This form of communication was received positively and helped keep field operations and data collection aligned. 215      LITERATURE CITED 216      LITERATURE CITED Anderson RL, Tanaka DL, Black AL, Schweizer EE (1998) Weed community and species response to crop rotation , tillage, and nitrogen fertility. Weed Tech 12:531-536 Blackshaw RE, Brandt RN, Janzen HH, Entz T, Grant CA, Derksen DA (2003) Differential response of weed species to added nitrogen. Weed Sci 51:532-539 Blackshaw RE, Molnar LJ, Janzen HH (2004) Nitrogen fertilizer timing and application method affect weed growth and competition with spring wheat. Weed Sci 52:614-622 Blickenstaff CC (1979) History and biology of western bean cutworm in southern Idaho, 19421977. 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