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University Microfilms International 300 N. Zeeb Road Ann Arbor, Ml 48106 8400560 Gold, A rthur J . CONSERVATION TILLAGE: IMPACT ON AGRICULTURAL HYDROLOGY AND WATER QUALITY IN THE SAGINAW BAY DRAINAGE BASIN M ichigan State University University Microfilms International 300 N. Zeeb Road, Ann Arbor, Ml 48106 PH.D. 1983 PLEASE NOTE: In all c a s e s this material has been filmed in the best possible way from the available copy. Problems encountered with this docum ent have been identified here with a check mark V . 1. Glossy photographs or pages / 2. Colored illustrations, paper or print______ 3. Photographs with dark background 4. Illustrations are poor c o p y ______ 5. P ages with black marks, not original 6. Print shows through a s there is text on both sid es of p ag e______ 7. Indistinct, broken or small print on several p a g e s 8. Print exceeds margin requirem ents______ 9. Tightly bound copy with print lost in spine______ 10. Computer printout pages with indistinct print______ 11. P ag e(s)____________ lacking w hen material received, and not available from school or author. 12. P ag e(s)____________ seem to b e missing in numbering only a s text follows. 13. Two pages nu m b ered ____________ . Text follows. 14. Curling and wrinkled p a g e s ______ 15. O ther__________________________________________________________ _____________ v ' copy_ S University Microfilms International CONSERVATION TILLAGE: IMPACT ON AGRICULTURAL HYDROLOGY AND WATER QUALITY IN THE SAGINAW BAY DRAINAGE BASIN by Arthur J. Gold A DISSERTATION submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Agricultural Engineering 1983 ABSTRACT CONSERVATION TILLAGE: IMPACT ON AGRICULTURAL HYDROLOGY AND WATER QUALITY IN THE SAGINAW BAY DRAINAGE BASIN by Arthur J. Gold Water borne edge-of-field losses of conservation sites were (chisel plow) investigated. undertaken for 20 and A months, sediment conventional field from scale March and nutrients (moldboard plow) monitoring from tillage program was 1, 19 8 1 to October 1, 1982 on adjacent plots. Flow from overland runoff and subsurface tile discharge was and recorded nutrient and sediment analysis performed. Precipitation characteristics, residue cover, crop stage, and antecedent soil moisture were analyzed to determine the conditions that generated substantial water borne losses from one or both Longterm weather of the study fields. records were then evaluated to find the likelihood of occurrence of those conditions that appeared to generate runoff and eros ion. Eleven hydrologic during the sampling precipitation. two fields events period; (tile and/or overland flow) two resulted from snowmelt and nine from The combined volume of overland and tile flow was almost identical for the study period, conservation tillage field had significantly more subsurface than the conventionally tilled field. total kjeldahl nitrogen than from the but the tile flow Subsurface tile flow on both fields had significantly lower concentrations of and occurred overland phosphorus, flow. sediment, Nitrate nitrogen concentrations were higher in tile flow than overland flow. Arthur J. Gold The conventionally tilled field lost substantially phosphorus and was in a soluble form. snowmelt runoff generated the fields. A sediment, total kjeldahl nitrogen than the conservation field. large portion of the nitrogen and systems more single phosphorus lost from both A tillage Sediment loss from both fields was low; largest quantity of sediment on both intense storm that occurred on emerging field beans accounted for much of the difference in sediment and phosphorus losses from the two tillage systems. Based on longterm weather records, conservation tillage practices will cause a larger reduction of phosphorus and sediment losses on sites planted to field beans than corn. November through May and water Erosive events are not expected borne losses management practice that diminishes overland flow. from can be reduced by any To Marion 11 Acknowledgements I wish to thank Dr. Ted L. Loudon, my major professor, for his thoughtful guidance and constant support throughout my graduate studies. I thank Dr. George Merva, Dr. Fred Nurnberger, and Dr. Boyd Ellis for the time and effort they devoted as members of my guidance committee and Dr. Don Edwards for his assistance on the final manuscript. My thanks are extended to the following individuals without whom this project could not have succeeded: Jerry Lemunyon, Bob Rossman, Peter D. Cooper, Bryan Hill, Steve Ferns, Larry Fay, Luke Reese, John Posselius and Eric Harmsen. A special appreciation is extended to the staff of the East Central Michigan Planning and Development Region for the funding and aid they pro vided and to the Great Lakes National Program Office at Region V of the United States Environmental Protection Agency for funding and supporting this project. Finally, I wish to thank my wife, Marion, for her constant faith, support, and love. TABLE OF CONTENTS D E D I C A T I O N ................................................................ii ACKNOWLEDGEMENTS ..................................................... iii LIST OF F I G U R E S ..................................................... vii LIST OF TABLES ....................................................... viii NOMENCLATURE ......................................................... x CHAPTER 1. 2. ................................................ 1 1.1 B a c k g r o u n d .............................................. 1 1.2 O b j e c t i v e s .............................................. 5 LITERATURE REVIEW ............................................ 6 2.1 Freshwater Contaminants from Croplands ................. 6 2.2 Sediment Loss from Agricultural Croplands ............... 8 2.3 Pesticide Losses from AgriculturalCroplands 9 INTRODUCTION ............ 2.4 Sediment as a Transport A g e n t ........................... .............. 12 2.6 Sedimentation Processes .................................. 14 2.7 Sediment Transport ...................................... 19 2.8 The Movement of Soluble N u t r i e n t s ....................... 24 2.9 Simulation Models of Edge-of-Field Losses from C r o p l a n d s ........................................ 29 2.10 Monitoring Approaches .................................. 30 FIELD INVESTIGATION ................................ 32 3.1 Site S e l e c t i o n .......................................... 32 2.5 Conservation Tillage for PollutionControl 3. 10 METHODS: 3.2 Site De s c r i p t i o n........................................ 34 3.3 Field Modifications .................................... 38 .................................. 40 3.4 Monitoring Procedures 3.5 Rainfall and Snowpack Measurement ..................... 50 3.6 Cold Weather D e s i g n .................................... 52 .................................... 53 3.8 Agronomic Activity ...................................... 54 3.9 Water Quality Analysis .................................. 54 3.10 Soil M e a s u r e m e n t s ...................................... 58 ........................ 58 METHODS: PREDICTING OVERLAND RUNOFF AND EROSIVE EVENTS ............................................ 62 4.1 O v e r v i e w ................................................ 62 4.2 Storm Frequency Analysis ............................... 63 4.3 Antecedent Soil M o i s t u r e ................................ 64 4.4 Estimates of Occurrence of Excessive Rate S t o r m s .......................................... 67 4.5 Occurrence of Excessive Rate Storms At Varying Levels of A M C ............................. 69 4.6 Precipitation Excess .................................... 70 EVENT DESCRIPTIONS ........................................... 72 5.1 S u m m a r y ................................................ 72 5.2 Snowmelt: February 16-February 22, 1983 ............... 80 5.3 Event 1: April 9-10, 1 9 8 1 .............................. 80 5.4 Event 2: April 28-29, 1981 82 5.5 Event 3: May 10-12, 1 9 8 1 .............................. 83 5.6 Event 4: September 3-5, 1 9 8 1 .......................... 85 5.7 Event 5: September 26-29, 1981 87 5.8 Event 6: September 30-0ctober 2, 1982 ................. 89 3.7 Residue Measurement 3.11 Statistical Model andAnalysis 4. 5. v 5.9 Event 7: 6. March 11-14, 1982 .......................... 1982 90 5.10 Event 8: March 14-30, 92 5.11 Event 9: March 30-April 1, 1982 ....................... 5.12 Event 10: June 15-17, 1982 93 5.13 Event 11: June 21-22, 1982 94 92 FIELD INVESTIGATION ................ 97 .................................. 97 6.2 Soil C h a r a c t e r i s t i c s .................................... 99 ANALYSIS AND DISCUSSION: 6.1 Precipitation Analysis 6.3 Antecedent Soil M o i s t u r e .................................. 104 6.4 Rainfall Erosivity ...................................... 106 ..................... Ill 6.6 Hydrologic Losses ........................................ 117 6.5 Comparison of Edge-of-Field Losses 6.7 Sediment L o s s e s ............................................. 118 6.8 Phosphorus Losses ........................................ 120 6.9 Nitrogen L o s s e s ............................................. 122 7. ANALYSIS OF LONGTERM CLIMATIC CONDITIONS ................... 126 7.1 O v e r v i e w ................................................... 126 8. 7.2 Probability of Occurrence ofOverland Flow Events . . . . 128 7.3 Probability of Occurrence ofErosive Events .............. 138 7.4 Precipitation Excess 146 .................................... C O N C L U S I O N S ..................................................... 149 8.1 Field Monitoring ........................................ 149 8.2 Analysis of Longterm Weather Patterns .................... 150 8.3 Management Recommendations .............................. 151 8.4 Recommendations for Future Research ..................... 151 vi LIST OF FIGURES FIGURE PAGE 1 Study Site L o c a t i o n ............................................. 35 2 Topographic Survey: Original Site ........................... 36 3 Topographic Survey: Modified Site ........................... 39 4 Field Monitoring Layout ........................................ 41 5 Tile Flow Measurement D e v i c e .................................. 47 6 Stage Discharge Relationship - 25 cm.30 degree V Notch Flume ................................................. 49 7 Median P Soil Test L e v e l s ......................... .'.......... 103 8 Rainfall Erosion Index-Eastern United States 107 9 10 .................. Rainfall Erosion Index-Starkey Farm .................. . . . . 110 Rainfall Erosion Index Impacting the Soil Surface (1981 C o m ) ................................................... 112 Rainfall Erosion Index Impacting SoilSurface (1982 Field Beans) .......................................... 113 12 24 Hour 2.5 and 10 Year S t o r m .................................. 131 13 Total Number of Excessive Rate Storms: Alpena, Flint and Deer-Sloan Network ....................... 139 ..................... 144 Excessive Rate Storm Probability vs. Crop Management Factor ( C ) - C o m ............................. 145 Mean Precipitation E x c e s s ...................................... 147 11 14 15 16 Excessive Rate Storm Probability vs. Crop Management Factor (C)-Field Beans LIST OF TABLES TABLE PAGE 1 Field Dimensions .............................................. 38 2 Agronomic Activity ............................................ 55 3 Water Quality Sample Analysis ............................... 57 4 Classification of Antecedent Moisture Conditions ............ 66 5 . Event S u m m a r i e s .............................................. 73 6 Event Summary: Hydrologic Characteristics ................... 74 7 Event Summary: Sediment Losses .............................. 75 8 Event Summary: Phosphorus Losses ............................ 76 9 Event Summary: Nitrogen Losses .............................. 77 10 Mean Concentration per E v e n t .................................... 11 Comparison of Monthly Precipitation March 1, 1981-October 1, 1982 to 30 YearM e a n .............. 78,79 98 12 Soil Physical P r o p e r t i e s ..................................... 100 13 Soil Chemical A n a l y s i s ........................................ 102 14 Precipitation Characteristics: Storms Generating No Edge-of-Field Flow ........................... 105 Crop Stage, Crop Management Factor (C) and Residue C o v e r .......................................... 108 16 Edge-of-Field Losses March 1, 1981-October 1,1982 ............. 114 17 Field Comparison - Tests for Differences .................... 115 18 Subsurface Tile vs. Overland Flow-Tests forDifferences 116 19 Precipitation Volume Required to Generate Overland F l o w .............................................. 15 viii . . . 128 20 21 Minimum Precipitation Required to Generate Overland Flow of Measurable Magntidue ....................... 129 Hydrologic Frequency Analysis: 24 Hour Storm P r e d i c t i o n ...................................... 130 22 Probability of Large Storms Occurring with 23 Probability of Moderate Magnitude Storms Occurring at High Antecedent Moisture Condition ....................... 134 24 Probability of Overland Runoff Events ......................... 136 25 Probability of Large Excessive Rate Storms Occuring with Antecedent Moisture Condition ............................... 141 26 AMC 2 or 3 ......... 133 Probability of Storms Likely to Generate Overland Flow and E r o s i o n ...................................... 142 ix NOMENCLATURE AMC = Soil antecedent moisture content C = Crop management factor ET = Actual evapotranspiration for a given crop species and stage ETo = Reference evapotranspiration K = Crop coefficient (ET/ETo) N = Nitrogen P = Phosphorus P(B) = Probability of B P(A1B) = Conditional probability of A given B P(A,B) = Probability of the intersection of A and B R = Rainfall erosion index (MT-m/(ha-hr))* Rs = Snowmelt erosion index (MT-m/(ha-hr))* S = 24 hour storm greater than or equal to 12.7 mm SL = 24 hour storm greater than or equal to 25.4 mm and less than 50.8or 60.0 mm during the dormant or growing season, respectively. SLL = 24 hour storm greater than SL SM = 24 hour storm greater than or T equal to 12.7 mm and less than 25.4 mm = Return period (years) TKN = Total kjeldahl nitrogen X = Excessive rate storm ♦Published units (Wischmeier and Smith, 1978) incorrectly representing (Kinetic Energy/Volume) x Intensity. Accepted British units are: (ft*lb/acre*in) x (in/hr) = A more accurate metric conversion would be: Toil 1p c (Joules/ha*cm) x (cm/hr) = The published units were utilized to facilitate comparison with other studies. CHAPTER 1 INTRODUCTION 1.1 Background Croplands have been cited as a major source Laurentian Great Lakes (PLUARG, 1978). of pollution to the Fertilizers and pesticides that promote large and consistent crop yields can become contaminants if they enter the ground or surface waters. Of the many sources of nonpoint pollution row crops planted on fine textur.ed soils have been credited with contributing the greatest amounts of phosphorus and sediment to the Great Lakes per unit area. Since 1978 considerable national and focused international attention has on measures to reduce agricultural pollution to the Saginaw Bay of Lake Huron. The water quality of the Saginaw Bay is among the worst in the Great Lakes, comparable to the western basin of Lake Erie and the Green Bay of Lake Michigan. contaminants from the recreation Reference and water Group on Within drainage supply Great the basin purposes. Lakes inner has In Pollution Bay the influx degraded its value 1978 from the of for International Land Use Activities (PLUARG, 1978) recommended that all potential nonpoint source problems related to agricultural practices be considered and economically viable plans to abate pollution be explored. In response Planning States and to recommendation Development Enivornmental conservation this tillage Region, Protection as a the East Central Michigan under the sponsorship of the United Agency (EPA), began a study of pollution control practice in the drainage basin of the region). southeast The Saginaw Bay (hereafter known as the study moldboard plow was the conventional tillage implement in the region and left the soil exposed to wind and water losses from tillage until the establishment of a crop fall canopy in early summer. Conservation tillage systems rely on crop residues to reduce soil and water losses. The focus of the study compare documented in this dissertation was to the discharge of water borne substances to a receiving ditch or water body tilled (edge-of-field losses) from conservation fields. Field monitoring was carried and conventionally out from March 1, 1981-October 1, 1982. The results of the study will be utilized by the USEPA changes the to model the expected in the water quality of southeast Saginaw Bay if conservation tillage is widely adopted drainage basin. Additional conservation tillage (Muhtar, (Merva and Peterson, 1983 ) studies on the 1982 ) and windborne in the economic feasibility of edge-of-field losses were undertaken to evaluate all pertinant aspects of conservation tillage as a best managment practice. Prior to this study research had tillage in the agricultural been landswhich conclusions of studies in Indiana (Lake and (Honey Creek, conducted conservation drain into Lake Erie. Morrison, 1977) and Although these studies and phosphorus warrant Ohio a fresh investigation tillage as a best management practice from were located within 300 km of the Saginaw Bay region several distinct differences exist between the that The 1980 ) indicated that conservation tillage systems could be expected to reduce water borne losses of sediment croplands. on areas of the feasibility of conservation in thestudy region. 3 Conservation tillage has been shown reducing soil detachment and sediment loss. to be reduce losses of nutrients also and be expected other contaminants. Water borne erosion losses in the study are to be relatively minor. expected effective fresh region soil detachment and transport, to water however, The land is flat, the soils have good cohesiveness, and the annual rainfall erosivity, the driving for in In areas where large annual losses of sediment occur, curtailing erosion can significantly very force is among the lowest that occurs in the United States east of the Mississippi River. The rainfall erosivity in the study region is less than one-half that expected on the Lake Erie drainage basin where conservation tillage was previously studied. lower to erosion determine With losses expected nutrient transport needs to be evaluated the extent of pollution abatement from conservation tillage. Phosphorus is considered the major water quality contaminant to the Saginaw Bay (PLUARG, 1978). In the last two decades the quantity of available P in the agricultural soils of the study region has by nearly quantity five and transported fold form from as increased a result of intense fertilization. (soluble or sediment bound) of the Both the phosphorus the cropland of the regions should be investigated in light of this unusually rapid increase in soil phosphorus levels. Overland runoff can transport substantial and nutrients from croplands. is that virtually all of A unique feature the prime on the influence of conservation of farmland infiltration as a result of subsurface tile drainage. perspective of sediment Practices that increase infiltration can be expected to diminish overland flow. region quantities To tillage the study has improved gain a full as a best management practice an evaluation of both the surface and subsurface discharge waters should be undertaken. The results of this study are not only intended to evaluate conservation tillage as a management practice, but also to determine the conditions that contaminants may result in significant losses from conventionally tilled systems. freshwater Once these conditions are identified, management practices can be utilized or are of developed that specifically tailored to reduce losses in the drainage basin of the southeast Saginaw Bay. planners and This study is viewed as the first step to enable management personnel to select and encourage effective pollution abatement programs for croplands in the study region. 5 1.2 Objectives The overall objective of the study was borne losses of sediment and to nutrients investigate from conventionally tilled croplands in the southeast basin. the conservation Saginaw Bay water and drainage The specific objectives of the study were: 1. To compare the climatic and physical features of the study region to other areas where conservation tillage has been used to reduce edge-of-field losses from croplands. 2. To monitor and quantify the losses of sediment and nutrients in subsurface and surface flow from conservation and conventionally ti 1 led croplands. 3* To determine the combinations of crop stage, soil conditions, and storm characteristics that generated substantial water borne losses from the croplands of the study region. k. To identify the conditions that resulted in a substantial reduction of sediment or nutrient losses from conservation tilled sites compared to conventionally tilled sites. 5- To determine the longterm probability of events that may gener­ ate water borne losses from one or both of the tillage systems studied. 6 CHAPTER 2 LITERATURE REVIEW 2.1 Freshwater Contaminants from Croplands Drainage from varying agricultural amounts of croplands freshwater has been contaminants found to depending carry on soil characteristics, tillage practices, canopy cover, fertilization methods, rainfall patterns, and field morphology. pollutant from croplands. and Sediment is the most visible However, many of the nutrients, herbicides, pesticides employed for modern agriculture can influence freshwater quality. The discharge receiving water body is of these substances from croplands to a commonly referred to as edge-of-field losses (Frere, 1976). Nutrient losses from agricultural degradation of surface waters. croplands can modern farmers. serious Most soils lack the necessary quantities of nitrogen, phosphorus, and potassium to generate high by cause Accordingly, these yields elements are desired added agricultural croplands each year by chemical fertilization or by manures. in the United States. agricultural Limnological aquatic systems nutrients whether from (Vatlentyne, sewage, 197*0* detergent, croplands studies phosphorus and nitrogen are the limiting nutrients to most animal Frere (1976) estimated that 2.6 million tons of phosphorus and 7 .8 million tons of nitrogen are added to year to have plant Additional rainfall, each shown that growth in inputs of these or agricultural runoff can degrade surface waters through cultural eutrophication. 7 Eutrophication is an aquatic process caused by an of plant nutrients. Photosynthesis and plant turbidity increases, species composition alter dissolved oxygen may occur in bottom and waters growth resulting from eutrophication can degrade increasing treatment costs and affecting increased growth accelerate, reduced (Wetzel, level levels 1975)* drinking Algal supplies taste and odor of by (Borchardt, 1970). Although every aquatic system may respond differently inputs, preliminary work done by Sawyer (19^7) to nutrient indicated that aquatic plant growth will be accelerated by nitrogen concentrations of O .3 0 mg/1 and ortho phosphorus (Shannon and Brezonik, concentrations of levels exceeeding 0.01 mg/I. Later 1972; V o l 1enweider, 1971) found that the critical phosphorus and nitrogen will depend on the buffering capacity of the receiving water, the trophic status, and the of the water studies Ma n y body. aquatic concentrations cited by Sawyers systems will not morphology change at the (19^7) while others would be expected to alter dramatically from inputs at even lower concentrations To obtain reasonable standards for management, concentration of nutrients coming off of croplands must be compared to "natural" nonpoint sources rather than to studies of algal and aquatic plant Nutrient concentration precipitation Background often from exceed concentrations nonpopulated the of critical forested levels requirements. areas cited and by from Sawyer. total phosphorus and nitrate nitrogen in the Great Lakes region have been estimated at 0.02-0.10 mg/1 and 0.2-0.5 mg/1 respectively (McElroy et al., 1976). Rainwater sampled for 18 years in northern Ohio was found to have mean concentrations of 0.5 mg/1 total phosphorus and 2.2 mg/1 nitrate nitrogen (Schwab et al., 1980 ). In a 6 month study in the Saginaw Bay region of Michigan mean concentrations nitrogen 1976). Nutrient concentrations in runoff from croplands can of (Hat*ms et al., mg/1 and 1981). Holt et a l . mg/1 197^5 Johnson et al., 1979* McDowell and (1976) Logan and in a review of research concerning subsurface water quality from croplands found that yearly flow mean widely. 1.0-28.0 19 8 0 ; Baker and Laflen, 1982; Schwab et al., 1980; McGregor, Adams, vary orthophosphate and nitrate nitrogen found in studies of overland runoff ranged between O.OO 5 -O. 95 O respectively had 0 .1 8 mg /1 orthophosphate and 0.61* mg /1 nitrate of (Richardson and Merva, Concentrations rainwater weighted concentrations of ortho phosphate and nitrate nitrogen ranged from 0 .001 -0 .5 2 mg/1 and from 1.0-33*0 mg/1 respectively. Based agricultural sources of combinations on the range croplands, nutrient of of all concentrations found in runoff from agricultural regions can not be veiwed as contamination to surface waters. Specific surface water characteristics, proximity, and cropland management can result in either non degrading situations or situations where agricultural runoff can lead to cultural eutrophication. 2.2 Sediment Loss From Agricultural Cropland Sediment is the croplands. Half largest by volume from agricultural of all sediment in the United States is the result of erosion of agricultural agricultural pollutant croplands lands (Wischmeier, 1976). Annual soil loss from range from 2.2 Mg/ha to greater than 220 Mg/ha; however,only 20% of the 179 million hectares of cropland lose more 17 Mg/ha per year. than Sediment that enters increase turbidity and freshwater can clog waterways. alter aquaticcommunities, Reduction in channel capacity and reservoir storage can result in increased flooding. survey showed that more than 33% of the midwest's reservoirs would become unusable by the year 2000 due (Beasley, 1972). Removing sediment burden costing the United States 250 from In the 19**0's a to waterways million water supply sedimentation is an expensive dollars a year (AStE, 1977) • Sediment in photosynthesis, waterways and can affects ruin light penetration, spawning grounds for fish. exists for tolerable concentrations of sediment losses. croplands the magnitude and decreases No standard On agricultural intensity of the sediment losses are not constant but vary with field conditions and storm events. The impact of sediment losses is affected by a field's proximity to surface water. has been suggested critical on agricultural where the delivery standard of (Skaggs et al., ratio 800mg/1 1982) that sediment control soil loss more croplands near coastlines, lakes,and rivers is (U.S. relatively EPA, 1973) high. The might croplands directly outletting to a waterbody. yearly is It EPA recommended serve as a target for This is equivalent of 1.2 Mg/ha for a region with 15 cm of below the tolerance limits for most Michigan soils to runoff, well currently set by United States Soil Conservation Service (6-11 Mg/ha) a the (USDA/SCS, 1981). 2.3 Pesticide Losses From Agricultural Croplands Losses of pesticides from agricultural cropland can not be in a treated singular fashion because of the variations that occur between the different chemicals in solubility, degradation time, adsorbtivity, and 10 application methods and timing. by the LC 50 of the pesticide, lethal to 50% of a Pesticide hazard is usually classified i.e. the concentration that proved to test species in a bioassay. The bioaccumulation factor is another parameter commonly used to evaluate potential The International Reference 1978 ) did not find serious Group on surface be hazard. Great Lakes Pollution (PLUARG, water degradation or biological contamination from agricultural pesticides in the Great Lakes. The highest concentrations of substances moderately or weakly adsorbed to sediment have been found in runoff events occurring close to the time of application (Smith et al., 197*0 • found a that runoff rapidly atrazine, occurring in later soon moderately after runoff et al. (1978) adsorbed substance was present in application. events. Triplett Concentrations declined Other researchers cited by Triplett have found that the majority of the annual pesticide loss occurred in the first one or two runoff events after application. 2 . U Sediment as a Transport Agent Water borne substances leave a field either in on sediment particles, or as solids. solution, Soluble nutrients and pesticides move more rapidly from a field than do solids and soil borne which are subject to the processes adsorbed of erosion substances and sedimentation. Edge-of-field losses of constituents strongly adsorbed to soil particles can be minimized by controlling sediment losses. Limiting losses of soluble constituents requires other management stategies. Water borne pollutants concentrations have been classified by their relative in water or on soil particles by an adsorptive partition coefficient, Ks (Steenhuis and Walter, 1979). Ks is the ratio of the concentration solution. of the substance adsorbed vs. (1000) such Substances with high Ks the as concentration in organic nitrogen, ammonium nitrogen, solid phase phosphorus, and toxaphene will move with the soil. Atrazine and soluble inorganic phosphorus have Ks values near five and are considered moderately adsorbed pollutants, while nitrate nitrogen has a very low Ks (0.05) and is highly soluble. A study carried out eroded material Stoltenberg contained phosphorus compared material by twice the and White(1953) concentrations to the soilfrom which it found that of nitrogen and originated. The eroded contained considerably more clay and organic matter which have greater cation exchange capacity than coarser particles and hold a proportion of the nutrients found in the soil. nutrient increase found in sediment carried quantified by an enrichment factor, The magnitude of the from which high the is field the has ratio been of the concentration of the constituent in the sediment to the concentration of the same constituent in the soil. enrichment was due to differences sediments. The lighter by particles adsorbed their in transport and suspension among clay and organic matter particles were not as subject to redepositon with Stoltenberg and White found that the runoff water. Once suspended these substances left the field more readily than larger heavier particles. Massey et al. (1952) found enrichment ratios to vary sediment concentration and net sediment loss. concluded that the enrichment increases with an increase ratio in relative to detachment by flow. energy decreases, the soil f.or Walter et al. clay detachment ratios matter by raindrop increase as to (1979) have and organic The authors suggest that enrichment inversely as the splash transport lighter 12 particles comprise a larger porportion of the sediment. The water quality impact of agricultural nutrients and pesticides lost from croplands must be assessed in terms of the availability of « a substance to the considered aquatic system. Whereas soluble Huellt influence the aquatic community. with was available to algae. the sediment In the case of phosphorus (1979) found that only 20-40% of the phosphorus sediment DePinto et al. associated total particulate with (19 8 1) in a bioassay study of sediment from Great Lakes tributaries concluded that the are to be readily available to algae and other aquatic organisms (Lee, 1978) only a portion of substances associated readily substances 21.8% of phosphorus was available to a common species of green algae. When soil loss is high, most of the phosphorus and nitrogen leaving a field is strongly associated with the sediment. Lake and Morrison (1977) reported that 90% of all phosphorus lost from the Creek agricultural watershed was attached to soil particles. Johnson et al. and (1979 ) found that sediment carried 80 -99 % of most losses in phosphorus the total phosphorus of the nitrogen lost from steep erodible watersheds. the study constituted were 90 % quite high (31 of the total Michigan with moderate erosion rates Mg/ha). Black Sediment Erosion bound losses from two watersheds in (Ellis and Erickson, 1977)* 2.5 Conservation Tillage for Pollution Control Controlling erosion losses from agricultural croplands will prevent many agricultural contaminants from reaching surface waters. in American agriculture since World War II have been field size, extensive monoculture and larger equipment. The trends towards larger Terrraces, once a popular conservation practice have been found required to till, to (Spomer et a l . 1976). practices regularly evaluated effectiveness Morrison, being and the time plant and harvest crops, detrimental features in an era of rising labor costs are increase compatibility with 1977; Siemens and Oschwald, Various to modern conservation study both agriculture their (Lake and 1978; Phillips and Young, 1973) • In the last decade conservation tillage has emerged as an agronomic practice to control water pollution from croplands. Conservation tillage systems rely on surface crop residues to reduce soil losses. Conservation conjunction with tillage traditional is now sheet widely erosion and water used in place of or in control practices. Wischmeier (1976) felt that residue management was one of the major tools for erosion control and an area which required futher research. Conservation tillage practices range from no occurs the where planting in the undisturbed residue of the previous crop to modified fall tillage practices such as chisel plowing, discing, where till a or ridge planting, portion of the residue is buried, leaving residue on 20 - 80 % of ground surface. Conservation tillage can effectively reduce sediment loss when no canopy exists and erosion hazard is considered the greatest (October-July). designed for farming. Currently one quarter of the nation's croplands are using some form minimum of use on or most Conservation row tillage practices have been crops and have been adapted to modern conservation ti1lage (Sterba, 1982). tillage practices can influence overland runoff and are in reducing sediment loss from croplands. Conservation very effective 2.6 Sedimentation Processes The mechanisms involved in erosion and sediment loss from croplands have received considerable research(Wischmeier and Smith, l^yjFoster and Meyer, is generated 1977; Beasley, through a process transport, and deposition. will 1972). which 1958;Harrold, Sediment loss from a field includes Factors affecting any soil of detachment, these processes influence the character and quantity of sediment loss. Predictive models have been losses from cropland. Conservation Service is (USLE)(Wischmeier, developed The model known as 197&)• to estimate soil erosion accepted for use by the U.S. the Universal Soil Loss Soil Equation In the equation: A-RKLSCP (1) where A*Soil Loss (kg/ha/year) R=Rainfall erosivity Factor (MT-m/ (ha-hr)) K*Soil Texture Factor LS*Topographic Factor C® Crop management Factor P® Support practice Factor The Universal Soil Loss Equation was intended soil and losses a over specific differences in to predict average extended periods given a set of management practices rotation. The model can not account for yearly antecendent soil moisture conditions, soil crusting, or other factors which influence runoff and sediment transport. When for loss based single precipitation events the USLE may predict soil used upon storm watershed. characteristics although Several have models no surface (Williams and Berndt, Soil detachment is caused by water. On impact upland is the primary Wischmeier (1969) uniform drop proportional sites size to either of that if Weather the volumes Service classification has of recorded an the detachment. experiments of the interrill detach intense soil This product known States (Wischmeier and Smith, aggregates and detachment is High intensity soil low than intensity The United States that meet the Excessive rate storms are as (5 + (Schwab, et al., 1981)* a rainstorm as the rainfall erosion 1978). from impact intercept raindrops and possible detachment. which occur during periods with canopy or residue cover and shield Intense storms will generate less erosion than storms occurring during periods without Greer et al. rainfall Meyer been computed for selected points throughout the United Crop canopy or residue cover can that flowing kinetic energy of the rainstorm times its maximum (R) cover. or (mm) equal to or exceeding the quantity index substantially compute intensity. rainstorms excessive rate storm. thirty minute intensity. has to of simulated rain with (1959) described the total erosive power of product soil soil where t is the storm duration in minutes Wischmeier impact of precipitation are equal. defined as storms of depth 0.25t) raindrop square of the rainfall storms will have higher potential to storms characteristics 1977; Onstad and Foster, 1975)- laboratory suggested the the without developed rills or gullies, raindrop source using left recently been developed that include runoff characteristics along with rainfall sediment loss runoff (1978) intensity in a six year and crop stage study in Mississippi found were the major factors that 16 produced runoff and accounted erosion from croplands. Excessive for 55% of the the runoff and 77% of the soil study period. rate storms loss during the Only 37% of all the rainfall events were intense enough to be considered excessive rate storms. Excessive rate storms had the greatest impact on sediment loss when the soil was unprotected following seedbed preparation. During this annual two month period, excessive rate rainstorms generated 50% of sediment period. crop loss while comprising only 6% of the total rainfall of the This contrasts with the results obtained during the growth and harvest 31% of the they produced only 25 % of the total soil periods period of when a 70-100% crop canopy covered the soil. Although excessive rate storms accounted for these the rainfall in loss from these per iods. In a three Michigan season (Ellis,et study al., of 1978) edge-of-field it losses conducted in was found that the majority of the sediment and total phosphorus lost during the study period occurred with one intense rainstorm on partially frozen soil. The Black Creek, Indiana investigation of agricultural water quality (Lake and 1977) concluded that the transport of sediment and nutrients was strongly associated with the large storm events of the year. al. (1976) found Morrison, Spomer et that a few large storms produced most of the sediment lost from croplands in western Iowa over a ten year period. In the Iowa study 92% of the annual sediment yield occurred in and June during seedbed preparation and crop establishment. During this period 30 % of the annual rainfall occurred comprising L5% of the rainfall erosion erosivity losses was (R). The mollifying demonstrated during effect one of season May annual canopy cover on when rainfall 17 was 321 units compared to the average annual erosivity of 160 erosivity units. Annual sediment loss for that year however instead of increasing dramatically, fell far below examination the authors storms accounted for the concluded this average that of the study. distribution discrepency. of Upon close the erosive Of the total erosivity that occurred during that year, 71% occurred during August and September when a substantial crop cover shielded the soil from direct raindrop impact. The distribution dramatically Bay, 1969). alter of excessive sediment loss rate shown In the second period the study to be double that effect of row direction. plots However only moldboard The authors expected erosion of the first period due to eleven years study. Annual rainfall erosivity was similar during the periods units), but different. In distribution the first period March through June was associated compares to The authors resulted 13% of the intense with excessive concluded from the ten (74 El was very rate storms. This for the same months during the second 11 year period. that second the lower average annual study occurred because erosion most of that the rainfall developed. In a watershed study in Watkinsvi1le, the rainstorms of 65 % of the total precipitation from erosivity came after a full canopy was 1979 ) the one-sixth of the soillost during the first period came off the plots during the second the from In the first period tillage was performed used up and down the 16% slope. from the later to from croplands in New York (Free and by a moldboard plow on the contour. was was Studies of erosion were undertaken on the same 1939“ 1948 and from 1956-1964. plow rainstorms Georgia (Walters, et al., largest storm events generated 95% of the sediment lost over a three year period. The presence of a canopy cover reduced sediment loss by 60% for storms of equal magnitude and intensity that generated similar runoff quantities. Crop canopy intercepts a proportion of the raindrops that cropland. on While some of the intercepted precipitation is evaporated or reaches the soil by stemflow, intercepted water reforms original raindrop size. these fall in large intense into drops which storms may The height of the canopy drops obtain before striking the ground. much of the be larger than the limits the velocity Ghadiri and Payne(1977) have shown soil splash and detachment to be a function of drop diameter times the velocity squared. Wischmeier and Smith (1978) have computed the ratio of the erosivity (R) striking rainfall soil protected by canopy cover to the rainfall erosivity impacting fallow ground. This ratio Management Factor They used both crop height and cover (C) in the USLE. density in their calculations. be expected to is known as the Crop Soil protected by a full crop canopy can between O . k and 0.2 of the rainfall erosivity receive that strikes bare soil. Residue impacting 1978). cover the is soil more effective surface fall by velocities. surface covered raindrop (Wischmeier and Smith, residue do not regain by the residue. extends beyond the soil any surface Foster (1982) using data derived from an unpublished Master's thesis by Lattenzi (1973) concluded that residue energy The role of surface cover in dissipating raindrop energy and soil detachment directly reducing than is crop cover Droplets intercepted appreciable at surface cover increases the hydraulic roughness of the flow surface and thereby increases the flow depth of surface runoff. Mutchler and Young (1975) suggested that a water depth of 6 mm. essentially eliminated 19 detachment by raindrop impact and depths up to reducing detachment. The surface is covered by the residue. the "C" factor for mulch at various canopy is over mm. were capable of roughness provided by conservation tillage can be expected to limit detachment on than 6 a larger Wischmeier and Smith levels of cover. surface area (1978) computed When no crop the soil surface, soil covered by mulch at 20%,A0%,and 60% cover will receive 0 .6 5 i0 .3 5 t and 0 .2 5 respectively of the rainfall erosivity striking bare ground. 2.7 Sediment Transport The hydrologic processes of rainfall and and sedimentation. Factors that affect runoff either directly affect erosion and sediment transport. generate rainfall Any erosion or runoff complete analysis of erosion and sediment yield from croplands must consider hydrology and runoff. Hydrologic factors that influence runoff such volumes and velocities, as surface porosity, soil antecedent moisture content, and surface roughness will alter sediment and nutrient losses from farmlands. et al. (1970) Meyer employed rainfall simulators to examine the influence of mulch rates on sediment losses. It was found that relatively light residue cover of O .56 Mg/ha and 3^% cover reduced erosion by one half on steep slopes compared significant to conventionally clean-tilled A decrease in runoff velocities on the mulched plot was cited as the major cause of the observed difference. mulch treatments. It was noted that the straw lying across the slope collected soil about it and acted as a series of reservoirs slowing the runoff thereby reducing its capacity for sediment. carrying 20 Romkens and rtannering (1973) monitored runoff from five residue with a rainfall simulator. levels Slopes ranged from 8-12%. of Chisel plowed plots with 38% cover after planting significantly reduced erosion losses. Runoff velocities were slower and sediment was trapped by both tillage ridges and corn residue. resulting from particles and sediment plots The authors noted that the sediment with residue had higher proportions of colloidal higher nitrogen and phosphorus concentrations. The was more enriched as a result of the reduced velocities of the runoff. Neibling and Foster (1977) compared runoff velocities types from several of residues at different levels of cover to velocities from bare, fallow, unrilled soil. Runoff levels of residue cover. velocities decreased with increasing Partially incorporated corn stalk residue at 2 Mg/ha, h Mg/ha, and 5 Mg/ha levels of cover decreased runoff velocities 10, 3 0 , and U0% respectively, compared to bare soil. During storm precipitation rate events, overland exceeds flow can not occur the infiltration rate of a soil. intense storms on bare soil can alter the porosity of the markedly decreasing its initial and final until However, surface infiltration the soil rates. If infiltration declines, runoff and sediment transport can be expected to increase. Ellison (19^7) found that raindrops on aggregates and displaced soil tested lost up to several minutes of rainfall splash. 90 % soil broke up particles in the raindrop splash. displaced particles caused surface soils bare puddling of to occur. Certain soil The clay their infiltrative capacity within inception due to surface sealing from soil 21 Duley soil (1939) made detailed studies of the effect of crop residue on infiltration. He found that soils mulched with 5 Mg/ha of wheat straw had significantly more infiltration than bare tested had high initial plots. All plots infiltration rates; however.the infiltration rate remained high on the mulched plots while unmulched plots. Microphotographs falling rapidly on the of the surface soils showed that a compacted crust approximately three millimeters thick had formed on bare soil as a the result of raindrop impact and movement of soil fines. Much less surface compaction was found on the mulched soils. (1966 ) using a rainfall Mannering et al. Mg/ha (95% cover) of dry hay on corn infiltration compared to conventional clean simulator ground found doubled tillage loss on the mulched field was essentially eliminated. 6 the total treatments. Soil In a three season study of three tillage practices on steep slopes Johnson found that et a l . (1979) that the ridge plant system with 59% residue cover reduced runoff by 60$ and erosion by 90 % systems. compared to losses from moldboard plowed Chisel plowed plots had a significant reduction in runoff and erosion compared to moldboard plowed 1978 ). Oschwld, provided plots in Illinois (Siemens and Increased surface roughness produced by the chisel plow additional storage areas for the runoff to settle and inf i1trate. Crop residues will decrease runoff quantity as soils have studies available moisture (Johnson and Moldenhauer, significant holding capacity. 1979: Meyer et long as Rainfall simulation al., 1970) was showed differences in runoff and infiltration between conservation tillage and conventional tillage only for their initial tests soil permeable dry or at field capacity. when the Follow up tests within the next 24 22 hours on partially saturated soil did not demonstrate runoff differences between tillage systems. Logan and Adams data, concluded permeable soils (1981), in a review of published and unpublished that surface residue will decrease overland runoff on with good internal drainage. On soils with low infiltration rates and poor internal drainage surface residue has little influence on runoff quantity and may increase drained in insulating runoff properties on poorly of residue, increase runoff. soils which was The observed attributed to the slowed soil evaporation elevating soil moisture level compared to fallow ground. The capacity of the soil to event can directly particulate materials. infiltration influence Thomas store water runoff et and during precipitation losses of both soluble and (19 8 1), al. a in an examination processes, found that the antecedent moisture condition of a soil dramatically affected the quantity of rainfall excess of rainfall of pattern. Mockus watersheds gave considerable (1972) weight regardless in his model of runoff from small to the influence moisture conditions on runoff volume and rate. the precipitation from an intense storm may of antecedent Under dry conditions all infiltrate into the soil A portion of the seasonal variation in sediment loss that has been generating no overland flow. observed in the literature can be attributed to the changes in soil moisture that occur throughout the year. In a study of overland conducted on a somewhat poorly drained loam soil, Aull during the six week period folowing initial snowmelt storms of very low runoff (1979) found that (March 3. 1979) maximum 30 minute intensities (less than 1 mm/hr) generated considerable runoff and sediment loss. The site did not have 23 subsurface drainage tile and after thawing remained near saturation unti1 mid Apri1. Subsurface drainage overland flow drained soils and to been associated proposed sediment reduce of the volume material and transported Reducing runoff volumes will curtailing a method to reduce and nutrient losses on poorly (1980 ) have concluded that peak Reducing volume and peak flow should have quantity as (Skaggs, et al., 1982 ). Schwab et al. found has off tile drainage has been flow rate of overland runoff. a not!cable the limit losses of field effect by soluble on the overland flow. nutrients, while peak flow rates should reduce the sediment carrying capacity of the runoff water. Tile drainage water can be expected to carry of sediment than overland runoff. Most lower concentrations of the sediment carried in surface water is filtered ‘out by the soil medium before it tile. Schwab et al. reaches the (1980) conducted a longterm field investigation to study sediment loss from tiled and untiled plots. Mean flow weighted concentrations of sediment in subsurface drainage were 50 - 90 % lower than in surface flow. Skaggs investigate influence the et a l . (1982) used a simulation model of tile drainage on sediment loss. sites modelled losses were calculated at 9 Mg/ha for untiled to For the conditions and 0.9 Mg/ha per year when subsurface tile was added. Bengtson et al. from (1982 ) compared the nutrient and sediment both tiled and untiled plots on alluvial soils in Louisiana. loss on all plots was relatively small however, tiled plots reduced (less than sediment loss reduction in sediment loss due to subsurface 2 by Mg/ha 17%* drainage per losses Soil year); The greatest occurred during 24 the winter when water tables were high and evapotranspiration low. During these periods, surface runoff was reduced by 34% and soil loss by 43%. Annual losses of phosphorus were reduced by 32% on the tiled plots. Logan and Schwab on (1976) monitored sediment losses in tile three watersheds in Ohio. 0.9 Mg/ha. surface Sediment hydrology. On all sites yearly losses were less than concentrations did appear to be to be influence by During several precipitation events, concentrations as high as 2,700 mg/1 were observed. thought effluent The elevated concentrations the result of soil fines flowing directly are into thetile through cracks in the soil. Management practices that increase infiltration may affect both the quantity suggested and quality that infiltration tillage may result into subsurface tile. from subsurface chisel plowed The of tile subsurface practices tile flow. that increase Holt et a l . (1973) soil porosity and in greater movement of nutrients and sediment Bengtson et al. (1982) found that sediment loss flow was significantly higher on plots that were (1.4 Mg/ha) than on plots with a grass cover (0.4 Mg/ha). authors concluded that chiseling contributed to an increase in soil loss from subsurface drainage. 2.8 The Movement of Soluble Nutrients When soil increases. loss is low, the soluble fraction of nutrients in Soluble phophorus phosphorus lost from 33 plots in study was conducted on runoff comprised the largest fraction of total Missouri (Smith et claypan soils with 3% slope. were slight (less than 1.5 Mg/ha per year). al. 1974). The Sediment losses Harms et al. losses in (1971*) in a two year study of nutrients South Dakota found that the sediment and bound fraction of phosphorus and nitrogen constituted 6*9% and 1*2% of the total rainfall events. sediment. In snowmelt runoff which was essentially 23 % only and Rainfall 11% of of total high from concentrations free kjeldahl For the entire study, all nitrogen independent of any sediment. and carried lost of of sediment, the total phosphorus and nitrogen lost from the fields was sediment bound. 69 % runoff sediment 27 % and of of the the nitrate, phosphorus were Most of the runoff was from snowmelt (68%) total sediment losses were low (less than 1.1 Mg/ha per year). The authors concluded that traditional soil and water conservation practices that limit rainfall runoff and erosion would not limit all the nutrients in agricultural drainage waters. However it was suggested that phosphorus losses could be curtailed by erosion control. Runoff nutrients from than snowmelt rainfall may have events. higher proportions of Ellis and Erickson (1977) found that soluble phosphorus constituted 29 % of the total phosphorus compared to snowmelt was in 7% of the total lost during rainstorm events. predominantly lost soluble as soluble nitrate snowmelt Nitrogen in and ammonium; whereas, during rainfall events 8 2 S k % of the total nitrogen loss was in the sediment phase. nutrients in The authors attributed the higher levels of soluble snowmelt to the nutrient content of the snow that fell on the fields. Concentrations of soluble runoff coming from release soluble desiccation, nutrients may be conservation tilled croplands. phosphorus freezing, and thawing soluble and nitrogen drying. relatively high in Plant material can when Timmons subjected et al. to (1975) 26 investigated the effect of extent of soluble changing nutrient environmental conditions release from crop residue. on the In laboratory analysis grain, straw, and forage crops were periodically frozen, dried, and subjected to leaching. Substantial quantities of soluble phosphate and nitrate were released to the leachate. Holt et al. (1973) reported that snowmelt from alfalfa land had concentrations and losses of soluble phosphorus two to four times greater than snowmelt from fallow moldboard plowed corn. Harms et a l . (197M land or found more soluble nutrients coming from noncultivated sites with forage or grain than from tilled si tes. Rainfall simulation tests have been used to soluble (1978 ) nutrients from evaluate various tillage systems. and soluble conservation tillage. sediment were not Johnson et a l . (1979) reduced soluble significantly by in a study of nutrient and losses from three different tillage systmes found that soluble concentrations Although nitrogen of Siemens and Oschwald in a study of seven tillage systems found that losses of phosphorus in runoff conservation increased tillage with reduced increased runoff minimized tillage systems. differences in residue cover. runoff and erosion compared to conventional tillage the higher concentration of soluble the movement net phosphorus in phosphorus losses from the Most of the nitrogen lost from all three sites was in the form of total kjeldahl nitrogen and controlling sediment appeared to control nitrogen losses. McDowell and McGregor(1980 ) also reduced soil loss while increasing found that soluble no till treatments phosphorus losses. The authors cited several reasons for this phenomena: 1) insufficient sediment in runoff to sorb phosphorus from 27 solution; 2) release of phosphorus from crop residues; and 3) decreased fertilizer incorporation The mean flow weighted concentration of soluble phosphorus was mg/1 from the no till plots vs. tilled plots. fertilizer. concentrations Soluble 0.02 mg/1 from the conventionally clean Both treatments received the same Barisas to be phosphorus residue cover. et al. (1978) did significantly concentrations The authors 0.4 not amount find correlated did concluded phosphorus nitrate with correlate that of nitrogen residue cover. significantly conservation with tillage was ineffective in reducing soluble nutrient losses in overland flow. Baker and Johnson (1982) observed greater concentration of phosphorus and nitrate nitrogen in runoff from plots with 1.6 Mg/ha of corn residue than in runoff from conventionally tilled the soluble conservation plots. However tillage plots lost less than one half of the quantity (kg/ha) of the soluble phosphourus and soluble nitrogen compared to conventional plots. This difference was the result infiltration and storage on the conservation tilled were performed on the runoff from the conservation flow. of plots. to ti1lage. from tests a well drained sandy loam soil and the magnitude of conventional plots was 3-3 times that of the tillage plots, offsetting the higher concentrations in the be nitrogen a likely phenomena associated with conservation tillage, net losses of these nutrients can only be acheived in runoff increased The Since elevated concentrations of soluble phosphorus and appear the conservation is situations where considerably less than from conventional 28 Tile drainage has characteristics been than found overland to have flow. Subsurface monitored during the water quality study at and Morrison, 1977)* Flow different Black water tile drainage Creek,Indiana water than in nitrogen were higher overland in was (Lake weighted mean concentrations of sediment, soluble phosphorus, and particulate phosphorus were much lower drainage quality tile flow flow. than Concentrations overland in of flow. tile nitrate The study concluded that best management practices that allow more water into tile drainage systems losses. will significantly reduce sediment and phosphorus Losses of nitrate nitrogen may be expected to increase. In a study of agricultural subsurface drainage water from farms in Michigan, Erickson and Ellis (1970) concluded that tile drainage carried low concentrations of soluble phosphorus. ortho Measured concentrations phosphorus ranged from less than 0.05 mg/1 to 0.30 mg/1. nitrogen losses were considerably higher, but the maximum observed was standard of fertilizer 11.1 10 to mg/1, mg/1. the Of just the of Mitrate concentration above the Public Health drinking water nitrogen and phosphorus applied as farmlands 1A% and 0 .3% respectively left the fields via tile drainage. Gianelli in tile (1971) found nitrate nitrogen to be the dominant drainage concentration concentrations of of less than 1 mg/1. Baker et al. in Iowa. in the nitrate total San nutrient Joaquin valley of California. nitrogen was 19.3 mg/1 while Average average kjehldahl nitrogen and ammonium nitrogen were Ortho phosphorus concentrations averaged 0.09 mg/1 . (1975) sampled agricultural tile flow for Concentrations of phosphorus were very low. four years Ortho phosphorus ranged from 0.001 to 0.038 mg/1 and total phosphorus from 0 .0 0 7 to 0 .1 8 2 29 mg/ 1 . The drainage. authors considered Tests of the subsoil phosphorus and was capable these concentrations indicated that of it typical of tile had low levels of adsorbing phosphorus from the surface water percolating to the subsurface tile. In the Iowa study nitrate nitrogen concentrations ranged from kk.2 mg/1. The flow weighted mean concentration was 21 mg/1. with subsurface drainage can be expected td lose more than undrained sites. On nitrate Sites nitrogen Denitrification, the principal process of nitrate removal requires anaeraobic conditions source. 2.3“ sites with in artificial the presence drainage of a saturated conditions in the carbon rich top soil are not maintained carbon anaerobic for extended periods and denitrification is minimized. 2.9 Simulation Models of edge-of-field Losses from Croplands The increasing use creation of complex of high simulation speed computers models to yield models was from agricultural lands. that precise characteristics with limited to approximated daily intense crusting. storms (1982). hydrologic available review of Frere et al., nutrient losses Weather that may sufficient generate inputs. Storm precipitation data; increments for most locations. where available, still do not generate brief detailed predict however, the long term records of the National are the The models require field based calibration and are limited by the availability of are A conducted by Foster (1982 ) have reviewed the various models permitted evaluate the influence of conservation practices on edge-of-field losses. sediment has Service (NOAA) Hourly records, information on the overland flow or cause soil None of the models surveyed in the literature account for the 30 influence of tile drainage on water quality. 2.10 Monitoring Approaches Field studies monitoring runoff during periods of precipitation and ruroff are the traditional approach for evaluating specific soil and water conservation practices. Studies are conducted both on small plots with numerous replications for statistical validity as well as on larger production scale areas. more sediment loss it has been suggested that small plots generate per unit area al. 197^; McGregor and Greer,1972). than field scale plots (Harms et Runoff from small plots may consist of a disproportionate quantity of sediment from soil splash. processes common in larger watersheds are often absent on Deposition short narrow plots. Large production scale field studies committment to fixed experimental practices. resources often restrict large comparisons. practices, While it field require a long term Limited financial and land studies to side by side plot this permits evaluation of actual production scale eliminates the replications necessary for stringent statistical tests. The conclusions drawn the weather functional. two to four patterns from a field study areextremely by that occurred while the monitoring apparatus was Many field studies reported in the literature are based years of monitoring (Von Stryk and Bolton, al., 1971*: Lake and Morrison, (I96 A) biased 1977: Ellis et al. 1979)* on 1977: Smith et However, Chow concluded that twenty years of records are required to produce a fair approximation of hydrologic patterns in a region. To circumvent the uncertainty of weather driven studies, artificial rainfall simulators (rainulators) have been employed simulators allow rapid data raindrop size and collection intensity. and (Meyer, excellent replication Small plot rainulators conjunction with (Swanson and Dedrick, The rainfall simulators are an excellent means of conditions. "worst various conservation treatments for under scenarios of high volume, records to comparing a given for with the of depicting long The term insure that runoff producing scenarios of weather, soil moisture, and crop stage typical of the study region are (Meyer, i960 ). set high intensity storms. studies need to be planned and analyzed in conjunction weather rainulators 1966). Rainfall simulators are particularly useful case" of introduced runoff attempt to simulate large field conditions of runoff and erosion effect The (1 m x 1 m) have been used to study soil splash and detachment, while larger in 1960). simulated 32 CHAPTER 3 METHODS: FIELD INVESTIGATION 3.1 Si te Selection The United States EPA was interested in the water quality resulting from typical rainulators production were scale available for agricultural the practices. project. Funding No large and time constraints limited the amount of field work and construction that could be undertaken so a rigorous selection process was carried out to find a large field that could be used for a side by side plot comparison study. Because most of the prime farmland in the study region was tiled, decided to find it was a site where both overland runoff and subsurface tile flow could be monitored. The predominant soil series in the study region are classified Michigan Soil Association 20 and 21 (Whiteside et al., 1968)of these associations conditions from loam, were developed under poor The soils naturaldrainage clay loam, or silty clay loam parent The principle hazards to crop production are naturally in material. poor drainage. When subsurface tile is utilized to improve drainage, these soils become some of the most productive agricultural sites in the state of Michigan. The topography of most of the study region 0-1% slopes. slopes 1- 3% of Agricultural erodible The is nearly level with flat landscape is broken by narrow sand ridges with intermittently located on the heavier soils. land with slopes as great a 4-5% do exist on silty, highly soils within the region of study. Conservation tillage 33 practices could be expected to sediment loss from such sites. study is located on flat, demonstrate However, since dramatic 90% of reductions in the region of poorly drained, fine-textured soils, site selection was limited to these conditions. Conservation tillage relies on crop residues to provide the soil surface and thereby minimize predominant crops grown in the region beets - only corn conservation tillage. provides a erosion corn, navy substantial cover for Of the losses. beans, residue and sugar cover following To monitor the influence of conservation tillage during 1981 and 1982, site selection was restricted to fields that would be planted to corn during I98 O and 19 8 1. Site selection was limited to fields that could isolated from surrounding measure flow as it exited the fields. could measurement and provide The study a means to Unobstructed discharge of surface and subsurface water was required during all flow hydrological1y surface and subsurface drainage. site required a natural configuration that accurate be prevent runoff events contamination to or insure artificial ponding and settling of suspended material. The monitoring project was conceived as a year round gathering samples from any snowmelt or precipitation event. project, Aul1 (1980) discussed the special problems associated with field monitoring in and wet conditions. Based upon Aull's concentrated on locations that could be experiences easily accessed cold site selection by motorized vehicles in order to enhance maintenance and sample transport and fields where 110 V A.C. electric service samplers during freezing weather. would be available to winterize Potential Conservation study sites were suggested by the Tuscola County Service, the Tuscola County Cooperative Extension Service, the Tuscola County Agricultural Stabilization and Conservation and Jerald reason for strictly Lemunyon, area Agronomist of the USOA/SCS. site disqualification adhered to type, tile was crop Service, The most common rotation. Area farmers a given rotation and were not willing to follow a pattern conducive to the study. soil Soil drainage Twelve sites were closely evaluated for and overland flow patterns before the final selection occurred. 3.2 Site Description The site selected was on a field belonging to located 2 kilometers west of the town of Fairgrove, Fairgrove Road. 1/2 of the flowed Starkey, immediately south of The legal description of the site was: W 1/2 of NW the E 1/4 of Section 19. Fairgrove Township, Tuscola County, Michigan (Figure 1). which Richard The field drained into the Spohn County to Saginaw Bay via the Northwest County Drain. Drain The study site is located approximately 12 kilometers from the Saginaw Bay. A detailed topographic November 10, 0.8% slope. the southern survey 1980 (Figure 2). A deep sand ridge boundary and of field was undertaken created a natural hydrologic divide a on The field slopes to the northwest at an roadside receives all the drainage from the field. and the ditch on on the northern border The field was evenly graded had no visible potholes or depressions that could pond runoff. The field was approximately 200 meters wide and 425 meters long. A subsurface tile system ran parallel to the prevailing drained only the study site. A separate system slope and drained the land Figure 1 Study Site Location SAGINAW BAY CARO Figure 2 Topographic Survey: Original Site » tsi ON north .30^ STARKEY FARM FAIRGROVE. MICHIGAN N8HA.wVEV NWV SEC-,B-R 8 E T I3 N CONTOUR INTERVAL 03M NOV 10. 1960 4 BM ROCK 193 2 M MSL Cr»>(v» ■P>- .•.tikt'i 37 adjacent to the plots. intervals field. and were Tile were spaced at meter found at a depth of 0.7 meters at the lower end of Based on farm records and field probings, the was found to follow a gridiron pattern. drainage network The system was installed during the 1950's with 10 cm clay laterals. the approximately •20 The tile main paralleled roadside ditch and exited at the northwest corner of the site. sand ridge at susbsurface the flow upper from boundary of the plots intercepted The any beyond the plot borders and transported it to a nearby gravel pit. Overland flow was directed to a single area on the northwest corner of the site. During the site selection process this area showed evidence of surface flooding and crop stunting due to excessive wetness. Free outflow from the field was obstructed by a small berm along the northern field border created from ditch spoils. The field had been farmed uniformly and had been during the 1978, 1979 and 1980 growing seasons. yields of aapproximately 7»7 MT/ha. planted to corn The site produced corn The only primary tillage tool used on the field had been a moldboard plow. Soil on the site was mapped textured poorly drained soil. as a Londo soil was loam argillic an complex, a fine Londo loam is classified in Michigan soil management group 21 as are most of the soils in The loam the region of study. alfisol with a loam surface horizon overlying a clay horizon. It was officially classified as an aerie glossaqualf, fine-loamy, mixed mesic soil. Drainage approximately from two the field meters deep. discharged into a county ditch Previous to the projects inception the 38 ditch had not been cleaned since the late 1940's. with cattails and had The ditch was choked accumulated approximately 0.3 m of silt. were still above the existing ditch bottom however. Slope on the Tile ditch was 0.3% for 0.6 km before the ditch joined with a deeper N-S drain with a 0.7% slope and crossed under Fairgrove Road. 3*3 Field Modifications The selected site was modified to create two hydrological 1y isolated plots, each approximately 100 m wide, extending south 400-1*50 m to the sand ridge. Field dimensions are given in Table 1. TABLE 1 Field Dimensions Conservation Tillage Plot Width (m) Max imum Length (m) Slope Area (ha) 98 Conventional Tillage Plot 98 488 0.7% 4.62 412 0.8% 3*89 The configuration of the site required the creation of berms on the eastern border subsurface flow the tile main plots. each plot (Fig. 3)• was cut at the intersection To isolate of the two An additional outlet was added at that location and received the subsurface flow from all the original of north-south outlet thus laterals draining the east plot. drained only the laterals of the west plot. The The cut main at the plot intersection was plugged with a plastic cap and set in concrete. The receiving ditch was cleaned during November, proved 1980 . The suitable for carrying runoff from precipitation events. ditch However Figure 3 Topographic Survey: Modified Site •im Ifos n o rth 30 5 M I----- 1 STARKEY FARM FAfRGROVE MICHIGAN N 8H A E ^ NWV4 SEC 19 R 8 E T U N CONTOUR INTERVAL 0 3 M DEC 1.1980 + 6M ROCK 193 2 M MSL 40 it did not provide a suitable outlet during snowmelt. during the first snowmelt filled with wind event packed snow. monitored the In February, ditch was completely No appreciable ditch flow occurred and the snowmelt runoff backed up and ponded on the plots for twenty hours. the winter of 1982 the ditch again filled with wind packed snow. During To avoid the outlet problems of the previous year was 19 8 1 employed began. to remove the snow a hydraulic backhoe from the ditch before the snowmelt This action resulted in free outflow and a satisfactory outlet during the 1982 period of snowmelt runoff. 3.4 Monitoring Procedures To compare edge-of-field losses from conservation and tillage practices, measuring conventional devices must be able to accomodate large infrequent runoff events as well as accurately measure the frequent flows expected from flat tiled lands. An ideal setup would not create artificial ponding in the fields or backup in the subsurface addition any low tile. In flow measurement device must be incorporated into designs that permit sampling of the drainage water before it leaves the field. A sampling station to monitor overland northwest corner of each plot (Fig 4). flow was located analysis (Section 7 . 2 ) , a 10 year 24 hour storm in was calculated for conventional Tuscola County was Peak runoff was calculated using the Soil Conservation Service curve number flow runoff Based on a hydrologic frequency expected to generate 70 mm of precipitation. Peak the . The maximum design flow chosen to be measured at each overland flow station was set as the peak resulting from a 10 year 24 hour storm. in method tillage (Kent, 1973)* since it can be 41 Figure U Field. Monitoring Layout FAIRGROVE RO A D • * - DITCH DITCH DROP INLETS A DROP INLET 15 M H-FLUMES STUB MAIN INSTALLED TILE FLO W . MEAS. FLUMES EXISTING TILE OUTLET i I7 EXISTING MAIN OIVIOED / A N D CAPPED TILE MAIN POWER POLE BERMS TO DIVIDE SURFACE FLOW BERM BERM CONSERVATION TILLAGE (SOIL SAVER) 490 M CONVENTIONAL TILLAGE (MOLDBOARD PLOW) | I EXISTING TILE LATERALS SOIL IS LONDO L O A M COMPLEX 98 M HYDROLOGIC OIVIDE 42 expected to generate more weighted curve number chosen planted parallel to runoff than for the plots the slope on a site conservation 81 was tillage. assuming row The crops in good hydrologic condition. Given the flat slopes of the plots, peak runoff was predicted as 0.32 cu m/s. Tiled agricultural cropland has been observed to runoff rates than similar untiled sites. in the state of Michigan recommends have lower peak The Soil Conservation Service (Emeron Christenson, Assistant State Engineer) that the hydrologic soil group be decreased one letter (from C to B for example) Recalculating when the calculating curve numbers peak for runoff on tiled fields. the plots using hydrologic soil group B rather than group C for tiled Londo loam yields a weighted curve number of 75 and a peak runoff rate of 0.25 cu m/s. The maximum flow to be measured by an overland flow device was therefore set in the range of 0.25 to 0 .3 2 cu m/s. Aull sample (1980) used a drop overland cu m/s flow. The box 90 degree device is accurate up (Grant, 1979) meeting the design sites. However, inaccuracies the partial the weir crest. of grassed buffer area Aull that reduced flow measure to flow rates of 0.40 criteria for velocity of the approaching the in water runoff velocities. the or weir The ponded area was intended to reduce sediment losses before the runoff left the field would study In his study on runoff from a (1980 ) created a ponded region above fluctuations and in flow measurement with a V notch weir are caused by changes in submergence V notch weir to and not be an acceptable phenomenon in a study investigating the edge of field losses of sediment and nutrients from tillage practices. *»3 Runoff velocities from the plots were expected to vary widely based on storm and residue cover. Flumes do not require constant velocities to accurately measure flow. A 0.66 M fiberglass and Fab Inc. calibrated by PLASTI H flume manufactured of Tualatin, Oregon was therefore chosen as the overland flow measurement device for the study. calibration tests performed by the measurements are possible up to 0 .3 1 watersheds. impeding Service to accurate flow measure mid 1930's runoff by from the small U.S. Soil agricultural The design was intended to permit passage of debris without accuracy (Brakensiek et al., 1979)- Partial submergence does not significantly affect the calibrated stage discharge relationship an H flume. H of Tests have shown that a submergence of 30% has less than a 1% effect on the calibration and a 50 % submergence has less effect. on cu m/s with this device. The H flume was developed in the Conservation manufacturer, Based flumes were than a 3% used sucessfully in Michigan during the water quality monitoring project carried out by Ellis et a l . (1978). Flow into the H approach (1979 )* pressure section flumes must be non turbulent. A rectangular was consturcted based on the recommendations of Grant The approach sections were fabricated from wolmanized l / U treated plywood. The plywood rectangles were reinforced with five frames each having a U x k board on the bottom and 2 x k boards the sides and top. inch The frames were glued and bolted together. on Pressure treated lumber was utilized and additional weather proofing was applied. Each H flume was bolted to the approach boxes. A rubber gasket was added to insure a tight seal. Since sampling was slated to special adaptations were occur during periods of snowmelt, made to the approach sections to prevent ice kk buildup. The floor of each approach section was grooved at intervals eight inch and construction grade heat tape was set in the grooves. heat tapes were activated by dropped below 3 degrees C. a thermostat when ambient The temperatures The interior floor and walls of the approach section was then lined with 20 gage stainless steel to create a smooth flow surface and to more evenly conduct the heat from the heat tapes. Outflow from the H flumes was discharged corrugated metal collection area. cm plastic pipe (CMP) that served into an upright 1.2 as a drop inlet and sample The CMP was connected to the receiving ditch by tile approximately U meters long. a the peak design rate of 0.32 cu m/s by open channel flow. bottom of the tile entrance was positioned at 0.3 m above the each drop inlet creating a basin for sample collection. water in the drop inlet was expected incoming discharge to from the flumes. be 38 The top of each tile was set below the invert of the H flume and the tile was sloped to carry least m constantly floor at The of During runoff, mixed by the The design required that the drop inlets be pumped and cleaned after each event to insure that no residue or sediment remained to contaminate the results of the next event. An area was excavated with a backhoe overland flow sampling station. m of gravel were placed under concrete the drainage tile was set in the gravel to carry avoid frost heave. the placement piers. a each Approximately approach boxes and a 10 cm off excess moisture and The 1.2 m CMP drop inlet was set in concrete. The soil around the tile outlet was covered with 6 mil plastic and creating of The approach box and H flume were set on nominal k x 6 stringers attached to 0.2 for concrete cutoff collar to prevent water from seeping around the tile and inducing soil piping. After the approach box, flume, and drop small concrete pad inlet were installed, was poured at the entrance to each approach box to minimize erosion of the soil that was disturbed during the process. Minor land grading plot to insure that the points on each a was undertaken with a bulldozer on each overland field. construction sampling stations were the lowest Slopes on the concrete pad and approach boxes were set at 0.1% to eliminate ponding. Samples of overland flow were obtained samplers. Aull (I98 O) used time characterize edge-of-field losses. technical feasibility of with activated Daniels et al. using a Isco 1580 discrete (1979) samplers compared during difference between the proportioned a runoff event. sampling to the flow proportional composite sample instead of discrete time based samples to determine losses constituents composite of selected The authors found no significant techniques and concluded that flow composite sampling would result in considerable reductions in analysis cost. Isco bubbler flow meters were used to sense stage on wells connected to the H flumes. occurred over a given period. recorded initiate the sampling process whenever sampling necessary. automatically a runoff event began. meters were checked for accuracy at least once a week when flow a predetermined quantity of flow had passed through the flume. The flow meters were always in operation and were able to start total The flow meters were electronically connected to the composite samplers and were able to whenever stilling These flow meters were programmed at the factory to convert stage to flow and directly that the and The flow recalibrated All automatic signaling between the samplers and flow meters were checked at that time. kG The composite samplers were usually set to draw 50 ml of sample for 1. k every cu meters of runoff that passed through the H flumes. sample containers could hold 19 liters and were capable of 380 samples predicted accomodating 532 cubic meters of runoff from the plots at representing the standard setting. The Runoff volume from a 10 year at 1500 cu. meters (Mockus, runoff the sampling increment was 1972). 2^ hour storm is During periods of intense increased. Samples were generally composited for 12-2** hours before being taken in for analysis. A sampling station to monitor subsurface tile drainage was located in the tile outlet of each study plot. Several measurement devices were considered to monitor Palmer utilized on a tile project flow. in A Macomb County, Bowles Michigan unpublished data, MSU Agricultural Engineering flow was relatively constant. It over a wide range of had (T.L. Department) been Loudon, where pipe was expected that flow rates from agricultural tile would vary widely demanding a accurate flume flows. device that could The primary disadvantages of Palmer Bowles flumes is that they have a relatively small of flow and are not considered to have good resolution useful range (Grant, 1979)• Tile flow measurements were obtained by using a 25 cm, 30 degree notch flume Department). designed by The flume was G.E. Merva constructed sampling basin at the entrance (Fig. 20 5)• (MSU of Agricultural plexiglass V Engineering with a small Each flume was connected to a cm plastic tile which received the entire each plot. be subsurface drainage of A 20 cm CMP carried the outflow of the flume to the drainage ditch. The flumes were located ground surface meters and 6 approximately 0.8 meters from the outlet of each main. below the Stilling wells of PVC pipe were connected to the flumes for stage measurement. Figure. 5 Tile Flow Measurement Device 30 Degree V Notch Flume FRONTAL VIEW OF FLUME LATERAL VIEW OF FLUME § APPROACH SECTION FIELD PLACEMENT i*8 The 30 degree V notch flume 0.0006 cu. m/s to 0.06 cu was m/s, designed a to measure range of 1:100. a from This was well excess of the average daily design rate of 0 .0 0 6 cu. m/s assuming flow calculated in by drainage coefficient of 12.5 mm/day and permits measurement during brief periods of peak tile flow. The calculated stage discharge relationships are presented in Figure 6. Leopold Stevens type F stage recorders were used to on the V notch flumes. days on a single chart. measure stage The meters were set to record the stage for 8 A 1:1 gage scale was selected for the recorder permitting resolution to a stage of 0 .0 0 3 n>. Tile water was sampled via surface risers placed upslope flumes. Flow meters were to be hydrographs. often more stable over time activated discrete suitable monitoring device. advance A period. rates were than typical overland runoff from agricultural flow maximum created based of therefore The samplers were manually 28 on rates were periods of percolation croplands to the soil. chosen activated as a in Sampling intervals ranged from 1/2 2 hour intervals for base flow samples could be stored in the samplers. From the discrete samples a single flow weighted manually flow samplers of an expected storm event. hour during peak sampling. time tile a "flashy" flow regime, the subsurface tile flow pattern is moderated by the infiltration and Isco However, Whereas overland flow rates display the not available that could be used to create flow.composited samples of tile flow. expected from the tile composite hydrograph sample was during the sampling Figure 6 STAGE-DISCHARGE RELATIONSHIP 25 CM 30 DEGREE V NOTCH FLUME DISCHARGE(L/S) 70 60 50 40 30 20 10 0 0 15 30 45 60 75 S0 105 120 135 STAGE(MM) 150 165 160 1S5 210 225 240 255 50 3.5 Rainfall and Snowpack Measurement A recording raingauge was installed on the 1981 to relate and volumes. rain gage events occurred. site April 15. runoff characteristics with specific storm intensities A Belfort 2 h hour, was study utilized. 12 inch dual traverse univeral weighing Charts were changed once a week if no major Following any appreciable storm the chart was changed to avoid confusion in analysis. All precipitation events greater than or equal to 12.7 mm were analyzed for the following characteristics from the recording rain gage: 1) maximum 30 minute intensity (mm/hr) 2) excessivive rate storm classification 3) depth k) (mm) 5 day antecedent precipitation (mm) 5) rainfall erosion index (R) Each storm was divided into successive uniform intensity permitting computation of index, R. the This is defined by Wischmeier and Smith of the maximum 30 minute intensity the increments of approximately the rainfall erosion (1978) as the product (cm/hr) and the kinetic energy rainfall divided by 100 (Mg-m/ha-hr). (E) of The kinetic energy per cm of rain was determined from the equation (Wischmeier and Smith, 1978): E - 210 + 8 9 . x log (I) where I* rainfall intensity (cm/hr) Individual events were defined by separations of at least without precipitation. maximum rainfall (2) As suggested by Wischmeier and Smith 6 hours (1978) the intensity used in computation of R was 78 mm/hr, since 51 the terminal rainfall not continue to intensity velocity and corresponding raindrop energy does increase above analysis was that restricted intensity. is not when small storms are left out of the analysis soil cover and residue cover reduce the surface. The actual proportion of the is considered to management impact factor the (C) . soil The addition storm to events greater than or equal to 12.7 mm.The annual rainfall erosivity Crop In surface significantly (Schwab et al., actual R that altered 1981). reaches the rainfall erosion index that is defined as the crop "C" factor of the USLE was determined on both plots for each storm event. Pertinant crop stage and residue data was used in conjunction with the work of Wischmeier and Smith (1978) for the C factor determination . All excessive rate storms with a magnitude greater than or equal to 12.7 mm were recorded. Excessive rate storms are defined by a depth (mm) greater than or equal to 5* + 0 .2 5 (t) for a givenduration t (minutes) . Records of the snowpack were period of obtained each year of sampling. the snowmelt Cores 5 cm in diameter were taken at randomly selected points on each plot. average just, before The snow depth of water on each plot was computed. was melted and The west edge of the conservation tillage plot was bordered by a wooded fence row and a snow collected drift there each winter. the deep The width, depth, and water equivalent of the drift was specifically measured each year. The erosive satisfactorily forces modelled. of snowmelt runoff have not yet been Many of the widely used models that simulate edge of field losses from croplands neglect snowmelt erosion (Tubbs Haith, 1977; Oonigian et al. 1977) - and During snowmelt the soil profile is 52 either partially frozen or detachment and processes Wischmeier saturated sediment than occur and Smith transport during of rainfall index event. In responds the snowmelt. R. winter precipitation (cm of runoff puddling snowfree to is a common. different periods of It is directly frozen. air set of the equivalent year. to the Rs is defined as 1.01 times the cumulative liquid calculating water) that precedes a snowmelt Rs winter precipitation was defined as that precipitation preceding snowmelt runoff which occurred contiguous Soil (1978) developed a subfactor, Rs, to account for the erosive force erosion and during the period when a portion of the soil profile was presumed to be The inception of frozen soil was assumed to occur when the mean temperature of the previous 20 days days was below freezing and no snow cover existed (Steenhuis, 1979)- 3*8 Cold Weather Design Aull evening (1980) found that considerable snowmelt runoff occurred during hours when temperatures dropped below freezing. monitoring at these times a number of steps were taken. was placed over the stilling prevent them from freezing. lines of all the wells All A plywood cover and a trouble light inserted to Heat tape was samplers. wrapped around winterization scheme proved very reliable. due to freezing conditions. the intake heat tape utilized at the site was activated by a thermostat when temperatures dropped below 3 The To permit degrees C. No information was lost 53 3>7 Residue Measurement To effectively investigations compare the results of this study with other of conservation tillage it was necessary to quantify the extent of surface residue on the fields. Residue was measured at three different times during the year: a) Following fall tillage (November) b) Before spring planting (April) c) Following planting and cultivation(June) Both percent percent of residue sampling method placed on cover on and gravimetric the fields was determined with the line point (USDA, 1982). the ground A measuring tape 15“30 diagonal to the rows. greater than 1 cm in length touching a interval were counted as cover. tape and percent cover was cover were tape measured. meters long The was Crop residue fragments mark at a predetermined One hundred points were checked on each calculated directly. A minimum of six samples at random locations on each plot were used in the determination. Estimates of gravimetric cover were obtained by collecting all visible residue contained Between six and twelve composited in sets before weighing. combined dry determine the with samples of three, a one were square yard (0.8 sq m) frame. taken then per plot. air dried for at Following the estimation methods of the weight lbs/acre of of residue residue in the ounces cover. Samples were least two weeks USDA-SCS the was multiplied by 100 to This bookkeeping method accounts for 99*2% of the actual lbs/acre on the field (USDA, 1982). 54 3.8 Agronomic Activity A survey was conducted in the winter of 1980 to methods 1982). plow commonly determine tillage used on rowcrops in Tuscola County, Michigan (Muhtar, The survey found that a majority of in the farmers fall for primary tillage on corn ground. farmers that responded to the survey used no-till that they tillage. used chisel plows 9% and Based on the results of the Table tillage. 2 None of the 106 20 % while indicated used a disc tiller for primary was followed farmer, the was the to compare conventional to conservation Cooperative tillage site. tillage primary made in fall conjunction Extension tillage with the Service, and the area A chisel plow with twisted tool used on the conservation Between 50-60% residue cover was expected to remain after (Colvin et I98 O ) . al., tillage on the conventional site. were the and chisel plows. agronomist of the USOA-SCS, Jerald LeMunyon. inputs moldboard survey, the agronomic schedule depicted All agronomic decisions were cooperating shanks a Secondary tillage was performed with field cultivators by majority of farmers using both moldboard in used identical on the A moldboard plow was used for fall All other agronomic conservation fields; a common practice in the study region and activities and conventional tilled (Muhtar, 1982). 3.9 Water Quality Analysis The water quality parameters chosen for analysis were intended to provide information regarding the affect of agricultural drainage on the cultural nitrogen, eutrophication of the Saginaw Bay. Annual loadings of phosphorus, and sediment to the Bay were necessary components Table 2 Agronomic Activity Convent ional Till age Date Conservat ion Till age November, 1980 Chisel plow (corn stubble) Anhydrous Ammonia applied Moldboard plow (corn stubble) Anhydrous Ammonia applied May 6, 1981 Field Cultivate Plant corn l.1* kg/ha Atrazine 384 kg/ha 10-20-20 fertilizer Anhydrous Ammonia 168 kg/ha Field Cultivate Plant corn 1 .1* kg/ha Atrazine 384 kg/ha 10-20-20 fertilizer Anhydrous Ammonia 168 kg/ha November, 1981 Harvest corn Chisel plow Harvest corn Moldboard plow June 1, 1982 Field Cultivate Plant Beans 308 kg/ha 10-20-20 fertilizer Field Cultivate Plant Beans 308 kg/ha fertilizer October 11, 1982 Harvest beans Chisel plow Harvest beans Chisel plow 56 of a water quality model sponsored by the gathered be in this project were to U.S. EPA. used as The field inputs and data model calibration. Samples were analyzed at Michigan for the following Snell Environmental parameters: Group Total in Lansing, phosphorus, soluble phosphorus, ortho phosphorus, nitrate nitrogen, ammonia nitrogen, kjeldahl nitrogen, total total suspended solids, and total volatile solids. Table 3 lists the analysis methods utilized. The USEPA did not consider investigating losses to be consistent with the projects goals. costly and the International Quality (PLUARG, 1978) agricultural runoff did Saginaw Bay. However, herbicide Joint Commission concluded not on and pesticide Sample analysis is Great Lakes Water that herbicides and pesticides from present water quality problems to the as part of a cooperative agreement between the Pesticide Research Center and the Agricultural Engineering Department of Michigan State University, atrazine analysis was performed on samples collected during Spring, 19 8 1. has monitored been frequently Atrazine is a common corn herbicide that in agricultural concentrations were determined by extraction with application of runoff. hexane, Atrazine evaporation, hydrosodium sulfate and analysis on a gas chromatograph (personal communication; R.A. Leavitt, MSU Pesticide Research Center). 57 Table 3 Water Quali ty Sample Analysis Methods1 Parameter Total Phosphorus EPA Method 365-2: Digestion with persulfate and sulfuric acid. Ascorbic acid colorimetric deter­ mination. Soluble Phosphorus Sample filtered before undergoing procedure described for total phos­ phorus analysis. Ortho Phosphate Sample filtered but not digested before ascorbic acid colorimetric determi nation. Nitrate Nitrogen EPA Method 353.3: method. Ammonia Nitrogen EPA Method 350.3: Electrometric determination with Orion specific ion electrode. Total Kjeldahl EPA Method 351.4: Digestion with sulfuric acid and potassium sulfate utilizing mercuric sulfate as a catalyst. Electrometric determination Orion ammonia ion electrode. Total Suspended Solids Nitrogen Total Volatile Solids Cadmium reduction EPA Method 1A0.3: Gravimetric determination of known sample volume at 10** degrees C. EPA Method 160.A: Gravimetric determination of a known sample volume at 550 degrees C. 1A 11 methods refer to U.S. E.P.A., 1979 3.10 Soil Measurements « Selected physical and chemical characteristics of the subsurface soil surface and horizon of each plot were analyzed periodically during the course of the study. Samples were analyzed at the Michigan State University Soil Testing Laboratory for: phosphorus potassium cation exchange capacity pH magnesium calcium organic mattercontent texture All surface samples composite of 20 (0-30 cm) samples Subsurface samples taken sent at to the testing lab were a different locations in the field. (30-70 cm) were each analyzed separately and average values of each parameter were then obtained for each plot. Ten soil cores were obtained from horizons of each plot on June 6, 19 8 1. the soil moisture vs. matric soil. characteristic potential) placed surface and subsurface These cores were used to develop curve (volumetric moisture content and to determine bulk density and porosity of the Gravimetric measurements samples the of the water content were made on on a pressure plate and subjected to pressures of 0.10, 0.33t 0.5' and 1.0 bars. 3.11 Statistical Model and Analysis Traditional statistical comparison tests employed in agronomic plot studies are not capable of describing the degree of difference in the 59 water borne edge of obtained from combinations hydrologic field weather losses driven of storm, events is from the occurrences soil, and crop two study are the plots. Data result of unique characteristics. Sampling not a controlled process that permits replicated observations of a specific process. Paired comparison tests are between treatments constant. often used evaluate differences when conditions affecting the outcomes are not held However paired comparison tests used in many plot studies are predicated on the assumption that the differences of each pair will be normally distributed. positively skewed Weather generated hydrologic processes tend to be with large variations expected in the magnitude of differences from each pair of hydrologic large to magnitude data. Infrequent storms of may generate runoff, nutrients, and sediment orders of magnitude greater than the expected mean loss from a given event. Aull (1980) utilized differences in water management practices. statistic can be non-parametric borne edge-of-field determined without regard The null to losses The null distribution of underlying population distribution. Wilcoxon statistics a quantify resulting from two non-parametric to the test shape of the (Ho) of the hypothesis rank-sum test for comparing two treatments postulates that the population distributions of each treatment are identical. hypothesis the postulates only that the distribution The alternate of one of the populations is shifted to the right or left of the other population. Non-parametric statistics are establishing population differences. a conservative approach for If the null hypothesis is rejected with non-parametric tests and the population actually fits a specific probability distribution the null hypothesis would also be rejected with 60 the appropriate parametric procedures. Parametric tests are generally more efficient and have shorter confidence intervals than non parametric methods. Cases arise,therefore, when the null hypothesis rejected by non parametric tests but rejection will will not occur be when parametric procedures are utilized. A two step approach was used to compare the differences between the conservation tillage treatment and the conventional tillage treatment. All constituents monitored during runoff events were tested to determine if identical distributions occurred in the losses from each field as well as the concentrations found in surface and Wilcoxon chosen signed since difference. it rank non-parametric encompasses both test the flow. The for paired comparisons was type and magnitude of the The results from each event constituted a single data pair from a unique set of storm and soil conditions. was subsurface rejected at the 95% probability level, If the null hypothesis no further testing was performed. The signed rank non-parametric test did not demonstrate significant differences in losses of sediment, total phosphorus, or TKN between the two tillage treatments. Over the course of the study field and lost 2.7. the conventional 1.5 times the quantity of those respective constituents than was discharged from the conservation field. Tests based on an lognormal distribution were employed to gain further insight into the relative differences of these constituents. The comparison of nitrate nitrogen losses from the two complicated by the was the suspected contamination of a runoff sample from the conservation tillage field during Event 5 restricting fields statistical (Section 5*2). Instead of analyses to the reported concentration of 61 that sample a range of concentration was utilized. were employed using a low estimate concentration found in the overland flow of Non parametric tests 2.3 from mg/1 the (equal to conventional the field during Event 5) as well as on the reported concentration of 29 mg/1. Hydrologic occurrences are frequently exponential distributions. modeled with lognormal or These distribution patterns account for the infrequent occurrence of large events which cause the mean to lie to the right of the median. For sediment, total phosphorus, and TKN, differences in the mean loss of the logarithm of the loss/event for each tillage system were tested. A Students t test was used to compare the means from all eleven events and from the six largest events. tests based on However, a lognormal distribution did not result in significant differences in the losses of any of the constituents tested. 62 CHAPTER k METHODS: PREDICTING OVERLAND RUNOFF AND EROSIVE EVENTS k.1 Overview The interactions of storm volume, storm intensity, soil cover and antecedent soil moisture combine to produce the variety of runoff events that occur at a given location. Large precipitation events are often capable of generating overland runoff during periods when the antecedent soil moisture is at or below field capacity. Large precipitation events however, are generally uncommon occurrences at a given location. of moderate depths that often occur on a yearly basis may overland not Storms generate runoff unless antecedent soil moisture is above field capacity or the event is of particularly high intensity. Overland runoff is the primary carrier of sediment from agricultural croplands. To and phosphorus gain insight into the likelihood of runoff and sediment loss occurring during periods of varying residue cover and crop development, the following analyses were performed: 1) The magnitude of 2k hour storm events of various return intervals was determined for monthly, seasonal, and yearly periods. 2) The probability of storms occurring at different antecedent moisture conditions during each monthly period from March I - October 31 was determined. 3) The probability of occurrence of excessive rate storms was found for each monthly period from March 1 to October 31* L) The probability of excessive rate storms occurring at different antecedent moisture conditions during various periods of the year was determined. 4.2 Storm Frequency Analysis The Extreme Value Method (Chow, 1964) was utilized to determine the the magnitude of a 24 hour rainfall event to be expected at 2, 5. and 10 year recurrence intervals. of This analysis also generated the probability various magnitude storms occurring at different periods of the year. Rainfall magnitude was analyzed basis. Chow (1964) concluded on a that monthly, seasonal, homogenity of and the yearly data can be maintained if data are selected from a specific period of the year. each period of interest, the extreme value series was obtained by selecting the maximum value of daily precipitation that occurred each of 31 years of record. The data For base during used in the analysis consisted of 31 years of daily precipitation (1950 - 1980 ) recorded to the nearest 0.01 inch at the Caro State Hospital (U.S. Dept, of , Commerce, 1950-1980); the nearest N0AA weather station to the data were study plots. The provided on computerized files by the Michigan Department of Agriculture/ Division of Climatology (MDA/DC). Analysis was performed on precipitation that occurred from March 1 to October 31 to assure that snowfall events were not included in the analysis. The general equation for hydrologic frequency analysis (Chow, 1964) was uti1ized: x/xmean«l+Cv*K where x: variate of a random hydrologic series xmean: arithmetic mean of the series (3) 64 Cv: coefficient of variation K: frequency factor Equation in (3) is applicable to many probability hydrologic frequency analysis. to obtain the frequency factor be distributions dsed A lognormal distribution was chosen (K) since the distribution is expected to bounded by zero on the left, and positively skewed (Haan, 1979)* In the lognormal distribution: y*ymean + K*Sy (4) where y=l n (x) ymean* arithmetic mean of the y values Sy^standard deviation of transformed x values K was obtained from Chow (1964) based on the transformed coeffient of variation and the desired return interval T-l/P (X.GE.x) (5) where T=*return interval P«Probabi1ity X“Randomly occurring storm GE*greater than or equal x*»storm of a given magnitude 4.3 Antecedent Soil Moisture The soil moisture precipitation overland event runoff and content will that influence subsurface tile exists the at the inception of a quantity and distribution of flow. Storms occurring when 65 antecedent soil moisture is near saturation have a greater likiihood to generate overland flow and carry sediment from the study plots. (1969) used the 5 day antecedent rainfall moisture. levels of each antecedent precipitation level to represent dry (AMC III) soil conditions. The transition occurs in one at the inception of the growing season. to be a rough approximation of soil infiltration (AMC I), average The AMC range (1,11, or I'll) is lower during the dormant season than during the growing season. and (AMC) as an indicator of soil The runoff model he developed for the USDA/SCS utilizes three (AMC II), and nearly saturated for Mockus were not step Mockus considered the AMC index moisture considered. used however, and represents a well discrete known since evapotranspiration The AMC index has been widely basis for comparison with other regions. To obtain the probability of occurrence of each level index at various time periods precipitation records for Caro Commerce, 1950-1980). of the AMC and conditions, the 31 years of daily Michigan were utilized (U.S. Dept, of A computer program was created to keep a constant tally of the previous 5 day precipitation. The AMC status of each during the 31 years was classified by the criteria listed in Table k . day 66 Table k Classification of Antecedent Moisture Conditions (AMC) (Numbers represent total PPT during previous 5 days) AMC I (mm) AMC II I (mm) AMC I I (mm) dormant season < 12.7 12.7-28.0 > 28.0 growi ng season < 35.6 35.6-53*3 > 53-3 The growing season was defined differently Corn is planted approximately May ^ studied. growing season was defined to be from June 1 beans, the other later than corn. season was division common crop, between as the dormant and the two crops in the study region. to September 30* Its Field are planted approximately three weeks The beans emerge rapidly defined for however and their growing period from June 16 to September 30. growing season was based The on when evapotranspiration might begin to accelerate due to the growing crop. The AMC statusof each generate the natural day was probability determined estimator and then summed for each AMC level. to The natural estimator is defined as the: Number of occurrences of a given AMC level/Number of total possible occurences. Three separate monthly evaluations of AMC occurrences were performed: 1) P(AMC) : The probability of each AMC condition occurring during each period, regardless of daily precipitation. 2) P ((AMC) iJSL) : The conditional probability of having a given antecedent moisture level when daily precipitation (SL) was greater than or equal to 2 5 .^ mm. and less than 5 0 .8 mm during the dormant season or 67 60 mm during the growing season. 3) P ((AMC) i jSM) : The conditional probability given a precipitation event of a given AMC level (SM) greater than or equal to 12.7 and less than 2 5 .^ mm. k.U Estimates of Occurrence of Excessive Rate Storms Excessive rate storms have been credited with the erosion and runoff from agricultural croplands. excessive rate Michigan. generating of Longterm records of storms do not exist for most of the weather Noweather station within 50 km. much stations in of the sampling sites had records on the occurrence of excessive rate storms. The nearest weather station to the site with a record of excessive rate storms is the Flint, Michigan station approximately 70 km south of the site. The Flint station, however, has only 16 years of record, less than the 20 years of record considered as the minimum for a representative climatic sample by Van Te Chow (1964). The most extensive record of excessive rate storms was found to be the Deer Sloan rain gage network located 1A0 km SSW of the study site in Ingham County, magnitude MDA/DC. analysis. and Michigan. Twenty-five years of date of all The records from excessive five of storms were available from the 22 gages were selected for Gage selection was based on the following criteria: 1) A gage eligible for selection problems the continuous records of the with wind, had to have had leakage, obstructions, or machinery no history of (Merva et al., 1971; Nurnberger, MDA/DC, personal communication). 2) The gages chosen were in the most northern portion of the network. 68 The gages selected for analysis were numbers 1, 3* 17* 18, and 19* These gages were located within a 6 x 2 km area. All the excessive storms with a total depth greater were recorded from each gage. than 12.7 mm The average number of excessive rate storms of various depths occurring during the semimonthly periods from March 1 to October 31 was then computed. To the check the applicibi1ity of the data set obtained from Sloan the Deer network to the study region, the data were compared graphically to the limited data available for Flint, Michigan (70 km south of the study region) and to Alpena, Michigan (130 km north of the study site). 1958-1972, records of excessive rate stations (U.S. permitting a Dept, of Commerce, storms comparison were 1958-1972). based from During the years kept on data 15 at all years three of data A similar distribution pattern of excessive rate storms occurred at all three locations (Figure 13) • The probability of estimated for October 31* had not each occurrence semimonthly of an and excessive monthly rate period storm from March 1 to Since a computerized data base of all precipitation been established for the was events Deer Sloan network, the number of excessive rate storms was compared to the total number of storms greater than 12.7 mm recorded at the East Lansing weather station for the same period of record. approximately 15 The East kilometers Lansing from the weather station gage network. probability of an excessive rate storm (X) occurring is located The conditional during any given period was computed as: P(X{S)« Number of excessive storms Total Storms where (1957“ 198l)per period/ (1957“ 1981) per period (6) X“ excessive rate storms greater than or equal to 12.7 mm. S= all 2 k hour storms greater than or equal to 12.7 mm. The actual probability of an excessive storm occurring during any period was computed as: P(X)=P(S) x P (X jS) (7) where P (S): l».2) was obtained from hydro logic frequency analysis (Section . It.5 Occurrence of Excessive Rate Storms at Varying Levels of AMC The amount of precipitation that occurred during the 5 clay previous to an excessive rate storm in the Deer Sloan sample area was estimated from rainfall records obtained by station. If an excessive rate storm the East East weather Lansing, the of the previous day and following day were checked to compensate for any errors due to the difference in the definition day. Lansing was recorded on a date when a comparable amount of precipitation did not occur in record periods of a recording The conditional probability of a given AMC condition given that an excessive rate storm occurred was found from: P ((AMC)i!X)* Total number of days of with excessive rate storms (AMC)i / Total number of days (8) where i-1,2, or 3. The actual probability of an excessive rate storm occurring at a given AMC level was then defined as: P (X, (AMC) i)* P(X) x P ((AMC) i |X) (9) 70 1».6 Precipitation Excess Crops can be expected to influence the daily soil moisture through evapotranspiration. Soil balance planted to an actively growing crop will lose considerably more moisture than fallow ground. As the soil moisture declines, both the storage capacity of the soil and the initial rate of infiltration conditions will can be reduce expected the to likelihood increase. of Both overland of these runoff during a precipitation event. Sites planted to corn can be expected to lose more soil moisture as evapotranspiration during May and beans. The comparatively drier corn runoff patterns than the sites June than sites sites planted to field should planted to generate different field beans during this per iod. To compare the relative influence of evapotranspiration crop on each potential overland runoff the mean weekly precipitation excess was computed. weekly from The precipitation excess is defined as the expected mean precipitation minus the predicted mean evapotranspiration from a given crop. developed Estimates of mean weekly precipitation (cm/week) have for been the study region based on 30 years of data from the Caro Weather Station (MDA/DC,Unpub 1ished data). The mean weekly evapotranspiration from corn and determined through evapotranspjration developed by Michigan based a (ETo) Vitosh on the et two was al. Julian step approach. calculated from Mean a field daily regression beans was reference equation (1980) for the East Central District of date. Mean daily expected from each crop (ET) was then computed as: evapotranspiration 71 ET - ETo x Kc (10) where Kc= a crop coeffecfent derived from a separate regression equation « for each crop based on the percentage of the growing season that has occurred by a given date. During the dormant season Kc was set at 0.15- The growing season was defined as maturity. In the study region the corn growing season and to emerge on May 25th. growing season and emerge period is from emergence expected to have a 115 day Field beans have an 80 day on approximately June 10th (Vi tosh et al., 1980; unpublished data, Dwight Quisenberry, State Agronomist, East Lansing, Michigan). to USDA-SCS, 72 CHAPTER 5 EVENT DESCRIPTIONS 5.1 Summary Edge-of-field water borne losses from • the study monitored from February 1, 1981 until September 30, 19 8 2 . plots During the 20 months of study, eleven separate hydrologic runoff events were A hydrologic event was any discharge from either field. period An event of was continuous defined were sampled. tile or overland to begin at the inception of flow and ended when measureable discharge ceased. Each event was generated by specific hydrologic precipitation or snowmelt. from either The runoff events varied in length from 24 hours to three weeks and the magnitude of ranged occurence; the tile and surface flow 30 cubic meters of water (3mm) per hectare up to 710 cubic meters of water per hectare (71 mm). that occurred during the study period. Table 5 lists the runoff events 73 Table 5 Event Summary February 1,1981-October 1,1982 Event Date * 2/ 16- 2 / 22/81 V 9 - V 10/81 4/28- 29/81 5 / 10- 12/81 9/3 - 5/81 9 / 26 - 29/81 9 / 30 - 10/ 2/81 3/11-14/82 3/14-29/82 3/30-31/82 6 / 15- 16/82 6 / 21 -2 3 /8 2 1 2 3 k 5 6 7 8 9 10 11 Conservation System Tile Flow Overland Flow * * Y N N Y Y Y Y Y Y Y Y Y Y Y N Y Y N N Y Y N Conventional Sys Tile Flow Overland ft ft Y N Y N Y Y Y Y Y Y Y Y N Y N Y Y N Y N Y Y Y: Occurrence N: No occurrence *: Sampling difficulty The hydrologic characteristics of each event are given in Table Table 7 summarizes 6. the sediment losses, Table 8 the phosphorus losses and Table 9 the nitrogen losses that occurred in each of the 11 events. The flow weighted mean concentrations of the tile and overland flow from each tillage system are found in Table 10. * Denotes Excessive Rate Storn EVENT SUMMARY: Date 4/09/81 Event Tillage Conservation 1 Conventional Hydrologic Characteristics Crop MGMT Max . 30 Minute R PPT Intensity MT-M/ Factor (C) (MM) (MH/hr) (ha-cm) <5.31 24.0 7.6 22.7 2 16.5 Conservation 61.0 3 4.4 Conservation SI.4 4 11.4 Conservation 85.1 5 55.9* Conservation 48.3 6 7.6 Conservation 21.6 7 9.6 Conservation Snow- 8 — Conventional Melt 23.5 9 27.9* Conservation 31.8 10 50.4* Conservation 19.0 11 Conventional 28.7* 0.44 2.7 0.0 30 0.27 1.1 17o. ill 0.54 2.3 220. 160. 0.13 1.3 73. 311. 0.20 2.0 129. 213 0.13 15.7 560. 72 0.20 24.2 560. 149 0.13 0.7 130. 300. 0.20 1.1 185. 285 MM Level 0 AMC 1 0 AMC 1 1.3 AMC 1 71.1 AMC 3 0 AMC 1 85.1 AMC 3 0.39 412. 63. Snow- 0.45 580. 0 Melt 0.39 0. 278. SnowMelt AMC 3+ AMC 3 0.45 — 0. 105. 0.39 5.6 0. 181. 0.45 6.4 0. 158. 0.27 11.2 0. 66. 0.6B 28.1 0. 88. 0.26 3.4 0. 86 54. 106 41.4 Conventional 6/21/82 32. 14.3 Conventional 6/15/82 0.0 — Conservation 3/30/82 1.4 5 Day AMC 10.3 Conventional <14-28/82 0.31 5.7 Conventional <11-13/82 63. 121.0 Conventional 9/30/81 0. 10.0 Conventional 9/26/81 1.5 4.2 Conventional 9/03/81 0.44 6.1 Conventional S/10/81 Tile Flow (M3ha.) 6s. 3.5 Conservation 4/28/81 RxC "1.1 Overland Flow (H3/ha.) u. 8.8 AMC 1 0 AMC 1 52.5 13.2 0.67 0 AMC 3 Table 7 Event Summary: Date 4/9/81 Event * < 1.0 Conservation 3.1 13.2 1.4 3.4 Conventional Conservation 1.5 5.7 10.7 12.7 1.0 < 1.0 2.6 1.2 Conventional Conservation 2.8 9.7 52.2 < 1.0 1.8 1.0 < 1.0 13.3 ^ Conventional 2.6 40.1 Conservation 6.7 22.8 < 1.0 ** 10.0 a* ^ Conventional 9.0 7 8 g 6/15/82 *: <: **: < 1.0 < 1.0 II < 1.0 Conservation 5 29-7 135.0 Conventional »« 413-0 Conservation 6/21/82 A A Conventional 9/3/81 3/30/82 < 1.0 < 1.0 < 1.0 3 3/1*1-30/82 A Conventional Conservation 5/10/81 3/11-13/82 Total Volatile Solids Overland Flow Tile Flow (kg/ha) (kg/ha) < 1.0 2 9/30/81 Total Suspended Solids Overland Flow Tile Flow (kg/ha) (kg/ha) Conservation 1 4/28/81 9/26/81 Tillage Sediment Losses Conventional Conservation Conventional Conservation 22.1 7.6 A * ** ** 1.0 15.0 » 52.0 5.6 < 1.0 * 25.0 A 5-0 17.0 A 8.0 < 1.0 A it 5.3 A Conventional Conservation 8.1 A 5.9 * 2.9 1.3 Conventional 9.6 264.0 1.4 No flow occurred Less than Not measured * * 34.5 Table 8 Event Summary: Total P Tile Overland Flow Flow Date 4/9/81 4/28/81 Event Tillage 9/26/81 2 || £ 9/30/81 3/11-13/82 3/14-30/82 (kg/ha) Ortho P (kg/ha) Tile Flow Overland Flow (kg/ha) (kg/ha) A 0.004 * < 0.001 * < Conventional Conservation 0.003 0.002 * < 0.001 * < 0.001 ft * < 0.001 * < 0.001 * < 0.001 * < 0.001 * 0.001 k 0.083 0.142 0.067 0.090 0.051 0.064 Conventional Conservation 0.044 0.052 0.208 0.050 0.027 0.042 0.163 0.015 0.026 0.042 0.147 0.015 Conventional Conservation 0.014 0.009 0.054 0.183 0.009 0.008 ■0.044 0.111 .009 0.005 0.037 0.083 Conventional Conservation 0.009 0.046 0.240 0.008 0.033 0.039 0.139 0.020 0.003 0.032 0.117 0.016 Conventional Conservation 0.032 0.014 * 0.029 0.063 0.072 0.023 0.002 0.044 0.056 0.016 .001 0.037 0.026 0.096 * 0.084 A 0.078 0.003 A Conventional Conservation < 0.001 A < < 0.001 < 0.001 0.012 * 0.004 ft 0.072 * 0.015 Conventional Conservation 0.059 0.009 * 0.012 0.002 ft ft Conventional 0.013 * 0.003 * II Conservation 0.027 * 0.008 * ** Conventional 0.027 0.297 0.005 0.032 it* 9 6/15/82 10 *: <: **: Soluble P Overland Flow Conservation ^ Conventional Conservation g Conventional Conservat ion 3/30/82 6/21/82 (kg/ha) Tile Flow 1 5/10/81 9/3/81 (kg/ha) Phosphorus Losses No flow occurred Less than No measurement taken * A 0.010 0.004 ft * A * < 0.001 0.002 A ft AA ♦ Table 9 Event Summary: Date *1/9/81 *i/28 /8 l 5/10/81 9/3/81 9/26/81 9/30/81 3/11-13/82 3/1*1-30/82 3/30/82 6/15/82 6/21/82 Event Nitrogen Losses Nitrate - N Tile Flow Overland Flow (kg/ha) (kg/ha) Tillage TKN Tile Flow (kg/ha) Overland Flow (kg/ha) Conservation 1.3 A < 0.1 J. Conventional 1.2 A < 0.1 A Conservat ion 0.6 * < 0.1 A Conventional 0.5 A < 0.1 * Conservation 3.9 2.0 < 0.1 0.5 Conventional 3.2 *».2 < 0.1 0.90 Conservation l.l < 0.1 Conventional 1 2 3 0.6 0.1 *1 0.8 0.1 • 0.3 0.2 Conservation 0.3 ? < 0.1 0.9 Conventional 0.*i 1.3 0.1 0.8 Conservation < 0.1 < 0.1 0.5 0.2 Conventional 0.18 0.1 0.3 o.*» Conservation 0.2 0.7 < 0.1 0.8 Conventional A 1.8 * * 2.0 5 6 7 0.2 A A 0.1 A 1.0 f: 0.3 Conventional 0.5 A Conservation 0.7 * Conventional Conservation 0.1 0.7 J. Conventional 0.9 1.5 Conservation 1.2 Conventional o.*» Conservat ion 8 A 9 0.3 < 0.1 A 10 II No flow occurred; <: Less than ■ < 0.1 < 0.1 A < 0.1 0.8 78 Table 10 Mean Concentration Per Event (mg/1) Total Phosphorus Event Station 1 2 3 6 5 6 7 8 9 10 11 .u * .06 * .03 .83 .41 0.68 0.17 0.42 0.07 0.33 0.13 0.25 0.15 0.17 0.22 * .10 * .40 .14 0.31 0.43 0.06 0.34 0.17 * A ft A .11 .37 .15 5.50 .25 CR CT 0.06 MR MT 0.05 A 0.95 .28 0.11 A Soluble Phosphorus Event Station CR CT 1 2 * ** * ft* ft MR MT A* ft AA 3 4 5 6l 7 8 9 10 11 .53 .33 .21 .14 .20 . 11 .11 .13 .24 .14 .03 .14 * .08 A A .03 .09 . 08 * * .01 * .04 * .03 .59 .05 •74 .17 •34 .04 .25 .05 A . 08 LSoluble phosphorus content estimated based on ratio from Event 4 and Event 5 (average ratio used) Ortho Phosphate Event Station 3 4 5 6* 7 8 9 A AA .38 .24 .21 .14 .15 .07 .10 .11 .06 <.01 0 <.01 0 A A .06 ** A AA .67 .16 .29 .04 .21 .02 .20 .06 .13 * 0 < .01 0 .03 <.01 * .03 1 2 CR CT A AA MR MT A AA 10 11 ** ** z0rtho phosphorus content estimated based on Op/Tp ratios In Event 4 and Event 5 CR: Conservation system overland runoff CT: Conservation system tile runoff MR: Conventional system (moldboard plow) overland runoff MT: Conventional system tile runoff *: No flow occurred **: Not measured 79 Table 10 cont'd Mean Concentration Per Event (mg/1 ) Total Suspended Solids 1 2 CR CT * 1. A MR * MT 1. Station 9 * 3 3 Event 5 6 1* 78 15 133 49 9. 98 13 18 7 8 9 10 A A A A 79 138 80 93 14 175 328 22 79 72 16! 32 712 17 it 11 A A A 72 108 92 69 4900 91 11 Total Volatile Sol ids Event Station 1 CR * CT ** MR MT * ** 5 24 7. 1* 16 2. 7 12. 6. 14 2. 2 3 * 20 ftft ft ftft 6 7 8 9 10 ** * JU A A aa 36 16 20 28 9 18 ** 90 3 aa A * 7 51 33 15 640 13 7 8 9 10 11 1.9 A A A 0.8 0.7 1.5 < 0.2 0.5 14.1 0.5 A A Total Kjeldahl Nitrogen Event Station 1 * 4 3 2 CR CT * <0.01 < 0. 01 2.9 MR MT * * <0.01 < 0.01 4. 1 0.1 0 . 1 5 6 1.6 2.0 1.6 0. 1 1. 8 1.7 1.8 1. 2 1.4 0.9 2.1 1-1 3.4 A A A A 1.1 2.1 0.2 A Ni trate Ni trogen Event Station 1 CR CT * 19.4 MR MT * 19.0 CR: 4 5 6 7 8 9 10 11 29.0 0. 1 A A A 3.9 0.3 1.7 2.7 A 19.5 0.4 3.6 4.3 5.8 2.0 8.1 19.1 0.6 2.3 0.5 3.1 A A A 12.4 20.0 3-8 2.9 0.6 A 3.7 3.0 8.1 8.1 2 A 17.9 a 17-9 3 11. 8 Conservation system overland runoff CT: Conservation system tile runoff MR: Conventional system (moldboard plow) overland runoff MT: Conventional system tile runoff A• No flow occurred AA; Not measure d 8o 5.2 Snowmelt: February l6 -February 22,1981 The first runoff event was marred by the backup and failure of receiving ditch, the Sphon drain. and deepened the preceding fall, snowmelt several to a runoff: Several the Although the ditch had been cleaned it did not provide an outlet for factors accounted for this failure. the During intense snowstorms the ditch had filled with densely packed snow depth of approximately 2.5 meters. In addition, the ditch ran on an east west transect and the southern bank shielded the snow direct rays of the sun for most of the day. from the Consequently the snow in the ditch melted more slowly than the snow on the field and exhibited a low permeability to flowing water. When overland runoff began to leave the unable to exit two study plots it was the fields since the snow in the ditch was effectively damming the outlets. Meltwater from the ditch and runoff waters from the plots backed up onto the fields and into the tile, contaminating the runoff waters and obscuring precise measurements of drainage volume. Flow was not accurately represented by stage height for overland or tile flow. Although samples were obtained they have not been used to calculate field losses. 5.3 Event Is Apri1 9*10,I9 8 I On April 9* >981 24.0 mm of precipitation fell on generating subsurface tile gage had not yet been fully rainfall records from flow from both fields. installed the Vassar at the Weather the study site The recording rain site, Station however, hourly (U.S. Dept, of 81 Commerce, storm 19 8 1) located 16 km south of was of low intensity maximum hourly precipitation Vassar was 8 mm/hr. the that the and occurred over a 10 hour period. The associated study with indicated the storm recorded at The rainfall erosion index (R) of the storm was 3*5 MT-m/ (ha-hr). No agronomic activity had occurred on either plot tillage. Residue 300 kg/ha of 0.31 for the The conventionally fall tilled residue with a 10% cover on the plot. plot Based on the (1978 ), the crop management factor findings of Wischmeier and Smith was the cover following fail tillage was 3500 kg/ha with 58 % cover on the conservation tilled plot. had since conservation plot (C) and 0.44 for the conventionally ti1led plot. Antecedent soil moisture at event was AMC I since the total inception precipitation of the precipitation during the 5 day period preceding the event was 8 .5 mm, below the 12.7 mm considered the average condition for runoff events in the dormant season. No tile flow was occuring when the precipitation event began suggesting that the soil was at or below field capacity. A total of 6 .3 mm of water was discharged tile of the conventional conservation field. Actual the No field overland through the subsurface compared to 6.8 mm of water from the runoff occurred on either field. losses of nutrients and sediment represented a small fraction of total generally measured low with over the the entire exception of period. Concentrations n?trate-nitrogen. weighted concentrations of nitrate-N on both fields were Mean were flow approximately 19 mg/1, among the highest measured in tile waters during the study. 82 5.4 Event 2: April 28-29, A low intensity storm generated plots on April 28, 1981. 13 hour period. subsurface tile flow from A total of 22 mm of precipitation fell over a The maximum 30 minute intensity was be classified as an excessive rate storm. measured at 16.5 storm was 6.1 MT-m/(ha-hr), The rainfall erosion index of nearly twice the "average" rainfall erosivity that is expected to occur during the second April both well below the 25 mm/hour intensity necessary for the event to mm/hour, the 1981 (3*9) part of (Wischmeier and Smith, 1978). No agronomic activity tillage. The crop management since the April 9th Event. the ground surface had occurred factors on either plot since fall (C) were essentially unchanged The actual rainfall erosivity that impacted (R-C) was 2.41 on the conventionally tilled field vs. 1 .70 on the conservation plot. During the occurred, 5 placing days the preceding antecedent below average runoff conditions. quite small; the event, no precipitation had soil moisture condition into AMC I, Subsurface flow from both plots was 3*0 mm from the conventional plot compared to 3 *2 mm from the conservation field. This represented the smallest quantity of from any event during the entire sampling period. flow As in Event 1, actual nutrient and sediment losses were very small, but the mean flow weighted nitrate nitrogen concentrations in the tile flow from both fields were approximately 18 mg/1, more than twice occurred over the entire study period. the mean concentrations that 83 5-5 Event 3: May 10-12, An unusually large, and subsurface 19 8 1 low intensity storm generated overland that 19 8 1. tile flow from both study plots during May 10-12, Over a period of 31 hours 61 mm of precipitation occurred. volume runoff fell The maximum a 2k hour period during the event was 5 0 .2 mm. over Based on hydrologic frequency analysis, this represents a 23 year return interval storm for the month of May. The maximum 30 minute intensity of the storm was only k . k mm/hr the lowest value of any of the precipitation events which generated surface or subsurface flow. MT-m/(ha-hr), the The rainfall erosion index (R) was found to be second lowest erosivity of the 11 events monitored. The surface conditions of both plots had been altered since of April. Secondary k.2 tillage (field cultivator), the events planting, fertilization had concluded on May 6, 19 8 1; four days before the and event. Residue was measured to be 2200 kg/ha with 35% cover on the conservation field compared to 300 kg/ha with 3% cover on the conventional field. crop growth emergence had occurred on either field. residue conditions, the crop management factors No Based on crop and (C) were 0 .5 k for the conventional field vs 0 .2 7 for the conservation field. The antecedent moisture condition at the inception of the event was classified as AMC I, below the normal conditions for overland runoff. Only 1.3 mm of precipitation had occurred during the the event. conventional days preceding Of the 6l mm of precipitation, 22 mm left the conventional field as overland runoff conservation 5 plot. plot compared Subsurface vs. 28 mm on to approximately drainage the removed conservation 17 mm 16 plot. mm from the on the Technical 84 difficulties with the Isco Bubbler flowmeter on the conservation plot prevented an accurate measurement of overland flow on estimate of overland runoff was based on the that plot. The curve number method « (Mockus, 1973) . accurately The runoff modelled by volume a curve on the conventional number 78. of field was Based on S.C.S recommendations for modelling fields with residue the curve number was reduced to 78 for estimate of 17 mm is probably in excess of left (USDA/SCS, 19 8 1) . the conservation field the actual quantity The which the field since the total drainage from the conventional field was 17% less than from the conservation field. During each of the four other events where both overland and subsurface flow occurred, the total water loss from each field was always within 12%. of the surface dramatically runoff A slight overestimate from the conservation field however, would not influence the total losses of any water borne constituent over the entire study period. On both suspended plots the May 10-11 event generated the solids of losses of that resulted from the six events with overland flow. Suspended sediment losses were under 20 kg/ha from levels lowest soluble nutrients both fields. High however, were lost from both plots. event discharged the largest quantity of soluble phosphorus lost The from each plot during the study. A total of 0.19 kg/ha of soluble phosphorus came off field the conservation conventional field. compared to 0 .1 6 kg/ha This represented 32%and 33% of all of phosphorus respectively,that was lost during the two seasons Soluble phosphorus field. the the soluble of study. comprised 70% of the total phosphorus lost from the conservation field vs. conventional from 75% of the total Of the 62 kg/ha of phosphorus lost from the phosphate fertilizer applied, 85 0.5% left each field as soluble phosphorus during this Event. Losses of nitrate nitrogen were also high compared monitored. Combined surface losses to each field. exceeded the events and subsurface losses totalled 7*4 kg/ha from the conventional field and 5*9 kg/ha from the Nitrate-N to conservation field. accounted for 3"4% of the nitrogen fertilizer applied The quantity during only one of nitrate-N Event, lost September from 26, each plot was 1981,-and that loss estimate is subject to question. A mixture the soil of 308 kg/ha of 10-20-20 fertilizer had been banded and an additional 168 kg/ha of anhydrous ammonium knifed the soil four days preceding the event. phosphorus was lost into Less than 0.5% of the into applied as soluble P whereas 3”4% of the applied nitrogen was lost as nitrate nitrogen. Atrazine had been applied at a runoff event, a total discharged from the concentrations rain of 1.4 kg/ha. 10.4% and 8.6% of the conventional and The event represented a worst immediately following application LC-50 mg/1 for by the applied atrazine was conservation samples had concentrations well below the cited During fields. Atrazine in the overland flow ranged as high as 0.6 mg/1 from the conventional site. major of rate Triplett et a ! . (1978) case scenario of a of the herbicide. All concentration 4.5 the of most sensitive fish species. 5.6 Event 4s September 3“5•1981 Surface and subsurface flow was generated on both plots by a moderate intensity storm that occurred on September 3•1981 - 53 mm of precipitation fell over a 12 hour period. The large A total of maximum 30 86 minute intensity was 11.4 mm/hour. A storm September is expected to have a return interval hydrologic frequency analysis. computed as 10.0 MT-m/(ha-hr) The of rainfall complete canopy cover over the soil. years erosion based index on (R) was event and afforded for the a (C) for conservation field. cover reduced the effective rainfall erosivity impacting on the soil surface 1.3 8 The crop management factor the conventional field was 0.20 vs. 0 .1 3 canopy this magnitude in for the storm. The corn crop was fully mature during this The of (R-C) to 2.0 MT-m/(ha-hr) on the conventional field and MT-m/(ha-hr) on the conservation field. These erosivity values are comparable to those which occurred during the low intensity event of May 10- 11 , 1981 . Antecedent soil moisture was in the AMC III category, moisture levels associated with normal runoff conditions. above soil A total of 71 mm of precipitation had occurred in the 5 days preceding the event. flow rates had Low been observed in the subsurface tile of both fields 48 hours before the event, indicative of the relatively high soil moisture 1evels. Losses of suspended solids were quite low with each field were under 20 kg/ha. greater than sediment bound nutrients. Losses total losses from of soluble nutrients were Soluble P comprised 56 % of the total P lost from the conservation field and 78 % of the total phosphorus from the conventional field fields, 64$ was (Table 8). Of the nitrogen which left the lost as soluble nitrate-N from the conventional field compared to 6l% on the conservation field (Table 9). Compared to total losses from all 11 events over the two seasons of study, however, losses of soluble P and N from event 4 represented only 9% of the cumulative 87 losses from the conventional field and 12% from the conservation field. 5.7 Event 5: September 26-29. On September 26, 1981 8l mm of plots over a three hour 19 8 1 precipitation period. fell necessary to be classified the study The storm was very intense with a maximum 30 minute intensity of 58 mm/hr, well above the mm/hr on as magnitude of the storm was exceptional. an minimum 25 of excessive rate storm. The storm's magnitude The equalled the largest recorded storm during 19^0-1980 at the Caro weather station. More rain fell in three hours than the average for the entire September this in region (U.S. Dept, of Commerce, 1971)* month of The annual expected return period for a storm of this magnitude is 25 years. The erosive force of the storm as estimated by the rainfall erosion index was 121 MT-m/(ha-hr), equivalent force expected during the period from existing corn surface 1 to November 30• The crop provided a total canopy cover and shielded the soil from direct raindrop impact. soil April to the total average erosive measured The effective erosive force impacting the by the rainfall erosion index (R-C in the USLE) (Wischmeier and Smith, 1978) was reduced to 2 k .2 MT-m/(ha-hr) on the conventional field and 15*7 MT-m/(ha-hr) on the conservation field. Soil antecedent moisture was at AMC I when precipitation the event began. had occurred during the 5 days previous to the event. unusually large portion of the 81 mm of precipitation exited the via overland flow. the An fields On the conservation field 56 mm of overland runoff was recorded compared to 7*2 mm of subsurface tile flow. from No conventional field Overland flow was 56 mm and subsurface flow was 15 mm. Records of overland flow from the conventional site were disrupted by a 88 malfunction of the Isco bubbler flow meter. The meter functioned correctly for part of the event and visual observation of stage on the H 30 flume at flow. From both plots 69 % of the precipitation came off the an overland minute intervals were utilized to estimate total overland runoff. fields as This is nearly twice the proportion that occurred during any of the other 11 events. During the runoff event the receiving ditch experienced some backup resulting in submerged field and 11* hours on tile the outlets for 10 hours on the conventional conservation field. Loss estimates for constitutients carried by subsurface flow during this event were for the period of free flow after the backup period. by ignoring the The total error incurred flow during the tile submergence is relatively minor, since most of the drainage was in the form of overland flow. Considering the great erosive force of the storm, were relatively small. sediment losses Suspended sediment losses were 53 kg/ha on the conservation field compared to 43 kg/ha on the conventional field. The mean flow weighted concentration of suspended sediment from either field did not exceed 100 mg/1, well below the 800 mg/1 standard recommended by the U.S. EPA. Although mean flow weighted concentrations of most not high relative to the other events, the nutrients large volume of water draining from the field generated comparatively high losses. events, 21% of the total conventional field during this P and event. were For all 11 25% of the soluble P came from the Losses from the conservation field accounted for 25% of the total P and 25% of the soluble P measured during the study period. Nitrate nitrogen losses were substantial from each tillage system. A single composite sample of overland flow from the conservation tillage field was found to have unusually high concentrations all other nitrate measurements of Since made during the month of September on both surface and subsurface flow did not concentrations (29 mg/1). exceed 5 mg/1 and the TKN the flow were within the normal range, contamination of the sample seems likely. 5.8 Event 6: September 30“0ctober 2,1981 Overland and subsurface flow from both plots were generated by a 48 mm, low intensity storm on September 30. 1981. intensity was 8.0 mm/hr. The storm magnitude The maximum 30 minute has a six year return period for the month of September and a two year annual return interval. The rainfall erosion index (R) was computed to be 5*7 MT-m/(ha-hr) for the event. The crop was at the same stage as it was during same crop management impacting the conventional soil field (C) factors were used. surface vs. (C-R) was These were the lowest values of any of the 5 and the The expected erosive force 1.1 0.7 MT-m./(ha-hr) event MT-m/(ha-hr) for the for the conservation field. six events that generated overland flow. When the event began, the soil antecedent moisture condition was in' the AMC earlier. subsurface III category; 81 mm of precipitation had occurred four days Most of the flow from both fields was discharged tile. Low concentrations of through the nutrients and sediment were measured in both the overland and subsurface discharge waters. of nutrients and sediment from the event were comparatively minor. Losses 90 5*9 Event 7: March 11-March 1A, 1982 All of the 1982 snow pack ran off the study fields during Event Snow cores taken March 6 , 1982 indicated an average of 32.3 mm of on liquid water equivalent on the conservation field compared the conventional field. On snow quicker the conventional conservation system's snow pack. 20 - 30 % mm 11, 1982 5.1 mm of rain fell, the March each on 3 0 .8 to temperature rose to 6 C and overland runoff began at cover 7* system melted By the evening of field. March The than the 12th, only of the conventional field had either snow or slush compared to a 50-60% snow cover on the conservation system. The antecedent soi1 moisture was AMC III since the ground was partially frozen and saturated from melting snow. During the first 38 hours of snowmelt overland flow discharged 1 9 .5 *nm of water from the conventional field compared to 11.0 mm from the conservation system. The receiving ditch proved to be a satisfactory outlet for snowmelt runoff. In for snowmelt monitoring, on February 18, 1982 preparation the ditch had been cleared of snow by a hydraulic backhoe, and was an On March 13. 1982, 16 mm of rain fell on the fields, generating an excellent transport system throughout the spring season. additional from the kO mm of overland flow from the conventional field and 30 mm conservation essentially free field. By March ]l»th, during the systems of snow or slush and overland flow ceased. began from the conservation field on March 13th water both next 2k hours. and drained were Tile flow 6 mm of No tile flow was generated from the conventional field during event 7* The erosive forces of rainstorms the and snowmelt runoff. runoff event were the result of 2 The snowmelt erosion index (Rs) was 6.6 91 MT-m/(ha-hr) . This estimate is based on the occurence precipitation from December 14, until the begining of event 7* the storms of March 11 1g81, Corn cm The rainfall erosion index computed and of for March 13 was 0.7 and 3-0# respectively, for the snowmelt residue on the conservation field was 2300 kg/ha with 56$ cover corresponding to a crop management cover 6.1*5 when the soil began to freeze resulting in a total erosion index of 10.3 MT-m/(ha-hr) event. of C factor of 0.39. Residue on the conventional field was at 10% for a C factor of 0.45* effective erosive force of the event was 4.0 for the conservation The field compared to 4.6 for the conventional field. Appreciable quantities of sediment left the fields. 50 % study, of the For the entire suspended solids lost from the conventional system came from this single event compared to 45% from the conservation field. Snowmelt sediment losses from the conventional field were 413 kg/ha, nearly three times greater than the loss from the conservation field Losses of nutrients were comparatively low (Tables 8 and 9) • Mean (135 kg/ha) . concentrations of total and ortho phosphorus in the overland flow were the lowest of the six overland flow period 8% of the total P and events. 14% of For the total the soluble P came from the conventional field compared to 10% and 12% from the conservation Mean flow weighted sampling field. nitrate nitrogen concentrations were well below 10 mg/1. A high proportion of the nutrients lost in the runoff were soluble fraction. Soluble in the P losses comprised 67% of the total P lost from the conservation field and 88% of the total P from the conventional field. Nitrate nitrogen comprised roughly 50$ of the total N lost from 92 each field. 5.10 Event 8: March H-March 30. 1982 During the period overland runoff from occurred. March Tile flow from each field displayed a afternoon and dropping each 1982 1^-30, no precipitation flow occurred from both fields. diurnal night. pattern, rising or The during the A snow drift in the conservation field melted during this period and comprised 25 % of the total tile flow off that field. The drift was along a windbreak on the west boundary of the field and covered roughly 8% of the field with 25 to 35 cm of The snow. losses given in Tables 8 and 9 have been multiplied by a correction factor of 0 . 7 ^ to eliminate the effects of the drift from the system compar isons. Corrected runoff losses during Event 8 were 105 conventional sediment were were low (Table 10). tile flow was small. conservation from field and 278 cu-m/ha from the conservation field. of all nutrients and concentrations cu-m/ha small since mean flow the Losses weighted The proportion of soluble P in the Only 10% of the total phosphorus field was in the soluble phase. lost from the On the conventional field soluble P comprised 33% of the total P measured. 5.11 Event 9: March 30-April 1, 1982 An intense storm of 25>*» mm magnitude occurred on generated subsurface tile flow from both tillage plots. March 30, The maximum 30 minute intensity of the storm was 28 mm/hour meeting the criteria of excessive rate storm. was 1L.3 Mt-m/(ha-hr). 1982 an The rainfall erosion index computed for the storm No agronomic activity had occurred since the 93 fall tillage. The residue status and C factors were the same as existed in event 7. and 8. The effective erosivity impacting the soil surface (R-C) was 6.1* on the conventional site and 5*6 on the conservation site. No rainfall had occurred during the 5 placing the antecedent runoff conditions. the soil moisture days status preceding field arid 16 mm suspended solids field from and total comparatively phosphorus. soluble phosphorus constituted only 20% of the total conservation water from the conventional field. subsurface drainage waters from both fields carried of event, in AMC I, below normal Subsurface tile runoff drained 18 mm of conservation concentrations the P loss and 22% from the conventional field. The high However from Actual (kg/ha) of all nutrients and sediment were minor compared to the the losses entire study period. 5.12 Event 10: June 15-17. 1982 An intense subsurface tile excessive flow rate storm on both fields. on June 15. 1982 generated The storm's volume was 31*8 mm. Based on frequency analysis, a storm of that magnitude occurring June is expected to have a k year recurrence interval. minute interval, 2 k mm of precipitation occurred. intensity recorded was 5 0 .8 during During one 15 The maximum 30 minute mm/hr, well above the 25 mm/hr intensity that is the minimum standard of an excessive rate storm. The erosive force of the storm was 55*2 MT-m/(ha-hr). had been Both fields planted to field beans 16 days previous to the event and were in the seedbed crop stage with small seedlings present. conservation field was Residue on the at 1700 kg/ha with 27% cover, giving it a crop management factor (C) of 0.27 (Wischmeir and Smith, 1978). The crop 3h management factor on rainfall erosivity conventional the (C-R) field vs conventional field was 0.68. impacting the soil 11.2 on surface the entire study. The was 28.1 the conservation field. largest difference in the magnitude of erosivity over The effective This was the (16.9) that occurred during the ponding occurred on the conventional No occurred study Soil crusting may have developed as a result of the event. occurred. the conventional field received the highest direct impact from raindrops that infiltration on field puddles suggesting period. Considerable that decreased were observed on the conservation field. No overland runoff occurred from either field. moisture condition at The antecedent soil the start of the precipitation event was AMC I, below normal runoff conditions. In the previous 5 days no precipitation had fallen. Relatively insignificant losses generated by this event. phosphorus, nitrogen, and the course ofstudy. The of event nutrients and sediment were generated less than 2% of the sediment that was lost from either field Soluble P constituted 20% of the total over P lost from each field. 5.13 Event 11: June 21-22, A brief high intensity conditions were edge-of-field intensity near storm that saturation, occurred generated losses from the two study fields. of the storm was 75 mm/hour. greater than this intensity have been raindrop 1982 energy (Wischmeier and found Smith, when large soil moisture differences The maximum 10 in minute Stormintensitiesequal to or to generate 1978). The the maximum storm met the 95 criteria for an excessive rate 30 minute storm with a maximum 30 intensity of 28.7 mm/hour. The storm erosivity as measured with the rainfall erosion index (R) was 13*2. provided by the field beans. surface (R-C) was Less than a 10% canopy cover was No field work had occurred since Event 10 and residue cover was unchanged. soil minute 8.8 The actual Mt-m/(ha-hr) erosivity on impacting the the conventional field compared to 3*^ o n the conservation field. Tile flow occurred from both fields. however, had overland runoff. Only the conventional The overland flow carried extremely high concentrations of suspended solids, volatile solids, and soluble phosphorus. total phosphorus, The tile flows from both fields had nutrient and sediment concentrations within the range found in tile flows the other ten field, events. Losses of conservation field constituted a small nutrient fraction and of sediment the total during from the losses recorded from the field over the study period. In contrast, the losses from the conventional field 28% of the total entire period. only 3*3% P and accounted for 33% of the suspended solids lost during the Overland runoff from this event was mm, representing of the 166.1 mm of overland flow that occurred on that field during the two years of study. Hydrologically, it was the smallest overland runoff event to occur. As a consequence of this single intense storm, the comparative losses of phosphorus and sediment from the conservation and conventional fields were markedly altered. total phosphorus from the Over all the previous 10 events losses of conventional field were 1.06 times greater than from the conservation field. Sediment losses from the conventional field were 1.8 times greater than from the conservation field. When the 96 losses f r o m Event 11 were added to the sum results of the other events, the demonstrate a substantial decrease in the losses of total P and sediment from the conservation field compared to the conventional field. For the entire study period the losses of total P and suspended solids are 1.4 and 2.6 times conservation field. greater than the cumulative did not from the Elevated concentrations of nitrate N were not found in the overland or tile flow from either field event losses measurably alter the during comparative event 11. The losses of nitrogen between the two fields. A unique set of conditions combined to generate losses of and P of such varying magnitude on the two fields. This was the only occurrence of an excessive storm when the soil antecedent high and no crop cover was present. moisture 5 days 52.5 During the mm of precipitation had occurred slightly less than the 53*3 mm defined as AMC III for the growing season, however event was Subsurface flow was occurring at low rates on each field when the precipitation event began. preceding sediment the occurred early in the growing season when crop evapotranspiration was well below the rate expected in midseason. Soil crusting on the conventional accounted for the difference observed. field may have partially While no measurements were taken on soil crusting, the intense storm of June 15# 1982 coupled with the high intensity precipitation of Event 11 may have effectively sealed the soil surface infiltration of and 27% residue cover condi tion. the unprotected promoting that conventional overland flow. should have field, reducing The conservation field had maintained a permeable surface 97 CHAPTER 6 ANALYSIS AND DISCUSSION: FIELD INVESTIGATION 6.1 Precipitation Analysis The field data collected during the strongly effected 20 month study period by the timing and magnitude of precipitation events. Although eleven hydrologic events were sampled, care must be attempting to draw long term conclusions precipitation volume and rainfall erosivity study were were from that the occurred used when data. The during the compared to long term norms to check the variability of the 20 month storm patterns. Table 11 compares the monthly precipitation Caro Michigan 19 8 1 during to be precipitation fell compared to a 30 year mean gamma distributions, dramatically March 19 8 1 was unusually dry. the expected mean. 95$ of all years of are 5>33 either field. However, usually be expected evapotranspiration since is during the low. soil During at During different Only I.U5 cm of cm. expected precipitation during March than occurred in 19 8 1. from recorded 1982 to 30 years of record. and several months, precipitation was found than quantity Based to on have more No drainage occurred March some form of drainage can is often March, partially frozen and 1982 for example, drainage occurred for approximately 19 days from each field. The other precipitation major was anomally 11.5^* cm occurred above during the mean. September The 19 8 1 19*08 precipitation recorded that September was larger than had been when cm of measured 98 Table 11 Comparison of Monthly Precipitation (PPT) March I, 1981 - October 31, 1982 To 30 Year Mean Caro Weather Station, Caro, Michigan Month Mean 1982 1981 (cm) PPT (cm) % of years with more PPT March 5.33 1.45 >95* 6.43 >30% Apri 1 6.38 10 .19 <15* 4.45 >75% May 6.l»8 7.54 <35% 4.17 >70% June 7.84 6.38 >60% 12.12 <15% July 7.42 7.82 <40% 4.67 >70% August 7.52 13.54 <10% 8.38 <40% September 7.54 19.08 <2% 7.01 >40% October 5.84 8.30 <25% 1.85 >85% November 5.77 3.58 >75% -- -- PPT(cm) % of years wi th more 99 in that month during the period 1950-1980 at the Caro Weather Station. Based on gamma distributions for the month of September the magnitude of precipitation during 1981 years (i.e. a subsurface flow accounting for 50 is expected to be exceeded in only 2% year return occurred 48% of from all the period). both Considerable fields runoff during that of all surface and September 1981 occurred from both the conservation and conventional fields over the entire 20 months of study. September Michigan. is not usually Considerable the expected to yield evapotranspiration soil from large runoff events in mature crops is occurring and is expected to have available moisture storage capacity. During 1982 no surface or subsurface flow exited either field throughout the month of September. 6.2 Soil Characteristics The volumetric moisture content and bulk density of the surface and subsurface soils of both fields are given in Table 12. 100 Tab 1e 12 Soil Physical Properties CT Surface Mean S.D. CT Subsurface Mean S.D. Saturation 0.10 Bar 0.33 Bar 0.50 Bar 1.00 Bar 0.U2 0.31* 0.31 0.30 0.30 0.02 0.01 0.01 0.01 0.01 0.39 0.27 0.27 0.27 0.26 Bulk Densi ty (g/cu cm) 1 .56 0.05 1.70 Parameter MP Surface Mean S.D. MP Subsurface Mean S.D. 0.42 0.32 0.31 0.38 Volumetric Moi sture Content 0.01 0.01 0.01 0.01 0.01 0 .3 0 0.29 0 .0 6 0.25 0.01 0.01 0.01 0.01 0.01 0.10 1.67 0.05 0.01 0.02 0.02 0.02 0.02 1.55 0 .2 8 0 .2 6 0 .2 6 CT: Conservation Tillage Field MP: Conventional Tillage Field Using a Students t test, no significant difference at the 95% level was found in bulk density or volumetric moisture content measured in surface horizons of the two fields. field had The subsurface horizon of the conventional a significantally greater volumetric moisture content at 0.1 bars, while the conservation field had a significantly higher volumetric moisture content at 0.33. 0.5, and 1.0 bars. The water storage capacity of each field was considered equal and the average from all measurements was used for calculating the equivalent depth of water at a given tension. The 70 cm approximately additional considered of 6.6 soil cm above the subsurface be could hold of water between saturation and 0.1 bars, and an 1.0 cm between 0.1 and 0.33 bars. to tile Since field capacity is between 0.1 and 0.33 bars of tension for a clay loam 101 soil, the soil at field capacity could hold as much as 6-8 cm of water before saturation occurred. A summary of pertinant chemical analysis is given in Table 13* The organic matter of the surface horizon was tested on October 12, 19 8 1 and found to be conventional k.7% on the conservation tillage field vs field. Using a paired on the comparison test, no significant differences were found between the surface horizons of the two fields in the quantities of phosphorus, calcium, magnesium or the cation exchange capacity. horizon Based on samples obtained October 1982 17, the subsurface of both fields had significantly lower quantities of P than the surface horizons. The cation exchange capacity of the two horizons was not significantly different. The available phosphorus content of the surface soil was very with the dates phosphorus the ranging from 83 - 1*»8 kg/ha during the study period. samples 5 samples was for were taken, the mean quantity of available field. corn These quantities yields of 9*2 MT/ha. are above the level \ Yields on the site average 7.7 MT/ha; however,the cooperating farmer banded 70 kg/ha of P and 61 Heavy application practice in of high the Service). Figure levels measured since 1962, Southeast 19 8 1 Saginaw Bay. 7 for (Warncke et al, 1978). phosphate study increase in soil phosphorus levels Testing in kg/ha of P in 1982 well above the 28 kg/ha recommended based on the soil tests to enhance seedling growth agronomic For kg/ha for the conventional field and 118 kg/ha for 120 conservation recommended high fertilizer is a common region and has resulted in a steady (Meints, unpublished data, depicts the MSU Soil the median phosphorus soil test counties which drain into the Within the study region soil phosphorus levels Table 13 Soli Chemical Analysis Site CEC P K CA Mg pH 5/26/81 MP Surface 18 110 350 6300 940 7.3 5/26/81 MP Surface 18 110 359 6400 970 7.4 5/26/81 CT Surface 17 104 413 5900 860 6.9 5/26/81 CT Surface 16 104 395 5774 830 6.9 8/14/81 HP Surface 18 83 6230 940 7.2 8/14/81 CT Surface 17 134 5870 940 7.2 10/12/81 MP Surface 17 131 6100 810 10/12/81 CT Surface 17 92 6230 830 6/16/82 MP Surface 18 127 380 6400 890 7.1 6/16/82 CT Surface 17 127 440 5870 820 6.7 10/17/82 MP(n=5) Surface CT(n=5) Surface 10/17/82 v 102 Date Mean 16 S.D. 1 Mean 148 S.D. 56 Mean 340 S.O. 65 Mean 5600 S.D. 170 Mean 860 S.D. 65 16 1 134 17 413 40 5200 190 840 55 6.8 .4 Mean S.D 7.0 .3 10/17/82 MP(n-3) Subsurface 15 3 6 8 200 150 5500 1550 700 85 8.1 .3 10/17/82 CT(n=3) Subsurface 14.0 3.0 4 2 140 21 5100 1200 770 70 7.7 .4 Figure 7 MEDIAN P SOIL TEST LEVELS SE SAGINAW BAY DRAINAGE BASIN KG/HA BAY COUNTY ^ 15a 1 135 SAGINAV d B h TUSCOLA COUNTY CSXZ3 m 105 * 75 45 30 15 h 0 » 104 have risen 5 fold since 19 6 2 . carry higher concentrations Overland runoff from of these soils may soluble P compared to even one decade ago. 6.3 Antecedent Soil Moisture As expected, antecdedent soil moisture appeared to influence the occurrence of overland runoff and tile flow from the study fields. Only the two largest storms during the generating period of study were capable overland runoff when the antecedent soil moisture was at AMC I, below the normal moisture content for annual runoff events . four other events where overland flow 1971). 19-51 mm. No comparable The In the occurred the antecedent soil moisture was at or near the saturation condition classified as (Mockus, of AMC III magnitude of those four storm events ranged from overland flow resulted from twelve magnitudes, that occurred when soil conditions were at AMC I (Table 14). One other storms of antecedent moisture large storm occurred in September 198 1 that did not generate drainage fromeither field although the soil was at AMC II, the average condition for runoff The degree of hydrologic affected by to a precipitation the presence of an actively growing crop. storms greater than 15 mm resulted response in tile that and/or occurred overland events. during flow event Each of the six the dormant from both season fields. €vapotranspiration is low when no crop is present and soil moisture be expected period. and 1982 to remain can near field capacity during much of the dormant A total of 15 storms growing was greater than 15mm fell during the 1981 season that generated no overland or subsurface flow Table 14 > « A t- <-> cx o uu 0 01> 1 0 14.19 .43 .21 6.10 2.98 Corn 2 5-Day AMC '(mm)_____ 11.4mm 6/13 6.3ron 6/14 22.2 6.3______ 2.42 .37 -20 .90 .48 Corn 2 0.5mm 6/16 7/17/81 12.7 14.0 '4.53 .20 .13 -31 .59 Corn 3i96________ 0______ 7/28/81 26.7 10-9 5.19 .20 .13 1.0*1 .67 Corn 3!96________ 0______ 8/7/81 36.1 38.3* 34.12 .20 .13 6.82 4.44 Corn 3196 8/28-29/81 25.4 23.4 12.16 .13 2.43 Corn 3!96________0_______ o° Date U 6/15/Bi 16.3 6/21-22/81 59.7* §' U U 0 3.3mm 8/13 8/14-15/81 27.3 M.4 5-68 .20 .13 1.14 .74 Com 3)96 2.5mm 8/12 _________________________________________________________________________________ 1.3mm 8/10 8/29-30/81 13.3 9/1/81 59J 11.8______ 3.04 9/16-17/81 25.*i 9/20-21/81 17.8 2.1_______ .56 11/20/81 14.0 6.5______ 1.56 11/26/81 25.19-8 39-2* 5M1 2.9______ 1.01 10.22 .20 1-58 .20 .13 .61 .40 Corn 3196 25.460% >3500 0.31 3% >3500 0.33 56% 2300 0.39 10% 400 0.45 27% 1700 0.27 7% 4oo 0.69 27% 1700 0.25 7% 4oo 0.57 27% 1700 0.24 7% 400 0 :3 8 27% 1700 0.23 7% 400 0.29 27% 1700 0.19 7% 400 0.20 27% 1700 0.15 7% 400 0.17 0.39 7% Not Obtained 0.38 27% Not Obtained Crop Stage Abbreviations: F: Fallow period; SB: Seed Bed; i: 10% canopy cover; 2: 50% canopy cover; 3180: 80% canopy cover; 3190: 90% canopy cover; 3195: 95% canopy cover; 4: Harvest to Tillage 108 6/25/81-7/1/81 Corn F Corn SB Corn 1 Corn 2 Corn 3180 Corn 3!90 Corn 3!96 Corn 4 Corn F Beans SB Beans 1 Beans 2 Beans 3180 Beans 3!90 Beans 3195 Beans 4 Residue 109 this same period, the C factor on the conservation tilled field was only 0.27 due to the corn residue left by the fall chiseling. erosivity resulting from The potential a storm at this period was 2.5 times greater from the conventionally tilled field than the conservation tilled field. Crop species conventional field strongly during affected June. the From maximum C factor over the soil for a C factor of 0.67. 10% yielding a C value of O. 3 8 . the conventionally tilled corn in canopy During the same period in 1981 the conventional field was planted to corn which provided a canopy the June 15 through June 25. 1982 field beans were at the seedbed stage providing less than a cover of 50 -80 % The potential raindrop erosivity on mid June, 19 8 1 was approximately one-half that which existed during the same period on the conventionally tilled field beans in 1982 . Figure 9 depicts the semimonthly magnitude of the rainfall erosion index (R) that occurred in 1981, 1982, as well as the long term expected value. during The greatest September, variations 19 8 1 from and June, 19 8 2 . the projected year (130 MT-m/(ha-hr)). potential erosive losses during force soil for the 20 months of study M*% of the during September, 19 8 1. Sediment A mature corn canopy provided a total cover to of both fields and intercepted most of the raindrop energy of the September, 19 8 1 storms. impacted than is expected 19 8 1 that period were not as large as might be expected based on the storm erosivity. the occurred For occurred The storms of September, resulted in a greater rainfall erosion index (19*0 the norm The rainfall erosion index that actually the soil surface during the month was 2 5 .2 on the conservation field and 3 8 .8 on the conventional field well below the 190 MT-m/(ha-hr) Figure 9 RAINFALL EROSION INDEX(R) STARKEY FARM, TUSCOLA COUNTY, MI 130 MEAN MT-M/(HA-HR) 120 110 1981 EgZ3 100 F 90 1982 80 m z i 70 60 50 40 30 20 10 0 t L 1 H r w 2 MAR iflr. 1 APR B T m I t 1 2 2 JU N E JU LY SEMI MONTHLY PERIODS SEPT 1 2 OCT Ill that would have fallen on fallow ground. Figures 10 and 11 display the actual erosive the soil recorded surface during conventional (R the field afforded almost no x C) study force during 19 8 1 and 1982 . occurred during that impacted The greatest R x C 1982 - June, The had been planted to field beans on May 31. 1982 and cover to the soil. The storms of 1982 June, generated only 8 % of the total runoff from the conventional field during the entire study period. all the total However, phosphorus discharged during June, of all the sediment lost from the conventional during June, 1982 was 20.3 MT-m/(ha-hr) losses were field of were minimal. Based the conservation less than one half of the erosive force that impacted the conventional field. P 29% 1982 . The rainfall erosion index impacting the soil of field and Sediment and total on the results of September, 1981 and June, 1982 ,it appears that soil cover provided by either residue or crop canopy is capable of reducing soil loss on the study site. 6 . 5 -Comparison of Edge-of-Field Losses The total edge-of-field during the 20 losses measured from study field months of observation is summarized in Table 16. The results of the statistical comparison tests of runoff two fields are the statistical given in Table 17« tests comparing the each losses from the Table 18 displays the outcome of concentrations of constituents monitored in the subsurface tile and overland flow from each field. Figure 10 RAINFALL EROSION INDEX IMPACTING SOIL SURFACE 12.7mm) P(X > 25.4imi) 70.4 >.99 0.98 31.5 37.8 0.99 0.44 43.6 57-0 68.0 >•99 0.98 13.0 20.3 28.4 0.56 0.13 33.4 0.75 0.20 40.2 0.74 0.30 Seasona1: Apri 1 17-4 1.59 16.7 25.2 May 18.9 1.69 18.0 28.6 June 23.6 1.63 22.4 34.8 47.9 0.90 0.42 July 23.1 1.91 21.5 38.5 59.5 0.82 0.42 August 24.6 1.70 23.3 37.6 53.1 0.89 0.45 September 22.3 1.99 20.7 38.1 60.9 0.79 0.40 October 16.1 1.93 14.9 26.8 42.1 0.60 0.24 T: Return period (years) 130 Spring (March-May) Summer (June-Sept) Monthly: March Figure 12 24 HOUR 2,5 AND 10 YEAR STORM CARO, MICHIGAN MM 100 2 YEAR STORM I I 5 YEAR STORM W777A 10 YEAR STORM 30 20 10 0 MAR APR MAY JUNE MONTH JULY AUG SEPT OCT 132 The expected return period of large magnitude from 2.4 - 9-0 years. large storms. storms (SL) ranged The month of June had the highest probability for March had the smallest probability (Table 22). For a large storm to generate overland flow, the antecedent soil moisture must be equal to or greater than normal conditions (AMC II or AMCIII). The conditional probability of AMC II or AMC III existing when a large storm occurred was greatest during May, April, O. 3 8 , and 0 .2 7 of respective months. all the and July representing 0.43, occurrences of large storms during those August had the lowest conditional probability of AMC II or AMC III occurring with large storms. The probability of represented by the a large intersection storm of generating the storm overland occurrence conditions greater than or equal to AMC II (Table 22). flow and May was found is AMC to have the greatest probability of runoff events generated by large storms followed by June and July. resulting During other times of the year overland flow from large storms is restricted by the low frequency of those events or by the lack of sufficient soil moisture when an event occurs. The probability of occurrence for storm of moderate magnitude (SM) was comparable during all the months of interest. The expected return period for a moderate storm ranged from 1.8 to years The conditional probability of 2.8 had the greatest moderate magnitude storm 0.214, probabilities occurred 23). nearly saturated soil existing when a moderate storm occurred varied widely between months. October (Table with 0.150, and 0.147, respectively. for May, saturated conditional April, soil and when a probabilities of From June through September the 133 Table 22 Probability of Large Storms Occurring with AMC 2 or AMC 3 P(SL) Month P(AMC 2;SL) P(AMC 3fSL) P(SL x AMC > 2) March 0.115 0.000 0.200 0.023 Apr i1 0.177 0.250 0.125 0.066 May 0.254 0.285 0.143 0.109 June (corn) 0.376 0.111 0.111 0.083 June (beans) 0.42 0.111 0.111 0.083 July 0.322 0.091 0.182 0.088 August 0.385 0.050 o.ooa 0.019 September 0.300 0.136 0.045 0.054 October 0. 182 0.076 0.076 0.028 P (SL): Pr'obabi Ii ty of a large storm (SL) occurring in a given period P(AMC(I)|SL): Conditional probability of soil antecedent moisture condition 2 or 3 existing when a large storm occurs P(SL x AMC 2. 2): Probability of a large storm occurring when soil antecedent moisture is greater than or equal to AMC 2 P(SL x AMC > 2) - P(SL) x [P(AMC 2JSL) + P(AMC 3JSL)] AMC 2: Average soil moisture conditions Chat produce runoff AMC 3: Near saturated soil moisture (Mockus, 1971) 134 Table 23 Probability of Moderate Magnitude Storms Occurring at High Antecedent Moisture Conditions Month P(SM) P(AMC 3!SM) March 0.43 0.028 0.012 Apr i1 0.55 0.150 0.083 May 0.44 0.214 0.094 June (corn) 0.48 0 0 June (beans) 0.48 0 .0 5 0 0.24 July 0.40 0.053 0.021 August 0.44 0.024 0.011 September 0.39 0.034 0.013 October 0.36 0.147 0.053 P(SM x AMC 3) P(SM) : ProbabiI 1ty of a 24 hour storm of moderate magnitude (SM) than is greater than or equal to 12.7 mm and less than 25.4 mm during a given period P(AMC 3 1SM): Conditional probability that a high antededent soil moisture conditions exists when a moderate magnitude storm (SM) occurs P(SM x AMC 3): Probability of a moderate magnitude storm occurring at high antecedent soil moisture conditions (AMC 3) 135 conditional probability of having AMC III when a moderate storm occurred dropped to a range of 0.0 - 0.053* The consistent and relatively lower P (AMC 3 1SM) found for the summer months contrasts with the pattern found for large storms where July had the second highest occurrence of AMC 3 when a large storm occurred. precipitation pattern is It appears dependent that the 5 day antecedent on storm magnitude during certain months and more precipitation can be expected before a large storm than in advance of a moderate magnitude storm. Table 2 k gives the monthly probabilty of the occurrence of overland flow events. The analysis predicts that overland runoff events will have a 20 year return interval during the month of March. However, snowmelt often occurs during March causing extended periods of saturated soil conditions. soley on 5 Soil moisture predictions cannot day antecedent precipitation during March. runoff probabilities predicted for the month of underestimate the therefore actual conditions. March be The overland are certain minor to No attempt was made to model the likelihood of runoff from snowmelt; however, during both both 1982 based 1981 and storms in conjunction with snowmelt generated overland flow from both study sites. May was found to have the runoff event. was U years. occurrence probability for an overland The expected return period for overland flow during May Most of the events are expected to result from the of moderate or large magnitude storms when the soil moisture is above field capacity. generate greatest runoff Storms of extraordinary magnitude that can during periods of low antecedent soil moisture account for approximately 18% of all the expected events in May. The runoff 136 Table 24 Probability of Overland Runoff Events P (SM x AMC 3) P(SLx AMC >. 2) P(SLL) P(R0) March 0.012 0.023 0.015 0.050 Apr i1 0.083 0.066 0.023 0.166 May 0.094 0.109 0.046 0.249 June (corn) 0.0 0.083 0.044 0.127 June (field beans) 0.024 0.083 0.062 0.169 July 0.021 0.088 0.098 0.207 August 0.01 1 0.019 0.065 0.095 September 0.013 0.054 0.100 0.167 October 0.053 0.028 0.058 0.139 Month P(SM x AMC 3): Probability of a 24 hour storm greater than or equal to 12.7 mm and less than 25.4 mm (SM) occurring during soil moisture condition AMC 3 p(SL x AMC ■* 2): Probability of a 24 hour storm greater than 25.4 mm and less than SLL occurring at soil moisture greater than or equal to AMC 2 P(RO): Probability of a storm occurring that is likely to produce overland runoff P(SLL): Probability of a 24 hour storm of extraordinary magnitude occurring. During dormant season SLL ^_50.8 mm. During the growing SLL >. 60 mm. 137 event of May 10, 1981 resulted from such an extraordinary storm when the soil was at AMC I. Runoff events in May can be expected to generate more nutrient losses from sites planted to corn than from sites in field beans. Corn is planted and fertilized during the first week of May, while field beans are not planted till June, and flow events that soon after fertilization appear to carry high occur concentrations of nutr ients. Most of the runoff that may occur during September is result from very large storms. magnitude account for September. The two is thirds of all the runoff events during storms monitored in 198 1, although unusual, are large present to Precipitation events of extraordinary not to be considered as freak occurrences. canopy expected throughout However, since a mature crop most of September, sediment loss can be expected to be low from these storms regardless of storm intensity or the type of fall tillage employed. During June, sites planted to field beans are expected greater likelihood for have overland flow than sites planted to corn. field bean sites are dormant for the first portion of June less to and a The require antecedent precipitation to generate saturated soil conditions and overland flow. During June, the frequency of overland runoff from sites is expected to be 0.127 compared to 0.1 69 for field beans. occurring immediately after field bean seeding may carry corn Events elevated nutrient concentrations as a results of recent fertilizer application. In the two years of monitoring no overland runoff during July. The probability analysis predicts events occurred that overland flow events during July will have a 5 year return period, the second highest 138 frequency of occurrence for any month. expected to be generated by storms of storms occurring runoff events. with One half of those events are extraordinary magnitude. Large high AMC account for almost all the rest of the During the study the largest storm that occurred in July was 26.7 mm and fell when the soil was at AMC I. 7.3 Probability of Occurrence of Erosive Events Erosive events are Records of et (formerly al, 1981 ). the limited United byhigh have been States intensity storms. published by the National Weather Bureau) since 1895 Storms are classified as excessive rate storms if the amount of rainfall is generated intense precipitation Climatic Center (Schwab, often in millimeters exceeds duration in minutes. The analysis (5- + 0 .2 5 t) where t of excessive rate storms was to storms With a minimum magnitude of 12.7 mm since smaller events are unlikely to cause discharge of overland flow from a field. The distribution of similar at the Deer excessive Sloan gage rate storms to be very network of Ingham County, the Flint Weather Station, and the Alpena Weather Station. excessive appears The total number of rate storms that occurred during each semimonthly period from 1958-1972 at these locations are depicted in Figure 13* Excessive rate storms appear to be an infrequent phenomenon from March through May at all the recording stations. incidence of excessive At each station a dramatic rise rate storms occurs during June. June-August experience four to five times the number of storms that occur from March through May. in the The months of excessive rate The study region is located within the region spanned by these stations and is expected to have similar semimonthly distribution pattern of excessive rate storms. a Figure 13 TOTAL NUMBER OF EXCESSIVE STORMS at Deer-Sloan Network* Flint and Alpena Greater Than 12.5MM 1958-1972 TOTAL # STORMS DEER-SLOAN NETWORK [ ] aiNT STATION mm ALPENA STATION m s m crL 1-15 16-31 1-15 16-30 1-15 16-31 1-15 16-30 1-15 16-31 1-15 16-31 1-15 16-30 1-15 MAR APR MAY JUNE JULY AUG SEPT OCT 140 Excessive rate storms that occur before a crop canopy is established can generate considerable soil detachment and transport from a field. After July the crop canopy will dissipate most of the energy in a high intensity storm, thereby reducing the likelihood of an erosive event. The excessive rate storm of September 26, 1981 caused little sediment loss although its intensity and volume were of an extraordinary magni tude. A high soil detachment will overland runoff occurs. An analysis of the probable antecedent moisture conditions present when an generate intensity edge excessive of storm field that losses causes unless rate storm occurs is summarized in Table 25• intensity storms can be expected to generate not Although high runoff at lower soil moisture levels than a low intensity storm of the same magnitude, Mockus (1973 ) does not consider storm runoff volume. condition were The same used to intensity minimum compute in his preditive precipitation the model of volumes at each AMC probability of overland flow regardless of storm intensity. Table 26 gives the monthly probability of study region. Few high erosive in the intensity storms occur in the period from November through May when cropland is in the fallow protective crop canopy. events stage and has no Erosive events during this period should have a low probability of occurrence even on conventionally tilled sites. The analysis shows that virtually all of the overland flow events that occur during May are the result of low intensity storms movement should be expected from any and management little practice. sediment During 141 Table 25 A. Probability of a Large Excessive Rate Storm Occurring with Soil Antecednet Moisture Condition AMC 2 or AMC 3 Month P (XL) P (AMC 2! XL) P(AMC3!XL) P(XLx AMC>2) Apri 1 0.05 0.33 0 0.017 May 0.05 0 0 0 June* 0.23 0.1 0.2 0.069 July 0.20 0.33 0 0.067 B. Month Probability of a Moderate Magnitude Excessive Rate Storm Occurring with Soil Moisture Condition AMC 3 P(XM) P(AMC 3 JXM) Apri 1 0.08 0.375 0.03 May 0.05 0.091 LT .01 June (corn) 0.20 0.083 0.017 June (beans) 0.20 0.125 0.025 July 0.14 0 0 XL: Excessive rate storm greater than of equal XM: Excessive rate storm greater than or equal less than 25-4 mm *No difference found between field P(XM x AMC 3) to 25.4 mm to 12.7 mm and beans and corn 142 Table 26 Probability of Storms Likely Generate Overland Flow and Erosion Month April P (XM x AMC 3) 0.030 May LT 0.01 P (XL x AMC 0.017 0.0 >. 2) P(EE) 0.047 LT 0.01 June (corn) 0.017 0.069 0.086 June (field beans) 0.025 0.069 0.094 0 O.O 67 0.067 July EE: Precipitation event likely to generate erosion on fallow grond H3 April,the occurrence of overland flow from excessive rate storms is expected to have a 20 year return interval. June was found to erosion and have sediment the loss. greatest likelihood for generating Based on antecedent moisture conditions, overland flow from excessive storms is more likely with field beans than with corn crops. The more mature corn crop will withdraw more soil moisture than field beans. In the study region sites planted to corn are expected 25% crop canopy on June 1 and a 50% cover by June 16. field beans have less than a 10% Figures 1i* storms to and 15 the conventionally canopy cover Crop tilled regardless the storms. a Sites planted to during Management field Factor (C) of for beans and corn. most of June. residue cover. conservation and Soil detachment from corn Sites sites planted following corn should be expected to benefit from since have contrast the monthly probability of excessive rate excessive rate storms should be minimized on canopy to by the crop to field beans conservation tillage residue will protect the soil during the high intensity June Conventionally tilled field experience soil detachment bean sites can be expected to and sediment movement much more frequently than conservation tillage sites during June. Based on the analysis, the infrequent occurrences of spring erosive months events. are The excessive rate storms account for virtually none of events that are expected flow to have analysis shows that the overland flow during May, the month predicted to have the greatest frequency of overland flow. overland expected During April,the occurrence of from excessive rate storms is expected to have a 20 year Figure 14 EXCESSIVE RATE STORM PROBABILITY VS. CROP MANAGEMENT FACTOR(C) PROB. OR C FACTOR CMKs* “.9 EXCESS.RATE STORM PROfi. o war ,7 144 rzp .6 .5 .4 .3 .2 .1 0.0 MAR APR MAY JULY JUNE MONTH AUG SEPT OCT Figure 15 EXCESSIVE RATE STORM PROBABILITY VS. CROP MANAGEMENT FACTOR(C) CONSERVATION TIU. CORN 1.0 PROB. OR C FACTOR EXCESS. RATE STORM PROS. CIH1 CONVENTIONAL TILL CORN 0.0 MAR APR MAY JUNE JULY MONTH AUG SEPT OCT 146 return period. 7.4 Precipitation Excess Pronounced differences in soil moisture are expected to occur between corn and field bean sites that were not fully illuminated by the probability analysis of overland runoff and erosion events. The criteria employed for predicting antecedent soil moisture (Mockus, 1971) does not account for differences between crop stages. a transpiring crop on the soil moisture The influence of balance is modeled by one discrete change in the minimum 5 day precipitation of each AMC condition from the dormant to the growing season. Although the field beans emerge in can mid June, substantially the more more mature corn evapotranspiration Using the criteria of Mockus (1970 be expected to generate during the latter part of June. however, the two crops are not separated at this period since both are in their growing season. Figure 16 displays the mean weekly expected precipitation excess (PPT-ET) during May and June on sites planted to field beans and corn. The earlier planting and emergence date of corn results in greater moisture use on corn sites than on sites planted to field beans. By the last week in May mean evapotranspiration is approximately equal to precipitation on soils supporting a evapotranspiration remains low until weekly precipitation exceeds evapotranspiration by 4-14 mm/week. to experience a corn crop. approximately the expected mean On field bean sites June 10 moisture Whereas corn sites can be and mean loss from expected precipitation deficit by the beginning of June, field bean sites are expected to have a precipitation excess until June 20. Figure 16 MEAN PRECIPITATION EXCESS CARO, MICHIGAN 22 20 MM/WEEK 16 16 14 12 10 6 6 4 2 0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20 5/3-9 5/10-18 5/17-23 5/24-305/31-6/6 6/7-13 6/14-20 6/21-276/28-7/4 7/5-11 7/12-18 DATE 148 Based on the expected during June for the two difference in the soil high frequency of analysis. June. Providing Given is the excessive rate storms that occur during June, bean sites may be quite susceptible to overland flow during balance crops, a pronounced difference in runoff expected than was predicted from the probability relatively moisture cover on the field bean and erosion sites through conservation tillage should reduce the extent of the erosion losses that may occur during June. li»9 CHAPTER 8 CONCLUSIONS Field Mon itor ing A large portion of the tillage systems nitrogen and was in a soluble form. phosphorus lost from both Soluble phosphorus constituted 51 % of the the total phosphorus lost from the conventional field and 57$ of the total phosphorus from the conservation field. Nitrate nitrogen accounted for approximately 75$ of the nitrogen losses from both fields. Sediment loss from both fields was low compared to other regions and may partially account for the relatively large proportion of soluble nutrients observed. standard of 800 Concentrations of suspended solids exceeded the EPA mg/1 only once during the field monitoring. greatest loss of sediment on both fields resulted from snowmelt however,nutrient concentrations in the The runoff; snowmelt water was relatively low. On both tillage systems overland flow had significantly higher concentrations of phosphorus, sediment, and total kjeldahl nitrogen than subsurface tile flow. Nitrate nitrogen however, was significantly higher in tile flow than overland runoff. Soluble phosphorus concentrations in overland runoff after planting and declined steadily with time. were highest 150 Significantly more overland runoff occurred from system than from the conservation tillage the system. (overland and tile) for the study period was almost conventional The total flow identical for the two fields. Over the entire substantially study the conventionally field lost more sediment, phosphorus, and kjeldahl nitrogen than the conservation tillage field. Most of the additional the field conventionally tilled occurred on emerging field beans. high tilled intensity storm resulted losses observed from from an intense storm that This was the only instance where a generated overland flow before a crop canopy was establi shed. Analysis of Long Term Weather Patterns Erosive events have a low probability of occurrence through May regardless of surface residue cover. from November Overland flow events that result from low intensity storms can be regularly expected. June was found to have the greatest frequency Conservation tillage practices can be expected of to erosive cause a greater reduction in edge of field losses from field beans than from corn during this period. events. sites 151 Management Recommendations 1) Management practices should be encouraged in the enhance infiltration. Conservation tillage study region practices that should be encouraged that provide protection to the soil and promote infiltration. 2) Subsurface tile drainage should be recognized as a best management practice to reduce phosphorus losses from the agricultural croplands of the Saginaw Bay drainage basin. 3) Conservation tillage should be particularly encouraged on sites that will be planted to field beans Recommendations for Future Research 1) The field monitoring program should be continued to verify the trends observed during the first two years of study. be Specific attention should focused on snowmelt runoff and analysis of any hydrologic conditions that generate overland flow. 2) Additional field work should be encouraged to investigate the effect of fertilizer management on edge of field losses. 3) The results from the field monitoring program should be employed to test and calibrate computer based predictive models losses. 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