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INTEGRATION OF POTATO PRODUCTION, DAIRY FORAGE AND
MANURE MANAGEMENT SYSTEMS: NITROGEN DYNAMICS
AND AGRONOMIC IMPLICATIONS

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Timothy John Boring

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INTEGRATION OF POTATO PRODUCTION, DAIRY FORAGE AND MANURE
MANAGEMENT SYSTEMS: NITROGEN DYNAMICS AND
AGRONOMIC IMPLICATIONS
by

Timothy John Boring

A THESIS
Submitted to
Michigan State University
In partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
DEPARTMENT OF CROP AND SOIL SCIENCES

2005

ABSTRACT
INTEGRATION OF POTATO PRODUCTION, DAIRY FORAGE AND MANURE
MANAGEMENT SYSTEMS: NITROGEN DYNAMICS AND AGRONOMIC
IMPLICATIONS
by
Timothy John Boring

The integration of potato and livestock agronomic operations has been proposed as a
means by which to improve overall system productivity and long-term sustainability.
Two-year potato (Solanum tuberosum L.) rotations with alfalfa (Medicago sativa L.) and
sorghum-sudangrass (Sorghum bicolor L. x S. bicolor L.) and 3-year potato rotations with
2-year stands of alfalfa and festulolium (F estuca pratensis Huds. x Lolium perenne L.)
were compared to the regionally prevalent 2-year corn (Zea mays L.) - potato rotation.
Liquid dairy manure was applied at 12,260 L ha'1 and evaluated against equivalent
mineral fertilizer applications balanced on available nitrogen. Forage crop rotation and
manure application increased soil N levels and potato petiole N throughout the growing
season in 2003 and 2004. Crop rotation was a more determining factor of N levels in
potato systems than manure application. Manure was more effective at increasing potato
yield than crop rotations alone; the synergistic effect of manure amendment and crop
rotation produced more significant increases in potato yields than either treatment alone.
C4 grasses corn and sudex increased potato yield more than C3 grass festulolium or
legume alfalfa. Manure application did not affect tuber scab disease in 2002 or 2003, but
did increase scab in 2004. F estulolium yields increased with manure application in 2003,

but not in 2004. Additions of high quality forage rotations and manure amendment can

improve N synchrony with potato N demand resulting in increased potato yields.

ACKNOWLEDGEMENTS

Thank you to Dr. Richard Leep and Dr. Doo-Hong Min, my advisors, for giving me the
opportunity to work with them on this project. A special thank you to Dr. Sieglinde
Snapp for her innumerable contributions and to Dr. Roy Black for his guidance in the

economic aspects of this project.

I would also like to extent thanks to all those who contributed to the field aspects of this
research. The farm managers at the Montcalm Potato Research Farm, Dick Crawford,
and at the Agronomy Farm, Brian Graff and Tom Galacka, have gone to great lengths to
help whenever and wherever they were able. Thank you to Gary Zehr, Keith Dysinger,
Bill Widdecombe, John Boyse, Lee Siler and Kitty O’Neil who provided time, resources
and knowledge. Also, special thanks to Tim Dietz, who has gone above and beyond with

his contributions of time and expertise.

iii

TABLE OF CONTENTS

LIST OF TABLES ......................................................................................................... vii
LIST OF FIGURES ......................................................................................................... x
CHAPTER 1
LITERATURE REVIEW AND INTRODUCTION
NITROGEN DYNAMICS ...................................................................................... 1
Nitrogen in Potato Production ..................................................................... 1
Nitrogen Behavior ........................................................................................ 4
Rotation Crop Effects on Nitrogen Dynamics ............................................ 9
Nitrogen Leaching ..................................................................................... 11
Measuring Nitrogen Availability .............................................................. 13
POTATO AND FORAGE AGRONOMY ............................................................. 19
Forage Rotation Effects on Potatoes .......................................................... l9
Manure Effects on Potatoes ....................................................................... 23
Manure Effects on Forages ........................................................................ 30
Measuring Nitrogen Availability .............................................................. 34
BACKGROND AND RATIONAL FOR INTEGRATION .................................. 34
POTATO AND F ORAGE AGRONOMY ............................................................. 40
Cropping Systems ...................................................................................... 40
OBJECTIVES ....................................................................................................... 43
LITERATURE CITED ......................................................................................... 46
CHAPTER 2
NITROGEN DYNAMICS
ABSTRACT .......................................................................................................... 58
INTRODUCTION ................................................................................................ 59
OBJECTIVES ........................................................................................................ 67
MATERIALS AND METHODS .......................................................................... 68
Experimental Design ................................................................................. 68
Manure Amendment ................................................................................. 70
Potato Production ....................................................................................... 73
Forage Production ..................................................................................... 73
Corn Production ......................................................................................... 73
Crop Fertility .............................................................................................. 75
Production Inputs ....................................................................................... 76
Soil Nitrogen Analysis ............................................................................... 78
Potato Plant Nitrogen Analysis .................................................................. 78
Statistical Analysis ..................................................................................... 79
Environmental Conditions ......................................................................... 79

iv

RESULTS AND DISCUSSION ........................................................................... 80

2003 Nitrogen Dynamics .......................................................................... 80

2004 Nitrogen Dynamics .......................................................................... 88

2003 vs. 2004 Nitrogen Dynamics ............................................................ 98

Furrow vs. Valley Placement of PRS Probes ........................................... 100

POTENTAIL IMPROVEMENTS FOR NITROGEN DYNAMICS .................. 102

CONCLUSION .................................................................................................... 107

LITERATURE CITED ........................................................................................ 108

APPENDIX .......................................................................................................... 119

CHAPTER 3

POTATO AND FORAGE AGRONOMY

ABSTRACT ........................................................................................................ 123

INTRODUCTION .............................................................................................. 124

OBJECTIVES ...................................................................................................... 127

MATERIALS AND METHODS ........................................................................ 128

Experimental Design ............................................................................... 128

Manure Amendment ............................................................................... 130

Potato Production and Analysis ............................................................... 133

Forage Production and Analysis .............................................................. 134

Corn Production and Analysis ................................................................. 136

Crop Fertility ............................................................................................ 136

Production Inputs ..................................................................................... 140

Colorado Potato Beetle Control ............................................................... 140

Statistical Analysis ................................................................................... 141

Environmental Conditions ....................................................................... 141

RESULTS AND DISCUSSION ......................................................................... 143

Corn Production ...................................................................................... 143

Forage Production ................................................................................... 144

Alfalfa .......................................................................................... 144

Festulolium .................................................................................. 147

Sudex ............................................................................................ 151

Potato Production ..................................................................................... 153

Potato Yield Following Corn ....................................................... 153

Potato Yield Following Forage .................................................... 154

Defender System Improvement ................................................... 155

Manure Effects ................................................................. 157

Crop Rotation Effects ...................................................... 159

Potato Scab ................................................................................... 168
ECONOMIC ASPECTS ...................................................................................... 175
CONCLUSION .................................................................................................... 1 77
LITERATURE CITED ........................................................................................ 178
APPENDIX .......................................................................................................... 185

vi

LIST OF TABLES

Table 1.1. Depth of effective crop rooting zone for several crops in Idaho potato

production .......................................................................................................................... 10
Table 1.2. Total tuber yields for potato in 2-year potato rotations over 9 years on a

fine sandy loam Podzol in Prince Edward Island .............................................................. 21
Table 1.3. Three year average total potato tuber yield in continuous, 2-year and

4-year crop rotations in Lumsden, Saskatchewan- 1968-1970 .......................................... 27
Table 2.1. 2002 initial soil characteristics at Montcalm Potato Research Farm ............... 68

Table 2.2. Crop rotation for 2002, 2003 and 2004 at Montcalm Potato Research
Farm ................................................................................................................................... 70

Table 2.3. Common, scientific, and cultivar names of species used in 2002, 2003
and 2004 at Montcalm Potato Research Farm ................................................................... 70

Table 2.4. Liquid dairy manure concentration characteristics in 2002, 2003 and
2004 at Montcalm Potato Research Farm .......................................................................... 71

Table 2.5. Total nitrogen applications for manure and conventional fertilizer
treatments in 2002, 2003 and 2004 at Montcalm Potato Research Farm .......................... 72

Table 2.6. Mineral fertilizer application in manure and conventional fertilizer
treatments in 2002, 2003 and 2004 at Montcalm Potato Research Farm .......................... 75

Table 2.7. Fertilizer formulations utilized in experiment at Montcalm Potato
Research Farm ................................................................................................................... 75

Table 2.8. Crop above and below-ground C/N ratios as complied from several

authors ................................................................................................................................ 85
Table 2.9. Observed C/N ratio“ by treatment, cutting, and average in 2002, 2003

and 2004 at Montcalm Potato Research Farm ................................................................... 86
Table 2.10. Effective rooting depth of selected crops. ..................................................... 97
Table 2.11. Location effects on soil N as measured by PRS probes. ............................. 100

Table 2.12. Temperature, precipitation and growing degree day monthly totals for
March — October and season totals during 2002, 2003 and 2004 at Montcalm
Research Farm. ................................................................................................................ l 19

vii

Table 2.13. 2003 PRS ion exchange probe soil NO3-N + NH4-N 2-week uptake

(pg N cm'z) ....................................................................................................................... 120
Table 2.14. 2004 PRS ion exchange probe soil NO3-N + NH4-N 2-week uptake

(pg N cm'z) ....................................................................................................................... 120
Table 2.15. 2003 potato petiole NO3-N % by sampling date .......................................... 121
Table 2.16. 2004 potato petiole NO3-N % by sampling date .......................................... 121
Table 2.17. 2004 fall soil % NO3-N by sampling depth ................................................. 122
Table 3.1. 2002 initial soil characteristics at Montcalm Research Farm ........................ 128

Table 3.2. Crop rotation for 2002, 2003 and 2004 at Montcalm Potato Research
Farm ................................................................................................................................. 129

Table 3.3. Common, scientific, and cultivar names of species used in 2002, 2003
and 2004 at Montcalm Potato Research Farm ................................................................. 130

Table 3.4. Liquid dairy manure characteristics in 2002, 2003 and 2004 at Montcalm
Potato Research Farm ...................................................................................................... 131

Table 3.5. Total nitrogen applications for manure and non-manure treatments in
2002, 2003 and 2004 at Montcalm Potato Research Farm .............................................. 132

Table 3.6. Mineral fertilizer application in manure and conventional fertilizer
treatments in 2002, 2003 and 2004 at Montcalm Potato Research Farm ........................ 138

Table 3.7. Fertilizer formulations utilized in experiment at Montcalm Potato
Research Farm ................................................................................................................. 138

Table 3.8. Phosphorus and potassium inputs from manure and fertilizer in manure
and conventional fertilizer treatments in 2002, 2003 and 2004 at Montcalm Potato

Research Farm ................................................................................................................. 139
Table 3.9. Corn yield and test weight- 2002, 2003 and 2004 ......................................... 143
Table 3.10. Alfalfa dry matter yield- 2002, 2003 and 2004 ........................................... 145
Table 3.11. Alfalfa crude protein, acid detergent fiber and neutral detergent fiber-

2002, 2003 and 2004 ........................................................................................................ 146
Table 3.12. F estulolium dry matter yield- 2002 and 2003 .............................................. 148

viii

Table 3.13. F estulolium crude protein, acid detergent fiber, and neutral detergent
fiber- 2002 and 2003 ........................................................................................................ 149

Table 3.14. Sudex dry matter yield- 2002 and 2004 ....................................................... 152

Table 3.15. Potato total and US#1 fresh weight tuber yield following corn rotation-
2002, 2003 and 2004 ........................................................................................................ 153

Table 3.16. Potato total and US#1 fi'esh weight tuber yield following l-year forage-
2003 .................................................................................................................................. 154

Table 3.17. Potato total and US#1 fresh weight tuber yield following 2-year forage-
2004 .................................................................................................................................. 154

Table 3.18. Percent increase of alternative system total and US#1 fi'esh weight tuber
yield above defender potato-com rotation with no manure amendment- 2002, 2003,

and 2004 ........................................................................................................................... 156
Table 3.19. Crop above and below-ground C/N ratios as complied from several

authors .............................................................................................................................. 162
Table 3.20. Alternative system scab rating and increase from defender potato-com
rotation with no manure amendment- 2002, 2003, and 2004 .......................................... 168
Table 3.21. Calcium applied through 12,260 L ha" liquid dairy manure amendment-
2002, 2003 and 2004 ........................................................................................................ 170
Table 3.22. Potato tuber disease infection ratings— 2002, 2003 and 2004 ...................... 185
Table 3.23. Potato tuber specific gravity- 2002, 2003, and 2004 .................................... 186

ix

LIST OF FIGURES

Figure 2.1. 2003 PRS probe 2-week N03 + NH4 uptake .................................................. 81
Figure 2.2. 2003 potato petiole N03-N ............................................................................. 82
Figure 2.3. 2004 PRS probe 2-week N03 + NH; uptake .................................................. 89
Figure 2.4. 2004 potato petiole NO3-N ............................................................................. 90
Figure 2.5. 2004 fall soil NO3-N ....................................................................................... 91

Chapter 1: Literature Review and Introduction

Nitrogen Dynamics

Nitrogen in Potato Production

Nitrogen management has been shown to be one of the most critical functions of
production efficiency in potato (Solanum tuberosum L.) cropping systems (Stark et al.,
1993). In sandy soils, N is typically the most limiting factor for tuber growth (Errebhi et
al., 1998). Nitrogen deficiencies have been shown to create management problems
including increased weed competition; enhanced susceptibility to diseases such as early
die complex; and limited production capability through reduced tuber size, tuber initiates,

and marketable tuber yields (Roberts et al., 1982; Rosen, 1991; Lang et al., 1999).

Surveys of Washington state potato producers have indicated that growers frequently
apply N at levels in excess of recommended levels in the belief that higher fertilization
rates prevent or overcome management and environmental challenges such as sub-
optimal irrigation and N fertilization timing, disease pressure, and excess precipitation
(Lang and Stevens, 1997). However, excess N levels have been shown to be as
detrimental to production efficiency as deficient N levels. Excess N may cause a variety
of negative physiological effects on potatoes, including delayed tuber growth, bulking,
and maturity; decreased specific gravity; and ultimately reduced yields (Ojala et al.,
1990; Griffin and Hestermann, 1991). High N levels, both prior to and during tuber
initiation and bulking result in an over-production of vegetative growth that delays tuber
maturity (Allen and Scott, 1980; Ojala et al., 1990). Increased post-harvest tuber bruising

and reduced storability have also been found to result from excess N fertilization (Ojala

et al., 1990; Baritelle et al., 2000). Internal defects such as brown center and hollow

heart become more frequent with excess N fertilization (McCann and Stark, 1989).

Further complicating N management, N losses due to leaching and subsequent
groundwater contamination are a concern both economically and environmentally for
Michigan potato producers. Potatoes have shallow rooting systems compared to other
crops, resulting in lower effective rooting volumes from which N may be extracted (Stark
et al., 1993). 90% of potato roots are found in the upper 30 cm of the soil. Nitrogen that
moves below this level becomes largely unrecoverable by potatoes (Lesczynski and
Tanner, 1976). The high propensity for N leaching on sandy soils (Vitosh and Silva,
1996) and small rooting volume for N recovery results in the leaching of nitrate from
excess N applications (Rourke, 1985). In a proposal for a national nitrate leaching index
assessment, Shaffer and Delgado (2002) stated that shallow rooted vegetable crops,
manure application, and course textured sandy soils combine to pose a ‘very high
potential for nitrate leaching vulnerability.’ The impacts of N leaching extend beyond the
individual producer economic implications of decreased fertilizer efficiency. Nitrate
leaching is receiving increasingly greater attention as a source of non-point source
pollution by the non-agricultural community. Michigan’s Natural Resources and
Environmental Protection Act, Act 451 of 1994, regulates quantities and/or
concentrations of nutrient releases that violate established water quality standards (State
of Michigan Legislature, 1994). As part of the Michigan Right to Farm Act, Act 93 of
1981, a set of statewide standard and acceptable management practices were established

in order to provide agricultural operations with a framework by which to comply with

environmental legislation (State of Michigan Legislature, 1981). Compliance with these
standards, Michigan’s Generally Accepted Agricultural and Management Practices
(GAAMPs) (MDA, 2005a), is voluntary and provides protection from public and private
litigation regarding agricultural management. GAAMP standards are based upon
scientific principles developed by, among others, university researchers. GAAMPs have
been developed for a number of agriculture practices with the greatest potential

environmental impacts, including nutrient utilization.

The potential for economic losses and environmental pollution associated with N
mismanagement has generated a recognized need for effective N management strategies
in the Montcalm potato producing region (J oern and Vitosh, 1995). This need is
amplified as historically traditional production practices including animal manure
amendment and diverse crop rotation use in potato systems have begun to receive
renewed interest by regional producers. Mineral N fertilizers emerged and gained
widespread use following World War II, supplanting manure amendment and crop
rotation as the predominate agronomic sources of plant N. Research on N management
followed this shift from non-mineral to mineral N fertilizers, though results from
researchers including Lang and Stevens (1997) demonstrate that 70 years of research on
the behavior of mineral N fertilizer sources has been insufficient to develop consistently
accurate and accepted nutrient recommendations. Nitrogen contributions from animal
manures and crop residues have received less research attention than mineral fertilizers
and as a result, considerable confusion and mismanagement of these N sources is

common.

Nitrogen Behavior

Nitrogen under agronomic conditions exists in both organic and inorganic forms.
Commercially prepared fertilizers do not contain carbon and are classified as mineral, or
inorganic, N sources. The N found in manures and crop residues exists in conjunction
with carbon, and is therefore an organic material. Plant N uptake is typically limited to
nitrate or exchangeable ammonium N forms. Both inorganic and organic N forms must
undergo conversions from the compounds in which they were applied to the soil to plant
available N forms for crop utilization. Mineral transformation, or the conversion of one
inorganic compound to another inorganic compound, is regulated by bacteria occurring in
the soil (Lewandowski, 2000). These transformations are not normally limiting in the
soil and do not receive an extensive research focus. The process of conversion from
organic N forms to inorganic N forms is called mineralization, which is regulated by
microorganisms. The rate at which microorganisms mineralization N forms is a complex
process that is not fully scientifically understood. A number of internal and external
factors such as soil temperature and C/N ratio control microorganism activity, and
therefore N mineralization. Despite extensive research on the subject, the mineralization
of N continues to be largely unpredictable because of weather patterns including

temperature and precipitation.

Nitrogen mineralization has been shown to be predominantly a function of source
material quality and quantity (van der Krift et al., 2001). Carbon/N ratio has been found
to be the most widely accepted measure of source material quality (Quemada and

Cabrera, 1995; Vigil and Kissel, 1991; Norman et al., 1990; Ford et al., 1989), though

other constituents including lignin (Quemada and Cabrera, 1995; Bruulsemann and
Christie, 1987; Vigil and Kissel, 1991) and structural carbohydrate (Wagger et al., 1998;
Ranells and Wagger, 1992) have been linked to N mineralization rates. Allison (1973)
found that a C/N ratio of 25 or above leads to N immobilization, or a net loss of plant
available N in the soil. The microorganisms responsible for converting non-mineral N
forms to mineral N forms are dependent on C and N for their existence. The addition of
either element to the soil system invokes micro consumption of the other. Nitrogen is
typically the limiting factor because of larger amounts of C in most residues and
inherently larger C stocks in the soil. If large quantities of residues or manure are added
to the soil, microbe populations grow in response to introduced C, with a corresponding
increase in N consumption. If N is not supplied in sufficient quantities along with C
inputs, existing soil N is used by soil microbes. This microbial N consumption reduces
soil N concentrations available for plant uptake. While not lost from the system, this N is
nonetheless not readily available, and thus ‘immobilized’. Aulakh et a1. (1991) observed
this effect of N immobilization in work with hairy vetch (Vicia villosa Roth), soybean
(Glycine max L.), corn (Zea mays L. ), and wheat (T riticum aestivum L.) residues with
UN ratios of 8, 43, 39, and 82 respectively. These residues were incorporated and
surface applied at a rate of 2.5 g kg“. Hairy vetch was found to release sufficient
amounts of mineral N to meet early season crop needs while the other residues

immobilized applied N for several weeks.

Nitrogen “priming effects” have frequently been observed with N amendments. Priming

was originally observed by L6hnis (1926) while examining green manure decomposition

effects on legumes. The effects and mechanisms of priming have become better
understood and more accurately defined since thnis’s studies. Kuzyakov et a1. (2000),
reviewing mechanisms of priming effects, found that many priming definitions excluded
non-plant interactions or only addressed mineralization acceleration. The authors
ultimately proposed the definition that “priming effects are strong short-term changes in
the turnover of soil organic matter caused by comparatively moderate treatments of the
soil.” However, the admission was also made that a complete understanding of the

mechanisms driving priming effects continues to elude researchers.

The incorporation of fresh organic materials has been found to stimulate soil organic
matter (SOM) mineralization. Wu et al. (1993) measured significant priming effects with
ryegrass amendment to a soil. Manure amendments have been shown to increase
microbial biomass, N mineralization, and enzyme activities (Kandler and Eder, 1993; Ma
et al., 1999). Curless and Kelling (2003) measured potato petiole NO3-N response to
liquid dairy manure and conventional mineral fertilizers balanced by available N
estimates and found that manure increased yields beyond those attributable to N inputs.
Webb et a1. (1997) noted increased mineralization rates from manure amendment in
potato systems. However, mineralization has been shown to be more than just a response
from increased microbial activity. Amendments of glucose, a more readily available
microbial energy source than the polymerized structures found in manure or plant
material, have not been shown to appreciably increase mineralization (Shen and Bartha,
1997). Fontaine et a1. (2003), in a review of priming effects, concluded that

mineralization is not a function of energy available to soil microbes. Rather, fresh

organic matter (F OM) and existing SOM are decomposed by separate microbial
populations, k-strategists and r—strategists. K-strategists are an ever-present population,
feeding on the nearly limitless existing SOM supply. In contrast, r-strategists feed
exclusively on FOM and are completely dependent on F OM supplies for subsistence.
Amendments of FOM allow for r-strategist activity and growth; substrate exhaustion
results in death or dormancy. The specificity of r-strategists activity is seen as an
explanation for the observations of unchanging SOM decomposition following FOM
amendments. From these assessments of mineralization dynamics, the authors proposed
two potential mechanisms of priming. First, enzymes produced to decompose FOM by r-
strategists may be partly effective in degrading SOM. This mechanism relies upon
biochemical similarities in F OM and SOM, thus the more chemically diverse the F OM,
the greater the likelihood that produced enzymes will degrade both organic matter
substrates. The second possible mechanism calls for utilization of both F OM and SOM
by k-strategists, stimulating greater SOM decomposition rates. The progression of this
mechanism is largely regulated by prevalence and competition from r-strategists. Both of
these mechanisms indicate manure amendment, with its chemically and biologically

diverse composition, would be particularly stimulating in the N mineralization processes.

Additions of manures and crop residues are also important for building overall soil
fertility. Hart et a1. (1986) observed that priming effects increased in soils with high C
and N concentrations. Mineralization rates as a whole have been found to be
significantly influenced by existing soil N levels. 60-90% of mineralized N during a

season may originate from a pool of existing, stabilized N, with the remainder of

mineralized N contributed from recently preceding crop residues (Matus and Rodriguez,
1994). Increases to soil fertility require multiple years of management before results
become discemable. Paul and Beauchamp (1993) observed that repeated manure
application and legume crop rotation increased soil fertility, leading to greater N priming
and mineralization rates. Ma et a1. (1999) found corn yield responses to cattle manure
amendment only after several years of annual application. Legumes especially have been
found to build long-tenn soil fertility levels by increasing organic N reserves (Frye et al.,
1985; Harris and Hestermann, 1990; Janzen et al., 1990; Ladd et al., 1981). However,
residual l5N research has shown that little fertilizer or legume N is taken up by a wheat
crop two years after initial application (Ladd and Amato, 1986). Harris (1993) indicated
that the true value of legume N inputs maybe from contributions to N mineralization

through conservation and cycling of soil N rather than short or long term direct N supply.

Environmental conditions such as temperature and precipitation influence N
mineralization (Goncalves and Carlyle, 1994; Vigil et al., 2002). Increasing spring
temperature, moisture availability, and crop residues increase N mineralization (Weinert
et al., 2002). Ma et a1. (1999) observed increased N mineralization in 1995 with 40 mm
greater precipitation and 2° C warmer temperatures compared to 1996. While no strong
correlations could be drawn between N mineralization and precipitation, a significant
positive linear correlation (r2=0.5, P>0.05) was found with temperature. Westermann
and Crothers (1980) measured N mineralization with buried polyethylene bags and found
that while moderate temperature fluctuations did not influence mineralization, overall

higher temperatures increased mineralization. Both Ma et al. (1999) and Ruffo and

Bollero (2003) determined that soil moisture was the limiting factor in decomposition-
day accumulation in non-irrigated conditions. Webb et a1. (1997) found that low winter
rainfall inhibits N mineralization. Wyland et a1. (1995) did not observe consistent
increases to soil N mineralization until irrigation was applied 20 days following crop

residue plowdown.

Rotation Crop Effects on Nitrogen Dynamics

The potential impacts of lost soil N due to spring NO3-N leaching has oflen drawn greater
attention by both researchers and producers than N losses during other periods of the
growing season. However, fall and winter N03-N losses have frequently been observed
in potato production (Mitchell et al., 2001). Overwintering crops have been shown to
reduce these N losses through the uptake and storage of N for subsequent crop utilization
and by the reduction of water percolation that may carry NO3-N through the soil profile

(Weinert et al., 2002).

Kristensen and Thorup-Kristensen (2004) found root depth, more so than above ground
biomass, to be a strong indicator of crop effectiveness in recovering leachable NO3-N.
Deep rooted crops have the ability to improve overall N use efficiency by recovering
deep soil N that would otherwise be lost from the system. Lesczynski and Tanner (1976)
determined that 90% of potato roots occur in the upper 30 cm of the soil profile; N
leached below this level becomes largely inaccessible for potato uptake. Pan et al. (1998)
used rhizotron computerized imaging to track potato root development through the

season, finding root elongation occurred through tuber initiation and early tuber bulking,

but declined thereafier. Total root depth was observed at 60 cm 4-6 weeks after planting.
Similar potato rooting depths were observed by Ashley et a1. (1997). These shallow
rooting depths result in a number of rotation crops to having greater access to soil N than
potato crops. Ashley et al. (1997) measured the effective rooting depths, or depth at
which crops extract the majority of their consumed water, for a number of crops in Idaho
potato production. While actual rooting depth may be greater, these depths indicate the
soil volume in which the majority of plant nutrients are drawn.

Table 1.1. Depth of effective crop rooting zone for several crops in Idaho potato
production.

 

 

Crop Maturity Depth (cm)

Alfalfa new stand 30 - 45
established stand 120

Cool season grass new stand 15 - 45
established stand 45 - 120

Potato 45 - 60

Corn 105

Winter cereal (rye) Haun .4-7 stage 30 - 60

-reproduced from Ashley et al, 1997
Other researchers have obtained similar rooting depth results measuring crop root
function. Alfalfa (Medicago sativa L.) recovery of injected 15N at 120 cm was measured
at 40% (Huang et al., 1996). Ashley et al. (1997) found that both alfalfa and cool season
grass roots extend deeper with multiple year production. Corn roots were detected at 75
cm in Minnesota and Indiana (Nickel et al., 1995; Kuchenbuch and Barber, 1987). Crop
characteristics other than rooting depth have been observed to impact N recovery
abilities. Shipley et a1. (1992) found forage grasses were better able to conserve residual

fertilizer N than forage legumes. Longer and more frequent root hairs result in surface

10

area and root volume several times that of legumes, giving grasses a strong competitive

advantage in water and nutrient uptake (Evans, 1977).

In addition to recovered residual soil N, legume crops have the potential to contribute N
through biological N fixation. Plant uptake of existing soil residual N or amended N,
however, will be used to fulfill growth requirements before N fixation is utilized as a N
source (Cherney and Duxbury, 1994; Lamb et al., 1995). Mohr et a1. (1998) noted that
alfalfa gradually releases N into the soil profile at a rate of up to 10% of that removed
through harvest. This slow N release has the potential of adding to the overall soil N
pool. Total N recovery from legume sources has been observed to exceed that provided
through inorganic fertilizer sources (J anzen et al., 1990). While per unit N recovery of
fertilizer N is often greater than that of legume N due to a greater initial availability, total
uptake from legume N sources is ofien greater due to increased long-terrn availability
(Ladd and Amato, 1986). These greater overall soil N supplies have been attributed to

legume stimulation of larger microbial populations (Bolton et al., 1985; Harris, 1993).

Nitrogen Leaching

Course textured soils common in potato production are particularly prone to N leaching.
Negatively charged N compounds, specifically NO3-N, do not bind to negatively charged
soil particles and are susceptible to leaching losses. Excessive irrigation (Middleton et
al., 1975) and high volume rainfall events of at least 2 cm move NO3-N out of the potato
rooting zone (Cameron et al., 1978; Bundy et al., 1986). Cameron et a1. (1978) obtained

soil samples at 10 cm intervals up to 75 cm at six points during the growing season,

11

providing detailed imagery of NO3-N movement through the soil profile. Above average
rains during late May and early June of 1975 moved NO3-N below 20 cm, but there was
no observed loss below 75 cm. Nitrate-N losses were also observed during the spring of
1976, correlated with several high rainfall events. Greater NO3-N losses were attributed

to fall leaching, but spring leaching had greater impacts of seasonal N plant availability.

Nitrogen from legume sources, largely as NH4-N, has been shown to be less initially
available in the soil and thus more resistant to leaching loss (USDA, 1980; Smith et al.,
1987; Magdoff, 1991). Ammonia, as a positively charged compound, must be first
mineralized into NO3-N before it is susceptible to leaching. Harris (1993) found that the
addition of legumes to potato cropping systems decreased leaching losses at the Rodale
plots in Pennsylvania. The addition of N through animal manures, however, has been
shown to be particularly susceptible to N03-N leaching. Nitrogen in manure exists in a
variety of forms, primarily R-NHz-N and NH4-N, while to lesser extents NH4-N, NOz-N,
and N03-N (Schmitt, 2002). Organic compounds and ammonium are largely immobile
upon application, but rapid mineralization of these compounds join with initially present
NO3-N to pose a leaching risk. Manure application increased N03-N leaching compared
to legume crop rotations systems or fertilizer based systems at Rodale (Harris, 1993).
Bagayoko et a1. (1992) associated precipitation and temperature with manure NO3-N
losses in the soil profile with two spring and one fall soil sampling events at 30 cm
intervals to a depth of 150 cm. Rainfall during May and June of 1988 was measured at
83 and 26 cm compared to 22 and 105 cm during the same period of 1989. Average

temperatures were 3 to 5° C lower in 1989 than 1988. Greater NO3-N concentrations

12

were measured at 150 cm depths for manure treatments during both spring sampling
periods in each year. Greater total N03-N was seen in 1988 at this depth, indicating
greater NO3-N movement with higher mean spring temperatures and greater early season
precipitation. Drinkwater et a1. (1998), in comparisons of conventional, manure, and
legume N fertility cropping systems over five years, found that while legume NO3-N
leaching losses tended to be lowest among the three systems, both legume and manure
systems cumulative NO3-N leaching over five years performed similarly compared to

conventional fertilizer applications.

Measuring Nitrogen Availability

Several researchers have explored the use Of ion exchange resin membranes as a means
by which to monitor in-season N availability. Plant Root Simulator (PRS) ion exchange
probes (Western Ag Innovations, Saskattoon, Canada) have been successfully used for
measuring N availability from crop residue and manure mineralization (Adderley et al.,
1998; Qian and Schoenau, 2002; Johnson et al., 2005). PRS probes are buried in the soil,
providing an in situ measure of nutrient supply rates by continuously adsorbing ionic
species on a charged membrane surface (Schoenau et a1, 1993). These probes are
encapsulated in a plastic sheath to assist with probe insertion and removal in field
conditions. PRS probes provide an integrated measure of supply rates as they are
subjected to all factors affecting nutrient supplies, including free ion activity, buffer
capacity, mineralization, immobilization and others (Sulewski et al., 2002). This
exposure to competing sinks, while important in providing a complete image of nutrient

dynamics, is also subject to site variability. Non-representative competition, specifically

13

from root proximity, will skew nutrient uptake and fail to provide an accurate assessment
of nutrient availability. For this reason, root exclusion cylinders are often used to ensure

competition free measurements (Sulewski et al., 2002).

Long-term burials (two weeks) have been shown to provide more detailed dynamics of
nutrient supplies than short-term burials (one hour) as they allow for ion diffusion from
greater distances, cation exchange, and uptake of slow release nutrients made available
through mineralization and dissolution (Qian and Schoenau, 1997). Long-term burials
provide an integrated assessment of initial soil conditions and gradual nutrient

availability; together this information closely represents actual nutrient supply rates.

Probes measure nutrient supply rates per unit surface area per time (eg. ug N/ 10cm'2/2
weeks) that are not comparable to typical nutrient availability indices used in
conventional soil tests, such as ppm (Hangs et al., 2002). This difficulty in matching
PRS probe data with conventional soil measurements initially relegated use of PRS
probes to that of a soil science research tool (Hangs et al., 2002). To an extent, the lack
of widespread use of PRS probes in many areas of the United States and Canada
precluded acceptance of this tool as a common soil testing technique. However, though
the establishment of a commercial laboratory, Western Ag Irmovations Inc. (Saskatoon,
Saskatchewan), providing grower consultation and accessible laboratory analysis of PRS
probes, recognition of this methodology as a practical soil testing technique has evolved

to a point of acceptance in the potato production industry.

14

PRS probes have been specifically used in research scenarios to measure differences in
manure and fertilizer fertility treatments. Qian and Schoenau (1999) applied liquid swine
manure and urea mineral fertilizer to canola (Brassica napus L.) plots, measuring soil N
supply rates and canola N uptake to determine the effect on N availability and assess the
relationship between measured N availability and actual plant N uptake. Manure
amended soils were found to be less effective at supplying available N than N balanced
fertilizer urea treatments, largely due to incomplete manure N mineralization. Strong r2
correlation coefficients ranging from .79 to .96 were observed between measured soil N
availability and plant N uptake. The authors concluded that PRS probes may serve as an
effective tool by which to evaluate amendment effects on available N. Crop residue
mineralization has been measured by several researchers using PRS probes. Adderley et
al. (1998) observed mineralization differences in pea and lentil residues over a period of
56 days. Increased N availability measured by PRS probes was found to positively

correspond with harvested wheat yields.

PRS probes have been demonstrated to be of comparable quality to other ion exchange
resin technologies. Johnson et a1. (2005) examined the abilities of two ion exchange
resins, PRS probes and Unibest resin capsules (Unibest Ine., Bozeman, MT), for
measuring soil nutrient availability compared to KC] extraction NIH and N03' soil tests
under varying temperature and moisture conditions. While soil tests and Unibest
capsules were able to detect soil mineral N responses to both temperature and moisture,

PRS probes were only able to detect moisture changes. However, PRS probes were

15

shown to more accurately approximate temporal patterns in soil N mineralization than

other tests.

Plant tissue analysis has evolved as a complementary means to soil measurement by
which at assess soil N concentrations. Petiole sampling is the most accepted plant tissue
measurement for determining the N status of potato crops (Westcott et al., 1993). The
level of N03-N observed in the petiole is a reflection of the balance between uptake and
transport of soil N-NO3 to the leaves and the relocation of that N to the tubers (Westcott
et al., 1991). In-season monitoring of petiole N samples has been widely adopted by
Michigan potato growers in an effort to improve N efficiency by matching fertilizer
applications with periods of greatest crop demand (Snapp et al., 2001). Petiole NO3-N
has been found to be highly correlated with fertilizer N application rates (r2 0.68- 0.94)
and yield potential (r2 0.88 - 0.99) across a variety of potato cultivars (Waterer, 1996).
However, a lack of information exists on how amendments such as crop residues and
manures provide N availability (Snapp and Fortuna, 2003), and growers have been
reluctant to credit these inputs as reliable sources of N (Snapp et al., 2001). Monitoring
the concentrations of petiole NO3-N through the season allows for an understanding of

how plants respond to N availability from a variety of sources.

Sufficient N supplies are crucial in achieving maximum potato yields. While excessive N
levels have been shown to cause a variety of developmental and physiological symptoms
such as delayed tuber maturity, lower quality, and reduced yield (Griffin and Hesterman,

1991; Ojala et al., 1990), insufficient N supplies can be equally problematic.

16

Nitrogen is important during early grth in order to produce sufficient above ground
biomass that will supply the photosynthetic energy and N reserves necessary for later
tuber development. High rates of N encourage vegetative development over tuber
development, delaying the period of maximum canopy N (Millard and MacKerron,
1986). This effect is desired, to an extent, in order to build a sufficient pool of above

ground resources to produce maximum tuber yields.

Nitrogen utilized in tuber production originates from either existing N storage pools in
petioles or may be absorbed from the soil, transported to leaves as N03, reduced, and
translocated immediately as organic N to the tubers (Robinson and Millard, 1987).
However, N used in tuber growth is drawn predominantly from existing plant capital N
rather than recently absorbed soil N. Potatoes accumulate N03-N in petioles during the
early vegetative growth stages (Millard and MacKerron, 1986). As tubers initiate and
bulk, N03-N in the petioles is used to meet tuber N demands. During periods of rapid,
short-term tuber growth, roots do not have the N absorption capacity to match petiole
NO3-N depletion (Millard and MacKerron, 1986). This makes adequate stores of petiole
NO3-N essential for sustained tuber production. Petiole NO3-N concentrations are
typically greatest early in the season, prior to tuber N demands (Roberts et al., 1989).
Rapid decreases to petiole NO3-N occur mid-season as tuber N demands increases,
tapering off late in the season as N uptake and demand slows. While roots have the
capacity for N uptake late into the growing season (Millard et al., 1989), rates of N
uptake decrease throughout the season (Millard and MacKerron, 1986) and tuber N

demands often outpace root supply abilities. When root N uptake becomes unable to

17

match tuber N needs, petiole N pools are diverted to fulfill tuber demands. Millard and
MacKerron (1986) observed maximum canopy N concentrations at 54 days after
emergence, followed by a steady decrease in N levels throughout the season. Nitrogen
fertilizer application, however, has been shown to influence root N uptake. Millard et a1.
(1989) found low rates of N fertilizer application resulted in earlier root N uptake decline

than higher fertilizer applications.

Consistent petiole sampling methodology is crucial for effectively monitoring N
concentrations. Sampling protocols call for the measurement of the third fully developed
petiole on a stem. The sampling of this established, but relatively young tissue, is based
on several morphological characteristics of potato N movement. Young growth located
in the top of the canopy acts as a greater sink of root absorbed N than older growth
located lower in the canopy (Robinson and Millard, 1987). Additionally, late season
tuber N demands led to the senescence and abscission of lowermost canopy leaves
(Millard and MacKerron, 1986). Sampling of lower canopy leaves is apt to provide an

unrepresentative portrait of N concentrations.

18

Potato and Forage Agronomy

Forage Rotation E ffects on Potatoes

Several studies have examined the effects of alfalfa crop rotation on potato yields in
Michigan. Wheeler (1946) initiated a study in 1934 at the Lake City Experiment Station
in Lake City, MI, 115 km north of the Montcalm Potato Research Farm in Entrican, MI.
Alfalfa in a three-year stand, sweetclover (Melilotus indica L.) in a two-year stand, and
corn as a one-year crop was rotated with potatoes in large 0.33 ha plots, using continuous
potatoes as a check. Rye (Secale celeale L.) was seeding into the corn as an over
wintering cover crop during summer cultivation. Rotations were replicated such that
each year of a rotation was represented in the first growing season, allowing for
comparisons between one, two, and three year alfalfa stands, and one and two years of
sweetclover stands. Through ten seasons, results indicated that higher yields of potatoes
could be achieved when alfalfa or sweetclover preceding potatoes rather than either corn
or continuous potatoes. On average, US. No. 1 potatoes in alfalfa and sweetclover
rotations out-yielded continuous potatoes by 46% and 23%, respectively. During the
same period, corn rotation reduced yields by 6% compared to continuous potatoes. The
length of the alfalfa stand prior to potatoes had an influence on potato yield as well. One
year of alfalfa increased yield by 20%, two years by 40%, and three years by 130%.
Control over potato scab was found to be greatest with alfalfa and corn rotation compared
to continuous potatoes or sweetclover. Scab levels, reported as the percent US. No. 1
potatoes free from scab, averaged 84% in alfalfa rotation, 87% in com, 43% in
sweetclover, and 70% in continuous potatoes. While high levels of scab in sweetclover

rotations were noted to be unexpectedly high, no explanation was provided that might

l9

offer insight for possible causes. Overall, Wheeler was able to conclude that long stands
of alfalfa improved both the quantity and quality of potato yields over those possible with

rotation of other legumes or a corn.

In 1987, six two-year potato rotations were established at the Montcalm Potato Research
Farm in Entrican, MI, and at the Kellogg Biological Station in Hickory Corners, MI
(Griffin, 1990). Rotation crops of corn, alfalfa, red clover (Trifolium pretense L),
birdsfoot trefoil (Lotus corniculatus L. ), hairy vetch, and sweetclover were managed,
with the exception of corn, as both hay and cover crops. Hay management called for the
harvest and removal of above-ground vegetation in accordance with typical hay
production techniques on a three-cut management schedule, while cover crops were not
harvested during the seeding year. Potatoes followed corn and legume production in
1988 and were not amended with mineral N fertilizers. A marked response in vegetative
potato growth following legumes was attributed to legume nitrogen contributions. At
both sites, potato vine N concentration, dry matter yield, and N yield were found to be
greater in legume crop rotations than corn rotations, while vine DM and N yields were
greater for cover crops than hay crops. However, no yield differences were detected
among crop rotations. This lack of yield boost was attributed to poor synchronization of
legume N mineralization with crop N demand and the possibility of other limiting factors

besides N.

Cool season grasses, such as Redtop (Agrostis alba L.), have also been researched in

potato rotations. A field study begun in 1951 at the Rhode Island Agricultural

20

Experiment Station compared three potato rotations: continuous potatoes, redtop-redtop-
potatoes, and red clover-red clover-potatoes (Odland and Sheehan, 1957). An identical
redtop-redtop-potato rotation that had been under management for 18 years was also
integrated into the experiment. Over the five years of the study, the 23-year stand of
redtop out yielded continuous potatoes by 20%, while 5-year stands of redtop and red
clover increased potato yield by 11% and 13%, respectively. Higher specific gravities
were also measured in the long-terrn redtop rotation. The higher yields with redtop
rotation were attributed to increases in soil organic matter levels from multiple years of

grass production.

Carter et al. (2003) established a series of 2-year potato rotations in 1985 in Prince
Edward Island utilizing Italian ryegrass (Lolium multiflorum Lam), barley (Hordeum
vulgare L.) plus Italian ryegrass, red clover, and barley. Biomass from these crops was
harvested and returned to the plots as a soil amendment. Italian ryegrass grown alone
produced the highest above-ground and below-ground biomass yields. These greater
biomass contributions respective to other rotation crops resulted in the maintenance of
soil organic matter levels, while barley and red clover rotations contributed to SOM
declines. Tuber yields for nine years are presented in Table 1.2.

Table 1.2. Total tuber yields for potato in 2-year potato rotations over 9 years on a fine
sandy loam Podzol in Prince Edward Island.

 

 

Rotation crop Yield
Mg ha'l
Italian ryegrass 34.8 ab
Barley + Italian ryegrass 35.0 a
Red clover 31.1 c
Barley 33.5 b
LSD (0.05) 0.90

-reproduced from Carter et al., 2003

21

The authors cited improved potato yield performance with ryegrass rotations to improved
soil fertility and structural properties associated with the greater organic matter
contributions. The incorporation of wide C/N ratio barley straw, in contrast to narrow

C/N ratio forage residue, contributed to N limiting conditions.

The effects of 2-year and 3-year crop rotation on potato yield and disease have been
studied in a long-term field laboratory in Prince Edward Island, Canada (Carter and
Sanderson, 2001). Established in 1994, a 2-year rotation of spring barley and potatoes
was compared to a 3-year rotation of spring barley, red clover, and potatoes.
Additionally, a tillage treatment of minimal till and conventional till was examined.
Within two years, Rhizoctonia levels increased in the 2-year rotation and continued to
become more severe over the next four years compared to the 3-year rotation. These
disease impacts resulted in yield reductions in the 2-year rotation within four years. Off-
sized tuber production increased in this rotation, further reducing tuber quality. The
ability of the 3-year rotation to resist disease infection was largely attributed to increased

microbe competition brought about from the addition of organic amendments.

Based upon the disease reduction observations seen by Carter and Sanderson (2001) in
extended rotations, Peters et al. (2003) initiated a study to examine a wider array of
disease pressures at this site beginning in 1999. They found stolon canker and black
scurf levels were reduced in the 3-year compared to the 2-year rotation. They also found

an interaction between rotation length and tillage, determining that 3-year rotations in

22

minimum tillage resulted in a reduction of all potato diseases caused by R. solani, H.
solani, and Fusarium spp. A series of greenhouse experiments were established in
conjunction with this study to determine if the reduction of potato diseases in longer
rotations involved transferable soil data. Potatoes were planted and grown in a
greenhouse with soil obtained fiom the two rotation schemes. Inoculum of Phytophthora
erythroseptica Pethybr., a casual agent of potato pink rot, was obtained from stored
potatoes exhibiting symptoms of pink rot and applied to the experimental potatoes. After
sixty days of growth, plants growing in soil managed under a 3-year rotation were
significantly taller, less diseased, and produced higher plant biomass than plants grown in
soil from a 2-year rotation. A second laboratory experiment was conducted to determine
natural resistance of potato tubers grown under different management schemes. Clean,
healthy tubers were obtained from field plots, inoculated with P. erythroseptica, and
stored for two weeks under high humidity conditions. Tubers originating from 3-year
rotations were found to have lower incidence and severity of pink rot than tubers grown
in 2-year rotations. Peters et al. (2003) and Carter and Sanderson (2001) both concluded
that 3—year rotations held the potential to reduce the incidence and severity of soil-bome

disease.

Manure E fleets on Potatoes

A long-term fertility study was initiated in 1948 in Prince Edward Island, Canada, to
examine the effects of mineral fertilizer and manure on potato yields (Black and Cairns,
1958). Potatoes were grown in a 4-year rotation with cats (Avena sativa L.), clover

(T rifolium x.), and a two-year stand of clover-timothy (Phleum pretense L.) hay in a 3 x 3

23

x 3 factorial fertilizer study. Combinations of N, P, and K were broadcast applied at a
low (50-59-70 kg ha"), medium (101-239-140 kg ha"), and high (151-118-209 kg ha")
rate to potatoes. These applications were the only fertilizer amendments in the four-year
rotation. Barnyard manure was fall applied to the clover-timothy hay crop following its
second year of production at 9.7 t ha’l, for a one year out of four amendment. No other

information was provided as to the source or content of the manure.

Black and Cimes (195 8) reported their results from the first eight years of research as
averages of each complete four-year rotation cycle. Tuber yields with manure
amendment were found to be significant at the P = 0.01 level after four and eight years,
with yield increases after eight years greater than those seen after four. Black and White
(1973) reported on an additional three rotation cycles as the experiment was continued
for twelve years following the initial 1958 report, for a total summary of twenty years of
field research. Beginning in 1960, the low fertilizer rate was increased so as to provide
the highest fertility levels at 202-148-279 kg ha]. Findings from the next three rotation
cycles corroborated with trends previously established, with manure amendment
continuing to increase marketable tuber yields at any fertilizer level. Some credit to
increased yields was given to higher levels of available nutrients provided through
manure application. However, the primary effects were attributed to increased soil
organic matter, better soil structure, greater water holding capacity, and an increased
presence of exchange sites for holding nutrients in the soil. Furthermore, it was noted

that applications of manure did not increase scab, levels, in contrast to expectations.

24

In order to determine the effects of manure on verticillium wilt and scab, a field
experiment was initiated in Alliston, Ontario, a chief potato producing region in Canada
(Conn and Lazarovits, 1999). Wood based chicken (66 t ha"), liquid swine (100 t ha"),
and solid manure (55 hL ha") was incorporated in the spring of the study’s onset before
potato planting at two commercial potato farms. No information was provided as to the
previous cropping histories of these sites. Nitrogen fertilizer was applied after the
manure amendment to equilibrate fertility across treatments. No manure was applied in
years two or three of the experiment as the site was managed under common commercial
production techniques. Verticillium wilt, nricrosclerotia (MS), and scab levels were
monitored for three years following manure application. Verticillium wilt is caused by
Verticillium dahliae Kleb., which in turns produces MS that are able to persist in soils for
up to a decade. Microsclerotia initiate infections that lead to verticillium wilt. Increased
initial soil pH resulted from chicken manure amendment, with a spike from pH 6.0 to 8.0
within two weeks. This increase was accompanied by an increase in ammonia levels,
which the authors speculated may be involved in reducing populations of S. scabies. Soil
pH levels returned to baseline levels within 21 weeks. Swine and cattle manure did not
effect soil pH initially, but after 4 weeks, a decrease was seen fiom both. This decline
may be attributed to the nitrification process. Potatoes treated with chicken manure
showed an 80-96% reduction of verticillium wilt in the first year. This trend continued
into the second year, but not the third. Swine manure in the first year reduced
verticillium wilt by 62% at one site, but had no effect on the second. Cattle manure in
year one reduced the level by 72% at the unaffected swine site, but had no effect on the

first site. Chicken and swine manures both reduced scab levels in year one. Cattle

25

manure had little or marginal reduction effects on scab. In the second and third years,
swine manure was the only treatment that significantly lowered scab incidence. Cattle
manure reduced scab levels slightly over the next two years at one site. Chicken manure
caused increased scab levels in year three at one site. None of the manure amendments
were found to increase tuber yields. However, the decrease in scab levels seen in some

years resulted in higher numbers of marketable tubers.

A laboratory experiment was performed in association with this field study, using soils
obtained from the two commercial potato operations, as well as soil from a research
station with no history of potato production. Samples of three chicken manures, one
liquid swine manure and one liquid dairy manure were used. After two weeks of
application, chicken manure reduced MS levels by 25 and 90% for the two potato field
soils and 10% for the research station soil. Swine and dairy manures reduced MS levels
in one potato soil, but had no effect on the second. Ultimately, it was concluded from
both field and laboratory studies that disease levels were only effectively reduced by
manure amendment in the first year after application. The authors suggested that armual
applications might be necessary in order for consistent MS reductions. Additionally, it
was observed that in some cases, manure amendment resulted in increased levels of
disease several years after application. While decreases to disease may be seen with
manure application, neutral or increased effects are also possible; soil conditions, manure

composition, and season of application all exerted influence on disease control.

26

A study in Limsden, Saskatchewan initiated in 1958 examined effects of a combination
of forage crop rotation and manure amendment in long-tenn potato rotations (Emmond
and Ledingharn, 1972). Three rotations were compared: continuous potatoes, a 3-year
rotation of potato followed by a 2-year stand of sweetclover hay, and a 6-year rotation of
potato, potato, 4-year stand of alfalfa-crested wheatgrass (Agropyron cristatum L.) hay.
Manure at 34 t ha'l was applied once every three years. Emmond and Ledinharn (1972)
reported three years of results recorded from 1968 to 1970, ten years after the initial

establishment of the experiment.

Table 1.3. Three year average total potato tuber yield in continuous, 2-year and 4-year
crop rotations in Lumsden, Saskatchewan— 1968-1970.

 

 

Rotation crop Yield
Mg ha'l
Continuous potatoes 32.76 c
2-year sweetclover 40.43 a
4-year alfalfa-wheatgrass 36.59 b
LSD (0.05) 2.93

-reproduced from Emmond and Ledingharn, 1972

The yields of total and marketable tubers were significantly higher in the 3-year, followed
by the 6-year and continuous potato rotation. High disease incidence was observed in
continuous potatoes, mainly from verticillium wilt, black dot, and rhizoctonia. The 3-year
rotation had the lowest incidence of disease over the three-year study, providing better
control of verticillium wilt and other diseases than the 6-year rotation. The 3-year
rotation had disease incidence rise only slightly over three years, while disease incidence
increased steadily in the 6-year rotation. The 6-year rotation included potatoes in back to
back years, and while the extended rotation of alfalfa-wheatgrass hay provided control of

verticillium wilt in the first potato crop, the second crop suffered from high infection.

27

The authors speculated that alfalfa may act as an intermediary host for verticillium wilt
producing fungi, though they could cite no previous occurrences of such an event in
Saskatchewan. While rotations had a significant effect on disease levels, manure

application was not found to impact disease severity.

Research specific to Michigan has also examined the effects of crop residue and manure
amendments on potato scab in an experiment initiated in 1937 in East Lansing.
(KenKnight, 1939). Blue grass and alfalfa crop resides were applied to potatoes at
planting in furrow at a fresh weight of 44.7 Mg ha", along with horse manure at 2.2 and
11.2 Mg ha'l rates. These treatments were compared to control treatments receiving no
plant or animal residue amendments. Both Blue grass and alfalfa crop residue treatments
had greater surface scab area, 55.3% and 59.7%, respectively, than those found in control
treatments at 38%. Scab incidence in the manure treatments at the low, 41.5%, and high,
37.8%, rates were found to be lower than those of the control, 45.3%. The author offered

no insight or explanation of these results.

A secondary effect of manure application is an increased supply of non-limiting nutrients.
Animal manure amendment in cropping systems functions essentially as well-balanced
fertilizer. Typical inorganic mineral fertilizer applications provide formulations of N, P,
and K in accordance with crop needs. Micronutrients are applied only on an as needed
basis. The compositional formulation of animal manures is a fixed value that is difficult
to tailor to crop needs. With most manure applications are balanced on a N or P need

basis, other primary and secondary nutrients are often supplied at higher than normal

28

rates. These changes to nutrient applications are important to consider when augmenting

mineral fertilizer application with manure amendments.

Responses to P, K, and Ca have been frequently observed in potato production.

However, response to these nutrients is typically only seen in soils initially testing low
for these compounds. Rhue et al. (1986) found yield increases across a gradient of K
fertilization levels ranging from 47 to 233 kg K ha" split between planting and sidedress
applications in soils initially testing between 32 and 74 mg kg". Westermann et al.
(1994) observed similar responses when applying 112, 224, and 448 kg K ha" to soils
with initially at 59-77 mg kg" K. Soils with higher initial soil nutrient levels have not
been shown to respond to fertilizer applications. Locasicio et al. (1992) did not observe a
yield response to K fertilization of 225 or 450 kg ha" in soils with high K concentrations.
Panique et al. (1997) proposed 104 mg K kg" as a critical preplant soil test level at which
K fertilization should be based. Yield responses to P have been similarly correlated with
soil P concentrations. Locascio and Rhue (1990) observed yield response to a variety of
P sources in soils initially ranging from 8 to 15 mg kg". Phosphorus rates of 56 and 112
kg P205 ha" were not found to increase tuber yields in soils at 237 mg P kg" (Yuan et al.,

1985).

Specific gravity has been shown to be affected by high nutrient rates. Panique et al.
(1997) found decreasing specific gravity with increasing K rates of 93, 187, 280, and 373
kg K ha". Westermann et al. (1994) observed highest specific gravity to be correlated

with the lowest applied K rate (112 kg ha").

29

 

Disease incidence, such as scab, has been found to be correlated with increased Ca levels.
Davis et al. (1976) found a linear increase in scab infection with Ca applications.

Suppression of scab was seen following P applications as free ion activities were altered.

Manure Effects on Forages

Manure application to forages has generated mixed results in terms of yield and quality.

A' n w. .u’ L...

Daliparthy et al., (1994) applied both liquid dairy manure and conventional N mineral
fertilizer at low (112 kg N ha") and high (336 kg N ha") rates in western Massachusetts
to 1 and 2-year old alfalfa stands annually for two years. Dry matter production was not
effected by manure or mineral fertilizer application in the first year. Alfalfa dry matter
production was decreased with high manure application at one site in year two, attributed

to low precipitation and delayed regrowth from application.

Liquid dairy manure effects on cool season grasses were researched by Griffin et al.
(2002) in Maine in long-term 30-year grassland plots. The plots were predominated by
Kentucky bluegrass (Poa pratensis L.), timothy, and couch (Agropyron repens L.), with
smaller concentrations of cocksfoot (Dactylis glomerata L.), reed canarygrass (Phalaris
arundinacea L.), white clover (T rifoh'um repens L.) and dandelion (T araxacum oflicinale
Weber). Four treatments were used to determine fertility effects: no fertilizer, N only,
NKP, and liquid diary manure. A11 fertility treatments were balanced to equal rates of N,
84 kg N ha" for the first cutting and 56 kg N ha" for subsequent cuttings. Manure
application rate was determined from the first year available N. The experiment was

conducted over a six year period, with fertilizer applied two out of every three years.

30

Manure fertilization significantly increased DM grass yields compared to the control
treatment; however, mineral fertilizer application was more effective in increasing DM
yields. These differences were attributed to a lack of precision in estimating the amount
of N mineralized from manure sources. Analysis of grass nutrient content indicated
lower N concentrations in manure fertility treatments were not from improper estimation

of available N, but rather a lack of synchrony between N availability and plant demand.

Forage quality of cool season grasses has been shown to increase with the application

WWI A-.L--O-n-.1

liquid dairy manure (Min et al., 2002). Stands of orchardgrass (Dactylis glomerata L.),
reed canarygrass, alfalfa-orchardgrass and alfalfa-reed canary grass were treated with
four rates of liquid dairy manure applied at 415, 690, 830, and 970 kg N ha"; mineral
fertilizer at 225 kg N ha"; and an untreated control. In the first year manure was applied
following the first cutting in June and following the third cutting in August. Mineral
fertilizer was applied following the first cutting only. In the second year, manure
application was increased from two to four applications: early spring prior to green-up
and once following each of three cuttings. Applications rates were increased for manure

to ~815, ~1230, 1590, and 2014 kg N ha"; and for mineral fertilizer to 560 kg N ha".

Manure application was found to have no effect on acid detergent fiber or neutral
detergent fiber. Crude protein (CP) was more variable, with variation between years,
cuttings, and manure rates. Higher rates of manure generally increased CP content in the
first year. In later cuttings, high manure rates increased CP content above those found

with low manure rates. This trend was also observed in the second year of the study.

31

Liquid dairy manure was shown to have positive effects on forage quality beyond those

achievable with conventional mineral fertilizers alone.

Applications of N and K to forage crops at greater than recommended rates through
manure amendment is a possible when manure rates are balanced based according to soil
P. Nitrogen applications in particular have been examined for their effects on alfalfa
production. Alfalfa’s biological N fixation allows for self-sustaining N production.
However, seedling alfalfa stands do not posses biological N fixation capabilities. Low
levels of N fertilization have been observed to benefit the formation of functional
nodules, thus increasing establishment year alfalfa yields (Hannaway and Sheler, 1993).
These effects have not been reproduced inestablished alfalfa stands (Jenkins and
Bottomley, 1984; Lamb et al., 1995). Rather, NO3-N has been shown to decrease root
hair formation and the number of infection threads in established stands, reducing the
amount of nodules (Truchet and Dazzo, 1982). This effect infrequently leads to yield
reductions as the indeterminate growth habit of alfalfa nodules result in their regrowth

with a retune to lower soil N03-N concentrations (Becana and Sprent, 1987).

Potassium responses in forage crops have been observed by several researchers.
Increased K fertilization has been shown to increase dry matter yields in ryegrass stands
(Keady and O’Kiely, 1998). Fertilization at 120, 180, and 240 kg K ha" increased dry
matter yields over that of 0 and 60 kg K ha" rates. Fertilizer applications did not affect in

vitro dry matter digestibility, crude protein, or modified acid detergent fiber.

32

 

Markus and Battle (1965) observed significant alfalfa yield responses with K fertilization
over a period of nine years and twenty-six harvest events. Rates of 0, 47, and 93 kg ha"
were progressively significant from one another, while rates of 187, 280, and 373 kg K

ha", were all statistically similar and returned the highest yields.

 

33

 

Background and Rational for Integration

The Montcalm county region in west-central Michigan is a state leader in dairy, wheat,
forage, vegetable, and potato production (USDA, 2002a). The area’s proximity to major
markets such as Grand Rapids, Detroit, and Chicago facilitated the county’s development
from a item a small-scale general agriculture region in the late 1800’s to a regional
supplier of high-end dairy and vegetable products following World War II. The
Montcalm county region has generally followed the productionist model that
characterizes much of the nation’s current agricultural landscape. Production efficiency
drives an increasingly intensified archetype, often down-playing the implications of
clashing cultural, social, economic, and environmental functions brought about by this
focused narrow minded system (Hinrichs and Welsh, 2003). Mounting pressures on
potato production from outside forces including urbanization, rising land prices, and
increasing input costs have resulted in decreased soil quality and increased pest pressure
brought about by a dependence on short, non-diverse rotations. Dairy production in the
Montcalm area, like that of in many locations of the country, has seen average herd size
and production per cow increase. Industry consolidation has reduced the number of dairy
farms by 70% nationally since 1969 (McBride, 1997). The long-term sustainability and
environmental ramifications of these systems has been called into question with an
increasing awareness of potentially negative local, regional, and global consequences

associated with agricultural industrialization (Matson et al., 1997).

In an attempt to minimize fixed costs and improve overall efficiency, many dairy farms

have increased herd numbers to a point where their associated land bases can no long

34

«tt‘fié‘q

 

provide sufficient feed production or manure disposal sites. The separation of animal
populations fiom feed sources disrupts the cyclical nature of animal feed inputs and
manure outputs (Bannon and Klausnet, 1996; Lanyon and Thompson, 1996). A shift in
dairy feed production from on-site, diverse rations to combination of on-site roughage
production and off-site importation of high energy and protein grains and supplements
has been able to compensate for the shift in head to acre ratios, but manure disposal and
environmental protection issues have only recently been addressed. Emerging federal
regulations from the Environmental Protection Agency in revisions to the Clean Water
Act mandated changes as to how large farms, or confined animal feeding operations
(CAFOs), deal with manure management (EPA, 2003). “Permit Regulations and Effluent
Guidelines for Concentrated Animal Feeding Operations (CAFOs)” defined farms as
CAF Os if they exceed a certain number of animals or meet certain other criteria dealing
with how the animals or their waste comes into contact with surface water. Farms may
also be designed as CAF Os if a permitting authority from the National Pollutant
Discharge Elimination System inspects the operation and determines the farm is a
significant contributor of pollutants to surface water. Any farm over 700 mature dairy
cows is automatically classified a large CAFO. A farm with between 200 and 699
animals becomes a medium CAFO if so designated or has manure in some sort of contact
with surface water. Any size farm can be designated a CAFO by the EPA. While many
dairy farms in Montcalm county are small enough to avoid automatic CAFO
classification, larger operations are required to submit to the manure management

policies set forth by the EPA.

35

The EPA issued its final revision of “Managing Manure Guidance for Concentrated
Animal Feeding Operations (CAFOs)” in December of 2004 (EPA, 2004). This
document provides NPDES permitting authorities, perrnittees, and technical service
providers guidance on how to implement the 2003 Clean Water Act revisions regarding
CAFOs. These regulations developed by the EPA, along with Michigan GAAMPs
specifically targeting manure management (MDA, 2005b), include both mandatory and
voluntary regulations. Among these regulations, specific management of manure for
nutrient loading is covered in great detail. As farms grow in size, the ratio of feed
producing land base to animals often decreases as more feed is imported from off-fann
sources. However, the increasing amount of manure must be spread on this constant or
shrinking land base. As a result, nutrient excesses, particularly phosphorus, can build up
with over application of manure. The CAFO and GAAMP regulations seek to monitor
and control these nutrient excesses, and will ultimately require the certification of manure
management plans. Realistic, long-term manure management strategies will be required
to comply with these regulations. Complying with the EPA regulations will require many
CAF Os to spread their manure over a larger land base than they are currently utilizing,

and most will need to move their manure to off-farm sites (Ribaudo et al. 2003).

The deterioration of soil properties involved in intensive potato production has been
attributed to a reduction in soil biological activity through lower organic material inputs
compared to conditions found under pasture or natural vegetation (Saini and Grant,
1980). Increasing organic material contributions is crucial to mitigating and reversing

yield declines. More effective rotation crops and carbon-based soil amendments hold

36

potential for realistic, achievable system improvement. Michigan potato agronomic
systems have been improved with forage crop rotation and manure amendment in both
pre-modern agriculture (KenKnight, 1941; Wheeler, 1946; D011 and Thurlow, 1965) and
in current intensive management systems (Griffin and Hestennann, 1991; Snapp et al.,
2005). The re-integration of dairy and potato farm operations is seen as a viable

substitute to the current segregated agricultural landscape; a substitute that by

- “"1

lengthening crop rotations and widening input distribution, will have an improved overall

efficiency of the integrated agronomic systems.

 

Potato- dairy agronomic integration potential draws credibility from previously
successful implementation. Potato and dairy producers in Maine have demonstrated
mutual benefit from an integrated cropping system (Merrill, 2001). Farmers facing
moderate to severe production stresses are more inclined to incorporate practices such as
lengthened crop rotations and unfamiliar crops compared to farmers not facing servere
production challenges (Corselius et al., 2003). The dairy industry, in contrast to other
livestock industries, generally remains characterized by small level owner-operator
producers with managerial and decision making control. These operations have been
shown to be more open to conversion to more sustainable production techniques.
However, recent trends in national dairy production indicate large-scale
commercialization of the dairy industry in imminent (J ackson—Smith and Buttel, 1996).
The integration of farming functions often necessitates a decline in individual control.
The addition of new crops and amendments accompanies new constraints and logistical

factors associated with their use. The degree to which integration is successful is a

37

function of its ability to meet individual system requirements and conform to particular
situations. While operations in Maine have neared total functional integration, the mere
incorporation of manure amendment programs in potato production may evoke yield, and

thus economic responses.

Integration of Montcalm county potato and dairy farms is seen as a method by which to
alleviate individual system challenges. Potato farms are in need of soil enhancing
rotation crops and carbon based soil amendments. Dairy farms need to expand their
manure application land base and secure off-site feed production. By effectively
executing land swaps, the constraints of one system become the benefits of the other.
The proposed potato — dairy integration calls for the management of forages as a rotation
crop with potatoes and the application of manure on potato soil. Forage crops needed for
diary feed provide a viable rotation crop for potatoes. Spreading manure over a wider
land base, including potatoes, serves to address concerns of excess nutrient loading while
enhancing organic matter on chronically organic matter-short potato fields. Dairy farms
benefit from this arrangement by obtaining a needed resource, quality forage, while
disposing of an unneeded resource, manure. Integration represents a better allocation of
resources to increase productivity and farm income while meeting the publics concerns

and regulations pertaining to the environment.
One of the more challenging aspects to the integration of animal and potato systems is

defining the viewpoints from each producer. Defining specific viewpoints is critical as

each producer has needs and requirements specific to their operation. In order to

38

integrate farming systems, management practices on one farm will be shifted to the other
farm. The extent to which those operations take place depends upon the individual farm.
For instance, a dairy farm will concentrate on forage production; potatoes will be utilized
in a rotation, but forages remain the focus crop. Likewise, forage production emphasis
on a potato farm is limited to a secondary rotation crop with the primary focus on potato
production. Manure application functions in a similar manner. Manure to a dairy farm is
a byproduct first and beneficial amendment second. The spreading of manure is a
necessary, ongoing practice. Manure to a potato operation is solely a beneficial
amendment and application is an occasional event only to be used to enhance soil

characteristics.

This experiment adopts a potato grower viewpoint in terms of the focus on crepping
systems and manure utilization. Forage production and manure application are not
necessary practices, but are used only for the enhancement of potato production. Stands
of perennial forages typically remain productive for multiple years with high
establishment costs prohibiting frequent rotation. However, the focus on high value
potato production relegates forages production to secondary concern and mitigates any
establishment costs. A mix of 2-year and 3-year cropping rotations were used in this
study to examine the need to keep potato production occurring at a relatively high

frequency in order to maintain system profitability.

39

Cropping Systems

A set of five cropping systems were used to evaluate the effects of rotation and manure
on potatoes production. Corn is a common rotation crop with potatoes in central
Michigan and was used in this study as the standard defender system. This rotation was
included in the study twice, staggered by year, in order to provide a baseline of potato
production each year. Three forage crops were used to access rotation impacts. Alfalfa,
a predominate legume for dairy feed production, was included as a 1 and 2-year crop.
Festulolium (F estuca pratensis Huds. x Lolium perenne L.), a cool season perennial C3
grass was also evaluated as a 1 and 2-year crop. Sorghum-sudangrass (Sudex) (Sorghum
bicolor L. x Sorghum bicolor L.), a warm season C4 grass, was evaluated as a 1-year
crop. Alfalfa and festulolium were managed as harvest crops, with all biomass harvested
in accordance with typical forage management schemes. Sudex was managed as a cover

crop, with all biomass chopped and returned to the soil surface.

Corn — potato

A potato and corn rotation was included as the standard defender system. This
rotation system is the predominant cropping system in Michigan potato
production. Corn provides a modest financial return and requires fewer
management resources than potatoes. However, the system is relatively inflexible
with major field operations of corn planting and harvesting conflicting with potato

planting and harvest.

40

Potato — alfalfa

Alfalfa, with over 420,000 hectares, is the primary legume dairy feed in Michigan
(USDA NASS, 2002b). While other rotation legumes such as red clover, hairy
vetch, and sweetclover have been researched in rotation with potatoes, the value
and importance of alfalfa as a feed source necessitates its inclusion in this study.
Legumes such as alfalfa can contribute significant soil nitrogen for following
crops. Additionally, the taproot characteristic of alfalfa allows it to obtain sources

of water and nutrients not typically assessable to other crops.

P_otato - festflium

Festulolium is a hybrid of meadow fescue (F estuca pratensis Huds.) and either
Italian ryegrass (Lolium multiflorum Lam.) or perennial ryegrass (Lolium perenne
L.). Duo, utilized in this experiment, has tetraploid perennial ryegrass lineage.
Commercial varieties of Festulolium, including Duo, have been breed to exhibit
fescues more developed root system, winter hardiness, midsummer growth, and
drought tolerance; at the same time exhibiting the rapid establishment and forage
quality of ryegrass (Thomas and Humphreys, 1991). Cool season grasses are
characterized by their fibrous roots systems, compared to the taproots of alfalfa
and corn. Festulolium variety trials in East Lansing, Michigan produced an
average yield of 10.01 Mg ha" over three years in non-irrigated conditions (Leep
and Dietz, 2004). Grass hays have also been shown to have higher acid detergent
fiber (ADF) and neutral detergent fiber (NDF) than alfalfa hays (von Keyserlingk

et al., 1996).

41

Potato — sudex

Sorghum-sugangrass hybrids are high biomass producing crops that require less
intensive management than other forage crops. High yields can be achieved with
low fertilizer inputs and infrequent mowing operations. Sudex is used extensively
as a cover crop following potatoes in southern portions of the United States for its
ability to reduce soil compaction, improve soil tilth, and reduce weeds (J ansson
and Lecrone, 1991). Sudex has been proposed as a viable summer cover crop in
vegetable production with its potential to suppress weeds, production of high
levels of biomass, and ability to function as an emergency hay crop (McKinney et
al., 2004). Sudex, a C4 grass as opposed to C3 crops such as alfalfa and
festulolium, posses an additional C02 pathway that increases photosynthetic
efficiency. C4 crops have higher water use efficiency and achieve optimum

growth at higher temperatures than C3 plants.

42

Objectives

Ultimately, this experiment is conducted with the goal of establishing potato — livestock
integration as a feasible endeavor in the central Michigan region. This study focuses on
the agronomic aspects of the proposed integrated system. Economic and environmental
aspects of these systems, while critical in the larger context, are beyond the scope of this
experiment and are only briefly covered. Rather emphasis is placed on the agronomic
effects of proposed integration upon soil fertility and crop yield. The impact of crop
rotation and manure amendment on soil quality, specifically nitrogen dynamics, are
important aspects of improved potato systems. Without demonstrable improvements to
current yields, adoption of alternative cropping systems or amendments will be difficult

to regardless of other benefits.

Nitrogen dynamics in potato production continue to be one of the greatest challenges
facing potato growers. The ability to increase available soil N and absorbed potato
petiole NO3-N with manure amendment or forage rotation, while applying equal or less
mineral fertilizers would be of significant value to producers. Equally important to
increasing these N levels is the ability to provide consistent N concentrations through the
season. The use of organic N compounds hold potential for more even N availability

throughout the growing season. The following hypotheses aim to prove these benefits:

1. Nitrogen fertilization regimes including liquid dairy manure amendment

preceding potato crop production will increase the amount and seasonal

43

distribution of soil N and petiole NO3-N compared to conventional mineral N
fertilizer regimes alone.

2. Potato rotations including forages will improve the amount and seasonal
distribution of soil N and petiole NO3-N compared to conventional potato — corn
rotations. Benefits of forage crop production on N dynamics will increase with
forage stand length.

3. Potato system N dynamics will benefit from antagonistic effects of forage rotation

and manure amendment to a greater extent than either factor alone.

Manure amendment holds the potential not only the decrease reliance on mineral
fertilizers, but also to increase the quantity and quality to forage and potato yields.
Likewise, forage crop rotation with potato production is expected not only to increase
potato yields, but also add external benefits beyond those currently found in the
conventional corn — potato rotation. The following hypotheses are established as means

by which to evaluate the effectiveness of these alternative inputs:

1. A minimum 3-year forage rotation is required to induce potato yield increases;
2-year forage rotation will not be sufficient to improve potato yields in an
intensively managed potato-com rotation.

2. The combination of forage rotation and liquid diary manure application will

result in higher potato yield than either amendment individually.

3. Forage yield will be improved by the amendment of liquid diary manure to
conventional inorganic fertilizers regimes compared to forage fertilization

regimes solely supplied by inorganic fertilizers.

45

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57

Chapter 2: Nitrogen Dynamics

Abstract

Effective N management strategies are needed for potato (Solanum tuberosum L.)
production region in west central Michigan. Organic amendments and diverse crOp
rotations have been shown to increase potato yields, though a lack of reliable information
on amendment and rotation impacts to overall system N dynamics present a barrier to
widespread adoption of these management approaches. In order to better understand
these influences on N, soil and plant N was measured during two seasons in potato
rotations with and without liquid dairy manure amendment. Corn (Zea mays L.)
preceded potatoes in both 2003 and 2004.. Forage crops of one-year sudex (Sorghum
bicolor L. x S. bicolor L.) and alfalfa (Medicago sativa L.) preceded potatoes in 2003,
while two-year stands of festulolium (F estuca pratensis Huds. x Lolium perenne L.) and
alfalfa preceded potatoes in 2004. Available soil N and plant absorbed NO3-N as
measured by PRS probes and potato petioles demonstrated similar trends within years.
Crop rotation had greater impacts on N levels than manure application. Rotations with
forage crops and manure amendment resulted in higher soil and plant N concentrations in
2003 than corn rotation or non-manure treatments. This trend was initially reversed in
2004, with corn rotation and non-manure treatments exhibiting higher N levels than
forage rotations or manure treatment. Rotation and treatment differences were less
significant in 2004 than in 2003. Additions of high quality crop rotations and manure
amendment hold the potential to improve N synchrony with potato demand, though
external variable including environmental conditions may play a significant role in N

availability and plant uptake.

58

Introduction

Nitrogen management is one of the most important functions of production efficiency in
potato cropping systems (Stark et al., 1993). In sandy soil potato production, N is
typically the most limiting factor for tuber growth (Errebhi etal., 1998). Nitrogen
deficiencies limit tuber size and marketable yield, allow weeds to compete, and enhance
susceptibility to early die complex (Rosen, 1991; Lang et al., 1999). Low levels of N
early in the season reduce the number of tuber initiates (Roberts et al., 1982), thereby
limiting total potential yield. A recent survey of Washington potato producers indicated a
belief that higher than recommended N levels are nesseary to avoid limiting conditions
brought about by poor management or environmental conditions such as sub-optimal
irrigation, N fertilizer application, disease pressure, and excess precipitation (Lang and
Stevens, 1997). However, excess N has been shown to cause a variety of negative
physiological effects on potatoes, including delayed tuber growth, bulking, and maturity;
decreased specific gravity; and ultimately reduced yields (Oj ala et al., 1990; Griffin and
Hestennan, 1991; Belanger et al., 2002). High N levels, both prior to and during tuber
initiation and bulking, result in an over-production of vegetative production, delaying
tuber maturity (Allen and Scott, 1980; Ojala et al., 1990). Post-harvest management is
also effected by excess N fertilization, increasing bruising and reducing storability (Oj ala

et al., 1990; Baritelle et al., 2000).

Further complicating N management, N losses due to leaching and subsequent

groundwater contamination are a concern both economically and environmentally for

59

Michigan potato producers. Potatoes have shallow rooting systems compared to other
crops, resulting in lower effective rooting volumes from which N may be extracted (Stark
et al., 1993). 90% of potato roots are found in the upper 30 cm of the soil. Nitrogen that
moves below this level becomes largely unrecoverable (Lesczynski and Tanner, 1976).
The high propensity for N leaching on sandy soils (Vitosh and Silva, 1996) and small
rooting volume for N recovery results in the leaching of nitrate fi'om excess N
applications (Rourke, 1985). In a proposal for a national nitrate leaching index
assessment, Shaffer and Delgado (2002) stated that shallow rooted vegetable crops,
manure application, and course textured sandy soils combine to pose a ‘very high
potential for nitrate leaching vulnerability.’ The impacts of N leaching extend beyond the
individual producer economic implications of decreased fertilizer efficiency. Nitrate
leaching is receiving increasingly greater attention as a source of non-point source
pollution by the non-agricultural corrrrnurrity. Michigan’s Natural Resources and
Environmental Protection Act, Act 451 of 1994, regulates quantities and/or
concentrations of nutrient release that violate established water quality standards (State of
Michigan Legislature, 1994). As part of the Michigan Right to Farm Act, Act 93 of
1981, a set of statewide standard and acceptable management practices were established
in order to provide agricultural operations with a framework by which to comply with
environmental legislation (State of Michigan Legislature, 1981). Compliance with these
standards, Michigan’s Generally Accepted Agricultural and Management Practices
(GAAMPs) (MDA, 2005), is voluntary and provides protection from public and private
litigation regarding agricultural management. GAAMP standards are based upon

scientific principles developed by, among others, university researchers. GAAMPs have

60

 

been developed for a number of agriculture practices with the greatest potential

environmental impacts, including nutrient utilization.

Utilization of alternative N sources for potato production, including legumes and animal
manures, has been the subject of increasing interest among Michigan potato producers in
recent years. Antidotal evidence of increased potato yields through the use organic soil
amendments by various producers has prompted widespread interest in the diversification
of conventional potato agronomic systems. Recent research efforts examining the
effects of organic amendments on soil fertility properties have shown promising results.
Perennial ryegrass (Lolium multiflorum L.) and red clover (T rifolium pretense L.)
forages, managed as production hay crops, increased total C and N, light fi'action C and
N, microbial biomass, and microbial activity in potato rotations in Prince Edward Island,
Canada (Angers et al., 1999). Increasing perennial forage frequency to at least 60% in
potato rotations was found necessary in order to avoid soil degradation seen in more
intensive forage and barley (Hordeum vulgare L.) rotations where potato fi'equency
exceeded 50%. Grandy et al. (2002) found that cattle manure and legume green manure
crop amendment increased organic matter, total C, and soil aggregation in Maine potato
production. Griffin and Porter (2004) found that amendments of dairy manure increased
total, particulate, and microbial biomass C and N compared to treatments not receiving
manure. Webb et a1. (1997) demonstrated greater soil N mineralization in potato crops
amended with organic manures. Porter et al. (1999) found application of beef manure

increased total tuber yields, in part due to increased nutrient availability from organic

61

amendments. Griffin and Porter (2004) found amendments of manure to significantly

increase total N pools.

Research in Michigan examining the use of organic amendments and crop rotations have ‘
considerable history. These studies, particularly the more dated, have typically focused
on measurement of potato yields rather than the factors potentially influencing those yield
increases. Wheeler (1946) found alfalfa rotations to increase potato yields over those
possible with continuous potato production. Doll and Thurlow (1965) found alfalfa and
bromegrass (Bromus L.) stands preceding potatoes increased potato yield compared to

row crops.

Manure amendment and crop rotation have been shown through the literature to have
credible positive effects on the N dynamics of potato agronomic systems. However,
significant variability in potato yields can be seen in many of these experiments. While
Snapp et al. (2005) found yield increases utilizing winter cover crops and low C/N ratio
crop rotations in 2003, these same crops were associated with lower yields in 2004.
Griffin and Hestermann (1991) found no yield increases when alfalfa preceded potatoes,
attributing these results to poor synchronization between N mineralization and crop
demand. A lack of consistent replicable responses to manure amendment or crop rotation

is a common theme in the aforementioned experiments.

Variability in environment, soil composition, and management techniques all affect the

rate and quantity of soil N mineralization (Vigil et al., 2002). Soil N levels available for

62

plant growth are a firnction of system inputs such as N fertilizer application, crop residue
contributions and system outputs including crop uptake and NO3-N leaching (Tran and
Grioux, 1991; Gasser etal., 2002). Much of the existing literature regarding N
availability in potato production focuses on inorganic fertilizer applications (eg. Carter
and Bosma, 1974; Tim et al., 1983; Webb et al., 2000) while a lack of information
exists on how various organic N contributions interact with climate and soil conditions to
supply N for crop uptake during the growing season (Snapp and Fortuna, 2003). Organic
N from crop residue, amended animal manure, and residual fertilizer N contribute to the
overall soil N pool, significantly impacting the N availability for future crops (Alexander,
1977; Campbell et al., 1991b). Accurate estimation of N release for plant uptake from
organic sources is necessary for optimum fertilizer efficiency. With the knowledge of not
only the quantity of organic N availability, but also the timing at which this N becomes
available, inorganic fertilizer applications can be adjusted so as to avoid over-

fertilization.

Effective methods by which to measure season N levels are necessary for accurate N
management. Petiole NO3-N sampling has become a widely accepted method for in-
season N management in Michigan due to its reliability and feasible sampling protocol
(Snapp et al., 2001; Vitosh et al., 2005). Potato petiole NO3-N concentrations are a
reflection of the balance between uptake and transport of soil NO3-N to the canopy and
the relocation of that N to the tubers (Westcott et al., 1991). A strong correlation
between N inputs and potato yields have been seen though petiole NO3-N concentrations

(Gardner and Jones, 1975; Porter and Sisson, 1999).

63

Soil N measurement is another means by which to determine N status through the
growing season. Ion exchange probes have been shown to be a reliable means to monitor
in-season N availability. Plant Root Simulator (PRS) ion exchange probes (Western Ag
Innovations, Saskatoon, Canada) are buried in the soil, providing an in situ measure of
nutrient supply by continuously adsorbing ionic compounds on a charged membrane
surface (Schoenau et al., 1993). PRS probes provide an integrated measure of supply
rates as they are subjected to all factors affecting nutrient supplies, including free ion
activities, buffer capacity, mineralization, and immobilization (Sulewski et al., 2002).
This measure of N availability has been successfully demonstrated for measuring the N
dynamics of manure and crop residue amendments in agronomic systems (Qian and

Schoenau, 1997; Adderley et al., 1998; Qian and Schoenau, 2002).

PRS probes have shown to perform comparably to other ion exchange resin membranes.
Johnson et al. (2005) examined the abilities of two ion exchange resins, PRS from
Western Ag. Innovations and Unibest resin capsules (Unibest Inc., Bozeman, MT) for
measuring soil nutrient availability compared to traditional NI-14+ and NO3° soil tests
under varying temperature and moisture conditions. While soil tests and Unibest
capsules were able to detect soil mineral N responses to both temperature and moisture,
PRS probes were only able to detect moisture changes. However, PRS probes were
shown to more accurately approximate temporal patterns in soil N mineralization than

other tests.

64

Qian and Schoenau (1999) were able to show strong correlations (r2 0.79 to 0.96)
between measured soil N availability and plant N uptake in manure and non-manure
amended treatments, validating their assessment of PRS probe technology as an effective

tool for measurement.

Crop residue quality and quantity have been shown to be the most important factors
influencing N mineralization (van der Krifi et al., 2001). A variety of compositional
characteristics have been used to quantify residue decomposition, and thus nutrient
mineralization and plant availability. Carbon/N ratio has evolved as the most widely
accepted predictor of N mineralization (Norman et al., 1990; Aulakh et al., 1991; Vigil
and Kissel, 1991; Quemada and Cabrera, 1995; Odhiambo and Bomke, 2001), though
other quality constituents including ligrrin (Bruulsemann and Christie, 1987; Vigil and
Kissel, 1991) and structural carbohydrate (Ranells and Wagger, 1992; Wagger etal.,
1998) have been linked to N mineralization rates. These researchers have consistently
proved an inverse relationship between C/N ratio and N mineralization. As a rule of
thumb, a C/N ratio of 25:1 has been found to be the balancing point of N availability
(Allison, 1973). At C/N ratios above 25:1, N immobilization and a temporary net loss of
available soil N is expected to occur. Below this point, residues are generally expected to
mineralize readily, providing rapidly available N. With the implication of C/N ratios on
N availability, C/N is frequently used to imply the quality of the residue; high C/N

residues are considered low quality and vise versa (Gil and Fick, 2001).

65

Manure amendments, like crop residue amendments, have been found to have significant
in-season impacts on soil N dynamics. Composition analysis for prediction of N
mineralization is often complicated by the heterogeneous nature of manure. Wilkerson et
al. (1997) noted that dairy cows within the same herd, depending in diet and lactation
period, can produce manure with variable compositions. Initial nutrient contributions of
manure amendments are typically expressed as first-year availabilities, with liquid dairy
manure N availability frequently cited in the neighborhood of 30% (Motavalli et al.,
1989; Klausnet et al., 1994; Curless and Kelling, 2003). Manure amendment benefits,
however, have often been found to extend beyond estimated nutrient availability.
Increased microbial biomass, enzyme activity and N mineralization have been observed
following manure application (Guenzi et a1, 1978; Kandler and Eder, 1993; Kandler et

al., 1994; Webb etal., 1997; Ma et al., 1999).

66

Objectives

Nitrogen dynamics in potato production continue to be one of the greatest challenges
facing potato growers. The ability to increase available soil N and absorbed potato
petiole NO3-N with manure amendment or forage rotation, while applying equal or less
mineral fertilizers would be of significant value to producers. Equally important to
increasing these N levels is the ability to provide consistent N concentrations through the
season. The use of organic N compounds hold potential for more even N availability

throughout the growing season. The following hypotheses aim to prove these benefits:

1. Nitrogen fertilization regimes including liquid dairy manure amendment
preceding potato crop production will increase the amount and seasonal
distribution of soil N and petiole NO3-N compared to conventional mineral N
fertilizer regimes alone.

2. Potato rotations including forages will improve the amount and seasonal
distribution of soil N and petiole NO3-N compared to conventional potato - corn
rotations. Benefits of forage crop production on N dynamics will increase with
forage stand length.

3. Potato system N dynamics will benefit from antagonistic effects of forage rotation

and manure amendment to a greater extent than either factor alone.

67

Materials and Methods

Experimental Design

This experiment was conducted at the Michigan State University Montcalm Potato
Research farm, MI (43°21' N, 85°10' W) on a McBride sandy loam (coarse-loamy,
mixed, frigid Alfic Fragiothods). Intensive potato rotations have dominated the farm for
several decades. These rotations have degraded soil properties such as organic matter
concentration to low levels. These conditions are expected to make changes in soil
quality more apparent, exacerbating any potential yield shifts.

Table 2.1. 2002 initial soil characteristics at Montcalm Potato Research Farm.
0-20 cm SE 20-50 cm SE

 

pH 6.59 ' 0.04 6.59 0.05
CEC emo'ks" 3.53 0.13 3.28 0.15
Phosphorus mg kg" 154 5.16 101 5.85
Potassium mgkg" 167 3.84 109 2.14
Magnesium mgkg" 94 2.26 86 3.26
Calcium mg kg" 391 12.49 373 22.47
Organic matter % 1.10 0.06 1.07 0.04

SE- Standard Error

Treatments consisted of twelve systems, six rotation sequences with and without liquid
dairy manure treatment. The experiment was arranged in a randomized complete block
design replicated four times. The rotations included two com-potato, two 2-year forage,
and two 3-year forage treatments (Table 2.1). Corn as a rotation crop with potatoes is
common cropping system in Michigan potato production and was included in this study
as a defender system by which to gauge alternative cropping systems. Two defender crop
rotations were staggered by annual entry point so that in each year both crops in the

rotation were present. Alfalfa and festulolium rotations were managed as production

68

forage systems, with all biomass removed from the plot at harvest. Sudex was managed
as a green manure crop, with all biomass chopped and returned to the soil surface. Rye

was planted as a winter cover crop each fall following potatoes in all rotations.

Two-year alfalfa and sudex rotations represent potato driven integration systems. Sudex
production offers no benefit for livestock producers as a green manure crop.

One-year alfalfa stands are a move toward integration with livestock Operations.
Establishment year yields in alfalfa production provide livestock operations with modest
feed supplies, though these limited production yields are below levels necessary for total
farm feed production. Greater yields from multiple year stands are necessary for feed
production on a reasonable landbase. High establishment costs of alfalfa also preclude
short-term production intervals; establishment costs from alfalfa seedings are generally
only recouped after several years of production. As such, one year alfalfa and sudex
production are expected to have greater benefits to potato production than dairy systems.
Three-year cropping systems of alfalfa and festulolium better suit the needs of integrated
dairy farms than shorter one-year forage production. A second production year beyond
establishment allows for production yields necessary to sustain dairy forage
requirements. These systems place a greater emphasis on dairy production than shorter,

2-year potato driven systems.

69

Table 2.2. Crop rotation for 2002, 2003 and 2004 at Montcalm Potato Research Farm.

 

 

Rotation 2002 2003 2004

1 Corn Potato Corn

2 Potato Corn Potato
3 Alfalfa Potato Alfalfa
4 Sudex Potato Sudex
5 Festulolium Festulolium Potato
6 Alfalfa Alfalfa Potato

Table 2.3. Common, scientific, and cultivar names of species used in 2002, 2003 and
2004 at Montcalm Potato Research Farm.

 

 

Common name Latin binomial Cultivar
Potato Solanum tuberosum L. Snowden
Corn Zea mays L. Pioneer 36G12
Alfalfa Medicago sativa L. Pioneer 53Q60
F estulolium F estuca pratensis Huds. x Duo

Lolium perenne L.
Sorghum/sudangrass Sorghum bicolor’ L. x Honeypot

S. bicolor L.

Plots measuring 3.7 by 15.2 meters were oriented such that rows ran east to west with a
gradual decreasing in elevation to the north. As a result of this slight hill, the north end
of the range suffered from slower water drainage and subsequent flooding. The wet
spring of 2004 resulted in a flooding event that prevented emergence of crops on the four

northem-most plots and the subsequent abandonment of these plots.

Manure Amendment

Liquid dairy manure from a nearby 2,500 head operation with liquid pit manure storage
was applied at 12,260 L ha", a regionally common application rate. A pull-type liquid-
manure applicator was used to inject manure to depth of 20 cm in the spring prior to
planting in 2002. The applicator utilized a hydraulic cutter for even distribution of

manure between four injection shanks. Sand bedding mixed with the manure resulted in

70

a liquid density higher than that of what the transfer pump on the applicator could handle,
necessitating the addition of water to increase the fluidity of the manure. Application
rates were adjusted so that 12,260 L ha" of initial product was applied. A higher
capacity, hydraulically powered pump was installed on the injector for amendment in
2003. With the presence of perennial forage crops in 2003 and 2004, manure was
broadcast on the soil surface for all treatments. The distribution pattern in 2004 was
refined so as to provide for more even surface coverage than that achieved in 2003. One
day following manure broadcasting, primary tillage using a rototiller (Great Plains Mfg.
Inc., Salina, KS) was performed on both manure and non-manure treatments. This tillage

event served to incorporate surface applied manure within GAAMP regulations.

Table 2.4. Liquid dairy manure concentration characteristics in 2002, 2003 and 2004 at
Montcalm Potato Research Farm.

 

 

2002 2003 2004
Moisture % 88.5 71.9 79.6
Solids % 11.5 28.1 20.4
pH 7.06 7.28 7.10
Nitrogen, total mgkg" 3256 4288 4586
Nitrogen, ammonium mgkg" 1602 2412 2924
Nitrogen, organic mg kg" 1654 1916 1664
Phosphorus mg kg" 438 676 1932
Potassium mg kg" 1970 2564 3822
OM by L01 8 kg" 332 810 589
Magnesium mg kg" 1120 1760 1540
Calcium mgkg" 3160 7440 410
reported on a dry weight basis

OM- organic matter
LOI- loss on ignition

71

Table 2.5. Total nitrogen applications for manure and conventional fertilizer treatments
in 2002, 2003 and 2004 at Montcalm Potato Research Farm.

 

 

 

 

Manure N Manure N Fertilizer N Total N
Total Available Available

2002 kg ha" kg ha" kg ha" kg ha"
Potato

Manure 204 1 54 91 245

Conv. - - 224 224
Corn

Manure 204 154 145 299

Conv. - - 207 207
Alfalfa

Manure 204 154 - 154

Conv. - - 0 0
Fest.

Manure 204 154 1 14 268

Conv. - - 171 171
Sudex

Manure 204 154 84 238

Conv. - - 168 168
2003
Potato

Manure 319 219 91 310

Conv. - - 224 224
Corn

Manure 319 219 145 364

Conv. - - 207 207
Alfalfa

Manure 319 219 - 219

Conv. - - 0 0
Fest.

Manure 319 219 114 333

Conv. - - 228 228
2004
Potato

Manure 326 238 91 329

Conv. - - 224 224
Com

Manure 326 238 145 383

Conv. - - 207 207
Alfalfa

Manure 326 238 - 238

Conv. - - 0 0
Sudex

Manure 326 238 84 322

Conv. - - 168 168

72

Potato Production

Potatoes were planted with a two-row potato planter (Lockwood Mfg, West Fargo, ND.)
at a seed spacing of 22.5 cm in row and 91 cm between rows. Potatoes were hilled
approximately five days prior to emergence. Weed control was achieved through
standard chemical herbicide application and manual hoeing as needed. Fertilizer was
applied in liquid form at planting and as broadcast granular for subsequent fertilizations.
Wet conditions following the 2004 planting resulted in sporadic emergence and required

replanting in spots in mid-May.

Forage Production

Forages were established with a John Deere ( Deere & Company, Moline, IL) 2.4m drill
followed by a Brillion Pulverizer (Brillion Farm Equipment, Brillion WI) equipped with
rolling press wheels to ensure soil to seed contact . Alfalfa was drilled at 18.0 kg ha",
with festulolium and sudex drilled at 30.0 kg ha". Plots were tilled with a rototiller
(Great Plains, Mfg, Inc., Salina, KS) at manure incorporation and finished with a field
cultivator (Kongskilde Industries, Bloomington, IL) prior to planting. Alfalfa and
festulolium were out twice in 2002, was out twice. Alfalfa and festulolium produced four
and five cuttings, respectively, in 2003. Alfalfa and sudex each were each harvested

twice in 2004.

Corn Production
Corn was planted with a custom plot planter (ALMACO, Nevada, IA) to a population of

74,300 seeds ha". Seed spacing was set 28 cm in row and 76 cm between rows. At

73

emergence, plots were thinned if stands exceeded the desired population and spot
replanted if needed. Weed removal was performed through chemical herbicide and
mechanical cultivation for moderate weed pressure, and hand hoeing for light weed

pressure.

Crop Fertility

Crop fertilization rates were based on Michigan State University Extension soil fertility
publications (Vitosh, 1990; Christenson et al., 1992; Warncke et al., 1992; Snapp et al.,
2002) and tailored to meet site conditions for potato (Dick Crawford, personal
communication), corn (Keith Dysinger, personal communication), and forages (Rich

Leep, personal communication) using MSU soil test laboratory recommendations.

Manure available nutrient contributions were calculated by plot for nitrogen, phosphorus
and potassium. Any deviations in available manure nutrients from conventionally
management treatments were corrected at the time of second fertilizer applications, with
manure plots receiving higher or lower levels of fertilizer than that applied to
conventional treatments. For potato, corn, sudex and festulolium, nitrogen was
calculated as the primary balancing nutrient; in alfalfa, phosphorus was used to balance
nutrients. Potatoes received a starter fertilizer applied at planting and subsequent
applications at hilling and two and four weeks following emergence. Alfalfa,
festulolium, and sudex received broadcast fertilizer at emergence and following the first

cutting in coordination with anticipated rainfall events. In addition, festulolium was

74

fertilized following cuttings l and 3 in 2002. Fertilizer was applied to corn at planting

and at the V5 stage.

Table 2.6. Mineral fertilizer application in manure and conventional fertilizer treatments

in 2002, 2003 and 2004 at Montcalm Potato Research Farm.

 

 

 

 

Fertilizer Manure

N P K N P K
2002 kg ha" kg ha" kg ha" kg ha" kg ha" kg ha"
Potato 316 38 - 204 - -
Corn 139 39 25 140 - -
Alfalfa - 204 612 - 146 437
Festulolium 17 l - - 1 l4 - -
Sudex 168 - - 84 - -
2003
Potato 316 38 - 204 - -
Corn 204 39 25 145 - -
Alfalfa - 204 612 - 146 437
Festulolium 228 - - 1 14 - -
2004
Potato 316 38 - 204 - -
Corn 204 39 25 145 - -
Alfalfa - 204 612 - 146 437
Sudex 168 - - 84 - -

 

Table 2.7. Fertilizer formulations utilized in experiment at Montcalm Potato Research

 

 

Farm.

Crop Timing Formulation

Potato starter 19-17-0
sidedress 49-0-0

Corn starter 19-19-19
sidedress 28-0-0

Alfalfa 0-13-39

Festulolium 34-0-0

Sudex 34-0-0

75

Production Inputs

Pesticides were applied as needed throughout the growing season. Nematicide was
applied over the entire range two years preceding the study’s onset and again in the
spring of 2003 to plots in which potatoes would be planted that season using a custom
built injection system. Fungicides were applied during the season on weekly intervals
beginning at a plant height of 15 to 20 cm and ended approximately two weeks prior to
vinekill. A tractor-drawn sprayer was used for fungicide applications. Insecticides and
herbicides were applied using a Hudson C02 backpack sprayer (H. D. Hudson Mfg. Co.,

Chicago, IL.).

Irrigation was provided as needed throughout the season, typically on a 7 to 9 day
interval. Water was applied in 2002 via a solid set pipe system, using two lines with
sprinklers set at 12 m intervals. For the 2003 and 2004 seasons, an overhead traveling

system was utilized.

Soil Nitrogen Analysis

Plant Root Simulation (PRS) probes (Western Ag Innovations, Saskatoon, SK, Canada)
were used to measure seasonal N availability during potato production in 2003 and 2004.
PRS probes are comprised of ion exchange resin membranes encapsulated in a plastic
sheath. These membranes measure 10 cm2 and are charged with either Na+ or HCO3'
ions to adsorb N03” or NH4+, respectively. Probes were inserted in the same soil slots
over the course of the season to minimize site variability. Probes were left in the soil for

a period of two weeks. Upon removal at the end of the two week burial period, probes

76

were removed from the soil and brushed in the field to remove large quantities of soil.
Probes were then placed in a seal bags for transport to campus. In the lab, probes were
rinsed with de-ionized water to remove any remaining soil. Probes are once again placed
in sealed bags and shipped in a cooler to Western Ag Innovation laboratories in

Saskatoon, Canada for analysis.

To determine N03 and NHa, probes were eluted with a 0.5N HCl solution for one hour.
The eluate was then used to determine nutrient concentrations using an automated
colorimetry and inductively-coupled plasma spectrometer. Nutrient supply rate was
calculated from the total volume of eluent and nutrient concentration, providing a
measurement of mass of nutrient ion per unit ion-exchange surface area over the burial

period (Hangs et al., 2002).

In firrrow measurements were made in order to better determine total soil N availability
rather residual N not absorbed by competing potato or weed roots. Root exclusion tubes
were used throughout 2003 and 2004 to provide a root competition free estimate of N
availability. During the second half of 2004, duplicate probes were inserted in-row in
com-potato rotations with exposure to competing roots to measure the influence of root

competition.

In addition to in-season N measurement, end-of-season soil NO3-N levels were measured

following the 2004 production season. A Giddings hydraulic soil probe (Giddings

Machine Company, Windsor, CO) was used to obtain three samples per plot, spilt at 0-8

77

inches and 8-20 inches. Soil was sealed in plastic bags, transported and stored at the

Crop and Soils field lab.

Nitrate-N levels were determined by combining a 10 g moist soil sample with 50 ml of a
1N KCl solution. Containers were caped and shaken for 30 minutes at 180 rpm.
Concluding the 30 minute shaking, samples were left to settle for 15 minutes. The
supernatant was then filtered though funnels lined with Whatrnan #1 filter paper into
vials and frozen. The Michigan State University Soil and Plant Nutrient Laboratory
utilized a modified Griess-Ilosvay (Keeney and Nelson, 1982) cadmium reduction
method to determine NO3-N. Copperized cadmium reduces NO3' to NO;' under the
principle that NOz' reacts with aromatic amines in acidic solution to give diazo salts.
These salts couple with aromatic agents to form colored azo compounds that a

spectrophotometer can use to determine color intensity (Geldermann and Beegle, 1998).

Potato Plant Nitrogen Analysis

Potato petioles were sampled with the maturation of the third petiole, 56 days after
planting (DAP) in 2003 and 64 DAP in 2004. Samples were taken on an average of 10
day intervals. Samples were obtained mornings between 6 and 9 am, placed in cooled
containers, and returned to campus. After a refiigeration period of several hours, petioles

were shipped overnight to A&L Great Lake Laboratories (Fort Wayne, IN).

78

Statistical Analysis

Analysis of variance (ANOVA) was performed on PRS ion probe potato petiole and soil
nitrates with Proc GLM (SAS Institute, 2004) using the Kenward-Roger method for
determining degrees of freedom. When significant effects of treatment occurred, means
were compared using Fischer’s Least Significant Difference. Unless otherwise stated,

differences were considered significant at an alpha level of 0.05

Environmental Conditions

Cool temperature predominated the two years during which nitrogen dynamics were
examined in this experiment. 2003 was 1.0° C below 30-year temperature norms and
2004 was 0.4° C below normal. The months of March, April, and May in 2003 were -
0.66°, -l.10°, and -1.89° C of normal temperatures, while those same months in 2004
were 2.4°, 0.6°, and 08° of normal. Rainfall in both 2003 and 2004 was below 30-year
averages. While this experiment is supplemented by artificial irrigation, the system is
operated only during periods of greatest tuber water demand in June, July and August.
Early season soil moisture was totally dependent upon natural precipitation. Early season
rainfall in 2003 was -2.97, -2.59, and 1.42 cm of normal for the months of March, April,
and May. Rainfall was 2.82, -3.94, 13.46 cm of normal for this same period in 2004.
While both growing seasons may be summarized overall cool and dry, the early season of

2003 was cool and dry compared to warm and wet in 2004.

79

Results and Discussion

2003 Nitrogen Dynamics

Soil nitrogen concentrations as measured by PRS probes at 76 and 90 days after planting
(DAP) showed significantly higher levels of total N based upon crop rotation and manure
amendment. Measurements after 90 DAP showed no differences between rotations or
manure amendment. Alfalfa rotation and manure amendment provided the highest total
N uptake at 76 DAP. While statistically similar to the alfalfa non-amended and corn
amended systems, the alfalfa with manure system had significantly greater soil N
availability than the corn with no manure system. This pattern was also seen at 90 DAP,
though differences in rotations and manure amendment decreased. Overall, the alfalfa
crop rotation with manure amendment provided the greatest concentrations of total N

availability throughout the growing season.

Crop rotation and manure application both had significant treatment effects. Both alfalfa
manure and non-manure treatments provided higher amounts of soil N than corn manure
and non-manure treatments. Significance between cropping systems at the P= 0.05 level,
however, was only found with the corn rotation treatment with no manure amendment.
This system, with the widest C/N ratio residue and lack of manure organic N amendment,
resulted in the lowest soil N concentrations. Treatment effects of rotation and manure on
available soil N were only found early in the season. PRS probe measurements alter 90

DAP until the end of the season indicated no rotation or manure treatment effects.

80

Initial sampling of petiole NO3-N showed no differences due to crop rotation or manure
amendment. A lack of initial petiole NO3-N response to soil N fertility has previously
been observed (Porter and Sission, 1991; Waterer, 1996). Petiole NO3-N declined from 2
to 2.25% initially to between 1 and 1.5% for alfalfa and sudex rotations and 0.5 to 1.0%
for corn rotations. Doll et al. (1971) found that petiole NO3-N concentrations peak when
plants are 4-6 weeks old, falling thereafter throughout the season. Earlier season petiole
NO3-N monitoring in 2004 indicated this peak may occur closer to 10 weeks, but
declining NO3-N concentrations following a peak occur regardless of seasonal timing.
A11 petiole NO3-N concentrations in 2003 followed this pattern, though not necessarily to

the same degree.

Crop rotation and manure amendment both had significant treatment effects on petiole
NO3-N. Alfalfa and sudex rotations, regardless of manure application, provided
statistically identical petiole NO3-N concentrations throughout the growing season. In
contrast, corn rotations provided consistently lower petiole NO3-N following the initial
sampling date 64 DAP. Effects of manure amendment were more apparent in corn
rotations than in alfalfa or sudex rotations. Manure amendment did not increase overall
petiole NO3-N, but manure was able to sustain N petiole concentrations to a greater
extent than non-manure treatment. Petiole NO3-N concentrations were similar between
manure and non-manure amendment treatments 81 DAP. While NO3-N concentrations
were lower in the non-amendment treatment at 92 DAP, the manure treatment had similar
concentrations to those observed 81 DAP. At 102 DAP, manure treatment NO3-N

concentrations were similar to non-amendment treatment concentrations. This same

81

Figure 2.1. 2003 PRS probe 2-week N03 + NH; uptake.

mod-lb ow;

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

95an .22 gen
03 N9. 9 _. 3.. cm mu.
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on consoaow 9 .3838 N .ooanom 9 v.32 m .262 um 22.
or
om
on
oz #85 one x cos. /I
mz mime 28 x .om o
m2 «mama Judaism - 9.
r. 88... ounces. lo
1.. 586 v eoeaom .. V8 on
r. 885 v one 4%
r .885 o_oo_m
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a
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flou— .>coo 85cm ‘ :30 Ill
00..

 

 

9.3% £2 + ”oz goosm 82o man 8cm

(z-wo N 611) Kiddns rHN + con

82

Figure 2.2. 2003 potato petiole NO3-N concentration.

 

 

 

 

 

 

mezzo—n. not< o>nn moons oo._
~: New No 3 on 8
_ b _ p _ o
8.391 m. 54.32 m .892. mm 22. t 22. o 22.
wz ONE Sou x :92 md
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oz 893 cos fem
oz 885 Pecos.
eooaom
load F
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2:52 "cannon 2825. ml.
.to..._ 5:00 "cannon. \ xouzw .79....
0.:an "250.". 23.83. I

 

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eon. scoo "cocoon a o:o=<|_..l
0.5an ”cannon—\Eoo .m I
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838588 2902 6.2.6.". cocoon 82.

83

trend was repeated at 112 DAP. This trend of increased petiole NO3-N concentration
with manure application and the ability to sustain those higher levels indicates promise
for manure application to increase soil fertility. These results are similar to other manure
treatment studies. Webb et al. (1997), specifically in potato production, and Ma et al.
(1999) have both previously observed increased soil N mineralization resulting from
manure amendment at levels above those seen with equal nutrient application with

mineral fertilization.

Crop rotation treatment effects as measured by PRS probes were expected with the
widely dissimilar alfalfa and corn residues inputs. Allison (1973) found that residues
with C/N ratios wider than 25:1 tend to immobilize soil N, with crop residue N only
slowly becoming available for plant use. In contrast, residues with narrower C/N ratios
are expected to immediately contribute available N. Both observed C/N ratios from
forage quality determination (Table 2.9) and literature values (Table 2.10) suggest that if
N mineralization were to proceed according to Allison’s observations, plant available N
early in the growing season would be greater from alfalfa rotation treatments than corn
rotation treatment. These anticipated results are substantiated through both PRS probe
observations and potato petiole measurements. Alfalfa crop rotation treatments

significantly increased N concentrations compared to corn rotation treatments.

84

Table 2.8. Crop above and below-ground C/N ratios as complied from several authors.

 

AG C:N BG C:N

 

Corn (stover) 60:1 1 48:1 2

Sudex 47:1 3

Alfalfa 18:14 21:14

Cool Season Grass 15:1 4 22:1 4
(Italian ryegrass)

AG DM- above ground dry matter
BG DM- below ground dry matter
1 Cowan, 2005

2 Havlin etal., 1999

3 Creamer and Baldwin, 2005

4 Baron et al., 2001

85

Table 2.9. Observed C/N ratio“ by treatment, cutting, and average in 2002, 2003 and
2004 at Montcalm Potato Research Farm.

 

Cutl Cut2 Cut3 Cut4 Cut5 Av.

 

 

 

2002

Alfalfa 13.8
Manure 17.3 10.7
Conv. 16.2 10.9

Sudex 26.7
Manure 25.0 29.4
Conv. 25.8 26.4

Festulolium
Manure 17.6 14.0 14.7
Conv. 13.3 13.9

2003

Alfalfa 12.5
Manure 12.6 11.5 11.9 12.8
Conv. 13.2 11.0 12.5 14.3

Festulolium 1 7. 1
Manure 22.6 13.8 13.4 14.5 17.8
Conv. 26.0 17.3 14.2 12.8 18.5

2004

Alfalfa 13.4
Manure 13.6 13.2
Conv. 14.5 12.4

Sudex 36.2
Manure 31.6 33.2
Conv. 37.7 42.4

* Total nitrogen was determined through forage quality analysis using the Hach
modified Kjeldahl procedure (Watkins et al., 1987), with crude protein estimated by
multiplying total N by 6.25. Crop C concentrations were estimated at 45% (Campbell et
al., 1991a) in order to determined C/N ratios.

86

Petiole NO3-N concentrations in potatoes grown after alfalfa and sudex rotations
treatments were statistically equivalent. These observations are in contradiction to
general assumptions regarding sudex residues. Sudex, physiologically, is much more
closely associated with corn than alfalfa. Both are C; grasses with similar structural
design and growth characteristics. Their cited C/N ratios of 60:1 and 47: 1, respectively
(Table 2.9), suggest that their residues should impact similar effects on subsequent season
N dynamics. However, sudex crop rotation effects on N uptake were more similar to the
alfalfa rotation treatment than the corn rotation treatment. By managing sudex as a high
production summer cover crop, high N fertilization and frequent cuttings likely
contributed to lower residue C/N ratios that those expected had the crop received lower N
inputs or reached greater maturity between harvests. Actual measured C/N ratios of
sudex were much lower (25:1 - 30:1) (Table 2.10) than those measured by Creamer and
Baldwin (2005) (Table 2.9). Sudex residue decomposition was also influenced by
multiple harvest events during the summer of 2002, with all biomass production returned
to the soil surface. The first cutting of sudex was exposed to decomposition for nine
months prior to 2003 potato planting, resulting in an extended period for residue
decomposition and subsequent N release. Alfalfa, as a production hay crop, had
substantial portions of biomass removed during the season. Late season cuttings,
common in high production hay crops, result in little overwintering biomass. Alfalfa
residue contributions in the spring are comprised of limited above-ground spring
regrowth and greater below ground root biomass. Literature values of below ground
alfalfa biomass (Table 2.9) are similar to those observed by sudex residues in this

experiment.

87

Environmental conditions, including temperature and soil moisture, play instrumental
roles in N mineralization (Goncalves and Carlyle, 1994). 2003 was a cool and dry
growing season, 1.0° C and 16.4 cm below 30-year temperature and precipitation
averages between the period of March to October. August was the only month with
above average temperatures, while May and July were slightly above average
precipitation levels. The cool, dry season-long conditions would be expected to retard
the microbial processes, effectively slowing mineralization and shifting N availability
later into the season. Ma et al. (1999) observed lower than expected mineralization rates
of manure during a dry, cool growing season in Ontario in 1996. Griffin and Hestermann
(1991) observed that during drought conditions in 1988, dry conditions delayed legume N
mineralization to such an extent that, while increases to plant N concentrations were
observed, no overall tuber yield increases were seen with the forage crop rotation.
Drought conditions existed throughout much of the Midwest in 1988, including the early
spring period before planting. April, May, and June averaged 30% of normal rainfall for
the period. The severe dry conditions during that spring likely slowed legume residue
decomposition to a point where significant mineralization began only with irrigation in
early June. The normal mineralization curve may have been shifted several weeks later
in the growing season. The dry conditions observed in 2003 would also be expected to

slow N release, though not to the extent of that observed in 1988.

2004 Nitrogen Dynamics
Nitrogen dynamics in 2004 demonstrated a very different trend that those in 2003.

Whereas narrow C/N crop residues and manure amendment increased available soil N

88

and potato petiole NO3-N levels in 2003, wide C/N ratio residues and non-manured
treatments increased soil and plant N in 2004. Initial PRS probe measurements showed
soil N levels at 54 DAP to be greatest in the corn rotation without manure amendment,
followed by the corn rotation with manure amendment and alfalfa rotation without
manure amendment. This pattern was also observed at 68 DAP, though the alfalfa
rotation with manure amendment replaced the corn rotation with manure amendment as
the system with greatest soil N uptake. As in 2003, statistical differences between the
four systems disappeared following the second burial period of the PRS probes.
However, at 110 DAP, levels of significance were once again detectable. Following 68
DAP, a trend developed over the next two burial periods of decreasing soil N supply from
the wide C/N, non-manure treatments. By 110 DAP, soil N concentrations were greatest
in alfalfa rotation and manure amendment treatment; a pattern identical to that observed

early in 2003.

Initial petiole NO3-N measurements at 56 DAP did not act as an effective precursor for
season N uptake trends. Alfalfa rotations with both manure and non-manure treatments
and festulolium rotation with manure treatment contained the highest initial petiole NO3-
N. Alfalfa rotation without manure amendments continued to supply greater, though not
statistically significant, amounts of petiole NO3-N through the rest of the season
compared to other systems. Alfalfa and festulolium rotations with manure amendment

had low petiole NO3-N over the remainder of the season. The corn rotation without

89

Figure 2.3. 2004 PRS probe 2-week N03 + NHa uptake.

 

 

 

 

 

 

   

 

 

 

 

 

 

 

 

 

  

 

 

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90

Figure 2.4. 2004 potato petiole NO3-N concentration.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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91

Figure 2.5. 2004 fall soil NO3-N.

  
    
 

 

 

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crop rotation beginning in 2002

     

 

 

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92

15

manure amendment emerged 68 DAP as the system with the highest petiole NO3-N,
remaining higher than other systems through 89 DAP. A small flush of petiole NO3-N
was observed at 89 DAP in all systems. While potato N uptake is generally considered to
cease 70 to 80 days following emergence (Millard and MacKerron, 1986), Waterer
(1996) measured increasing petiole NO3-N as late as 88 DAP that could be correlated
with increased tuber yields. No discemable differences in petiole NO3-N concentrations

between systems were observed at 98 or 110 DAP.

The observed soil and plant N levels in 2004 were in contrast to the expected
mineralization characteristics of organic N sources. These predicted trends were, by and
large, adhered to in 2003, though envirOnmental conditions were suspected of subtly
influencing mineralization. Climatic effects are theorized to have played a much larger
role in 2004, likely explaining the observed N trends. While 2004 was, on a whole, a
cool and dry season like that of 2003, early season environmental abnormalities
significantly altered the N dynamics. Unseasonably warm temperatures in late March
and mid April resulted in March and April temperatures 2.4° C and 06° C degrees above
30-year averages. Those warm conditions likely initiated considerable N mineralization
of high quality alfalfa and festulolium residues. However, several significant rainfall
events beginning in late April and continuing through late May likely resulted in high
leaching losses of that early mineralized N. Rainfall events of over 2 cm have been
shown to move NO3-N out of the potato rooting zone (Cameron et al., 1978). Rainfall of
2.1 cm (April 25), 4.9 (May 8), 3.8 (May 9), 2.4 (May 14) 1.5 (May 21), and 3.7 (May

23) were among the events that contributed to a record 20.8 cm of precipitation during

93

May, 13.5 cm above long-term averages. These rainfall events followed manure
application, perennial forage termination, primary tillage, and crop planting that was
conducted between April 3 and April 6. Those rainfall events facilitated the conversion
of organic N into leachable mineral N forms, with subsequent loss of available soil N for
potato production. A large body of literature exists showing NO3-N leaching losses can
be exacerbated during periods of high precipitation following legume stand termination
(Low and Armitage, 1970; Robbins and Carter, 1980; Adams and Pattison, 1985). Soil N
availability measurements in 2004 indicated that manure treatments had lower N levels
than non-manure treatments, particularly when coupled with alfalfa rotation. Rapid
mineralization of organic N forms present in crop residues and animal manures to
leachable inorganic compounds could be expected during the uncharacteristically warm
conditions of early 2004. Harris (1993) noted in work conducted in 1989 at the Rodale
Institute Research Center in east central Pennsylvania that leaching losses are potentially
increased with the application of manure immediately after legume crop termination
following heavy spring rainfall. Residual soil N existing following legume rotations was

more susceptible to leaching than mineral fertilizer N.

The loss of mineralized N from forage crop and manure amendment sources dramatically
altered the available soil N and potato petiole NO3-N uptake during the 2004 season.
Measurement of soil N availability and potato petiole NO3-N concentrations in 2003
indicated greater soil N availability and plant N uptake from forage crop rotation and
manure amendment. These effects would be expected to continue through the 2004

season, likely to a greater extent from longer forage stands and three years of annual

94

manure amendments. Two-year forage stands of alfalfa and festulolium established in
2002 resulted in a three-year interval between potato crops in these rotations. Extended
production intervals have been observed to increase potato yields, particularly when
rotated with forage crops (Carter and Sanderson, 2001). Forage stands, particularly
legumes with organic N contributions, have been cited as strong contributors to overall
soil fertility levels (Frye et al., 1985; Harris and Hestermann, 1990; J anzen et al., 1990).
Annual manure amendments have been shown to increase soil fertility much the same
way (Paul and Beauchamp, 1993; Porter et al., 1999; Sanchez et al., 2001). The
combination of perennial alfalfa and annual manure amendment would be expected to
dramatically increase soil N pools (Paul and Beauchamp, 1993). However, the leaching
events of early 2004 altered the expected N dynamics. Residue mineralization from
narrow C/N crop residues and manure amendments resulted in a loss of those N
contributions. The increased N mineralization potential following manure amendment

(eg. Ma et al., 1999) acted to exacerbate this phenomenon.

Wide C/N ratio residues has been shown to mineralize N more slowly than narrower C/N
residue crops (Bruulsema and Christie, 1987). However, the processes governing the N
mineralization of crop residues are subject to a variety of factors, including
environmental influences. Slower decomposing corn residues were able to retain more
N during the high rainfall events in early 2004, releasing this N later in the season. These
effects, however, were not shown to be consistent through the growing season, as
changes in soil N availability was detected in the later stages of the 2004 growing season.

Alfalfa and corn rotations with manure amendment provide increased available soil N in

95

mid August, similar to that exhibited early in 2003 and similar to predicted mineralization
patterns. Petiole NO3-N concentrations increased slightly at 89 DAP. Though potato N
uptake is assumed to negligible 70-80 days after emergence (Millard and MacKerron,
1986), Waterer (1996) observed petiole NO3-N uptake at 88 DAP positively correlated
with increased yields. These results might be best explained through increased soil
microbial activity in treatments with greater diversity. Stimulation of soil N pools has
been observed with alfalfa rotation and dairy manure treatment (Rasse et al., 1999;
Masciandara et al., 2004). Despite the loss of available N sources early in the season,
alfalfa and manure treatments provided improvement in season-long N availability. This
observation raises concerns regarding N synchrony and possible detrimental effects of
excessive N late in the season (Ojala et al., 1990; Griffin and Hestermann, 1991).
However, the lack of response by petiole NO3-N concentration to increased soil N levels
indicates potatoes utilized little of this available N. Rather, this soil N may facilitate
residue decomposition and additional N mineralization. The overwintering rye cover
crop following potato production is expected to recover much of this residual N,
recycling it for subsequent utilization the following year. Kristensen and Thorup-

Kristenson (2004) showed an overwintering rye crop was able to uptake 90.5 kg N ha".

Soil nitrate analysis conducted in the fall of 2004 at depths of 0-20cm and 20-50 cm
measured residual soil N. Three of the six crop rotation treatments had been planted to
potatoes in 2004 allowing feasible comparisons between two-year corn and three-year
alfalfa and festulolium forage rotations. Despite a lack of significant rotation or manure

treatment effect, manure application showed a trend toward increased soil N levels above

96

non-manure treatments in the 0-20 cm depth. At the deeper 20-50 cm sampling depth,
there were no differences between manure and non-manure treatments. However,
manure treatment in alfalfa rotations and non-manure treatment in alfalfa and festulolium
rotations showed greater soil N levels. Residual soil N at this depth following alfalfa or
festulolium might be expected due to the deep rooting characteristics of these crops and
the relatively shallow rooting depth of potatoes. Ashley et al. (1997) determined the
depths which several crops are effective at utilizing water (Table 2.11). Established
stands of both alfalfa and festulolium were found to have functional rooting at 120 cm
depths, making deposition of N upon root decomposition likely. Potato roots at only 45
to 60 cm are unable to recover those sources of N. Residual soil N at depths up to 120
cm following potato production present leaching threats as there is no means by which to

reincorporate this N back into production.

Table 2.10. Effective rooting depth of selected crops.

 

 

Crop Maturity Depth (cm)

Alfalfa new stand 30 — 45
established stand 120

Cool season grass new stand 15 — 45
established stand 45 — 120

Potato 45 - 60

Corn 105

Winter cereal (rye) Haun 4-7 stage 30 - 60
-reproduced from Asheley et al., 1997

97

2003 vs. 2004 Nitrogen Dynamics

Total accumulated season soil and plant N concentrations were markedly higher in 2004
than 2003. Soil available N concentrations in 2003 initially ranged from 36 - 66 pg N
cm’2 at 76 DAP, rapidly decreasing at 104 DAP to levels under 21 pg N cm'2 for the rest
of the season. In 2004, soil N levels ranged from 68 - 87 Spg N cm'2 54 DAP, increasing
to 84 - 99 pg N cm'2 68 DAP. Soil N level gradually decreased to 30 - 10 pg N cm'2 by

the end of the season.

Similarly, petiole NO3-N concentrations were lower in 2003 than 2004. Initial soil NO3-
N concentrations in 2003 ranged from 2 - 2.25%. End of season NO3-N concentrations
ranged from 1 - 1.5% for alfalfa and sudex rotations and 0.5 - 0.1% for corn rotations.
Petiole NO3-N concentration in 2004 was initially lower at 1.5 - 2.0 %, but did not drop
though the season as drastically as the 2003 levels. At season end, petiole NO3-N

concentration was at 1.0 - 1.5%.

As noted previously, suppressed N mineralization has been observed in cool, dry
environmental conditions such as those in 2003. However, a more likely explanation of
these observations may be due to the increased overall N mineralization potentials from
greater labile N pools. Kuzyakov et al. (2000) described this increase in N
mineralization, or priming effect, as “strong short-term changes in the turnover of soil
organic matter caused by comparatively moderate treatments of the soil.” The addition of
N to the soil stimulates soil microbial activity, resulting in greater overall available N

than that applied from the amendment. This effect has been cited in both annual manure

98

amendment and legume crop rotation (Paul and Beauchamp, 1993; Webb et al., 1997; Ma
et al., 1999). Harris (1993) suggested that legume N input increases in soil N priming
potentials may be of more value than legume contributions to either short or long-term

direct N supplies.

Other researchers at this site observed effects of the environmental conditions of 2003
and 2004 as well. Snapp et al. (2005) observed increased potato yields in 2002 and 2003
with winter cover crops and high biomass production sweet corn (Zea mays L.) and
wheat (Triticum aestivum L.) rotation crops. In 2004, these two management practices
were associated with lower potato yields than systems including no winter cover crops or
lower biomass production rotation crops. Highest yielding potato rotation utilized no
winter cover crops. In systems with cover crops, rotations with a summer wheat or snap
bean (Phaseolus vulgaris L.) crop followed by rye produced higher potato yields
compared to a rotation with sweet corn or legume winter cover crops. These results
suggest that grass crops may recover and recycle residue soil N more effectively than
legumes. This conclusion is in agreement with research results of Shipley et al. (1992),
where it was found that cereal rye and annual ryegrass recovered fall applied N better
than hairy vetch, crimson clover, or native weeds. Additionally, wheat and snap beans
residues should leave more residual N in the soil profile than sweet corn. Sweet corn and
wheat C/N ratios are generally similar, but wheat residues with a mid-summer harvest
date have greater exposure to favorable decomposition conditions prior to winter. Snap
beans are expected to mineralize quickly because of their low C/N ratios. A key

management variable was winter crop termination and primary tillage. Whereas

99

overwintering crops in this study were terminated and incorporated prior to the high
rainfall period of May, Snapp’s overwintering crops were incorporated in late May.
Actively growing perennial crops have been shown to reduce NO3-N leaching losses
(Henseler and Attoe, 1970; Long and Hall, 1987). However, the incorporation of high
biomass winter cover crop residues into severally NO3-N depleted soils may have
resulted in initial N immobilization. Temporary immobilization of N from crop residues
has often been observed (Aulakh et al., 1991; McKenney et al., 1995), which may lead to
N supply poorly synchronized with potato N demand, as witnessed by Griffin and

Hestermann (1991) at this site.

Farrow vs. Valley Placement of PRS Probes

Over the last three sampling periods of 2004, a duplicate set of PRS probes were placed
in-row in order to determine the effect of placement on soil N measurement. PRS probes
had been placed in furrow, within root exclusion cylinders for the main 2003 and 2004
experiments. Under this management scheme, total soil N availability was measured free
of competing sinks. Placed in-row, probes measured soil N levels while competing with

potato uptake.

100

 

Table 2.11. Location effects on soil N as measured by PRS probes.

 

 

Aug 9 Aug 23 Sept 6

Hill

Manure 46.80 a 19.83 a 18.73 a

Conv. 44.38 a 11.98 ab 10.33 b
Furrow

Manure 418711 15.17 ab 12.10 ab

Conv. 30.47 b 10.43 b 10.20 b
P- value

Manure treatment 0.023 0.004 0.013

Location 0.005 0.086 0.074

Manure x location 0.108 0.359 0.084

Comparisons made by date

Furrow soil N, particularly in non-manure treatments, was consistently lower than those

of in-row hill soil N.

101

Potential Improvements for Nitrogen dynamics

The results of this study suggest that the use of diverse crop rotations and animal manure
amendments hold potential to improve N availability and uptake in potato production
systems. However, these results also highlight the large influences environmental
conditions can have on N dynamics. In order for any widespread reliance on organic N
sources, effective means by which to mitigate uncontrollable environmental factors must
be developed. Proactive management of organic inputs is currently unfeasible until long-
term forecasting evolves to a point where seasonal climatic trends may be accurately
predicted. Currently, management control is relegated to reactionary methods. More
intensive management of crop residues and manure amendments may be able to fine-tune
seasonal N dynamics, including N release and availability of organic materials. Shifts in
manure amendment management are frequently more difficult than crop management
adjustments. Aspects such as storage, incorporation, and application timing are controlled
by on-farm logistics and environmental regulations that complicate management
flexibility. Despite these challenges, a better understanding of factors influencing

organic amendment N may allow for better N utilization.

The nutrient constituency variations of various crop residues have been explored in
length in this study. As evidenced in this work and by others (eg. Aulakh et al., 1991;
Vigil and Kissel, 1991), crOp species can dramatically alter residue biochemical
composition. High C/N ratios of corn residues release and mineralize N very differently
than low C/N ratio alfalfa residues. Animal manures are inherently even more variable in

composition than crops residues. Manure nutrient content is a function of animal type,

102

animal age, feed ratio, and manure storage system. Animal species is a major influencing
factor. Eghball et al. (2002) compared literature values of several animal species and
found first year N availability ranging from 90% in swine and poultry manures to 32% in
dairy manure, with second year N availability was similarly broad. Variability within
species, and even with herds, also prevents consistent manure nutrient prediction.
Wilkerson et al. (1997), in modeling estimated manure N excretions, emphasized the
differences in manure compositions within a dairy herd with a range of lactating, non-

lactating, growing, and replacement cattle.

The C/N ratio of manure has been shown to cause variations in N mineralization by up to
40% (Chadwick et al., 2000). Qian and Schoenau (2002) observed a negative correlation
between cattle manure C/N ratio and N mineralization. They found that manure C/N
ratios above 15:1 delayed initial N mineralization, a result corroborated by Beaucharnp
and Paul (1989). Van Kessel et al. (2000) examined the influence of manure components
including residual feed stuffs, forage cell walls, simple N compounds, and nondietary
metabolic components on N mineralization, determining that improving estimates of N
mineralization requires research on both readily available N compounds and N
immobilizing compounds. The demonstrated variability between not only different
manure types, but also variability within a single manure source itself, makes

management adj ustrnents impacting N release very difficult.

While the modification of crop residue and manure characteristics to better meet crop

demands though improved N synchrony has not been directly addressed, a limited

103

amount of research has recorded the compositional shifts in manure from various
management approaches. Powers and Van Horn (1998) demonstrated that dietary
manipulation in dairy and swine production alters the nutrient composition of manure.
Supplying limited amino acids, for example, allows for a reduction in total dietary protein
needs, thereby reducing the excretion of N. Adjustments to N composition effects overall
C/N ratios, with implications on N availability for crops following soil amendment.
Manure handling and storage systems have been shown to significantly alter manure
characteristics from initial excrement to field application. Schoenau et al. (2000)
observed that solid dairy manure contains less inorganic N and is less immediately
available compared to liquid dairy slurry. Stockpiling or aging manure lowers the C/N
ratio, increasing the release of available N upon amendment (Qian and Schoenau, 2002).
The use of manure handling techniques including composting, solid separation, anaerobic
lagoons, and anaerobic digestion, in contrast to the more conventional liquid pit or solid
pack, have also been shown to influence nutrient composition (Van Horn et al., 1994).
The modification of manure handling prior to storage influences N concentrations as
well; Muck and Richards (1983) found that nearly half of manure N from lactating dairy

cows may be lost before manure reaches storage facilities.

The physical quality of crop residues impacts N mineralization as well. Residue particle
size reduction through general tillage processes may be able to modify N dynamics.
Vaughan and Evanylo (1998) demonstrated increased N release by mowing and disking
crop residues. Greater residue particle surface area increases the soil micro-biota

colonization area and influences the exchange of water, nutrients, and oxygen between

104

the residue and soil (Swift et al., 1979). Particle size also controls the extent to which
residue contacts clay and silt soil particles. Hassink (1997) found that these soil particles
act to protect residues from microbial decomposition by occupying available surface area.
Bending and Turner (1999) found that particle size effects on N mineralization were
correlated with residue quality. Reducing the particle size of high-quality residues
(Brussels sprout (Brassica oleracea L.), CfN of 15:1) promoted rapid microbial
respiration and N mineralization. In contrast, particle size reduction of low quality
residues (ryegrass (Lolium perenne L.) root, C/N of 38: l; wheat straw, C/N of 91 :1)

caused N immobilization and a delay in microbial respiration.

Timing of crop residue desiccation was shown in this research to have an impact on N
availability. Sudex and corn residues are structurally and compositionally similar; their
high C/N ratios typically result in slow N release. The early termination of sudex
residues in the summer of 2002 led to much greater N release synchrony with potato
demand in 2003 than corn residue termination in the fall of 2002. Sudex residues
effected potato petiole NO3-N more similarly to high-quality alfalfa residues than corn
residues. Early termination of a low-quality reside may assist in synchronizing N
availability. Phillips and Stopes (1995) demonstrated this effect as well, finding higher
quality residues were more effective as N suppliers when followed immediately after
incorporation with a crop. Effects from low-quality residues were greater when the
following crop was delayed by a month. Wagger (1989) evaluated the effect of delayed
crop termination and found that N mineralization rates could be slowed by allowing crop

C/N ratios to increase with a two week delay in termination.

105

Residue placement has also been shown to alter short-term soil N mineralization. Crop
residue incorporation, as opposed to surface placement, has been observed to initially
depress N mineralization rates (Smith and Sharpley, 1990; Aulakh et al., 1991; Baggs et
al., 2000). However, this N immobilization was frequently found to be positively
correlated with C/N ratio. Smith and Sharpley (1990) observed greater N mineralization
in the short-term (84 day) from higher quality residues, in the order of alfalfa > peanut
(Arachis hypogea L.) > soybean (Glycine max L.) > oat (Avena sativa L.) 2 sorghum
(Sorghum bicolor L.) > wheat > corn. In addition to N mineralization effects, residue
placement may affect early season soil temperature and moisture. Surface applied
residues help conserve soil moisture that might otherwise be lost with residue
incorporation. Early desiccation of winter crops through mechanical mowing was found
by Vaughan and Evanylo (1998) to provide ample time for mineralization prior to corn

planting while conserving soil moisture.

Despite a general understanding of the effects of termination timing, residue placement,
and particle size modification, knowledge of when to implement management changes to
fine-tune N releases is necessary. Currently, no reliable protocols exist on N dynamic

modification.

106

Conclusion

Ultimately, the observed variation in N availability and uptake demonstrates the need for
more accurate methods of predicting N dynamics in potato production. Crop rotation
was found impact soil and plant N dynamics to a greater extent than manure amendment.
Forages rotation and manure application improved overall potato N availability and
uptake in 2003. This trend was reversed in 2004 when com rotation and no manure
amendment increased N availability and uptake. Environmental conditions, particularly
above average temperatures early in April followed by record May precipitation, were
cited as primary influences for these dissimilar N dynamics. The lack of response to
forage crop and manure amendment N contributions in 2004 was in direct contrast to the
commonly observed increasing yield response over time to reduced potato cropping
frequency, diverse crop rotation, and annual manure amendment. When functioning as
expected, forage crop rotations and manure amendments are capable of significantly
increasing both soil available N and plant absorbed NO3-N. However, as shown in this
research, these effects are neither consistently reproducible nor always beneficial. More
research is needed on the impact of N sources, particularly organic, on overall N
dynamics under a range of field conditions. The ability to modify management effects in
response to uncontrollable outside forces is a prerequisite for more intensive organic N

source use.

107

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Appendix

Table 2.12. Temperature, precipitation and growing degree day monthly totals for March
— October and season totals during 2002, 2003 and 2004 at Montcalm Research Farm.

 

bs Norm Dev Obs Norm
-0.4 11.2 14.3
-0.11 10.57 7.32
-5 211 310
12 137 228
18 82 154
0 125 195
-1.10 12.4 14.3
-2.59 8.74 7.32
-13 246 310
-10 160 228
-7 85 154
4 130 195
0.6 13.5 14.3
-3.94 20.78 7.32
6 275 310
4 197 228
6 124 154
12 160 195

 

 

 

 

 

 

 

 

 

 

 

JULY AUG
Obs Norm Dev 0.
amp. 23.0 21.7 1.4 20.7

Free. 9.19 6.35 2.84 18.08
g GDD 4.4 576 539 37 504
GDD 7.2 490 453 37 418
GDD 10 404 367 37 332
GDD MD 393 359 34 330
emp. 20.8 21.7 -O.9 21.
Free. 6.60 6.35 0.25 6.60
GDD 4.4 506 539 -34 519
GDD 7.2 420 453 -34 433
GDD 10 333 367 -34 347
GDD MD 331 359 -28 344
emp. 20.0 21. -1.7 17. 2
Free. 4.37 6.35 4.98 5.05
g GDD 4.4 481 539 -58 417
GDD 7.2 395 453 -58 330
GDD 10 309 367 -58 244
GDD MD 310 359 -49 261 335 -74 260 230 30 85 118 -33

 

2003

 

 

 

 

 

 

Temp 8 Mean temperature ('C)

Proc 8 Precipitation (cm)

GDD MD= Growing Degree Days calculated with 10'C and 30'c cutoffs
Obs = Totals observed

Norm = Normals calculated over 30 year period (1951-1980)

Dev = Deviation of observed from normal

119

Table 2.13. 2003 PRS ion exchange probe soil NO3-N + NH4-N 2-week uptake (ug N
cm' ).

 

Days after planting (date)

 

76 90 104 1 18 132 146
(7-22) (8-5) (8-19) (9-2) (9-16) (9-30)

Corn
Manure 74 b 80 ab 67 47 20 15
Conv. 87 c 99 be 74 44 12 10
Alfalfa
Manure 68 ab 84 ab 69 49 3O 30
Conv. 76 b 88 ab 61 54 23 27
LSD a=0.05

Table 2.14. 2004 PRS ion exchange probe soil N03-N + NH4-N 2-week uptake (pg N
cm' ).

 

Days after planting (date)

 

54 68 82 96 1 10 124
(6-28) (7-12) (7-26) (8-9) (8-23) (9-6)

Corn
Manure 45 ab 24 b 20 15 15 ab 12
Conv. 36a 19a 16 15 14b 12
Alfalfa
Manure 66 b 29 ab 19 21 21 a 16
Conv. 53 ab 26 ab 18 17 17 ab 12
LSD a=0.05

120

Table 2.15. 2003 potato petiole NO3-N % by sampling date.

 

Days afier planting (date)

 

 

 

64 70 81 92 102 112
(7-9) (7-17) (7-28) (8-8) (8-18) (8-28)

Corn

Manure 2.12 1.55 ab 1.39 b 1.36 a .81 b .81 ab

Conv. 2.06 1.43 b 1.41 b .98 b .81 b .53 b
Alfalfa

Manure 2.21 1.83 a 1.95 a 1.63 a 1.28 a 1.29 a

Conv. 2.15 1.81 a 1.74 a 1.64 a 1.30 a 1.09 a
Sudex

Manure 2.05 1.79 a 1.84 a 1.60 a 1.23 a 1.21 a

Conv. 2.11 1.82a 1.80a 1.51a 1.24a 1.16a
LSD a=0.05
Table 2.16. 2004 potato petiole NO3-N % by sampling date.

Days after planting (date)
56 68 77 89 98 1 10
(6-30) (7-12) (7-21) (8-2) (8-13) (8-23)

Corn

Manure 1.46 be 2.03 c 1.34 c 1.66 bc 1.32 1.20 a

Conv. 1.80 b 2.70 a 1.82 a 2.00 a 1.42 1.34 ab
Alfalfa

Manure 2.08 a 2.09 be 1.41 be 1.43 c 1.36 1.34 a

Conv. 1.94 a 2.31 b 1.63 ab 1.78 b 1.41 1.37 a
F estulolium

Manure 1.84 ab 2.12 be 1.46 be 1.60 be 1.42 1.10 b

Conv. 1.62 b 2.18 be 1.36 be 1.66 be 1.35 1.32 ab
LSD a=0.05

121

Table 2.17. 2004 fall soil % NO3-N by sampling depth.

 

 

Depth Depth
0-20 Std 20- 50 Std
cm Dev cm Dev
Com / Potato % %
Manure 1.82 0.71 2.31 0.37
Conv. 1.03 0.29 1.72 1.20
Potato / Com
Manure 2.26 1.20 1.47 0.80
Conv. 1.53 1.08 1.44 1.10
Sudex / Corn
Manure 1.30 0.27 .68 0.42
Conv. 1.24 0.75 1.12 1.15
Alfalfa / Potato
Manure 1.16 0.37 .44 0.23
Conv. 0.68 0.21 .34 0.09
Alfalfa / Alfalfa / Potato
Manure 1.80 1.95 2.34 1.29
Conv. 1.19 0.48 1.82 1.11
Festulolium / F estulolium / Potato
Manure 2.06 0.57 1.47 0.98
Conv. 1.76 1.09 2.21 0.98
LSD a=0.05

122

Chapter 3: Potato and Forage Agronomy

Abstract

Michigan dairy and potato producers posses system integration potential in the state’s
mid-central region. An understanding of the agronomic effects of integrated crop-
livestock systems with manure transfers for potato (Solanum tuberosum L.) and forage
production is essential in order to determine system viability. Forage crops as l-year and
2-year stands were incorporated into potato rotations to determine effects on potato and
forage yield and quality on a site historically predominated by intensive potato rotations.
Two-year potato rotations with alfalfa (Medicago sativa L.) and sorghum-sudangrass
(Sorghum bicolor L. x S. bicolor L.) and 3-year potato rotations with 2-year stands of
alfalfa and festulolium (F estuca pratensis Huds. x Lolium perenne) L. were compared to
the regionally common 2-year com (Zea mays L.) - potato rotation. Liquid dairy manure
was applied at 12,260 L ha" and evaluated against equivalent conventional mineral
fertilizer applications balanced to available nitrogen. Manure was shown to be more
effective at increasing potato yield than crop rotation alone. The combination of manure
and crop rotation produced the most significant increases in potato yields. C4 grass
residues of corn and sudex were more effective as rotation crops than C3 grass or legume
residues of festulolium and alfalfa. Scab disease infection increased with manure
application. Festulolium yields increased with manure application in 2003. The
integration of forage crop rotation and manure amendment holds the potential to increase

the potato yield and quality.

123

Introduction

Intensive cropping tends to deteriorate the physical condition of most soils, ultimately
making them more difficult to manage and resulting in decreased crop yields (Saini and
Grant, 1980). Rapid declines to soil organic matter and soil structure brought about by
short, intensive potato production systems are common. At potato cropping frequencies
of 33 to 50 percent, yields can be expected to decline at some point over the long term
(Vos and van Loon, 1989). These trends are brought on primarily by reduced soil
biological activity due to lower organic material inputs compared to soil under pasture or
natural vegetation (Saini and Grant, 1980). The use of beneficial rotation crops and
manure amendments has been shown to be key to mitigating and ultimately reversing

these trends; increasing the quantity and quality potato yields.

Studies examining the effects of alfalfa, cool season grasses, and corn in potato rotations
in Michigan have shown mixed results. In a 10-year study located at the Lake City
Experiment Station in Lake City, Michigan, Wheeler (1946) found alfalfa rotation
increased potato yields above com rotation or continuous potatoes. Conversely, Griffin
and Hesterman (1991) found alfalfa did not increase potato yields on the current
experimental site in Entrican, Michigan. Elsewhere, studies in Rhode Island found 3-
year redtop (Agrostis alba L.) - redtop - potato rotations outyielded 3-year red clover
(Trzfolium pretense L.) - red clover - potato rotations (Odland and Sheehan, 1957).
Increasing the length of potato rotations utilizing legumes has been shown to influence

increase potato yields. Carter and Sanderson (2001) found that a 3-year rotation of barley

124

(Hordeum vulgare L.) -red clover-potato increased potato yields above those seen in a 2-

year rotation of barley-potato.

Manure amendment has been shown to increase potato yields above those possible with
conventional mineral fertilizer alone. In a long-term study applying barnyard manure in
addition to several rates of mineral fertilizers on 4-year potato rotations, manure
amendment was found to consistently increase marketable tuber yield at any fertilizer rate

(Black and Cairns, 1958; Black and White, 1973).

Liquid dairy manure effects on forages have been, as a body, inconclusive. Daliparthy et
a1. (1994) found no increase to alfalfa dry matter yields with manure and various mineral
fertilizer applications. Similarly, Griffin et a1. (2002) compared liquid dairy manure
application to several mineral fertilizer regimes in cool season grasses, finding manure
did not increases yields above those achieved with conventional fertilization. Chemey et
a1. (2002) found that four years of annual manure amendment increased cool season grass
yield relative to conventional fertilization. These effects become more pronounced with
time, even after annual application had ended. Greater responses to manure application
have been observed in cool-season grasses compared to alfalfa (Min et al., 1999).
Legume N fixation limits nutrient responses, but the high nutrient demands of perennial
grass crops, particularly N (Bittman et al., 1999) makes cool-season grasses more

responsive to manure application.

125

The existing literature indicates that the three main objectives of this research, to increase
potato yield using forage crop rotation, to increase potato yield using manure amendment,
and to increase rotation forage and com yield using manure amendment are generally
possible. Previous research, including studies conducted in Michigan and at this site, has
shown that none of these goals have been found to be consistently reproducible, but a
significant trend exists indicating a likelihood of success in any one particular attempt.
The literature indicates that in the degraded potato production region of Montcalm
county, forage crop rotation and liquid dairy manure amendment will have positive

effects on potato production.

126

Objectives

The main focus of this experiment is to explore the agronomic implications of potato and
livestock system integration. Manure amendment holds the potential not only the
decrease reliance on mineral fertilizers, but also to increase the quantity and quality to
forage and potato yields. Likewise, forage crop rotation with potato production is
expected not only to increase potato yields, but also add external benefits beyond those
currently found in the conventional com — potato rotation. The following hypotheses are

established as means by which to evaluate the effectiveness of these alternative inputs:

1. A minimum 3-year forage rotation is required to induce potato yield increases;
2-year forage rotation will not be sufficient to improve potato yields in an
intensively managed potato-com rotation.

2. The combination of forage rotation and liquid diary manure application will
result in higher potato yield than either amendment individually.

3. Forage yield will be improved by the amendment of liquid diary manure to
conventional inorganic fertilizers regimes compared to forage fertilization

regimes solely supplied by inorganic fertilizers.

127

Materials and Methods

Experimental Design

This experiment was located at the Michigan State University Montcalm Potato Research
farm, MI (43°21' N, 85°10' W) on a McBride sandy loam (coarse-loamy, mixed, fiigid
Alfic Fragiothods). Intensive potato rotations have dominated the farm for several
decades. These rotations have degraded soil properties such as organic matter to low
levels, making conditions ideal in terms of exacerbating yield improvements. These
conditions are expected to make changes in soil quality more apparent, exacerbating any

potential yield shifts.

Table 3.1. 2002 initial soil characteristics at Montcalm Potato Research Farm.
0-20 cm SE 20-50 cm SE

 

pH 6.59 0.04 6.59 0.05
CEC cmolkg" 3.53 0.13 3.28 0.15
Phosphorus mgkg" 154 5.16 101 5.85
Potassium mgkg" 167 3.84 109 2.14
Magnesium mg kg.' 94 2.26 86 3.26
Calcium mgkg" 391 12.49 373 22.47
Organic matter % 1.10 0.06 1.07 0.04

SE- Standard Error

Treatments consisted of twelve systems, six rotations with and without liquid dairy
manure treatment. The experiment was arranged in a randomized complete block design
replicated four times. The rotations included two com-potato, two 2-year forage, and two
3-year forage treatments (Table 3.2). The use of two defender com -potato rotations,
staggered by year, allows for accurate comparisons to other potato rotations each year.
Alfalfa and festulolium rotations were managed as production forage systems, with all

biomass removed from the plot with each cutting. Sudex was managed as a green

128

manure crop, with all biomass chopped and returned to the soil surface. Rye was planted

as a winter cover crop each fall following potatoes.

Two-year alfalfa and sudex rotations represent potato driven integration systems. Sudex
production offers no benefit for livestock producers as a green manure cr0p.

One-year alfalfa stands are a move toward integration with livestock operations.
Establishment year yields in alfalfa production provide livestock operations with modest
feed supplies, though these limited production yields are below levels necessary for total
farm feed production. Greater yields from multiple year stands are necessary for feed
production on a reasonable landbase. High establishment costs of alfalfa also preclude
short-term production intervals; establishment cOsts from alfalfa seedings are generally
only recouped after several years of production. As such, one year alfalfa and sudex
production are expected to have greater benefits to potato production than dairy systems.
Three-year cropping systems of alfalfa and festulolium better suit the needs of integrated
dairy farms than shorter one-year forage production. A second production year beyond
establishment allows for production yields necessary to sustain dairy forage
requirements. These systems place a greater emphasis on dairy production than shorter,

2-year potato driven systems.

Table 3.2. Cr0p rotation for 2002, 2003 and 2004 at Montcalm Potato Research Farm.

 

 

Rotation 2002 2003 2004

1 Corn Potato Corn

2 Potato Com Potato
3 Alfalfa Potato Alfalfa
4 Sudex Potato Sudex
5 Festulolium Festulolium Potato
6 Alfalfa Alfalfa Potato

129

Table 3.3. Common, scientific, and cultivar names of species used in 2002, 2003 and
2004 at Montcalm Potato Research Farm.

 

 

Common name Latin binomial Cultivar
Potato Solanum tuberosum L. Snowden
Corn Zea mays L. Pioneer 36G12
Alfalfa Medicago sativa L. Pioneer 53Q60
Festulolium F estuca pratensis Huds. x Duo

Lolium perenne L.
Sorghum/sudangrass Sorghum bicolor L. x Honeypot

S. bicolor L.

Plots of 3.7 measuring 15.2 meters were oriented such that rows ran east to west with a
gradual decreasing in elevation to the north. As a result of this slight hill, the north end
of the range suffered from slower water drainage and subsequent flooding. The wet
spring of 2004 resulted in a flooding event that prevented emergence of crops on the four

northem-most plots and the subsequent abandonment of these plots.

Manure Amendment

Liquid dairy manure from a nearby 2,500 head operation with liquid pit manure storage
was applied at 12,260 L ha", a regionally common application rate. A pull-type liquid-
manure applicator was used to inject manure to depth of 20 cm in the spring prior to
planting in 2002. The applicator utilized a hydraulic cutter for even distribution of
manure between four injection shanks. Sand bedding mixed with the manure resulted in
a liquid density higher than that of what the transfer pump on the applicator could handle,
necessitating the addition of water to increase the fluidity of the manure. Application
rates were adjusted so that 12,260 L ha’1 of initial product was applied. A higher
capacity, hydraulically powered pump was installed on the injector for amendment in

2003. With the presence of perennial forage crops in 2003 and in 2004, manure was

130

broadcast on the soil surface for all treatments. The distribution pattern in 2004 was
refined so as to provide for more even surface coverage than that achieved in 2003. One
day following manure broadcasting, primary tillage using a rototiller (Great Plains Mfg.
Inc., Salina, KS) was performed on both manure and non-manure treatments. This tillage

event served to incorporate surface applied manure within GAAMP regulations.

Table 3.4. Liquid dairy manure concentration characteristics in 2002, 2003 and 2004 at
Montcalm Potato Research Farm.

 

 

2002 2003 2004
Moisture % 88.5 71.9 79.6
Solids % 11.5 28.1 20.4
pH 7.06 7.28 7.10
Nitrogen, total mg kg“ 3256 4288 4586
Nitrogen, ammonium make" 1602 2412 2924
Nitrogen, organic mg kg" 1654 1916 1664
Phosphorus mgkg" 438 676 1932
Potassium mg kg“ 1970 2564 3822
OM by L01 8 kg" 332 810 589
Magnesium make" 1120 1760 1540
Calcium mg kg" 3160 7440 410
reported on a dry weight basis

OM- organic matter
LOI- loss on ignition

131

Table 3.5. Total nitrogen applications for manure and conventional fertilizer treatments
in 2002, 2003, and 2004 at Montcalm Potato Research Farm.

 

 

 

 

Manure N Manure N Fertilizer N Total N
Total Available Available

2002 kg ha" Kg ha" kg ha" kg ha"
Potato

Manure 204 154 91 245

Conv. - - 224 224
Corn

Manure 204 154 145 299

Conv. - - 207 207
Alfalfa

Manure 204 1 54 - 154

Conv. - - O 0
Fest.

Manure 204 154 l 14 268

Conv. - - l 71 171
Sudex

Manure 204 1 54 84 238

Conv. - - * 168 l 68
2003
Potato

Manure 319 219 91 310

C onv. - - 224 224
Corn

Manure 319 219 145 364

Conv. - - 207 207
Alfalfa

Manure 319 219 - 219

Conv. - - 0 0
Fest.

Manure 319 219 114 333

Conv. - - 228 228
2004
Potato

Manure 326 23 8 91 329

Conv. - - 224 224
Corn

Manure 326 23 8 145 383

Conv. - - 207 207
Alfalfa

Manure 326 238 - 238

Conv. - - O 0
Sudex

Manure 326 238 84 322

Conv. - - 168 1 68

132

Potato Production and Analysis

Potatoes were planted using a two-row potato planter (Lockwood Mfg., West Fargo,
ND.) at a seed spacing of 22.5 cm in row and 91 cm between rows. Potatoes were hilled
approximately five days prior to emergence. Weed control was achieved through
standard chemical herbicide application and manual hoeing as needed. Fertilizer was
applied in liquid form at planting and as broadcast granular for subsequent fertilizations.
Wet conditions following the 2004 planting resulted in sporadic emergence and required

replanting in spots in mid-May.

Potatoes were harvested using the center two of four rows for yield. In 2002 and 2003, a
custom built self-propelled mechanical harvester was used to lifl and bag the entire 15.2
m length of the two yield rows. Plant maturity variability resulting from late replanting
necessitated by poor emergence required a more selective harvest method in 2004. A
John Deere (Deere & Company, Moline, IL) one-row lifier was used to lay the two center
yield rows on the ground. Two 1.5 m lengths were then collected for yield. Following
harvest, regardless of harvest method, samples were graded and weighed for total yield,
US#1, A, B, pickout, and oversize tubers. Specific gravity was measured from US#1
tubers from each plot. Internal defects were determined for hollow heart, internal brown
spot, vascular disorder, black spot, and heat neurosis through random sampling of ten

tubers. Scab was accessed through a visual rating on 0 (no scab) to 5 (high scab).

133

Forage Production and Analysis

Forages were established with a John Deere (Deere & Company, Moline, IL) 2.4m drill.
Alfalfa was sown at 18.0 kg ha", with festulolium and sudex drilled at 30.0 kg ha". Plots
were tilled with a rototiller (Great Plains, Mfg. Inc., Salina, KS) at manure incorporation
and finished with a field cultivator (Kongskilde Industries, Bloomington, IL) prior to
planting. A combination of adverse weather conditions, including eroding rains and soil
crusting, along with possible herbicide carry-over, resulted in unacceptable alfalfa and
festulolium initial stands in 2002. Atrazine application the previous year may have
resulted in a carry-over effect, reducing germination of alfalfa. A subsequent reseeding
of these crops also had poor stands, necessitating a third planting in early July. The late
final planting date resulted in a shortened growing season for alfalfa and festulolium;
only two cuttings were taken from each crop. Alfalfa and festulolium in the second year
production during 2003 produced four and five cuttings, respectably. Alfalfa was drilled
in 2004 with Brillion Pulverizer (Brillion Farm Equipment, Brillion, WI) equipped with
rolling press wheels pulled behind the planter for improved soil to seed contact so as to
avoid the emergence difficulties of 2002; two cuttings were harvested. Sudex in 2002

produced three cuttings and two cuttings in 2004.

A Carter flail harvester (Carter Manufacturing Co. Inc., Brookston, IN) was used to
harvest a 0.91 by 6.1 m randomly selected representative subplot area at a cutting height
of 8.9 cm from the soil surface. Care was taken to avoid sampling areas of poor
emergence or higher than average weed pressure. Moisture content of harvested alfalfa

was determined by measuring dry weight from a 500 g wet weight sample of the

134

harvested alfalfa dried at 60 degrees C for 72 hours. This sample was retained for
determination of forage quality. The dried sample was ground to pass through a 1mm
screen using a Christy Mill (Christy-Tumer Group, Ipswich, Suffolk, UK) with an

attached, custom fabricated, cyclone separator.

Total nitrogen was determined by the Hach modified Kjeldahl procedure (Watkins et al.,
1987), and crude protein was estimated by multiplying total N by 6.25. The Goering and
Van Soest (1970) method was used for neutral detergent fiber (NDF) and acid detergent
fiber (ADF) determination with the addition of 1 ml of alpha-arnylase to the neutral
detergent solution for the breakdown of starch. Dry matter (DM) content was determined
by drying a 0.5 g sample in a ceramic crucible at 100°C for 12 hrs. The samples were

then ignited in a muffle fumace at 500 degree C for 6 hrs to determine ash content.

Forage digestion protocol is directly proportional to particle characteristics. The size,
shape, and integrity of forage particle effects the degree to which digestion will occur.

To this end, the method by which forages are ground has bearing on overall digestion.
The protocol for the Hach modified Kj eldahl method (Watkins et al., 1987) for crude
protein and the Goering and Van Soest (1970) procedure for NDF and ADF were created
using a hammer mill to reduce particle to 2 mm, followed by a deterioration mill reducing
particle size to 1 mm. Samples for this experiment were ground using a deterioration mill
to reduce particle size to 1 mm in a single milling event. The absence of a cutting mill in
the grinding operation is likely to reduce overall particle length, and therefore size. A

decrease in particle size will increase surface area of a given volume, increasing

135

digestion. Forage digestions performed on one-pass deterioration ground sample may
have digestions upwardly skewed; consideration to this fact should be made when

comparing other experimental results.

Corn Production and Analysis

Com was planted with a custom plot planter (ALMACO, Nevada, IA) to a population of
74,300 seed ha". Seed spacing was 28 cm in row and 76 cm between rows. At
emergence, plots were thinned if stands exceeded this population and spot replanted if
needed. Weed removal was performed through chemical herbicide and mechanical
cultivation for moderate weed pressure, and hand hoeing for light weed pressure. Corn
yields and test weights were detemlined through mechanical harvesting with a Massey
Ferguson 8XP combine (AGCO Corporation, Duluth, GA). The center two rows of the
four row plot were measured for yield. Plots were trimmed to 12.2 m to minimize edge
effects. Moisture content and field weight were measured by a GrainGageTM, a
HarvestMaster SystemTM (Juniper Systems, Inc., Logan, UT), mounted on the plot
combine. Grain yield was reported at standard 15.5 percent moisture. Grain test weight

was reported at harvest moisture.

Crop Fertility
Crop fertilization was developed fiom Michigan State University Extension soil fertility
publications (Vitosh, 1990; Christenson et al., 1992; Warncke et al., 1992; Snapp et al.,

2002) and tailored to meet site conditions for potato (Dick Crawford, personal

136

communication), com (Keith Dysinger, personal communication), and forages (Rich

Leep, personal communication) based upon MSU soil test lab recommendations.

Manure available nutrient contributions were calculated by plot for nitrogen, phosphorus
and potassium. Any deviations in available manure nutrients fiom conventionally
management treatments were corrected at the time of second fertilizer applications, with
manure plots receiving higher or lower levels of fertilizer than that applied to
conventional treatments. For potato, corn, sudex and festulolium, nitrogen was
calculated as the primary balancing nutrient; in alfalfa, phosphorus was used to balance
nutrients. Potatoes received a starter fertilizer at planting and subsequent applications at
hilling and two and four weeks following emergence. Alfalfa, festulolium, and sudex
received broadcast fertilizer applied at emergence and following the first cutting in
coordination with anticipated rainfall events. In addition, festulolium was fertilized
following cuttings 1 and 3 in 2002. Fertilizer was applied to corn at planting and at the

V5 stage.

137

Table 3.6. Mineral fertilizer application in manure and conventional fertilizer treatments

in 2002, 2003 and 2004 at Montcalm Potato Research Farm.

 

 

 

 

Fertilizer Manure

N P K N P K
2002 kg ha" kg ha" kg ha" kg 118" kg ha" kg ha"
Potato 316 17 - 204 - -
Corn 139 17 21 140 - -
Alfalfa - 89 508 - 57 326
F estulolium 1 71 - - 1 14 - -
Sudex 168 - - 84 - -
2003
Potato 316 17 - 204 - -
Corn 204 17 21 145 - -
Alfalfa - 89 508 - 38 217
Festulolium 228 - - 1 14 - -
2004
Potato 316 17 - 204 - -
Corn 204 17 21 . 145 - -
Alfalfa - 89 508 - 41 234
Sudex 168 - - 84 - -

 

Table 3.7. Fertilizer formulations utilized in experiment at Montcahn Potato Research

 

 

Farm.

Crop Timing Formulation

Potato starter 19-17-0
sidedress 49-0-0

Com starter 19-19-19
sidedress 28-0-0

Alfalfa 0-13-39

Festulolium 34—0-0

Sudex 34—0—0

138

Table 3.8. Phosphorus and potassium inputs from manure and fertilizer in manure and
conventional fertilizer treatments in 2002, 2003 and 2004 at Montcalm Potato Research
Farm.

Manure Fertilizer Total Manure Fertilizer Total

 

 

 

P P P K K K

2002 kg ha" kg ha" kg ha" kg ha" kg ha" kg ha"
Alfalfa

Manure 32 57 89 144 326 470

Conv. - 89 89 - 508 508
F estulolium

Manure 32 0 32 144 0 144

Conv. - 0 0 - O O
Sudex

Manure 32 0 32 144 0 144

Conv. - O 0 - 0 0
2003
Alfalfa

Manure 51 38 89 190 217 407

Conv. - 89 89 - 508 508
F estulolium

Manure 51 0 5 1 190 0 190

Conv. - 0 O - O O
2004
Alfalfa

Manure 48 41 89 271 234 505

Conv. - 89 89 - 508 508
Sudex

Manure 48 0 48 271 O 271

Conv. - 0 O - 0 0

139

Production Inputs

Pesticides were applied as needed throughout the growing season. Nematicide was
applied over the entire range two years preceding the study’s onset and again in the
spring of 2003 to plots in which potatoes would be planted that season using a custom
built injection system. Fungicides were applied during the season on weekly intervals
beginning at a plant height of 15 to 20 cm and ended approximately two weeks prior to
vinekill. A tractor-drawn sprayer was used for fungicide applications. Insecticides and
herbicides were applied using a Hudson COz backpack sprayer (H. D. Hudson Mfg. Co.,

Chicago, IL.).

Irrigation was provided as needed throughout the season, typically on a 7 to 9 day
interval. Water was applied in 2002 via a solid set pipe system, using two lines with
sprinklers set at 12 m intervals. For the 2003 and 2004 seasons, an overhead traveling

system was utilized.

Colorado Potato Beetle Control

This trial was located adjacent to ongoing Colorado Potato Beetle (CPB) research,
conducted by the Michigan State University Entomology Department. In order to
determine specific potato plant’s biological pest control, potato plants in the trial receive
no chemical or cultural pest control. The majority of potato plants in this trial are quickly
decimated, forcing beetles into the surround area. In 2002, potato defoliation was
complete in the adjoining CPB trial by early July. Despite chemical control with

insecticides, near complete defoliation of this study occurred by mid-July. The

140

subsequent potato yield was severally compromised. In early 2003, a 45 cm deep trench
was dug between the Entomology study and the Potato Forage Integration study. The
trench’s sides were steeped and line with black plastic. The CPB inability to fly forces
the insect to move across the ground. When a trench of this sort is encountered, the
insects fall in and can’t climb out. The combination of frequent irrigation flooding the
trench and the black plastic tendency to become very hot in sunlight is effective in killing
most of the beetles trapped in the trench. The use of a trench to impede beetle movement

was used in 2004 as well.

Statistical Analysis

Analysis of variance (ANOVA) was performed on potato and forage yields and quality,
with Proc GLM (SAS Institute, 2004) using the Kenward-Roger method for determining
degrees of freedom. When significant effects of treatment occurred, means were
compared using Fischer’s Least Significant Difference. Proc Reg of SAS was used for
regression analysis. Unless otherwise stated, differences were considered significant at
an alpha level of 0.05. Scab data, complied though a visual rating system, was assessed

for normality and found to be normal.

Environmental Conditions

Cool temperature predominated the two years during which nitrogen dynamics were
examined in this experiment. 2003 was 1.0° C below 30-year temperature norms and
2004 was 0.4° C below normal. The months of March, April, and May in 2003 were -

0.66°, -1.10°, and -1.89° C of normal temperatures, while those same months in 2004

141

were 2.4°, 0.6°, and -0.8° of normal. Rainfall in both 2003 and 2004 was below 30-year
averages. While this experiment is supplemented by artificial irrigation, the system is
operated only during periods of greatest tuber water demand in June, July and August.
Early season soil moisture was totally dependent on upon natural precipitation. Early
season rainfall in 2003 was -2.97, -2.59, and 1.42 cm of normal for the months of March,
April, and May. Rainfall was 2.82, -3.94, 13.46 cm of normal for this same period in
2004. While both growing seasons may be summarized overall cool and dry, the early

season of 2003 was cool and dry compared to warm and wet in 2004.

142

Results and Discussion

Corn Production

Corn grain yields were significantly higher for non-manure treatments in 2002, along
with a trend toward higher test weight (Table 3.9). There were no differences between
manure treatments for grain yields in 2003 or 2004, or test weights in 2003. However,

test weight was significantly higher for the manure treatment in 2004.

Table 3.9. Corn yield and test weight- 2002, 2003, and 2004.

 

Yield Test Wt.

 

Mg ha" kg ha"
2002
Manure 9.66 b 69.60 “
Conv. 10.82 a 71.29 “
LSD a=0. 05 0.61 3.88
2003
Manure 11.56 a 62.35 a
Conv. 11.43 a 62.19 ‘
LSD a=0.05 2.16 1.14
2004
Manure 12.68 a 68.71 a
Conv. 12.42 a 67.71 b
LSD a=0.05 2.39 0.71

While manure application had a detrimental effect on corn yields and test weights in
2002, yields in manure amendment treatments were comparable to those receiving
conventional fertilizer by 2004. This trend has been seen by others using liquid dairy
manure on sandy soils. J okela (1992) found that manure application had little effect on
com yields after one year of application, but manure amendment increasingly boosted
corn yields in the second and third year of the study. Annual manure application effects
becoming more discemable after several years of amendment might be expected in a

degraded soil system, such as those often found in the Montcalm region.

143

Forage Production

Alfalfa

Alfalfa dry matter production and forage quality was not influenced by manure
application in any of the three years. A lack of dry matter yield response from liquid
dairy manure applications was previously demonstrated by Daliparthy et al. (1994) in
Massachusetts. Neither low (112 kg N ha") nor high (336 kg N ha") rates of surface
applied manure to existing alfalfa stands in June influenced yield. A similar lack of
response to low and high mineral N fertilizer applications at equal rates in control
treatments was observed. Other researchers have found contradictory evidence to these
results. In studies in Wisconsin and Minnesota, Peters (1991) and Schmitt et al. (1993)
both observed alfalfa dry matter responses to pre-plant liquid dairy manure amendment.
These manure responses were greater than correspondently balanced mineral fertilizer
applications. However, Schmitt et al. (1993) noted a lack of response to manure and
fertilizer in one of the three study locations, citing high initial P and K soil test levels.
Soil P and K concentrations were similarly high at this studies inception (Table 3.1).
These results suggest that dry matter response may be regulated by limiting nutrient
levels rather than possible soil microbial stimulation or soil conditions (Kelling and

Schmitt, 2003).

144

Table 3.10. Alfalfa dry matter yield- 2002, 2003, and 2004.

 

 

 

 

Yield Yield
2002 Mg ha" Mg ha"
Total Cut 1
Manure 2.28 a Manure 2.00 a
Conv. 2.53 a Conv. 2.19 a
LSD a=0.05 1.16 LSD a=0.05 1.10
Cut 2
Manure .35 a
Conv. .28 a
LSD a=0. 05 1.99
2003
Total Cut 1
Manure 9.59 a Manure 4.59 a
Conv. 10.38 a Conv. 5.19 a
LSD a=0.05 2.22 LSD a=0.05 1.37
Cut 2
Manure 1.87 a
Conv. 1.77 a
LSD a=0. 05 0.26
Cut 3
Manure 1.66 a
Conv. 1.65 a
LSD a=0.05 0.32
Cut 4
Manure 1.46 a
Conv. 1.77 a
LSD a=0. 05 1.09
2004
Total Cut 1
Manure 4.20 a Manure 2.45 a
Conv. 4.26 a Conv. 2.45 a
LSD a=0.05 1.92 LSD a=0. 05 0.69
Cut 2
Manure 1.76 a
Conv. 1.81 a
LSD a=0.05 1.28

145

Table 3.11. Alfalfa crude protein, acid detergent fiber and neutral detergent fiber- 2002,

 

 

 

 

2003, and 2004.
CP ADF NDF
2002 g kg " g kg" g kg"
Cut 1
Manure 159.28 a 272.48 a 406.40 a
Conv. 170.05 a 307.38 a 466.78 a
LSD a=0.05 21.5 47.99 75.20
Cut 2
Manure 256.53 a 265.31 a 300.24 a
Conv. 252.81 a 267.80 a 365.11 a
LSD a=0. 05 26.60 23.79 61.21
2003
Cut 1
Manure 218.13 a 304.58 a 412.03 a
Conv. 208.65 a 307.75 a 405.98 a
LSD a=0. 05 33.67 57.50 66.89
Cut 2
Manure 240.08 a 272.58 a 466.40 a
Conv. 249.30 a 257.25 a 398.65 a
LSD a=0.05 42.80 48.01 140.54
Cut 3
Manure 231.03 a 265.30 a 434.38 a
Conv. 219.68 a 268.48 a 446.03 a
LSD a=0. 05 25.84 27.73 39.26
Cut 4
Manure 215.03 a 321.80 a 550.35 a
Conv. 192.83 a 317.75 a 533.65 a
LSD a=0.05 71.96 63.67 135.99
2004
Cut 1
Manure 201.98 a 258.48 a 439.55 a
Conv. 189.48 a 294.78 a 425.33 a
LSD a=0.05 68.77 58.25 45.73
Cut 2
Manure 208.85 a 244.40 a 410.20 a
Conv. 221.73 a 223.70 a 367.35 a
LSD a=0.05 29.16 27.63 45.54

146

Dry matter yields were consistent between manure and non-manure treatments through
the three years of the study, with one exception. Manure treatment yields, while not
significant, were reduced in the first cutting of 2003. The effect may be attributed to
delayed regrowth and smoothing following broadcast manure operations early in the
2003 season. Vehicular traffic and compaction problems associated with manure
application have previously been cited as additional causes of yield reduction in manure

amended plot research (Schmitt et a1, 1993).

F estulolium

Festulolium yields were not affected by manure application in 2002. While conventional
fertilizer treatments seemed to demonstrate a trend toward increased yields, no cutting
event was found to significantly differed by fertility source. Manure treatment in 2003
increased overall dry matter production. Cuts one and three produced higher manure
treatment yields and, while not significant, out two showed a trend toward higher yields.
The lack of yield response to manure application in 2002 may be attributed to a lack of
available N. Nitrogen supplied by manure may not have mineralized during the growing
season in sufficient quantities to match that supplied by conventional fertilizers, thereby
reducing yields for the manure treatment. However, overall dry matter production in
2003 seemed to benefit from the previous season’s manure application. Kafflca et a1.
(1996) noted a similar effect in multiple years of cool season grass production under
manure application. Observed dry matter yields in the first year were similar,

irrespective of manure or fertilizer N source. In year two, yields were higher in manure

147

Table 3.12. Festulolium dry matter yield- 2002 and 2003.

 

 

 

Yield Yield
2002 Mg ha" Mg ha"
Total Cut 1
Manure 2.86 a Manure 1.94 a
Conv. 3.71 a Conv. 2.33 a
LSD a=0. 05 0.95 LSD a=0.05 l. 16
Cut 2
Manure .92 a
Conv. 1.38 a
LSD a=0.05 0.63
2003
Total Cut 1
Manure 12.59 a Manure 3.68 a
Conv. 7.73 b Conv. .98 b
LSD a=0. 05 2.71 LSD a=0.05 1.49
Cut 2
Manure 1.78 a
Conv. 1.11 a
LSD a=0. 05 1.01
Cut 3
Manure 2.44 a
Conv. 1.35 b
LSD a=0.05 0.84
Cut 4
Manure 1.66 a
Conv. 1.66 a
LSD a=0.05 1.71
Cut 5
Manure 3.03 a
Conv. 2.63 a
LSD a=0.05 1.09

148

Table 3.13. F estulolium crude protein, acid detergent fiber, and neutral detergent fiber-

 

 

 

2002 and 2003.
CP ADF NDF
2002 8kg " 8kg" 8kg"
Cut 1
Manure 156.58 b 287.85 a 559.38 a
Conv. 206.58 a 279.05 a 553.63 a
LSD a=0.05 30.10 48.95 79.36
Cut 2
Manure 196.50 a 256.80 a 503.50 a
Conv. 197.40 a 292.38 a 556.30 a
LSD a=0.05 79.39 100.53 198.66
2003
Cut 1
Manure 121.43 a 251.65 a 479.40 a
Conv. 105.78 a 201.20 b 420.53 b
LSD a=0.05 4907 36.93 51.08
Cut 2
Manure 198.75 a 293.15 a 549.85 b
Conv. 159.05 b 317.15 a 591.28 a
LSD a=0.05 29.49 51.00 25.83
Cut 3
Manure 204.73 a 261.73 a 533.73 a
Conv. 194.25 a 253.45 a 454.88 a
LSD a=0.05 79.97 58.79 200.99
Cut 4
Manure 190.08 a 290.55 a 529.45 a
Conv. 214.55 a 282.15 a 542.83 a
LSD a=0.05 56.94 19.24 19.53
Cut 5
Manure 154.75 a 286.13 a 589.78 a
Conv. 148.93 a 307.28 a 608.15 a
LSD a=0.05 28.10 51.25 58.62

149

treatments, largely attributed to N contributions from the previous year. In a more long-
tenn system, Chemey et al. (2002) found that annual dairy manure amendments

improved cool season grass yields after two years of application compared to equivalent
mineral fertilization rates. This trend continued for three years after manure amendment

had ceased, evidently fi‘om the residual impacts of manure application.

F estulolium forage quality was only marginally affected by manure amendment. Four of
seven harvest events between 2002 and 2003 experienced treatment effects for either CP,
ADF, or NDF. Conventional mineral fertilizer resulted in higher CP levels for the first
cutting of 2002. Manure increased CP in the second cutting of 2003. Manure also
increased ADF and NDF levels in the first cutting of 2003. Manure application
decreased NDF for the second cutting of 2003. VanWieringen et al. (2005) observed that
perennial ryegrass and orchardgrass CP levels increased with liquid dairy manure
application, with CP levels increasing as the season progressed. These effects were
attributed to increasing N availability from manure mineralization. Min et a1. (2002) also
studied the effects of various rates liquid diary manure on orchardgrass and reed
canarygrass. While manure application had no effect on ADF or NDF, CP was increased
with manure. Increased festulolium CP compared to alfalfa following manure
amendment is expected due to the alfalfa’s ability to fix its own N. Cool season grasses
are more responsive to manure application as they are wholly dependent upon external

inputs for nitrogen supplies.

150

Adjustments in nutrient fertility between manure and non-manure resulted in greater P
and K application in manure treatments (Table 3.8). While most fertilizer
recommendations for hay crops are limited to N, dry matter yield responses have been
observed from other nutrient applications, including K. Keady and O’Kiely (1998)
demonstrated that applications of 120, 180, and 240 kg K ha" increased yields over that
of 0 and 60 kg ha'1 rates. Fertilizer applications were not found to influence in vitro dry

matter digestibility, crude protein, or modified acid detergent fiber.

m

Sudex yields did not differ by manure amendment in 2002 or 2004. The depressed yields
seen in 2002 were a result of late planting date. Sudex yield has been shown to be a
function of nutrient amendment. Kilcer et al. (2002) in New York were able to
demonstrate increased dry matter yields when N applications were split during the
season. Fertilization with 168 and 224 kg N ha'1 split into two applications, one planting
and the second following the first cutting significantly increased yields over single
applications at planting. While no significant differences were observed between manure
and non-manure treatments in 2002 or 2004, a trend toward increased dry matter yields
with manure application was observed. Greater N availability over an extended period
though N mineralization would be expected in these treatments. The clear advantage of
lower N rates over a greater period of time demonstrated by Kilcer et al. (2002) offers

one explanation for this observation.

151

Sudex fertilization for manure and non-manure treatments was, like festulolium, balanced
on available N resulting in higher nutrient applications of P and K in manure treatments
(Table 3.8). Previous research indicates that these increased fertility levels have little
impact upon sudex dry matter production. Ketterings et al., (2005) studied brown mid-rib
sudex across three K fertilization levels, 0, 92, and 184 kg K ha", but did not observed a

yield response.

Table 3.14. Sudex dry matter yield- 2002 and 2004.

 

 

 

Yield Yield
2002 Mg ha" Mg ha'l
Total Cut 1
Manure 8.18 a Manure 3.73 a
Conv. 7.37 a Conv. 3.89 a
LSD a=0.05 1.94 LSD a=0. 05 0.58
Cut 2
Manure 2.48 a
Conv. 3.17 a
LSD a=0. 05 1.39
Cut 2
Manure 1.16 a
Conv. 1.12 a
LSD a=0. 05 0.37
2004
Total Cut 1
Manure 17.28 a Manure 8.42 a
Conv. 14.48 a Conv. 6.66 a
LSD a=0.05 7.09 LSD a=0. 05 2.15
Cut 2
Manure 8.87 a
Conv. 7.82 a
LSD a=0.05 5.93

152

Potato Production

Potato YieLd Following Corn

The effects of year and manure treatment were not interacting for US #1 or total tuber
yields in potato—com rotations, so comparisons were made across years. Manure
treatment increased both US #1 and total tuber yields over three years. However, these
changes were not incremental, but rather occurred largely in 2004. Manure amendment
had no effect on potato yield in 2002, and while a trend existed for higher US #1 and total

yields with manure amendment in 2003, no significant yield effects were seen until 2004.

Table 3.15. Potato total and US#1 fresh weight tuber yield following corn rotation— 2002,

2003 and 2004.

 

 

Total US #1
2002 Mg ha" Mg ha"
Manure. 15.31 c 11.12c
Conv. 15.35 c 11.03 c
LSD a=0.05 8.72 9.90
2003
Manure. 30.28 b 28.24 b
Conv. 24.51 b 22.36 b
LSD a=0. 05 10.08 10.38
2004
Manure. 39.57 a 36.09 a
Conv. 31.23 b 26.16 b
LSD a=0. 05 8.27 9.18

Comparisons made between years

153

Potato Yield Following Forage

Manure treatment had no effect on potato yield following l-year forages stands of alfalfa

or sudex in 2003 or 2-year forage stands of alfalfa or festulolium in 2004.

Table 3.16. Potato total and US#1 fresh weight tuber yield following l-year forage-
2003.

 

 

Total US #1
Alfalfa Mg ha" Mg ha"
Manure 30.87 a 28.82 a
Conv. 29.04 a 27.14 a
LSD a=0.05 5.12 5.39
Sudex
Manure 33.24 a 31.41 a
Conv. 29.62 a 27.70 a
LSD a=0.05 11.28 11.80

Comparisons limited to cr0p

Table 3.17. Potato total and US#1 fresh weight tuber yield following 2-year forage- 2004.

 

 

Total US #1
Alfalfa Mg ha" Mg ha"
Manure 37.42 a 33.09 a
Conv. 35.20 a 31.01 a
LSD a=0.05 16.67 15.49
Festulolium
Manure 36.16 a 32.83 a
Conv. 34.31 a 30.53 a
LSD a=0. 05 4.77 6.14

Comparisons limited to crop

154

Ma System Improvement

The ultimate assessment of a cropping system rests in the potential improvement of the
new system above that of the previous standard. In Montcalm county, a 2-year potato—
com rotation has become one of several prevalent cropping systems. Corn is a high
biomass cr0p with demanding relatively low input and management requirements. For
cropping system shifts to occur, new systems must demonstrate an improvement upon the
previous system. The effectiveness of forage rotation crops and manure inputs to
increase yields above those of the current com-potato rotation with no manure inputs, or
‘defender system’ is measured through yield and disease comparisons. The percent yield
increase above the defender system is determined by setting the potato-corn rotation with
no manure inputs as the baseline level. This system is replicated twice in the experiment,
staggered by year for potato comparisons each year. Statistical analysis determines
significance of each system compared to the defender system. As each system is
compared to that year’s defender potato production, comparisons between years are not

possible.

The effects of annual manure amendment were more dramatic in potato crop following
corn. There was no significant difference in marketable tuber yield due to manure
application in the first year of the study. Significant increases in US #1 yields were
observed in 2004 fiom manure application with a 23.6% tuber yield that was significant
at the P=0.l level. However, the combined three years of manure application increased
yields by 38.8 and 26.7% of US #1 and total tuber yields, respectively, that were

significant at the P=0.05 level.

155

Table 3.18. Percent increase of alternative system total and US#1 fi'esh weight tuber
yield above defender potato-com rotation with no manure amendment- 2002, 2003, and

 

2004.
Year Preceding Crop Total US #1
% %
2002 Com
Manure -0.3 0.8
2003 Corn
Manure 26.3 23.6 +
2004 Corn
Manure 38.8 * 26.7 *
2003 Sudex l-yr
Manure 35.6 * 40.5 *
Conv. 20.8 23.9
2003 Alfalfa l-yr
Manure 26.0 + 28.9 +
Conv. 18.5 21 .4
2004 Alfalfa 2-yr
Manure 19.8 + 26.5 *
Conv. 12.7 18.5
2004 Festulolium 2-yr
Manure 15.8 25.5 +
Conv. 9.9 16.7
+ significant at P=0. 10
"' significant at P=0.05

Defender system = potato after corn with no manure amendments. Rotations compared to each season's
defenders system, no comparisons possible between years

A 2-year crop rotation of potatoes and sudex was shown to produce the greatest yield
increases above the defender system. Sudex with manure amendment produced 40.5 and
35.6% significant increases to US #1 and total tuber yields, respectively, in the second
year of rotation. Yields of non-amendment treatments, while not a statistically
significant, still improved yields above the defender system and were 20.8 and 23.9%
higher for total and US #1 tubers compared to the defender system. These yield increases
were the highest occurring from non-manure amendment systems. Alfalfa and
festulolium in rotation with potatoes significantly increased tuber yields above that of the

defender system, though not to the extent of sudex. One-year alfalfa increased yields by

156

26 and 28.9% for total and US #1 potatoes, both significant at the P=0.1 level. Two-year
alfalfa was the most effective non-sudex forage crop at increasing yields with a 19.8%
increase for total tubers, significant at P=0.1, while US #1 yields increased by 26.5%,
significant at P=0.05. Two-years of festulolium resulted in the least effective rotation
crOp, with an insignificant 15.8% increase for total tubers and a 25.5% increase for US

#1, significant at P=0.1.

Manure eflects

Manure application in this study resulted in significant potato yield increases. No system
produced a significant yield response above the standard defender system without the
application of manure. This effect is in large part attributed to improved nitrogen
availability throughout the season. Both manure and non-manure treatments received
equal levels of available N. However, the manner in which N was supplied varied by
treatment. Non-manured treatments received inorganic N as a liquid starter fertilizer and
in two granular applications post-emergence. Manure treatments also received two
granular inorganic fertilizer post-emergence applications, though no liquid starter
fertilizer at planting. Rather, manure treatments relied solely on nutrients supplied by the
pre-plant manure application for initial N fertility demands. Laboratory analysis of
manure samples determined available N contributions fi'om manure application, with N
application rates increased as needed for manure treatments at the first post-emergence

fertilizer application to equilibrate N rates.

157

Nitrogen supplied by manure contains fractions of immobile, organic N not in mineral
fertilizers. These organic fractions are slow to decompose and are initially immobile in
the soil, compared to the mobile, readily available inorganic N found in mineral
fertilizers (Paul and Beauchamp, 1994). This immobile manure N mineralizes slowly
throughout the season, providing N on a more continuous basis than inorganic N fertilizer
applications. In addition to the differing availabilities of N fractions, manure application
impacts N dynamics by enhancing existing soil N mineralization and reducing N loses
through the stimulation of microbial biomass (Ma et al., 1999). Microorganisms mediate
the mineralization of N from organic to inorganic forms. The application of manure
increases microbial activity, in effect “priming” the system, increasing overall N
mineralization through exponential microbial growth. While much of the N supplied by
manure amendment is organic, and thus initially unavailable for plant uptake, the
unavailability seems to be mitigated by the accompanying increase to N mineralization

rates.

The effects of manure became more pronounced as the experiment progressed over the 3-
year period. Manure N canies over from one year’s application to the next, continually
becoming available multiple seasons after application (Klausner et al., 1994;
Sommerfeldt et al., 1988). Total levels of mineralized N following multiple years of
manure amendment increase each year until an equilibrium is reached. The increasing
effects of manure application on potato yields suggest such an equilibrium was not
reached in the three years of the study. First year available organic N was estimated

through laboratory analysis to be ~30%, with N fertilization levels balanced between

158

manure treatments according to this first year availability. Paul and Beauchamp (1993)
examined multiple year availability of N from liquid dairy manure in com production and
found that one year following amendment, 16.2% of the first year’s N uptake could be
recovered. However, three years after manure application, 27.3% of total applied N was
recovered. Multi-year N availability from manure, in the case of 11.1% seen by Paul and
Beauchamp (1993), is typically not included in fertilizer calculations, and results in more
total N available in manure systems than non-manure systems. Curless and Kelling
(2003) found that liquid dairy manure provided growth responses in potatoes above those
seen with equal amounts of conventional fertilizer treatments. Their results suggest

increases in multi-year nutrient availability from manure applications.

Multi-year nutrient availability from manure application is the most likely explanation for
the significant yield increases of manure amendment in this experiment. Tuber yields
were higher in response to manure application as the experiment progressed, suggesting a
cumulative benefit. Potato yields in rotation with corn demonstrate this effect well. With
potato yield measured each year in this system, the annual benefits of manure application
are clear. The results of this experiment indicate that the greatest benefit of manure

amendment may be realized only after several years of an annual amendment regime.

Crop Rotation Effects
Forage rotation crops, and their associated residue quantity and quality, significantly
influenced potato yield. The l-year sudex rotation significantly increased US #1 and

total tuber yields compared to the l-year alfalfa, 2-year alfalfa, and 2-year festulolium

159

crop rotations. Potatoes following corn in 2004, after three years of manure amendment,
and potatoes following 2-year alfalfa were the only other systems increasing US #1 yields
at the P=0.05 level. The quality of crop residues has a large bearing on their overall
impacts to the cropping system. C/N ratios are frequently used to predict the rate of
residue decomposition, and thus N mineralization and plant availability (Wagger, 1989;
Odhiambo and Bomke, 2001). These C/N ratios are used to imply the quality of the
residue (Gil and Pick, 2001). Corn and sudex have high C/N ratios, and are thus termed
“low quality” residues, as opposed to low C/N ratio, “high quality” residues of alfalfa and
festulolium. The difference in these ratios is a function of the differing nature of each
crop. Legumes, such as alfalfa, contain high levels of N due to symbiotic N fixation
(Carpenter-Boggs et al., 2000). Festulolium, When managed in a high production,
multiple cut system with high N inputs, builds significant N stocks. Corn and sudex, as
C4 grasses, contain more carbon than a C3 grasses, such as festulolium, due to more
efficient fixation of C02 (Al-Kaisi et a1, 2004). These C/N ratios influence the
mobilization of N in the soil. Carbon/N ratios narrower than 30:1 such as those of alfalfa
and festulolium lead to net mobilization of N (Alexander, 1977), resulting in rapid N
availability. Conversely, the broad C/N ratios of com and sudex lead to net
immobilization of N, with slow availability. Environmental conditions, including
temperature and rainfall, influence N dynamics including residue decomposition and N
leaching (Wagger, 1989). The spring of 2003 was much colder than normal and while
below average in total rainfall, had several high volume precipitation events. 2004 was
also cooler than normal with above average higher precipitation. These events may have

contributed to lower than expected potato yield response to alfalfa and festulolium.

160

Honeycutt et al. (1996) determined that various legume and non-legume crops in rotation
with potatoes had more of an influence on yield in dry years. The same rotations can
produce different results in considerably more moisture-limiting conditions. The soil
conditions at this site could have influenced N mineralization rates as well. Verbene et
al. (1990) observed that crop residues decompose more rapidly in sandy soils than clay
soils. Low quality residues in sandy soil, such as that in this experiment, will experience

more rapid N mineralization than rates found in other soil types.

Residues in this experiment may be divided into two groups: those of the C4 grasses corn
and sudex, and those of the C3 grass festulolium and the legume alfalfa. F estulolium and
alfalfa are managed as production forage crops, subjected to multiple cutting events and
removal of most aboveground biomass. Late season cutting provides only stubble and
belowground biomass residues for incorporation prior to potato production. In contrast,
com and sudex provide above and below ground biomass residue contributions. Sudex is
managed as a green manure cover crop, with all biomass retuned to the soil surface. Corn
managed for grain production has significant biomass returned from stover. The C/N
ratios of these two groups of residues differ dramatically. Com stover and sudex have
been found to have high aboveground C/N ratios of 67:1 (Burgess etal., 2002) and 47:1
(Creamer and Baldwin, 2005), respectively. Their belowground C/N ratios, however, are
lower at approximately 48:1 (Havlin et al., 1999), and thus more readily mineralized.
Alfalfa and festulolium have much lower aboveground C/N ratios, 18:1 and 15:1

respectively (Baron et al., 2001). However, the main residue contributions of these crops

161

 

in a hay system are belowground, were C/N ratios are slightly higher at 21 :1 and 22:1

(Baron et al., 2001).

Table 3.19. Crop above and below-ground C/N ratios as complied from several authors.

 

AG C:N BG C:N

 

Corn (stover) 60:1 ‘ 48:1 2

Sudex 47:1 3

Alfalfa 18:14 21:14

Cool Season Grass 15:1 4 22:1 4
(Italian ryegrass)

AG DM- above ground dry matter

BG DM- below ground dry matter

' Cowan, 2005

2 Havlin et al., 1999

3 Creamer and Baldwin, 2005

4 Baron et al., 2001

Italian ryegrass (Lolium multiflorum Lam.)

Corn and sudex residues, with above and belowground components, contain more diverse
fractions than those of alfalfa and festulolium. The management of corn for grain leads
to more diverse residues, with cob and husk residues in addition to the stem and leaf
resides common to both corn and sudex (Burgess et al., 2002). Cobs and husks combine
to comprise 29% of the total residue and have C/N ratios of 147:1 and 103:1,
respectively. These high ratios lead to very little N mineralization, only 17.3% of total
residues. Stems and leaves comprise 38% and 32%, respectably, of corn residues and
82.7% of mineralized N. Stern and leaf C/N ratios differ as well, at 80:1 and 42:1
respectively. This wide array of C/N ratios has a significant bearing on residue
mineralization. Separate residue constituents mineralize at different rates, providing N
availability over a wide period of time. Sudex residues consists of stem and leaf

vegetative growth, with mowing events prior to seed production. While sudex stem and

162

leaf residues differ in composition from those of com, the same general trend of variable
N mineralization fi'om differing residues can be drawn. A heterogeneous collection of
crop residues with differing N mineralization rates provides a more consistent supply of

plant-available N over time than homogenous crop residues.

The difference in corn and sudex rotation impacts on potato yield is likely a firnction of
these residue dynamics. Com residues, on average, have greater C/N ratios than those of
sudex. The broader average C/N ratio residue of com will mineralize and become
available over a longer period of time than the narrower C/N ratio residue of sudex.
However, management of these crops in the field results in the opposite situation. Sudex
is managed as a summer cover crop, with large amounts of crop residue returned to the
soil surface with each mowing event. Even with a late first mowing in 2002, residues
began to decompose July, eight months prior to potato planting. Corn residues were not
applied to the soil surface until late in the fall preceding potato production. With the
large impact of environmental conditions, including temperature, on N mineralization
(Eghball et a1, 2002; Wagger, 1989), sudex residues were able to mineralize to a much
greater extent than corn residues. In addition to the greater time period for sudex residue
mineralization, sudex residues mineralize at a faster rate than corn residues, particularly

in non-soil incorporated conditions (Smith and Sharpley, 1990).

While sudex and corn rotations resulted in the greatest yield responses in potatoes tubers,

alfalfa as a rotation crop also produced significant tuber yield increases. The mechanisms

for this response must be independent of the slow residue N mineralization characteristic

163

of sudex and corn. Alfalfa belowground contributions are the lowest of the four rotation
crops in the experiment, leading to the assumption that yield responses must be induced
more fi'om residues quality than quantity. Through N fixation, alfalfa crowns and roots
have been shown in Michigan to retain 115 kg N ha'1 after two years of growth (Rasse et
al. 1999). The presence of these additional levels of N are not indicative of tuber yield
response, as seen both by the lack of response in the non-manure amendment system and
from the experiments of Griffin and Hesterman (1991) at this site in 1988 and 1989.
While they observed increased potato vine DM and N content in alfalfa rotations, no
yield responses were seen. They concluded that while N fi'om soil incorporated legumes
becomes available during the season, lack synchrony between that N availability and
potato demand negates any yield increases from N. However, in the current experiment,
the response of tuber yields to alfalfa rotation in a manure amended system suggest that
the manure N mineralization priming effect releases otherwise unavailable N. The
combination of alfalfa N and manure N have an antagonistic effect that results in N

availability concurrent with potato N demand.

There was no significant yield response from potatoes associated with festulolium
rotations. The belowground residue C/N ratio of festulolium favors rapid N
mineralization and availability, and the total root biomass exceeds that of any other crop.
However, root masses were observed to decompose slowly following their incorporation
in 2004. While grass roots are efficient scavengers of N and accumulate significant
amounts of the N in roots (Gasser et al., 2002), the observed presence of undecomposed

roots at potato harvest indicates that N and OM release from these residues was unable to

164

supply N to potatoes to the same extent of the other rotation crops. Gasser et a1. (2002)
suggested that perennial crops such as alfalfa and grass may only begin to decompose and
release N after plant termination. If decomposition of alfalfa and festulolium residues
began with tillage shortly before potato planting, it is unlikely that the N mineralization
rate of festulolium would provide adequate available N during periods of greatest potato
tuber demand. Wagger (1989) concluded that legume residues decompose quickly in the
soil after incorporation, with increasing rates of decomposition up to four months
following incorporation. Grass residues decomposed more slowly, with steady

decomposition rates four months after incorporation.

Previous research has indicated that reside mineralization is linked to factors other than
C/N ratio, including lignin, carbohydrate, and cellulose content (Herman, etal., 1977;
Ranells and Wagger, 1996). Van Soest (1964) noted that lignin linkages differ between
legumes and non-legumes, with linkages in non-legumes resulting in greater proportions
of dry matter resistant to decomposition. In an attempt to characterize N mineralization
using various residue characteristics, Vigil and Kissel (1991) found that lignin content is
a second independent variable which can strengthen already robust equations based on
C/N ratio. Although lignin and other crop residue components play a role in residue
decomposition, direct comparisons between cellular constitute composition and C/N
ratios have indicated that C/N ratios are more accurate predictors of residue

mineralization (J anzen and Kucey, 1988).

165

 

Manure was shown in this study to have a more significant effect on tuber yield than crop
rotation. This trend was also observed by Porter et al. (1999) in Maine potato production.
Cattle manure and compost increased potato tuber yield more than oat (A vena sativa) and
legume green manure rotations. These effects were attributed to increased nutrient
availability, improved soil physical properties, and greater soil water holding capacity.
The yield responses to manure may also be associated with N mineralization priming
effects. With the equilibrated N fertilizer applications between manure and non-manure
treatments, the only differences in fertility levels are attributed to multi-year N
availability from manure and alfalfa. Increased fertility levels have been shown to
increase N mineralization of aboveground, but not belowground residues (Soon and
Arshad, 2002). Increased aboveground residue mineralization would explain tuber yield

increases seen in com and sudex rotations.

Shifts in commonly accepted agronomic practices may be necessary in order to fully
utilize organic amendment benefits. Fall termination of perennial alfalfa and festulolium
may hasten N mineralization in the following season, allowing for N availability to better
match tuber demand. The adoption of a nondormant alfalfa is feasible for use as a single
season crop. Groya and Sheaffer (1985) found comparable biomass and N production
with a nondormant alfalfa compared to a dormant variety. A nondormant alfalfa
terminated by winter conditions would decompose and mineralize more rapidly than a
conventional, dormant variety, shifting the window of N availability earlier in the season

for better utilization by potatoes.

166

The use of legume-grass binary mixtures have been identified as a means to modify C/N
ratios, increasing N mineralization above that commonly found in grasses (Ranells and
Wagger, 1996). While the authors reduced the mineralization rates typically associated
with cereal grasses using crimson clover (T rifolium incarnatum L.) and hairy vetch (Vicia
villosa Roth) legumes, the use of cool-season grass and alfalfa binary mixtures could
modify C/N dynamics such that N availability more evenly matches potato tuber
demands. A cool-season grass legume mixture would still retain the nutritive feed

qualities necessary for dairy feed use in an integrated system.

167

Potato Scab

Table 3.20. Alternative system scab rating and increase from defender potato-com
rotation with no manure amendment- 2002, 2003, and 2004.

 

Year Preceding Crop Rating Increase

 

from
defender
%
2002 Corn
Manure 2.38 8.7
Conv. 2.19 -
LSD a=0. 05 1.31
2003 Corn
Manure 3.00 33.3
Conv. 2.25 -
LSD a=0. 05 1.52
2004 Corn
Manure 3.00 38.3
Conv. 2.17 -
LSD a=0. 05 1.76
2003 Sudex l-yr -
Manure 3.00 33.3
Conv. 2.75 22.2
LSD a=0.05 0.80
2003 Alfalfa l-yr
Manure 3.00 33.3
Conv. 2.25 0
LSD a=0. 05 0.80
2004 Alfalfa 2-yr
Manure 3.50 * 61.3 *
Conv. 2.25 0
LSD a=0. 05 0.76
2004 Festulolium 2-yr
Manure 2.50 15.2
Conv. 2.38 9.7
LSD a=0.05 2.38

+ significant at P=0.10

"' significant at P=0.05

Defender system = potato afier com with no manure amendments. Rotations compared to each season's
defenders system, no comparisons possible between years

Manure application had greater influences on surface scab levels following alfalfa
rotation compared to other crops rotations in this study. When potatoes followed com,

sudex, or festulolium in rotation, surface scab levels were not significantly increased by

168

manure application. Alfalfa as a rotation crop increased surface scab levels, both as a 1-
year rotation crop and as a 2-year rotation crop. Scab levels following l-year of alfalfa
did not differ statistically from those following 2-years of alfalfa, but demonstrated a

slight trend toward less scab following l-year alfalfa rotation.

When comparing scab levels of individual treatments against the non-manured com-
potato rotation defender system, increases to scab levels were only observed with manure
amended 2-year alfalfa as a preceding crop. While no other rotation or treatment
significantly increased scab levels, it is worthy noting that no forage crop was effective in
reducing scab levels. Non-amended l-year alfalfa was the only treatment not to increase
overall scab levels. Forage crops, regardless 0f manure application, increased scab
levels. The addition of manure amendments exacerbated this trend, increasing scab

levels in all instances.

Scab incidence has been correlated with higher soil N in previous research (Lapwood and
Dyson, 1966). High soil N levels were found to promote vegetative growth and delay
tuber initiation, shifting the times at which tubers were most susceptible to scab infection.
Manure application, particularly when annually applied, increases available N throughout
the growing season. Similarly, alfalfa as a preceding crop contributes high levels of N to
the soil (Rasse et al., 1999). Multiple years of alfalfa production may result in higher
residual N contributions to potatoes than other rotation crops, delaying the tuber initiation
in potatoes following alfalfa. This delay in tuber formation may provide a possible

explanation for the increased levels of scab seen following 2-year alfalfa production.

169

While manure amendment does not add greater amounts of overall N to the system above
that of mineral fertilizer, the organic and inorganic forms of N from these two sources do
not necessarily behave the same over the course of the season. The organic N contributed
by manure must be mineralized in order to be available to plants, whereas N supplied
through commercial fertilizers is available at a faster rate. Alfalfa also contributes to the
organic N pool with these effects compounded by N contributions to the system from N
fixation. Nitrogen levels in both the 1-year and 2-year alfalfa rotations may be expected
to be higher due to N fixation, with a 2-year stand adding more N than a 1-year stand.
The combined effects on manure amendment and 2-year alfalfa rotation changed the soil

N dynamics enough to significantly increase surface scab infection.

Scab infection has also been found to increase with application of Ca. The nutrient
diverse composition of manure results in the application of sizable quantities of

compounds not otherwise agronomically applied.

Table 3.21. Calcium applied through 12,260 L ha" liquid dairy manure amendment-

 

 

2002, 2003 and 2004.
Total P" yr aval
kg ha'1 kg ha'I

2002 232.6 127.9
2003 553.0 304.1
2004 277.3 156.1

Lambert and Manzer studied the effects of Ca application in potatoes with applications of
6.4 t ha" gypsum (17% Ca) and 4.5 t ha'l dolomitic lime (24% Ca) measured against a

control treatment at Preque Isle, Maine in 1989. These three fertilizer rates were then

170

split between treatments with and without Streptomyces scabies inoculation. Inoculated
treatments in both 1989 and 1990 for the control and gypsum applications ranged from 18
to 22% infection. Non-inoculated treatments had no infection. Dolomitic lime
application resulted in 53% infection in 1989 and 80% infection in 1990 with inoculation.
Non-inoculated treatments were 32% infected in 1990. Scab infection was found to be
more correlated to soil pH modification from liming than Ca application. Davis et al.
(1976) applied Ca(NO3)2 and (N114)S04 at 200 kg N ha", 5 at 673 and 897 kg ha", N-
serve [2-chloro-6-(trichloromethyl)-pyride] at .6, 1,1, and 1.7 kg ha", and PCNB
(pentachloronitrobenzne) at 28 kg ha'1 in Blackfoot, Idaho. Triplie-super phosphate
(P205) was applied to all plots at 168 kg ha". Significant positive linear correlation (r=
0.56) was observed between Ca levels and tuber peeling and scab severity. The effects of
Ca on scab severity were found to be mitigated by applications of phosphate, with
Ca:phosphate-P ratios highly correlated to scab infection (r= 0.99). These studies suggest
that while Ca applications may not have direct implications of scab infection, indirect
effects may compound scab issues. However, with no mechanism to measure Ca soil or

tuber concentrations, it is difficult to determine the effects of Ca in this experiment.

Goss (1936) examined the effects of long-term crop rotation, including alfalfa, upon the
effects of scab in potatoes. One, two, three, and four year rotations with sugarbeets (Beta
vulgaris L.), oats, corn, and alfalfa resulted in decreasing scab levels with increasing
lengths of crop rotation and lengths of alfalfa stands preceding potatoes. Weinhold et al.
(1964) found 3-year stands of alfalfa in rotation with potatoes decreased scab levels

compared to l-year barley, sugarbeet or cotton (Gossypium hirsutum L.) rotations.

171

 

Regional studies in Michigan have not found similar beneficial results from alfalfa
rotation effects on potato scab. Wheeler (1946) found that alfalfa provided similar
control of scab to that of corn rotations, though better than other legumes or grasses.
Griffin and Hesterman (1991), at this site, found that alfalfa hay as a preceding crop to
potatoes moderately increased scab levels compared to other legumes. Scab levels in

alfalfa were similar to com.

The reduction in potato scab levels seen following alfalfa in the literature validates the
assumption that the observed scab increases following alfalfa are a result of altered N
dynamics. Nitrogen mineralization is largely dependent on fluctuating environmental
conditions. The likelihood exists that unusual weather conditions led to N levels in
which scab initiation was abnormally favorable in 2003 and 2004. Lapwood and Dyson
(1966) postulated such a theory to explain their observations when scab levels increased

with increasing N levels.

Manure amendment has long been discouraged in potato production due to a belief that
manure is a major cause of scab infection (Wheeler and Tucker, 1895; Stuart, 1937;
Smith, 1968). Anecdotal accounts from farmers show both positive and negative potato
disease effects from manure application, though the risk of increased disease pressure
often prevents the use of manures (Conn and Lazarovits, 1999). The mechanisms by
which animal manures effect scab levels are not well understood (Loria etal., 1997), with
conflicting reports from research results showing no consistent evidence of scab increases

from manure application. Goss (1936) found that manure increased scab levels within

172

several different potato rotations. In studies conducted in East Lansing, Michigan,
KenKnight (1941) found that applications of horse manure decreased potato scab levels.
Conn and Lazarovits (1999) found that solid cattle manure had no effect on scab levels
one year following application, while inducing slight decreases two and three years after
amendment. They also examined poultry and liquid swine manure effects on scab,
finding that swine manure reduced scab at one of two sites and poultry manure reducing
scab at both sites. They postulated several theories for this occurrence, including manure
changes to soil pH and stimulation of biological control. Swine and cattle manures were
shown to temporarily decrease soil pH levels 4 weeks following amendment, reducing
soil pH from about 6.0 to 5.5. Scab is found in soils with a pH ranging from 5.2 to 8.0
(Loria et al., 1997) with a positive correlation between increasing scab and increasing pH
(Lambert and Manzer, 1991). Thus, a reduction of soil pH to 5.5 is likely to suppress
most scab infection. The soil pH at MRF was measured as 6.59 at the study onset,
making it unlikely that manure amendment would reduce pH level below that of scab
tolerance. Potato production in Michigan is recommended on soils with a pH fi'om 5.2 to
6.5, with a liming recommendation of 6.0 (Vitosh, 1990). Many Michigan potato soils
may be able to have soil pH levels temporarily decreased with manure application,

thereby reducing scab activity.

The few experiments in the literature that do report increases in scab infection with
manure application offer no explanation for their findings. However, one explanation for
the increased scab levels seen in this experiment may be linked to the same mechanisms

that increased scab levels with alfalfa rotations. The excess N available throughout the

173

season with manure amendment compared to conventional fertilization may push the
window of tuber initiation later into the season, thereby shif’ting the period of highest
tuber susceptibility later into the growing season for manure treatments compared to non-

manure treatments.

174

 

Economic Aspects

System-wide integration shifts revolve wholly around their accompanying economic
ramifications. The current agronomic systems in place are practiced because at some
point, they provided benefits over the previous systems. Thus, the adoption of new
systems, such as the integrated potato-dairy model suggested in this research, is
dependent on demonstrable, tangible economic benefits. Potatoes and milk are two high
value agricultural enterprises that under high intensity management systems often operate
near their current maximum profit potentials. The agricultural landscape is dominated by
low commodity prices, high land values, and high input costs. Profit margins are tight
and economies of scale are commonly called into practice. However, serious questions
arise as to the sustainability of this current model. There are no indications in the
foreseeable future that commodity prices will raise or input costs lower. At some point,
building larger and larger farming enterprises will no longer prove pragmatic. The need
for a paradigm shift is essential for the way in which farming operations are conducted.
However, enacting widespread reform throughout the agricultural community is only
feasible when the risk of adoption is below a certain level. Research study results
examining farmers facing moderate to severe production stresses find that these
producers are more inclined to incorporate practices such as longer crop rotations and
utilization of new crops than farmers not facing as severe of production challenges
(Corselius et al., 2003). Integration utilization can only achieved if the economic
implications are addressed. Accurate assessments of the costs of yearly potato and forage
production are required to establish baselines by which to measure firture decisions.

Additionally, manure economics must be incorporated. Manure represents a unique

175

challenge as the divergence viewpoints of its intrinsic worth as a waste product or
potential fertilizer and soil conditioner result in different values to different players. The
utilization of manure as nutrient source may hold particular promise as a mineral
fertilizer substitute. Costs associated with agronomic production shifts fi'om grain to
forage production must be adsorbed by corresponding increases in production and return
on investment. Above all, and often forgotten by producers, are the unrealized costs in
gaining necessary proficiency in new management practices, shifts in required
manpower, and other unforeseen barriers to economic viability associated with wide-
spread agronomic change. Potato —— livestock integration may hold legitimate economic
promise for one set of producers while remaining an unfeasible enterprise for others.

Extensive utilization of agronomic integration hinges on individual economic practicality.

176

Conclusion

This experiment shows that agronomic integration of dairy and potato operations offers a
production increase potential for potato producers. US #1 tubers yields were found to be
responsive to manure and crop rotation effects. Liquid dairy manure significantly
increased tuber yields and slightly increased surface scab infection to a greater extent
than crop rotation. No crop rotation induced significant increases to potato yields without
manure amendment. There was a synergistic effect of crop rotation and manure
application as crop rotation with manure application was shown to increase US #1 tuber
yields most effectively in a 2-year rotation with sudex managed as a green manure,
followed by grain com in a 2-year rotation and a 2-year stand of alfalfa managed as a hay
crop with crop biomass removed. One-year alfalfa and 2-year festulolilnn did not result
in significant yield responses of potato tuber yields. Forage rotation crops managed for
hay production in l-year and 2-year stands were not as effective at increasing potato
tuber yields or decreasing tuber scab infection as 2-year rotations with corn produced for
grain or sudex managed as a green manure cover crop. The combination of manure
application and C4 grass crop rotation was the most effective at increasing tuber yields.
Manure application increased festulolium yield, but did not increase alfalfa or sudex
forage yields. No consistent forage quality effects could be drawn between manure
treatments. Manure application decreased corn grain yield in 2002, but increased test
weight in 2004. This study indicates that crop rotation and manure amendment holds the

potential to increase potato yields.

177

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184

Appendix

Table 3.22. Potato tuber disease infection ratings- 2002, 2003 and 2004.

 

 

 

 

2002 HH VD BC IBS HN
Corn
Manure 0.625 a 2.25 a 0 0.125 a 0.25 a
Conv. 0.125 b 2.13 a O 0.125 a 0.25 a
2003
Corn
Manure 4.0 ab 0.25 a 0.75 a 0 a 0
Conv. 4.75 a 0 a 0 b 0 a 0
Sudex
Manure 2.5 ab 0.50 a 0.5 ab 0 a 0
Conv. 2.75 ab 0.25 a 0 b 0.25 a 0
Alfalfa l-yr
Manure 1.25 b 0 a 0 b 0.25 a 0
Conv. 3.25 ab 0.25 a 0.75 a 0.25 a 0
2004
Corn
Manure 0.125 ab 2.88 a O a 0 0
Conv. 0 b 2.63 a 0.75 a O 0
Alfalfa 2-yr
Manure O b 2.25 a 0 a 0 0
Conv. 0.125 ab 4.75 a 0.13 a 0 0
Festulolium 2-yr
Manure 0.75 a 2.13 a 0.13 a 0 0
Conv. 0.38 ab 2.25 a 0.25 a O 0

Comparisons made inner-year, comparisons between years not applicable

 

HH- Hollow heart

VD- Vascular disorder
BC- Brown center

IBS- Internal brown spot
HN- Heat neurosis

Potato disease is determined through internal analysis of 10 oversized or US#1 tubers.

185

Table 3.23. Potato tuber specific gravity- 2002, 2003, and 2004.

 

 

 

 

 

2002 gravity
Com
Manure 1 .0663
Conv. 1.0655
2003
Com
Manure l .079
Conv. l .059
Sudex
Manure 1.078 E
Conv. 1 .080 :1
Alfalfa l-yr ,.
Manure 1.075 "
COHV. 1075 f
2004 F
Corn 1;.
Manure 1 .075 E
Conv. 1 .082
Alfalfa 2-yr
Manure 1 .075
Conv. 1 .078
Festulolium 2-yr
Manure l .078
Conv. 1 .082

No statistical differences observed within year or between manure treatments.

 

 

P- value
Year 0.043
Rotation 0.321
Manure treatment 0.503
Rot x manure 0.847

186