cover crops to enhance soil productivity in organic

COVER CROPS TO ENHANCE SOIL PRODUCTIVITY IN ORGANIC

VEGETABLE CROPPING SYSTEMS

By

ANDREW JAMES LAWSON

A thesis submitted in partial fulfillment of

the requirements for the degree of

MASTERS OF SCIENCE IN SOIL SCIENCE

WASHINGTON STATE UNIVERSITY

Department of Crop and Soil Science

DECEMBER 2010

ii

To the Faculty of Washington State University:

The members of the Committee appoint to examine the thesis of ANDREW JAMES

LAWSON find it satisfactory and recommend that it be accepted.

___________________________________

Craig G. Cogger, Ph.D., Co-chair

___________________________________

Ann Marie Fortuna, Ph.D., Co-chair

___________________________________

William L. Pan, Ph.D.

iii

ACKNOWLEDGEMENT

First, I would like to express thanks to my committee: Craig Cogger, Ann-Marie Fortuna,

and Bill Pan. They showed patience in my development as a student and scientist. Their

guidance has been invaluable to the completion of this work and my graduate program. I am also

grateful to Ann Kennedy for her professional encouragement and advice.

The research assistance I have received in both Puyallup and Pullman has been important

to the completion of this work. Andy Bary and Liz Myhre provided essential support in

conducting field trials in Puyallup. Without their efforts, this research would not have been

possible. In Pullman, Tami Stubbs conducted a fiber analysis that has been a valuable component

of this research. I would also like to acknowledge Margaret Davies for processing hundreds, if

not thousands, of my samples. Many student workers helped make this research possible: Jill,

Bethany, Ted, Katie, Kyle, Belinda, Katrina, Deanna, Ryan, Brent, and Kayla. We have shared

many happy moments together in the field and lab. Finally, I appreciate the financial support I

received, which was provided by Washington State University Emerging Issues in Agriculture

and the USDA Integrated Organic Program.

I would like to express many thanks to the Crop and Soil Science faculty, staff, and

graduate students for all their encouragement and advice. Both of my loving parents deserve

acknowledgement for their encouragement and guidance. Finally, I am grateful to Olivia for all

her love and support.

iv

COVER CROPS TO ENHANCE SOIL PRODUCTIVITY IN ORGANIC

VEGETABLE CROPPING SYSTEMS

Abstract

by Andrew James Lawson, M.S.

Washington State University

December 2010

Co-chairs: Craig G. Cogger and Ann-Marie Fortuna

The supply of plant available nitrogen (N) is often limiting in organic vegetable cropping

systems. Cereal and legume cover crop mixtures may enhance plant available N to subsequent

crops. But cover crops often require adjustments to the timing of field operations. The rate of N

release from cover crops is also uncertain due to variations in climate, residue quality, and N

content. We conducted two field studies and one laboratory incubation study to optimize cover

crop growth and N availability to a subsequent crop.

A field trial was conducted to assess the effect of planting date, harvest date, and rye

(Secale cereal)-hairy vetch (Vicia villosa) seeding ratio on cover crop establishment, N

accumulation, and residue quality. While late harvest favored larger biomass, there was an

increase in C:N ratio and fiber content. Seeding ratio did not have a large effect on cover crop

biomass yield or composition. In a related N mineralization laboratory incubation study, hairy

vetch and a 75:25 rye-hairy vetch blend released similar amounts of N over 70 d. But the initial

rate of N release was nearly 3-fold greater for hairy vetch. The slower rate of N release from the

75:25 rye-hairy vetch blend may result in N release that is better timed with crop N uptake.

Nitrogen release was well correlated with residue C:N ratio, and therefore may be used to predict

N release from rye-hairy vetch residues.

v

The effect of a fall planted 50:50 rye-hairy vetch cover crop on organic sweet corn

nitrogen use efficiency was determined in a second field trial. Feather meal was applied over top

of cover crops at four rates. A trend of increased sweet corn dry matter and ear yield was

noticeable in cover crops treatments when no feather meal was applied. But a large contribution

from the soil N pool made it difficult to separate the N contributions from cover crops and soil.

Early and late planted cover crops had fertilizer replacement values of 57 and 27 kg N ha-1

. Our

results demonstrate that a 50:50 rye-hairy vetch blend may supply significant amounts of N to a

subsequent crop.

vi

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENT ....................................................................................................... iii

ABSTRACT ............................................................................................................................. iv

LIST OF TABLES ................................................................................................................. viii

LIST OF FIGURES ...................................................................................................................x

CHAPTER 1: Cover crops in organic vegetable cropping systems: a literature review

1. INTRODUCTION ........................................................................................................1

2. OVERVIEW OF ORGANIC VEGETABLE PRODUCTION ....................................2

3. EVALUATION OF COVER CROP BENEFITS ........................................................6

4. COVER CROP MANAGEMENT .............................................................................11

5. NITROGEN AVAILABILITY FROM COVER CROP RESIDUES ........................17

6. CROP N RESPONSE AND UPTAKE EFFICIENCY ..............................................24

7. LITERATURE CITED ...............................................................................................28

CHAPTER 2: Evaluating fall cover crop blends for biomass production, residue quality,

and weed suppression

1. INTRODUCTION ......................................................................................................45

2. MATERIALS AND METHODS ...............................................................................48

3. RESULTS AND DISCUSSION ................................................................................56

4. CONCLUSIONS ........................................................................................................73

5. LITERATURE CITED ...............................................................................................74

CHAPTER 3: Nitrogen release from rye-hairy vetch cover crop residues with and

without a semi-fast release organic fertilizer in a laboratory incubation

1. INTRODUCTION ......................................................................................................79

vii

2. MATERIALS AND METHODS ...............................................................................82

3. RESULTS AND DISCUSSION ................................................................................90

4. CONCLUSIONS ......................................................................................................102

5. LITERATURE CITED .............................................................................................104

CHAPTER 4: Response of organic sweet corn to a fall planted 50:50 rye-hairy vetch

cover crop blend

1. INTRODUCTION ....................................................................................................111

2. MATERIALS AND METHODS .............................................................................114

3. RESULTS AND DISCUSSION ..............................................................................123

4. CONCLUSIONS ......................................................................................................132

5. LITERATURE CITED .............................................................................................133

CHAPTER 5: General conclusions and recommendations

1. SUMMARY OF FINDINGS ....................................................................................140

2. RECOMMENDATIONS .........................................................................................142

viii

LIST OF TABLES

CHAPTER 1: Cover crops in organic vegetable cropping systems: a literature review

1. Winter cover crops, biomass, N accumulation, and C:N ratio typical in

maritime Pacific Northwest ........................................................................................27



1. Dates of sampling and field activities ........................................................................52

2. Analysis of variance for cover crop biomass, N concentration, N content, and

C:N ratio as affected by experiment year, harvest date, planting date, and cover

crop seeding ratio .......................................................................................................53

3. Cover crop biomass as a function of growing degree days ........................................54

4. Cover crop biomass yield and total C and N content as affected by planting and

harvest date and rye-hairy vetch seeding ratio ...........................................................54

5. Analysis of variance for fiber fractions as affected by cover crop, planting date,

harvest date, and year .................................................................................................55

6. Neutral detergen fiber (NDF), acid detergent fiber (ADF), and acid detergent

lignin (ADL) by harvest date, and rye-hairy vetch seeding ratio ...............................55



1. Cover crop-feather meal treatments used in (nitrogen) N mineralization

incubation study, including the equivalent rates of cover crop biomass

application and total applied N ...................................................................................87

2. Total C and N concentration of residue and soil, and residue quality ........................88

4. Parameters of first-order model fitted to net N mineralization from cover crop

residues .......................................................................................................................88

4. Pearson correlation coefficients between net N mineralization and residue

quality .........................................................................................................................89


cover crop blend

ix

1. Dates of sampling and field activities ......................................................................119

2. Cover crop dry matter production, N concentration, total N content and dry

matter composition in 2009 ......................................................................................119

3. The effect of cover crop and sample date on soil nitrate (NO3-)-N

concentration. Total nitrogen (N) content of early and late cover crops was 70

and 39 kg N ha-1

.......................................................................................................120

4. Degree day elapsed between cover crop incorporation and soil sampling ...............120

5. The effect of cover crop and feather meal on post-harvest soil (NO3-)-N................121

6. Sweet corn fresh ear yield and dry matter as affected by feather meal ....................121

7. Effect of cover crop and available feather meal nitrogen (N) on ear leaf N status

at silking and total plant N uptake. The interaction between cover crop and

feather meal was not significant at P = 0.05.............................................................122

8. Linear regression equations for sweet corn nitrogen (N) uptake as a function of

feather meal available N. Effect of cover crop on apparent N recovery and

calculated reduction in feather meal N requirement ................................................122

x

LIST OF FIGURES



1. Mean monthly precipitation and mean monthly maximum (max.), minimum

(min.) and daily temperatures from 1995-2010 ..........................................................66

2. Cover crop establishment measured as a percent ground cover excluding weeds

for early (a) and late (b) planted cover crops. Cover crop treatments are hairy

vetch (Vetch), 25:75 rye-hairy vetch blend (R25V75), 50:50 rye-hairy vetch

blend (R50V50), and pure rye (Rye) (P < 0.0001) .....................................................67

3. Cover crop biomass yields as affected by planting date, harvest date, and rye-

hairy vetch seeding ratio (P < 0.05) ...........................................................................68

4. Percentage of above ground biomass from rye, hairy vetch, and weeds at four

rye-hairy vetch seeding ratios (Rye, %) at early (a) and late (b) planting ...... dates

(P < 0.05) ....................................................................................................................69

5. Weed biomass yield as affected by planting date and rye-hairy vetch seeding

ratio .............................................................................................................................70

6. Cover crop residue N concentration as affected by harvest date and rye-hairy

vetch seeding blend (P < 0.0001) ...............................................................................70

7. Neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent

lignin (ADL) by rye-hairy vetch seeding ratio and harvest date. Values within the

same group for each seeding ratio treatment followed by the same letter are not

significantly different (P < 0.05) ................................................................................71

8. Mid-June soil NO3--N as affected by rye-hairy vetch seeding ratio and

experiment year (P < 0.001) .......................................................................................72



1. Cumulative N release from cover crops residues and soil over 157 d incubation

(P < 0.05) ....................................................................................................................99

2. Cumulative net N release from cover crop residues (soil (NH4++NO3

-)-N has

been subtracted) over 157 d incubation (P < 0.05).....................................................99

xi

3. Cumulative N release from cover crops and feather meal residues and soil over

157 d incubation (P < 0.05) ......................................................................................100

4. Cumulative net N release from feather meal (FM) and cover crop residues (soil

(NH4++NO3-)-N has been subtracted) over 157 d incubation (P < 0.05) ...............100

5. The effect of cover crop residue and feather meal (FM) on mean nitrification

potentials over 70 day laboratory study (P < 0.05) ..................................................101

6. The effect of time and feather meal (FM) on nitrification potentials (rates

averaged across all cover crop treatments) (P < 0.05)..............................................101


cover crop blend

1. Sweet corn total nitrogen (N) uptake as a linear function of available feather

meal N. Unique regression models plotted for each cover crop treatment because

cover crop treatments were significantly different at P = 0.05 ................................131

2. Nitrogen (N) use efficiency of sweet corn dry matter production per unit N

supply, which includes soil N (P < 0.01) .................................................................131

xii

DEDICATION

For my Olivia

1

CHAPTER 1

Cover crops in organic vegetable cropping systems: a literature review

1. INTRODUCTION

Grass-legume cover crop blends have the potential to supply all or a significant portion of

nitrogen to subsequent cash crops (Burket et al., 1997; Griffin et al., 2000; Cline and Silvernail,

2002; Tonitto et al., 2006; Sainju and Singh, 2008). Inclusion of cover crops in crop rotations

provides a range of other benefits, including reduced soil erosion and runoff, improved N

cycling, weed and pest control, enhanced soil quality, and increased crop yields (Sarrantonio and

Gallandt, 2003; Fageria et al., 2005). Despite these benefits, cover crops often require

adjustments to the timing of field operations (Teasdale et al., 2004; Snapp et al., 2005). The rate

of release of N from cover crops is also uncertain due to variations in climate, residue quality and

nutrient content (Rannels and Wagger, 1996; Ruffo and Bollero, 2003a; Ruffo and Bollero,

2003b). Therefore, growers have been slow to adopt cover crops in crop rotations.

There is renewed interest for including cover crops in rotation for the purpose of soil

fertility management and enhanced crop production; especially among organic growers who are

prohibited from using synthetic fertilizers (USDA, National Organic Program, 2010). The

organic sector has experienced rapid growth since inclusion in the Organic Foods Production Act

of 1990, with 20-25 % annual increase of organic food product sales (Lotter, 2003). One of the

largest challenges to efficient production of organic crops is adequate and timely N supply and

efficient use (Berry et al., 2002). Numerous studies have estimated the N fertilizer value of cover

crops to subsequent cash crops (Rannels and Wagger, 1996; Burket et al., 1997; Griffin et al.,

2000; Sarrantonio and Malloy, 2003; Tonitto et al., 2006; Sainju and Singh, 2008). However, use

among organic growers is limited because of lack of research on optimal dates of establishment,

2

effect of early incorporation, and influence of cereal-legume seeding ratio on stand

establishment, N accumulation, and N availability to subsequent crops (Cogger, personal

communication).

Greater understanding of N release from cover crop residues, N availability to subsequent

crops, and ability to predict plant available N supply might provide a “keystone service”

necessary for widespread adoption of cover crop use in crop rotations (Cherr et al., 2006).

Research is necessary at a regional scale because rates of N release are affected by variations in

climate, residue quality, and nutrient content (Cabrera et al., 2005). Grower uncertainty

concerning the effect of planting and harvest date and cereal-legume seeding ratio on cover crop

biomass production, N accumulation, and N availability to crops in rotation varies across regions

due to climate differences and crop rotation restrictions (Snapp et al., 2005). Therefore, research

is needed to optimize planting and harvest dates and cereal-legume seeding ratio, and N

availability to crops grown in rotation.

2. OVERVIEW OF ORGANIC VEGETABLE PRODUCTION

The organic farming sector has been one of the most rapidly expanding segments of

agriculture for over a decade (Greene, 2006), during which demand has periodically outpaced

supply (Dimitri and Oberholtzer, 2009). In response to consumer interest, the number of certified

organic crop acres has increased from 638,500 acres in 1995 to 2,655,382 acres in 2008 (USDA,

Economic Research Service, 2010). Fresh produce continues to be the top selling organic

product (Organic Trade Association, 2010). The number of certified acres in vegetable

production more than tripled between 1997 and 2008 to a total of 168,776 acres, nearly 5% of

total vegetable farmland in the United States (USDA, Economic Research Service, 2010).

Organic vegetable production in Washington

3

According to the 2008 Organic Production Survey (USDA, National Agriculture

Statistics Service, 2010), Washington was the second leading producer of certified organic

vegetables in the country. Harvested organic vegetable acreage in Washington State doubled

between 2004 and 2007; however, there was little growth in 2008, with 19,836 acres recorded

(Kirby and Granatstein, 2009). The lag in growth may be related to the recent economic

recession and higher cost of organic products versus conventional (Dimitri and Oberholtzer,

2009). Washington had 887 certified and exempt organic producers (USDA, Economic Research

Service, 2010), of which one-third were located west of the Cascade Mountains (Kirby and

Granatstein, 2009). Besides Whatcom and Lewis counties, which had larger farms and 8 percent

of the state‟s vegetable production acreage, farms in western Washington were characterized as

small, diverse, direct market enterprises (Kirby and Granatstein, 2010). In particular, land in

King, Pierce, and Thurston Counties tended to be farmed intensively and net a high economic

return on a per acre basis. Climate and production systems are distinct from Eastern Washington,

a main agriculture region in the state, and therefore research must reflect those differences

(Granatstein et al., 2010).

Despite a growing demand for organic food products, many farmers have not been

willing to transition to organic management production. High costs, low yields, and lack of

understanding of organic management practices have been cited as obstacles to adoption of

organic production (USDA, Economic Research Service, 2010). In a statewide survey of organic

farmers in Washington, Goldberger (2008) found that production expenses and variable or low

yields were the greatest challenges to organic production. Organic farmers in the Puget Sound

region of western Washington have similarly expressed concerns over yield reduction due N

deficiency (Cogger, personal communication). A number of studies have validated this concern,

4

demonstrating 20-41% lower yields in organic and transitional cropping systems when compared

to conventional systems (Mader et al., 2002; Cavigelli et al., 2008; Dresboll et al., 2008;

Herencia et al., 2008).

Soil fertility management

Soil fertility management has been listed as one of the largest challenges to growing

crops organically (Walz, 2004; Gaskell and Smith, 2007). Organic crop production has

prohibited the use of synthetic fertilizers. While soil fertility is not different in organic and

conventional cropping systems, there is greater reliance on the soil biology that transforms

nutrients into plant available forms because mineral fertilizers cannot be used (Mader et al.,

2002; Tu et al., 2006). It is more crucial to manage nutrient pools and the processes and rates that

dictate nutrient transformation from one form to another (Stockdale et al., 2002). The quality and

quantity of organic inputs and the affect on soil microbiology is of particular concern because of

its influence on N mineralization and soil organic matter accumulation (Cabrera et al., 2005). It

is widely held that soil organic matter formation and decomposition forms the foundation of N

supply to crops grown organically (Magdoff and van Es, 2000; Gaskell and Smith, 2007).

Similar importance on soil fertility has been emphasized in the USDA National Organic Program

standards that mandate growers to develop a crop production management plan that builds the

inherent fertility of soil by managing organic matter; a crop rotation must include cover crops,

green manures, and catch crops that build soil organic matter, effectively limit erosion, and

properly manage limiting or excessive plant nutrients (USDA, National Organic Program, 2010).

A variety of products and management practices have been used to supply N to crops in

organic production, including animal manures, compost, cover crops, and specialty products

(Cogger, 2000; Watson et al., 2002; Gaskell, 2006). But none of these means are without

5

challenge. Livestock manure is often used as a source of fertility and organic matter, however

there are restrictions on timing of application (Riddle and McEvoy, 2005) and high variability in

N content and availability between types and sources has been reported (Bary et al., 2000). Using

manure as a fertilizer can also result in excessive application of phosphorus and contamination of

groundwater (Hao et al., 2004). Well-composted materials decompose slowly, solving P loading

issues but supplying smaller amounts of plant available N (Gale et al., 2006). In contrast, some

commercial organic fertilizers, such as sea bird guano, fish powder, feather meal, and blood

meal, consistently provide relatively rapid and predictable nutrient availability. Farmers often

complain that specialty products are expensive and cost-prohibitive while compost and manures

are bulky and costly to import and apply (Gaskell and Smith, 2007). Legume cover crops are

often worked into rotation as a source of short-term nitrogen fertility. Both summer interseeded

and winter legume and cereal-legume cover crop mixtures have been shown to provide

significant amounts of nitrogen to subsequent crops (Rannels and Wagger, 1996; Burket et al.,

1997; Griffin et al., 2000; Sarrantonio and Malloy, 2003; Teasdale et al., 2008). But it is difficult

to predict N availability to subsequent crops (Cabrera et al., 2005) because N mineralization of

residues is controlled by many factors, including residue composition (Ranells and Wagger,

1996), soil temperature and water content (Ruffo and Bolero, 2003b), and soil characteristics

(Whitmore and Groute, 1997).

The challenge in organic farming is matching inorganic N supply with crop demand on a

temporal basis (Pang and Letey, 2000). Berry et al. (2002) found that while Organic farming

systems that use cover crops, manures, and composts have the potential to supply large amounts

of N, release is often not timed with N uptake in subsequent crops. Because synthetic fertilizers

cannot be used in organic systems, delivery of readily soluble nutrients is not possible. There is a

6

general need for greater understanding and ability to predict N release from various organic

products and green manures so fertility recommendations can be accurately made (Granatstein et

al., 2010). Recently, work has been done to measure N release from manures, composts, and

specialty products in the Pacific Northwest (Gale et al., 2006). But, current research concerning

cover crop use for N management is almost entirely based on synthetic inputs of a conventional

system, which are inadequate for effective management in organic production (Cherr et al.,

2006), and it fails to address N availability issues and parameters for cover crop establishment

(Kramberger et al., 2009). Regional information on cover crop growth, N accumulation, and N

release patterns is needed in organic cropping systems.

3. EVALUATION OF COVER CROP BENEFITS

Cover crops have been an integral part of crop rotations for many millennia, providing a

range of on-farm benefits and ecosystem services (Sarrantonio and Gallandt, 2003; Fageria et al.,

2005; Cherr et al., 2006). Earliest uses date to 500 BC, where Chinese records acknowledge

understanding of its value as fertilizer (Paine and Harrison, 1993). Clovers and other legumes

filled traditional fallow periods in turnip-grain rotations in the eighteenth century in Europe and

winter cover crops were common in cropping systems in the early twentieth century in North

America (Pieters, 1917). But cover crop use declined in most industrial countries after

commercialization of Haber-Bosch process and widespread availability of commercial fertilizers,

as fertility systems based on soluble nutrient sources supplanted cover crop practices in most

cropping systems (Galloway and Cowling, 2002). There is renewed interest for including cover

crops in rotation for the purpose of soil fertility management and enhanced crop production,

especially in organic cropping systems where mineral fertilizer use is prohibited (USDA

National Organic Program, 2010).

7

Cover crops are grown between periods of normal production or inter-seeded between

rows of cash crops or trees or vines in orchard or vineyard for the purpose of soil and water

conservation and enhanced soil productivity (Hartwig and Ammon, 2002; Sarrantonio and

Gallandt, 2003). These crops are not grown for purpose of sale or feed, but are often plowed

under and incorporated into the soil (as green manures) or desiccated and left on the soil surface.

Inclusion of cover crops in crop rotations provides on-farm benefits and environmental services,

including reduced soil erosion and runoff, improved N cycling, N fixation and supply to crops,

weed and pest control, enhanced soil quality, and increased crop yields (Fageria et al., 2005;

Snapp et al., 2005; Cherr et al., 2006). However, benefits of inclusion of cover crops in rotation

vary among different soils types, crop rotations, environmental variables, type and species of

cover crop, and management schemes (Fageria, 2007).

Improved N management

Improved N cycling is an advantage to inclusion of cover crops in crop rotations

(Sarrantonio and Gallandt, 2003). Significant amounts of residual soil N can be captured by

catch crops and reduce leaching by recycling N for subsequent crop uptake (BrandiDohrn et al.,

1997). Legumes biologically fix atmospheric N, which enhances short-term soil N fertility. Cherr

et al. (2006) suggest that N supply from cover crop residues to cash crops grown in rotation

provides a “keystone” service that makes cover crop use attractive to farmers. But low N

utilization efficiency by cash crops and unreliable N supply from cover crop residues represent

nutrient management challenges (Pang and Letey, 2000; Teasdale et al., 2008).

Non-leguminous winter cover crops can take up significant amounts residual soil nitrate

to reduce leaching to waterways and improve N cycling (Sainju and Singh, 2008; Moller and

Reents, 2009; Thorup-Kristensen and Dresboll, 2010). This is important in humid, temperate

8

climates such as the maritime Pacific Northwest, where mild temperatures can make winter

mineralization significant and high rainfall causes extensive leaching and removal of nitrates

from the soil profile by spring (Kuo et al., 1997; Hooker et al., 2008). Studies show that variation

in N uptake by winter cover crops are dependent upon rainfall patterns and the cover crop

species grown. In an 11 year-study of fall-seeded cover crops in the Willamette Valley, Oregon,

water quality benefits of reduced N leaching were controlled by the timing and quantity of

annual rainfall. Early rainfall following a dry year increased leaching potential regardless of

cover crop treatment (Feaga et al., 2010). However, in the case of a dry winter season, N uptake

by winter cover crops has reduced N availability to subsequent crops, causing pre-emptive

competition (Thorup-Kristensen and Dresboll, 2010). Cereal and brassica cover crops are

adapted for high N uptake (Weinert et al., 2002). Although some research demonstrates that

legume cover crops are not effective in reducing soil nitrate leaching over winter (Rosecrance et

al., 2000), others find cereal-legume mixtures plausible (Moller and Reents, 2009). In a study of

the effect of winter grown oats, lupins, and an oats-lupins mixture on soil nitrate leaching,

Fowler et al. (2004) found a 50 % reduction in winter nitrate leaching compared to bare soil, but

no difference between cereal and cereal-legume cover crop treatments. In general, cereal-legume

cover crop blends are more efficient at N uptake from soil than legume monoculture (Rinnofner

et al, 2008).

Biological N fixation by legume cover crops can supply significant N to crops grown in

rotation and replace off-farm N fertility inputs (Tonitto et al., 2006; Gselman and Kramberger,

2008), making it a sustainable and renewable source of N. The amount of atmospheric N fixed

by winter legumes is affected by soil N status at the time of cover crop growth. Moller et al.

(2008) found that high soil inorganic N content reduced legume growth and N fixation when

9

combined in mixture with cereal. Similarly, Kramberger et al. (2009) demonstrated that legumes

are better adapted to low N fertility soils than cereal cover crops because of their ability to fix N.

Soil temperature has been shown to affect N fixation efficiency of legumes and has impacted

what legume species are best suited to a given crop rotation and climate (Power and

Zachariassen, 1993). A variety of legume cover crops are adapted for winter growth in temperate

climates, including Trifolium spp. (clovers), Vicia spp. (vetches), Medicago spp. (alfalfa, trefoils,

and other medics), and Lupinus spp. (lupins) (Rannels and Wagger, 1996; Jeranyama et al.,

1998; Griffin et al., 2000; Zemenchik et al., 2001; Ross et al., 2001; Fowler et al., 2004;

Kankanen and Eriksson, 2007; Teasdale et al., 2008).

A cereal-legume cover crop blend can serve the “dual purpose” of recycling residual fall

soil N, supplying additional N by biological fixation, and increasing N availability compared to

pure cereal (Clark et al., 2007). But Cline and Silvernail (2002) found that N availability

following cereal-legume mixtures was lower than pure legume cover crops. Manipulating cover

crop residue N content and quality by optimizing planting and kill dates and cereal-to-legume

biomass ratios can have a significant impact on N availability following cover crop incorporation

(Kuo and Sainju, 1997; Wagger et al., 1998). This is a chief concern to growers because the

timing of N availability is not always synchronized with crop N uptake demands, decreasing

crop N use efficiency (Pang and Letey, 2000).

Weed control

Cover crops are an effective management option for weed control and suppression.

Competition by cover crops for light, water, and nutrients and microclimate modification is one

means for weed control (den Hollander et al., 2007). Isik et al. (2009) cited this mechanism in

finding that hairy vetch, ryegrass, oats, and common vetch cover crops grown over winter

10

reduced total weed biomass by 87-91 % compared to winter fallow. Summer inter-seeded cover

crops can effectively reduce weed biomass but competition with crop and yield reduction can be

a problem (den Hollander et al., 2007). However, relay planted cover crops planted between

main crop rows after crop establishment can provide effective weed suppression without

reducing yields (Vanek et al., 2005). Cover crops may also control weed emergence and

germination by releasing allelopathic chemicals (Weston, 1996). Malik et al. (2008) suggested

that ten identified glucosinolates, or possible allelopathic elements, in wild radish cover crop

residue contributed to 35 % reduction in weed biomass in a corn rotation. However, other

research demonstrated that N availability can influence weed germination and biomass. Kumar et

al. (2008) found that buckwheat (Fagopyrum esculentum) residues suppressed shepherd‟s purse

(Capsella bursa-pastoris) growth and emergence through N immobilization. Similarly, Sung et

al. (2010) reported 65% less weed biomass following rye but an increase in weed biomass in

hairy vetch incorporated treatments due to higher N availability. In contrast, hairy vetch mowed

at flowering and left on surface prior to planting cash crops reduced weed biomass by 40%

(Campiglia et al., 2010). Residue placement can impact N availability and provide physical

barrier to weed emergence (Teasdale and Mohler, 1993; Campiglia et al., 2010).

Improved soil quality

Soil organic matter content is commonly used as the principal indicator of soil quality

and health (Doran, 2002) because of its role in nutrient cycling, soil tilth, biological activity, and

water availability (Magdoff and van Es, 2000). Studies have shown that cover crop residues can

supply large amounts of C to the soil (Kuo et al., 1997, Sainju et al., 2005; Fortuna et al., 2008),

resulting in increases or maintenance of soil organic matter (Nyakatawa et al., 2001). Cereal

cover crops increase or maintain soil organic matter levels relative to legume cover crops and no

11

cover crop management by supplying greater C inputs in the form of plant biomass (Sainju et al.,

2000; Ding et al., 2005). Legumes can increase or maintain soil organic matter if the biomass is

large enough. In Kentucky, a continuous corn-hairy vetch cropping system increased total soil C

and N compared to management without hairy vetch because of greater residue inputs (Fortuna

et al., 2008). Another study found that soil organic carbon increased in a cropping system with

legume cover crops in comparison to a no legume, fertilizer-based system, which was likely

because of greater C input from plant biomass inputs (Bakht et al., 2009).

4. COVER CROP MANAGEMENT

Implementing a cover crop management scheme depends on targeted goals or benefits

desired and crop rotational niche (Sustainable Agriculture Network, 2007). Goals and ground

availability affect what species are most suitable to a given rotation and environment (Snapp et

al., 2005).

Niches in rotations for cover crops

Defining spatial and temporal niches where cover crops can be integrated into crop

rotations can be the greatest obstacle to widespread cover crop use (Snapp et al., 2005). Vanek et

al. (2005) explain that cover cropping is limited in vegetable production because of frequent

tillage, complex rotations, and continuous cropping for harvest. There are a number of

considerations for identifying where and when cover cropping is possible, including seeding

method, weather restrictions, soil conditions, cover crop growth habit, method of kill and

subsequent bed preparation, and effect on economic crop growth and yield (Sustainable

Agriculture Network, 2007; Cherr et al., 2006). Sarrantonio (1992) lists non-simultaneous cover

cropping, relay planting, and intercropping as living mulch between crop rows as options for

position in rotations. Relay planting is a system where cover crops are planted into standing cash

12

crops, allowing early establishment of cover crops without negatively impacting cash crop

growth. Winter cover crops planted after cash crop harvest are most common in temperate

climates because full-season or summer cover crops represent income loss from field that is not

cropped for an entire growing season (Griffin et al., 2000).

Cover crops are usually planted in a fallow period of a rotation when weather is not

favorable for production of a cash crop (Cherr et al., 2006). Winter grown cover crops are grown

without sacrificing ground for cash crop production. But establishment can be troublesome in

temperate climates because of low temperature at time of sowing and significant loss to

winterkill (Teasdale et al., 2004; Brandsaeter et al., 2008). Growers in cold climates, such as

Maine, often have a narrow window of opportunity for establishing cover crops after harvesting

a cash crop in fall, which can result in inadequate biomass or winterkill (Griffin et al., 2000). A

number of studies list rapid germination and establishment, extensive rooting systems, good

winter-hardiness, and early spring growth as characteristics for successful winter cover crops in

cool, temperate climates (Nelson et al., 1991; Creamer et al., 1997; Delate et al., 2008).

However, variability in annual weather conditions can result in inconsistent cover crop biomass

yield and N accumulation between years despite cover crop vigor and cold-tolerance (Burket et

al., 1997; Odhiambo and Bomke, 2000; Rinnofner et al., 2008). The literature demonstrates that

promising winter cover crop for temperate climates include monoculture or combinations of

barley, rye, ryegrass, wheat, hairy vetch, crimson clover, and red clover (Nelson et al., 1991;

Creamer et al., 1997; Teasdale et al., 2004; Branstaeder et al., 2008).

Cover crops are often inter-seeded with a main crop and maintained as a living ground

cover over the cropping season (Hartwig and Ammon, 2002). Relay or simultaneous planting of

cover crops with a cash crop is attractive because a soil improving crop can be grown without

13

taking land out of cash crop production and it can potentially control weeds (Sarrantonio and

Gallandt, 2003). Cover crop species and timing of planting in relation to crop establishment has

an impact on cash crop yield because of competition for nutrients, water, and light, and

modification of growing conditions (Biazzo and Masiunas, 2000; Brainard and Bellinder, 2004).

For example, annual medic planted simultaneously with corn reduced early growth and

subsequent yield by decreasing N availability to the crop (Smeltekop et al., 2002). However,

Negrini et al. (2010) found that intercropping white lupin with lettuce did not affect lettuce

performance when planted at the same time. In the same study, black oat or cowpea sown 20, 40,

and 60 days prior to lettuce were found to negatively influence lettuce growth and yield via

competition for sunlight. Relay planting cover crops can benefit crops by contributing N to

intercropped or subsequent cash crops without reducing crop growth and yield (Jeranyama et al.,

1998). Additionally, wide row spacing and rapid growth habits of some crops, such as pumpkins,

make some crop systems better suited to intercropping systems than others (Vanek et al., 2005).

Therefore, intercropping schemes are specific to site and cropping system.

Cereal-legume cover crop blends

Mixed cereal-legume cover crop blends are considered to be a better management option

than growing either species alone because it can reduce risk of stand failure, enhance biomass

productivity, and prevent N immobilization after spring incorporation (Sustainable Agriculture

Network, 2007). A number of studies demonstrate that mixtures have increased yield stability

compared to monocultures because together species have a wider range of tolerance to adverse

environmental conditions than when grown alone (Creamer et al., 1997; Gaskell, 2006). In some

cases, the cereal crop can act as a nurse crop for the legume, enhancing winter hardiness by

reducing exposure to harsh weather. A cereal can also enhance the performance of a legume

14

when grown in biculture. For example, the support from rye plants prevented lodging in winter

pea in one study (Karpenstein-Machan and Stuelpnagel, 2000). Further, cereal crops, such as rye,

can provide structure for sprawling crops like hairy vetch, thereby increasing use of solar energy

and biomass (Sustainable Agriculture Network, 2007).

Cover crop blends that include cereal and legume species optimize N cycling and N

availability to subsequent crops. This is because cereals are capable of recycling residual soil

nitrate after fall harvest to minimize leaching and legumes fix atmospheric N, which increases N

concentration in residue (Clark et al., 1997). But in one rye-winter pea mixture, high residual soil

N decreased winter pea establishment and vigor because rye exhibited greater competitive

advantage in high N conditions (Burket et al., 1997). In some cases, the N concentration of a

cereal in mixture with a legume is higher than when it is grown alone (Rannels and Wagger,

1996). Burket et al. (1997) observed that cereal residue had 28% higher N concentration when

grown in mixture with red clover than when cropped alone. Mineralization of decomposing

legume roots can enhance soil (NH4++NO3

-)-N for uptake by a simultaneously grown cereal

(Evans et al., 2001)

Cereal and legume cover crops grown mixtures often produce greater biomass and

accumulate more N than grown when grown in monoculture (Ranells and Wagger, 1996; Clark

et al., 1997; Sainju et al., 2005). For example, Teasdale et al. (2008) found that hairy vetch

accumulated 4.67 to 5.75 Mg ha-1

of dry matter while a rye-hairy vetch mixture produced 8.95 to

11.17 Mg ha-1

. In one study, rye-hairy vetch biculture dry matter was no different than pure rye

(Cline and Silvernail, 2001). In that same study, the biculture accumulated significantly more N

than a pure cereal crop because of higher N concentrations of the residues in the blend. While

monocropped cereals, such as rye, can immobilize N following incorporation, cereal-legume

15

bicultures can supply N to subsequent crops because of increased residue N concentration (Kuo

and Sainju, 1998).

Suitable winter cover crops for the maritime pacific northwest

In the maritime Pacific Northwest, winter cover crops are typically planted by late

September and incorporated in late April to ensure sufficient biomass and N accumulation

without interrupting common crop rotations (Kuo and Jellum, 2000). The climate in this region is

characterized by cool, wet winters that leach residual soil NO3- out of the soil profile (Feaga et

al., 2010), and warm, dry summers, which can limit cover crop establishment without irrigation

(Burket et al., 1997). Minimum annual temperatures ranged from -13 to -3 °C over the past 15

years in Puyallup, WA (Washington Agriculture Weather Network, 2010), which makes freeze

tolerance an important trait. Date of planting can also affect winter survival. Brandsaeter et al.

(2002) found a negative correlation between freeze resistance and age in hairy vetch and clover

spp. Although delay of spring incorporation can increase cover crop dry matter production,

excessive C accumulation in residue can lead to N immobilization (Thorup-Kristensen and

Dresboll, 2010). High rainfall during fall establishment can create saturated soil conditions and

stand failure in some species.

Cereal rye is a standard winter cover crop in many temperate climates, including the

maritime Pacific Northwest, because it is winter-hardy and tolerant of late planting (Managing

Sustainable Agriculture Network, 2007). Dry matter production ranged from 1.42 to 4.19 Mg ha-

1 in a study in Puyallup, WA when planted in early October and killed in late April (Kuo and

Jellum, 2000). Winter wheat and annual ryegrass produced similar dry matter in other locations

in the Pacific Northwest when sown before October (Sattell et al., 1999; Odhiambo and Bomke,

2000). Rapeseed and canola are other non-leguminous cover crops that have been grown in the

16

region. Difficulties with establishment and winterkill have been reported on some occasions and

some researchers have viewed these species as unsuitable for winter growth in this region (Kuo

et al., 1996; Sattell et al., 1999). Hairy vetch has proven to be a cold tolerant winter annual

legume (Brandsaeter and Netland, 1999). In a study in south coastal British Columbia, hairy

vetch produced more reliable stands than crimson clover, which was susceptible to winter kill

during below average winter temperature conditions (Odhiambo and Bomke, 2000). In Puyallup,

hairy vetch yielded 0.91 to 3.48 Mg ha-1

of dry matter when planted by late September (Kuo and

Jellum, 1997). Crimson clover, red clover, and subterranean clover produced similar biomass and

were consistent in growth in a study in the Willamette Valley, OR (Sattell et al., 1999). Austrian

winter pea has been listed as a potential winter annual for the maritime Pacific Northwest.

However, occasional stand failures have been noted in wet years (Kuo et al., 1996; Sattell et al.,

1999).

Past research at the WSU Research and Extension Center in Puyallup, WA demonstrates

that rye-hairy vetch cover crop blends are well suited for the climate and cropping systems of

this region (Kuo and Sainju, 1997; Kuo and Jellum, 2000; Cogger et al., 2008). Cereal rye

establishes rapidly when planted by early October and it can effectively utilize residual soil

nitrate because rapid root development puts it in contact with soil N (Kuo and Jellum 2000;

Thorup-Kirstensen et al., 2003 Feaga et al., 2010). In contrast, hairy vetch is known to have slow

fall growth and low soil cover (Holderbaum et al., 1990), possibly because its optimum

temperature for root growth is relatively high (20-25 °C) (Mosjidis and Zhang, 1995). But hairy

vetch has high winter survival in northern temperate climates (average minimum temperatures

from -2 to -10 °C) (Teasdale et al., 2004; Brandsaeter et al., 2007) and it accumulates biomass

rapidly in the spring as soil temperatures increase (Holderbaum et al., 1990; Kuo and Jellum,

17

2000). Further, hairy vetch consistently accumulates more N than rye, which impacts N

availability to subsequent crops (Kuo et al., 1997). A summary of biomass, N content, and C:N

ratio of winter cover crops typical in the maritime Pacific Northwest is found in Table 1.

5. NITROGEN AVAILABILITY FROM COVER CROP RESIDUES

Winter cover crops are commonly included in crop rotations to supply N to successive

cash crops but N release patterns from residues are uncertain (Griffin et al., 2000; Cabrera et al.,

2005; Teasdale et al., 2008). Soil microbial processes, which are affected by residue composition

and various environmental factors, are responsible for the decomposition and release of nutrients

from organic materials (Wolf and Wagner, 2005). Specifically, microbes transform organic N to

ammonium via mineralization and immobilize ammonium through assimiliation in microbial

biomass (Myrold, 2005). Nitrification, the process by which microbes convert ammonium to

nitrate, is considered to be the fate of most ammonium in N-rich agricultural soils (Robertson,

1997). Ammonium and nitrate compose the soluble pool of soil N, which is subject to future

immobilization and re-mineralization (Burger and Jackson, 2002), losses via leaching (Moller

and Reents, 2009; Thorup-Kristensen and Dresboll, 2010) and denitrification (Rosecrance et al.,

2000), and plant uptake. The factors that affect the cycling of N into soil inorganic pools,

microbial biomass, and more stable soil forms play a large role in the timing and amount of N

available for plant uptake (Myrold and Bottomley, 2008).

Influence of environmental factors

The rate of decomposition of organic residues and release of N is influenced by soil

environmental conditions, including temperature, moisture status, and soil texture. Variability in

N mineralization and nitrification of soil organic N and amended materials have been studied in

the laboratory, via incubation using different soils and under controlled climate (GonzalezPrieto

18

et al., 1996; Sierra, 1997; Griffin et al., 2002), and in the field (Quemada and Cabrera, 1997;

Delin and Linden, 2002; Watts et al., 2010).

The biological processes involved in soil N transformations are temperature-dependent

(Davidson and Janssens, 2006), generally increasing with temperature until some optimum is

reached. In general, temperatures between 20 and 30 °C are considered ideal for N mineralization

and nitrification (Robertson et al., 1999; Curtin and Campbell, 2008). The effect of temperature

on N mineralization can be standardized using a Q(10) factor, which calculates the increase in

mineralization rate for every 10 °C increase. Research has demonstrated that N mineralization is

also a function of growing degree days when moisture is adequate (Honeycutt and Potaro, 1990;

Griffin and Honeycutt, 2000). The advantage to using growing degree days to account for the

effect of temperature on N mineralization is that it allows for comparison between laboratory and

field trials (Ruffo and Bollero, 2003b). Some studies have demonstrated that N mineralization

rates increase exponentially with temperature up to 35 °C (Sierra, 1997; Cookson et al., 2002;

Wang et al., 2006). Others have shown linear correlations for rates of N mineralization

(Quemada and Cabrera, 1997) and nitrification (Griffin and Honeycutt, 2000). Soil properties

and management practices likely account for differences between these results (Kruse et al.,

2004; Wang et al., 2006). For example, in a study in China the Q(10) of net N mineralization

increased from 1.70 in grazed grassland to 2.24 in an adjacent, non-grazed site (Wang et al.,

2006).

Soil moisture fluctuations can have a large affect on N mineralization and nitrification

rates (Paul et al., 2003). It is often reported that soil moisture at field capacity is most favorable

for N transformation processes, but it is difficult to compare results from different studies

because of the variety of methods used to measure soil water status (i.e. water holding capacity,

19

water-filled pore space [WFPS], and water potential) (Griffin, 2008). In one study, soil water

status was linearly related to N mineralization rate from 35 to 60% WFPS (Sierra, 1997). Drury

et al. (2003) reported a similar relationship, also demonstrating that denitrification is likely at

high soil water contents (>70% WFPS). The drying and rewetting of soil, which is common in

summer irrigated cropping systems, was reported to significantly reduce N mineralization of

cotton leaf residue and compost (Kruse et al., 2004). But Griffin et al. (2002) found the effect of

water status on N mineralization to be less profound in soil amended with animal manures.

Several studies have shown that the influence of temperature on soil N transformations

varies with soil moisture (Sierra, 1997; Knoepp and Swank, 2002; Wang et al., 2006). These

interactions are most obvious at relatively high temperatures (15 to 30 °C). Variation in N

mineralization rate as affected environmental conditions (Odhiambo and Bomke, 2000; Delin

and Linden, 2002) can be accounted for by using degree- and decomposition-day modeling

(Ruffo and Bollero, 2003b) or Q10 parameters in soils not limited by moisture (Rey et al., 2005;

Pavelka et al., 2007) to correct for seasonal or climatic differences.

Soil properties affect N mineralization and nitrification processes (GonzalezPrieto et al.,

1996; Delin and Linden, 2002) primarily via variation in soil texture (Gordilla and Cabrera,

1997; Cabrera et al., 2005). For example, in a laboratory incubation measuring N release from

swine slurry, N mineralization was highest in coarse textured soils (Griffin et al., 2002), which is

likely because of increased aeration in soils with high sand content (Thomsen et al., 1999). Soil

texture variation across landscape positions within a field influenced N mineralization due to

changes in relative water holding capacity (Watts et al., 2010). In that study, a bottomland loam

soil with high water content mineralized 9 to 10 % more N than a loam or sandy loam on

sideslope and summit under identical management. Soil properties can affect N mineralization

20

from organic residues in other ways, including physical protection of organic residue via

formation of macroaggregates in clayey soils (Egelkraut et al., 2000) and variability in soil

microbial activity and biomass C:N ratio (Hassink, 1994). Additionally, GonzalezPrieto et al.

(1996) found that soils with high pH and base saturation are more likely to immobilize N in a

study of N transformations of 112 native and agricultural soils. Nitrification reactions are

generally more sensitive to pH than N mineralization (Griffin, 2008).

Impact of residue quality on net N mineralization

Under constant environmental conditions and management schemes, short-term N

mineralization-immobilization processes are primarily a function of available C and N.

Amending soil with organic residues stimulates microbial growth via addition of available C

(Wang et al., 2003; Tu et al., 2006). But microbial biomass must assimilate a certain amount of

N, which is determined by microbial C:N ratio (Kaye and Hart, 1997). If the N concentration

available from the residue is greater than what is needed by microbial biomass, there will be net

N mineralization (Myrold and Bottomley, 2008). Research has often shown that the C:N ratio

and total N concentration of amended substrate explain N mineralization-immobilization

dynamics fairly well (Vigil and Kissel, 1991; Ranells and Wagger, 1996; Gilmour et al., 1998;

Chaves et al., 2004; Justes et al., 2009). A number of studies report a critical C:N ratio, which is

used to describe the tipping point between net mineralization and immobilization, ranging

between 24 and 36 for incorporated plant residues (Kuo and Sainju, 1998 Trinsoutrot et al.,

2000; Chaves et al., 2004; Jensen et al., 2005). But the C:N break-even point has been reported

to be as low as 15 (Gilmour, 1998) and has high as 40 (Whitmore, 1996). Such wide variation in

the critical C:N value is likely related to variation of the C:N ratio of the microbial biomass and

differences in biochemical quality of the residue (Cabrera et al., 2005).

21

Some research has demonstrated that C:N ratio is only initially correlated with N

mineralization because residue biochemical composition changes as substrate decomposes and

releases nutrients (Chaves et al., 2004; Myrold and Bottomley, 2008). Others have demonstrated

that it is neither an adequate measure of residue quality (Ruffo and Bollero, 2003a) nor a useful

parameter for estimating N mineralization rate (Vigil and Kissel, 1995). Several studies have

characterized fiber fractions groups in organic residues and related these measurements to N

release patterns (Wagger et al, 1998; Kuo and Sainju, 1998; Chaves et al., 2004; Jensen et al.,

2005). But there is no consensus on what residue qualities best correlate with N release.

Lignin:N ratio is often cited as correlating well with net N mineralization (Vigil and Kissel,

1991; Constantinides and Fownes, 1994; Kumar and Goh, 2003). For example, Vigil and Kissel

(1991) found that including lignin:N ratio in a regression model of crop residue N mineralization

bolstered the rigor of the equation. In another study, lignin:N ratio was well correlated with rate

constants of a first-order kinetic model for N mineralization of plant residues of varying quality

(Chaves et al., 2004). However, Jensen et al. (2005) found that C:N and lignin:N ratios of plant

residues were poor parameters for estimating N release. In that study, net N mineralization of

plant residue was initially most closely related to water soluble N content (r = 0.76), and neutral

detergent soluble N and total plant N were best correlated after three weeks (r = 0.90 to 0.94).

Other research has reported similar findings (De Neve and Hofman, 1996; Bending et al., 1998;

Trinsoutrot et al., 2000). But additional research is necessary to enhance our understanding of the

variability in results and better estimate net N mineralization from plant residues (Cabrera et al.,

2005).

Management practices influence N release dynamics

22

Management practices can impact N release dynamics from plant residue by

manipulation of residue quality via kill date (Wagger et al., 1998), enhanced mineralization

through interaction with fertilizer (Snapp and Borden, 2005), and increased access of residue to

microbial community though tillage (Drinkwater et al., 2000) and residue size reduction

(Giaconimi et al., 2007). First, delaying cover crop kill date in spring may result in slow release

of N because residue quality has become more recalcitrant (Wagger, 1989). In one study, an

eight day delay in spring kill of hairy vetch resulted in a decrease in residue N concentration,

which could reduce the rate of N mineralization (Cline and Silvernail, 2001), and therefore N

release may not be harmonious with crop N uptake (Crandall et al., 2005). Multiple

incorporation dates of rye cover crop between early March to late April demonstrated decreased

net N mineralization with increased delay, which was likely due to an increase in residue C:N

ratio (Thorup-Kristensen and Dresboll, 2010). But Vaughan and Evanylo (1998) demonstrated

that spring kill date of hairy vetch had no influence on N availability or subsequent corn N

concentrations as long as it was desiccated before early flowering stage. This is probably because

the approximately three week delay in desiccation had no influence on hairy vetch residue C:N

ratio, like it did with rye and rye-hairy vetch cover crop residue. Influence of climate and desired

N fate will influence the ideal kill date.

Combining fertilizer applications with organic substrate can increase apparent N

mineralization. For example, ammonium nitrate stimulated N mineralization of compost when

applied together in comparison to compost alone (Sikora and Enkiri, 2000). In another study,

mixed granulated hen-manure and compost fertilizer amendments enhanced total N

mineralization compared to the sum of individual N supplies (Ribeiro et al., 2010). But a

combination of clover green manure and either farmyard cattle manure or green compost did not

23

increase N mineralization rates compared to either component separately (Canali et al., 2010).

Combining mineral fertilizer with corn stover in an incubation study had a negative interactive

affect on N availability (Gentile et al., 2008). But mineralization of the stover was increased in

relation to stover without fertilizer. Retaining residues of crops such as corn or grain, which have

low N concentrations and recalcitrant fractions, can temporarily immobilize fertilizer N, and

therefore help retain N in the cropping system (McSwiney et al., 2010; Starovoytov et al., 2010).

Residue management can affect N mineralization rate via increased microbial access to

substrate. For example, reducing tillage can decrease net N mineralization from plant residues

(Schellenberg et al., 2009). Drinkwater et al. (2000) found that N availability was much higher in

chisel-disc and moldboard plow treatments than under no-tillage management, which is likely

because of increased microbial contact with substrate (Giacomini et al., 2007). Increased soil

compaction, which is common in no-tillage systems, decreased N mineralization, probably due

to decreased aeration (Pengthamkeerati et al., 2006). However in one case, reduced tillage

enhanced N mineralization of crop residue because of improved soil moisture conservation

(Soon et al., 2004). In a mixed tillage system, cultivation for weed control increased

mineralization of hairy vetch residue during maximum crop N uptake (Drinkwater et al., 2000).

Smaller substrate size, which may simulate mowing, increased N mineralization of crop residues

(Giacomini et al., 2007). In one study, mowing rye or rye-hairy vetch cover crop residue

enhanced harmony of cover crop N release and crop N uptake (Vaughan and Evanylo, 1998).

Snapp and Borden (2005) reported enhanced N mineralization of rye and rye-hairy vetch-oriental

mustard cover crops when either mowed or sprayed with glyphosate eight days prior to spring

incorporation, likely because of increased microbial access. But killing by either mowing or

tillage did not impact potential N mineralization of rye or triticale cover crops in a California

24

vineyard (Steenwerth and Belina, 2008). In that study, moisture limitations during summer

season might account for discrepancies.

6. CROP N RESPONSE AND UPTAKE EFFICIENCY

Cover crops influence subsequent crop yield primarily via their affect on N availability

(Torbert et al., 1996; Vaughan and Evanylo, 1998; Kuo and Jellum, 2000; Cherr et al., 2006).

Crop yields can be maintained by replacing or supplementing N fertilizer application with winter

legume or cereal-legume cover crop residues (Sainju et al., 2005; Fortuna et al., 2008). But there

must be sufficient cover crop biomass and N accumulation, and timely N mineralization for

cover crops to supply sufficient N to crops (Griffin et al., 2000; Teasdale et al., 2008). Reported

N fertilizer replacement values for winter grown cover crops to subsequent cash crops vary

greatly. Several studies examine sweet corn performance after legume and mixed cereal-legume

cover crops because of its marked response to N fertility. Some have shown that it can produce

yields as good as N-fertilizer treatments when grown in rotation with hairy vetch (Griffin et al.,

2000; Cline and Silvernail, 2002; Carrera et al., 2004). But Cline and Silvernail (2002)

demonstrate poor yield response to rye-hairy vetch blends. In Florida, hairy vetch and rye-hairy

vetch blends contributed 62 to 75 kg N ha-1

, much lower than agronomic rates (Zotarelli et al.,

2009). Often crop yield potential may be optimized when cover crops are combined with low

supplemental N fertilizer rates. Schellenberg et al. (2009) recommended that legume-based cover

crops systems be combined with modest sidedress N fertilizer to maximize organic broccoli

yield. But Cherr et al. (2006) demonstrated that sweet corn yields were greater with fertilizer N

than a cover crop-fertilizer combination.

Lack of synchrony between N supply from cover crop residue and crop N uptake may

influence efficiency of crop N use (Teasdale et al., 2008). But this depends on the timing of field

25

events and types of crops grown. For instance, a delay in spring cover crop desiccation may

result in a late flush of N release, which is better timed with crop N uptake (Cline and Silvernail,

2001). Cover crop residue characteristics or cereal-legume mixture ratio can influence N

availability patterns (Kuo and Sainju, 1998). In one study, legume cover crops achieved higher

crop N utilization efficiency than cereals because of more rapid mineralization and therefore

greater N availability to the subsequent crop (Lenzi et al., 2009). Thorup-Kristensen et al. (2006)

demonstrated that deep-rooted crops utilized legume-derived N more efficiently than shallow

rooted crops (i.e. carrot and cabbage vs. onion and lettuce), likely because of access to a larger

pool of soil (NH4++NO3

-)-N.

There are mixed results for crop N utilization efficiency of cover crop derived N.

Sarrantonio and Molloy (2003) reported that sweet corn utilized between 19 and 62% of clover

N. These data demonstrated that high N utilization efficiency is possible under optimal

conditions in a legume-based system. But lower N utilization efficiencies may be expected under

poor conditions (e.g. dry conditions that limit the rate of N mineralization). In another study,

cabbage shoot biomass only recovered an average of 27% of hairy vetch N, but 43% when hairy

vetch shoots were amended in fallow soil (Haas et al., 2007). Low N concentrations and the

more recalcitrant quality of hairy vetch roots probably caused difference. Interestingly, Henry et

al. (2010) observed a yield response in corn from clover plus 90 kg N ha-1

UAN fertilizer but not

in clover without fertilizer. This could reveal improved N use efficiency when a cover crop and

fertilizer are combined. In contrast, Teasdale et al. (2008) found that N use efficiency by sweet

corn was higher for ammonium nitrate than hairy vetch and lowest when these treatments were

combined.

26

In some cases, crop N use efficiency of cover crop-derived N is low but overall efficiency

is high because of high N recovery in soil (Seo et al., 2006). For example, broccoli and lettuce

grown in succession after a clover cover crop recovered 11 and 4 % of total residue N,

respectively, but 81 and 79 % remained in soil after each crop (Holness et al., 2008). Likewise,

Collins et al. (2007) found that potatoes utilized 29 % of total cover crop N and 66 % remained

in soil after crop harvest. Further, Seo et al. (2006) indicated that legumes were twice as efficient

in building soil N as ammonium sulfate fertilizer but only one-half as effectively in supplying N

to crops. These studies indicate a high plant-soil N percent recovery. Recovery of cover crop N

in soil may be reduced in sandy soils with high leaching potential (Cherr et al., 2006). Pang and

Letey (2000) suggest that crops with high maximum uptake rates have low N utilization

efficiencies because it is difficult to meet peak N crop demands with relatively slow release

materials. In general, there is a need to optimizing timing of N mineralization with N uptake

demands of subsequent crop. The research focus needs to shift from maximum N supply to

synchronizing N release with the N uptake demands of a subsequent crop.

28

7. LITERATURE CITED

Bakht, J., M. Shafi, M.T. Jan, and Z. Shah. 2009. Influence of crop residue management,

cropping system and N fertilizer on soil N and C dynamics and sustainable wheat

(Triticum aestivum L.) production. Soil & Tillage Research 104:233-240.

Bary, A., C. Cogger, and D.M. Sullivan. 2000. Fertilizing with manure PNW0533. Washington

State University Cooperative Extension, Oregon State University Cooperative Extension

System, US Department of Agriculture.

Bending, G.D., M.K. Turner, and I.G. Burns. 1998. Fate of nitrogen from crop residues as

affected by biochemical quality and the microbial biomass. Soil Biology & Biochemistry

30:2055-2065.

Berry, P.M., R. Sylvester-Bradley, L. Philipps, D.J. Hatch, S.P. Cuttle, F.W. Rayns, and P.

Gosling. 2002. Is the productivity of organic farms restricted by the supply of available

nitrogen? Soil Use and Management 18:248-255.

Biazzo, J., and J.B. Masiunas. 2000. The use of living mulches for weed management in hot

pepper and okra. Journal of Sustainable Agriculture 16:59-79.

Brainard, D.C., and R.R. Bellinder. 2004. Weed suppression in a broccoli-winter rye

intercropping system. Weed Science 52:281-290.

BrandiDohrn, F.M., R.P. Dick, M. Hess, S.M. Kauffman, D.D. Hemphill, and J.S. Selker. 1997.

Nitrate leaching under a cereal rye cover crop. Journal of Environmental Quality 26:181-

188.

Brandsaeter , L.O. and J. Netland. 1999. Winter annual legumes for use as cover crops in row

crops in northern regions. I. Field experiements. Crop Science 39:1369-1379.

Brandsaeter, L.O., A. Olsmo, A.M. Tronsmo, and H. Fykse. 2002. Study of freezing resistance of

winter annual and biennial legumes at different developmental stages. Crop Science

42:437-443.

Brandsaeter, L.O., H. Heggen, H. Riley, E. Stubhaug, and T.M. Henriksen. 2008. Winter

survival, biomass accumulation and N mineralization of winter annual and biennial

legumes sown at various times of year in Northern Temperate Regions. European Journal

of Agronomy 28:437-448.

29

Burger, M., and L.E. Jackson. 2003. Microbial immobilization of ammonium and nitrate in

relation to ammonification and nitrification rates in organic and conventional cropping

systems. Soil Biology & Biochemistry 35:29-36.

Burket, J.Z., D.D. Hemphill, and R.P. Dick. 1997. Winter cover crops and nitrogen management

in sweet corn and broccoli rotations. HortScience 32:664-668.

Cabrera, M.L., D.E. Kissel, and M.F. Vigil. 2005. Nitrogen mineralization from organic

residues: Research opportunities. Journal of Environmental Quality 34:75-79.

Campiglia, E., F. Caporali, E. Radicetti, and R. Mancinelli. 2010. Hairy vetch (Vicia villosa

Roth.) cover crop residue management for improving weed control and yield in no-tillage

tomato (Lycopersicon esculentum Mill.) production. European Journal of Agronomy

33:94-102.

Canali, S., C. Ciaccia, D. Antichi, P. Barberi, F. Montemurro, and F. Tittarelli. 2010. Interactions

between green manure and amendment type and rate: Effects on organic potato and soil

mineral N dynamic. Journal of Food Agriculture & Environment 8:537-543.

Carrera, L.M., A.A. Abdul-Baki, and J.R. Teasdale. 2004. Cover crop management and weed

suppression in no-tillage sweet corn production. Hortscience 39:1262-1266.

Cavigelli, M.A., J.R. Teasdale, and A.E. Conklin. 2008. Long-term agronomic performance of

organic and conventional field crops in the mid-Atlantic region. Agronomy Journal

100:785-794.

Chaves, B., S. De Neve, G. Hofman, P. Boeckx, and O. Van Cleemput. 2004. Nitrogen

mineralization of vegetable root residues and green manures as related to their

(bio)chemical composition. European Journal of Agronomy 21:161-170.

Cherr, C.M., J.M.S. Scholberg, and R. McSorley. 2006. Green manure approaches to crop

production: A synthesis. Agronomy Journal 98:302-319.

Clark, A.J., A.M. Decker, J.J. Meisinger, and M.S. McIntosh. 1997. Kill date of vetch, rye, and a

vetch-rye mixture .1. Cover crop and corn nitrogen. Agronomy Journal 89:427-434.

Clark, A.J., J.J. Meisinger, A.M. Decker, and F.R. Mulford. 2007. Effects of a grass-selective

herbicide in a vetch-rye cover crop system on nitrogen management. Agronomy Journal

99:36-42.

30

Cline, G.R., and A.F. Silvernail. 2001. Residual nitrogen and kill date effects on winter cover

crop growth and nitrogen content in a vegetable production system. Horttechnology

11:219-225.

Cline, G.R., and A.F. Silvernail. 2002. Effects of cover crops, nitrogen, and tillage on sweet

corn. Horttechnology 12:118-125.

Cogger, C.G. 2000. Soil management for small farms. EB 1895. Washington State University

Cooperative Extension, Oregon State University Extension Service, University of Idaho

Cooperative Extension System, US Department of Agriculture.

Cogger, C., A. Bary, and L. Myhre. 2008. Organic cover crop research at WSU Puyallup.

Washington State University Puyallup Research and Extension Center.

Collins, H.P., J.A. Delgado, A.K. Alva, and R.E. Follett. 2007. Use of nitrogen-15 isotopic

techniques to estimate nitrogen cycling from a mustard cover crop to potatoes. Agronomy

Journal 99:27-35.

Constantinides, M., and J.H. Fownes. 1994. Nitrogen Mineralization from leaves and litter of

tropical plants - relationship to nitrogen, lignin and soluble polyphenol concentrations.

Soil Biology & Biochemistry 26:49-55.

Cookson, W.R., I.S. Cornforth, and J.S. Rowarth. 2002. Winter soil temperature (2-15 degrees

C) effects on nitrogen transformations in clover green manure amended or unamended

soils; a laboratory and field study. Soil Biology & Biochemistry 34:1401-1415.

Crandall, S.M., M.L. Ruffo, and G.A. Bollero. 2005. Cropping system and nitrogen dynamics

under a cereal winter cover crop preceding corn. Plant and Soil 268:209-219.

Creamer, N.G., M.A. Bennett, and B.R. Stinner. 1997. Evaluation of cover crop mixtures for use

in vegetable production systems. HortScience 32:866-870.

Curtin D. and Campbell C.A. 2008. Mineralizable nitrogen. p. 599-606. In M.R. Carter and

E.M. Gregorich (eds.) Soil Sampling and Methods of Analysis. CRP Press, Boca Raton,

FL.

Davidson, E.A., and I.A. Janssens. 2006. Temperature sensitivity of soil carbon decomposition

and feedbacks to climate change. Nature 440:165-173.

31

De Neve, S., and G. Hofman. 1996. Modelling N mineralization of vegetable crop residues

during laboratory incubations. Soil Biology & Biochemistry 28:1451-1457.

Delate, K., C. Cambardella, and A. McKern. 2008. Effects of organic fertilization and cover

crops on an organic pepper system. HortTechnology 18: 215-226.

Delin, S., and B. Linden. 2002. Relations between net nitrogen mineralization and soil

characteristics within an arable field. Acta Agriculturae Scandinavica Section B-Soil and

Plant Science 52:78-85.

den Hollander, N.G., L. Bastiaans, and M.J. Kropff. 2007. Clover as a cover crop for weed

suppression in an intercropping design - II. Competitive ability of several clover species.

European Journal of Agronomy 26:104-112.

Dimitri, C., and L. Oberholtzer. 2009. Marketing U.S. Organic Foods. 15 Aug 2010.

< http://www.ers.usda.gov/Publications/EIB58/EIB58.pdf>.

Ding, G.W., X.B. Liu, S. Herbert, J. Novak, D. Amarasiriwardena, and B.S. Xing. 2006. Effect

of cover crop management on soil organic matter. Geoderma 130:229-239.

Doran, J.W. 2002. Soil health and global sustainability: translating science into practice.

Agriculture Ecosystems & Environment 88:119-127.

Dresboll, D.B., G.K. Bjorn, and K. Thorup-Kristensen. 2008. Yields and the extent and causes of

damage in cauliflower, bulb onion, and carrot grown under organic or conventional

regimes. Journal of Horticultural Science & Biotechnology 83:770-776.

Drinkwater, L.E., R.R. Janke, and L. Rossoni-Longnecker. 2000. Effects of tillage intensity on

nitrogen dynamics and productivity in legume-based grain systems. Plant and Soil

227:99-113.

Drury, C.F., T.Q. Zhang, and B.D. Kay. 2003. The non-limiting and least limiting water ranges

for soil nitrogen mineralization. Soil Science Society of America Journal 67:1388-1404.

Egelkraut, T.M., D.E. Kissel, and M.L. Cabrera. 2000. Effect of soil texture on nitrogen

mineralized from cotton residues and compost. Journal of Environmental Quality

29:1518-1522.

32

Evans, J., A.M. McNeill, M.J. Unkovich, N.A. Fettell, and D.P. Heenan. 2001. Net nitrogen

balances for cool-season grain legume crops and contributions to wheat nitrogen uptake:

a review. Australian Journal of Experimental Agriculture 41:347-359.

Fageria, N.K., V.C. Baligar, and B.A. Bailey. 2005. Role of cover crops in improving soil and

row crop productivity. Communications in Soil Science and Plant Analysis 36:2733-

2757.

Fageria, N.K. 2007. Green manuring in crop production. Journal of Plant Nutrition 30:691-719.

Feaga, J.B., J.S. Selker, R.P. Dick, and D.D. Hemphill. 2010. Long-Term Nitrate Leaching

Under Vegetable Production with Cover Crops in the Pacific Northwest. Soil Science

Society of America Journal 74:186-195.

Fortuna, A., R.L. Blevins, W.W. Frye, J. Grove, and P. Cornelius. 2008. Sustaining soil quality

with legumes in no-tillage systems. Communications in Soil Science and Plant Analysis

39:1680-1699.

Fowler, C.J.E., L.M. Condron, and R.D. McLenaghen. 2004. Effects of green manures on

nitrogen loss and availability in an organic cropping system. New Zealand Journal of

Agricultural Research 47:95-100.

Gale, E.S., D.M. Sullivan, C.G. Cogger, A.I. Bary, D.D. Hemphill, and E.A. Myhre. 2006.

Estimating plant-available nitrogen release from manures, composts, and specialty

products. Journal of Environmental Quality 35:2321-2332.

Galloway, J.N., and E.B. Cowling. 2002. Reactive nitrogen and the world: 200 years of

change. Ambio 31: 64-71.

Gaskell, M. and R. Smith. 2007. Nitrogen sources for organic vegetable crops. HortTechnology

17:431-441.

Gaskell, M. 2006. Organic nitrogen sources for vegetable crops. HortScience 41:957-957.

Gentile, R., B. Vanlauwe, P. Chivenge, and J. Six. 2008. Interactive effects from combining

fertilizer and organic residue inputs on nitrogen transformations. Soil Biology &

Biochemistry 40:2375-2384.

33

Giacomini, S.J., S. Recous, B. Mary, and C. Aita. 2007. Simulating the effects of N availability,

straw particle size and location in soil on C and N mineralization. Plant and Soil 301:289-

301.

Gilmour, J.T., A. Mauromoustakos, P.M. Gale, and R.J. Norman. 1998. Kinetics of crop residue

decomposition: Variability among crops and years. Soil Science Society of America

Journal 62:750-755.

Goldberger, J.R. 2008. Summary Report: Certified organic production the experiences and

perspectives of Washington farmers. Washington State University. CRS Information

Series No. 1-08.

GonzalezPrieto, S.J., A. Cabaneiro, M.C. Villar, M. Carballas, and T. Carballas. 1996. Effect of

soil characteristics on N mineralization capacity in 112 native and agricultural soils from

the northwest of Spain. Biology and Fertility of Soils 22:252-260.

Gordillo, R.M., and M.L. Cabrera. 1997. Mineralizable nitrogen in broiler litter: II. Effect of

selected soil characteristics. Journal of Environmental Quality 26:1679-1686.

Granatstein, D., A. Stone, C. Williams, C. Miles, D. Bezdicek, and C. Perillo. 2010. Organic

farming research in the pacific Northwest. 14 Aug 2010.

<http://www.sarep.ucdavis.edu/organic/complianceguide/intro3.pdf>.

Greene, C. 2006. U.S. Organic Agriculture. p. 159-167. In K. Wiebe and N. Gollehon (eds.)

Economic Information Bulletin No. (EIB-16). USDA Economic Research Service.

Griffin, T.S., and C.W. Honeycutt. 2000. Using growing degree days to predict nitrogen

availability from livestock manures. Soil Science Society of American Journal 64: 1876-

1882.

Griffin, T., M. Liebman, and J. Jemison. 2000. Cover crops for sweet corn production in a short-

season environment. Agronomy Journal 92:144-151.

Griffin, T.S., C.W. Honeycutt, and Z. He. 2002. Effects of temperature, soil water status, and soil

type on swine slurry nitrogen transformations. Biology and Fertility of Soils 36:442-446.

Gselman, A., and B. Kramberger. 2008. Benefits of winter legume cover crops require early

sowing. Australian Journal of Agricultural Research 59:1156-1163.

34

Haas, G., H. Brand, and M. Puente de la Vega. 2007. Nitrogen from hairy vetch (Vicia villosa)

as winter green manure for white cabbage in organic horticulture. Biological Agriculture

& Horticulture 25:37-53.

Hao, X.Y., C. Chang, and X.M. Li. 2004. Long-term and residual effects of cattle manure

application on distribution of P in soil aggregates. Soil Science 169:715-728.

Hartwig, N.L., and H.U. Ammon. 2002. 50th Anniversary - Invited article - Cover crops and

living mulches. Weed Science 50:688-699.

Hassink, J. 1994. Effect of soil texture on the size of the microbial biomass and on the amount of

C and N and on the amount of C and N and mineralized per unit of microbial biomass in

Dutch grassland soils. Soil Biology & Biochemistry 26:1573-1581.

Henry, D.C., R.W. Mullen, C.E. Dygert, K.A. Diedrick, and A. Sundermeier. 2010. Nitrogen

Contribution from Red Clover for Corn following Wheat in Western Ohio. Agronomy

Journal 102:210-215.

Herencia, J.F., J.C. Ruiz, S. Melero, P.A.G. Galavis, and C. Maqueda. 2008. A short-term

comparison of organic v. conventional agriculture in a silty loam soil using two organic

amendments. Journal of Agricultural Science 146:677-687.

Holderbaum J. F., A.M. Decker, J.J. Meisinger, F.R. Mulford, and L.R. Vough. 1990. Fall-

seeded legume cover crops for no-tillage corn in the humid east. Agronomy Journal 82:

117-124.

Holness, R.L., M.R. Reddy, C.R. Crozier, and C.E. Niedziela. 2008. Evaluating inorganic

nitrogen and rye-crimson clover mixture fertilization of spring broccoli and lettuce by

(15)nitrogen tracing and mass balance. Journal of Plant Nutrition 31:1033-1045.

Honeycutt, C.W., and L.J. Potaro. 1990. Field-evaluation of heat units for predicting crop residue

carbon and nitrogen mineralization. Plant and Soil 125:213-220.

Hooker, K.V., C.E. Coxon, R. Hackett, L.E. Kirwan, E. O'Keeffe, and K.G. Richards. 2008.

Evaluation of cover crop and reduced cultivation for reducing nitrate leaching in Ireland.

Journal of Environmental Quality 37:138-145.

Isik, D., E. Kaya, M. Ngouajio, and H. Mennan. 2009. Weed suppression in organic pepper

(Capsicum annuum L.) with winter cover crops. Crop Protection 28:356-363.

35

Jensen, L.S., T. Salo, F. Palmason, T.A. Breland, T.M. Henriksen, B. Stenberg, A. Pedersen, C.

Lundstrom, and M. Esala. 2005. Influence of biochemical quality on C and N

mineralisation from a broad variety of plant materials in soil. Plant and Soil 273:307-326.

Jeranyama, P., O.B. Hesterman, and C.C. Sheaffer. 1998. Medic planting date effect on dry

matter and nitrogen accumulation when clear-seeded or intercropped with corn.

Agronomy Journal 90:616-622.

Justes, E., B. Mary, and B. Nicolardot. 2009. Quantifying and modelling C and N mineralization

kinetics of catch crop residues in soil: parameterization of the residue decomposition

module of STICS model for mature and non mature residues. Plant and Soil 325:171-185.

Kankanen, H., and C. Eriksson. 2007. Effects of undersown crops on soil mineral N and grain

yield of spring barley. European Journal of Agronomy 27:25-34.

Karpenstein-Machan, M., and R. Stuelpnagel. 2000. Biomass yield and nitrogen fixation of

legumes monocropped and intercropped with rye and rotation effects on a subsequent

maize crop. Plant and Soil 218:215-232.

Kaye, J.P., and S.C. Hart. 1997. Competition for nitrogen between plants and soil

microorganisms. Trends in Ecology & Evolution 12:139-143.

Kirby, E., and D. Granatstein. 2009. Profile of organic crops in Washington State. 14 Aug 2010.

<http://csanr.wsu.edu/publications/techreports/Organic%20Stats/WA_CertAcres_08.pdf>

Kirby, E. and D. Granatstein. 2010. Current status of organic agriculture in Washington State. 14

Aug 2010. <http://csanr.wsu.edu/publications/techreports/wa_orgstats_09_final.pdf>

Knoepp, J.D., and W.T. Swank. 2002. Using soil temperature and moisture to predict forest soil

nitrogen mineralization. Biology and Fertility of Soils 36:177-182.

Kramberger, B., A. Gselman, M. Janzekovic, M. Kaligaric, and B. Bracko. 2009. Effects of

cover crops on soil mineral nitrogen and on the yield and nitrogen content of maize.

European Journal of Agronomy 31:103-109.

Kruse, J.S., D.E. Kissel, and M.L. Cabrera. 2004. Effects of drying and rewetting on carbon and

nitrogen mineralization in soils and incorporated residues. Nutrient Cycling in

Agroecosystems 69:247-256.

36

Kumar, K., and K.M. Goh. 2003. Nitrogen release from crop residues and organic amendments

as affected by biochemical composition. Communications in Soil Science and Plant

Analysis 34:2441-2460.

Kumar, V., D.C. Brainard, and R.R. Bellinder. 2008. Suppression of powell amaranth

(Amaranthus powellii), shepherd's-purse (Capsella bursa-pastoris), and corn chamomile

(Anthemis arvensis) by buckwheat residues: Role of nitrogen and fungal pathogens.

Weed Science 56:271-280.

Kuo, S., and E.J. Jellum. 2000. Long-term winter cover cropping effects on corn (Zea mays L.)

production and soil nitrogen availability. Biology and Fertility of Soils 31:470-477.

Kuo, S., and U.M. Sainju. 1998. Nitrogen mineralization and availability of mixed leguminous

and non-leguminous cover crop residues in soil. Biology and Fertility of Soils 26:346-

353.

Kuo S., U.M. Sainju, and E. Jellum. 1996. Winter cover crops influence on nitrogen

mineralization, presidedress soil nitrate test, and corn yields. Biology and Fertility of

Soils 22: 310-317.

Kuo, S., U.M. Sainju, and E.J. Jellum. 1997. Winter cover cropping influence on nitrogen in soil.

Soil Science Society of America Journal 61:1392-1399.

Lenzi, A., D. Antich, F. Bigongiali, M. Mazzoncini, P. Migliorini, and R. Tesi. 2009. Effect of

different cover crops on organic tomato production. Renewable Agriculture and Food

Systems 24:92-101.

Lotter, D.W. 2003. Organic agriculture. Journal of Sustainable Agriculture 21: 59-128.

Mader, P., A. Fliessbach, D. Dubois, L. Gunst, P. Fried, and U. Niggli. 2002. Soil fertility and

biodiversity in organic farming. Science 296:1694-1697.

Magdoff, F. and H. van Es. 2000. Building Soils for Better Crops. Sustainable Agriculture

Network handbook series, bk. 4. Sustainable Agriculture Publications, Burlington, VT.

Malik, M.S., J.K. Norsworthy, A.S. Culpepper, M.B. Riley, and W. Bridges. 2008. Use of wild

radish (Raphanus raphanistrum) and rye cover crops for weed suppression in sweet corn.

Weed Science 56:588-595.

37

McSwiney, C.P., S.S. Snapp, and L.E. Gentry. 2010. Use of N immobilization to tighten the N

cycle in conventional agroecosystems. Ecological Applications 20:648-662.

Moller, K., and H.J. Reents. 2009. Effects of various cover crops after peas on nitrate leaching

and nitrogen supply to succeeding winter wheat or potato crops. Journal of Plant

Nutrition and Soil Science-Zeitschrift Fur Pflanzenernahrung Und Bodenkunde 172:277-

287.

Moller, K., W. Stinner, and G. Leithold. 2008. Growth, composition, biological N-2 fixation and

nutrient uptake of a leguminous cover crop mixture and the effect of their removal on

field nitrogen balances and nitrate leaching risk. Nutrient Cycling in Agroecosystems

82:233-249.

Mosjidis, J.A., and X. Zhang. 1995. Seed germination and root growth of several Vicia species at

different temperatures. Seed Science and Technology 23:749-759.

Myrold, D.D. and P.J. Bottomley. 2008. p. 157-172. Nitrogen mineralization and

immobilization. In J.S. Schepers and W.R. Raun (eds.) Nitrogen in Agricultural Systems.

American Society of Agronomy, Madison, WI.

Myrold, D.D. 2005. Transformations of Nitrogen. p. 333-372. In D.M. Sylvia, J.J. Fuhrmann et

al. (eds.) Principles and Applications of Soil Microbiology, Prentice Hall, Upper Saddle

River, NJ.

Negrini, A.C.A., P.C.T. de Melo, E.J. Ambrosano, R.H. Sakai, E.A. Schammass, and F. Rossi.

2010. Performance of lettuce in sole cropping and intercropping with green manures.

Horticultura Brasileira 28:58-63.

Nelson, W.A., B.A. Kahn, and B.W. Roberts. 1991. Screening cover crops for use in

conservation tillage systems for vegetables following spring plowing. HortScience

26:860-862.

Nyakatawa, E.Z., K.C. Reddy, and K.R. Sistani. 2001. Tillage, cover cropping, and poultry litter

effects on selected soil chemical properties. Soil & Tillage Research 58:69-79.

Odhiambo, J.J.O., and A.A. Bomke. 2000. Short term nitrogen availability following overwinter

cereal/grass and legume cover crop monocultures and mixtures in south coastal British

Columbia. Journal of Soil and Water Conservation 55:347-354.

38

Organic Trade Association. 2010. Organic Industry Survey. 15 Aug 2010.

<http://www.ota.com/pics/documents/2010OrganicIndustrySurveySummary.pdf>.

Paine L. and H. Harrison. 1993. The historical roots of living mulch and related practices

HortTechnology 3:137-143.

Pang, X.P., and J. Letey. 2000. Organic farming: Challenge of timing nitrogen availability to

crop nitrogen requirements. Soil Science Society of America Journal 64:247-253.

Paul, K.I., P.J. Polglase, A.M. O'Connell, J.C. Carlyle, P.J. Smethurst, and P.K. Khanna. 2003.

Defining the relation between soil water content and net nitrogen mineralization.

European Journal of Soil Science 54:39-47.

Pavelka, M., M. Acosta, M.V. Marek, W. Kutsch, and D. Janous. 2007. Dependence of the Q10

values on the depth of the soil temperature measuring point. Plant and Soil 292:171-179.

Pengthamkeerati, P., P.P. Motavalli, R.J. Kremer, and S.H. Anderson. 2006. Soil compaction and

poultry litter effects on factors affecting nitrogen availability in a claypan soil. Soil &

Tillage Research 91:109-119.

Pieters, A.J. 1917. Green manuring: a review of the American experiment station literature.

Journal of the American Society of Agronomy: 62-82.

Power, J.F., and J.A. Zachariassen. 1993. Relative nitrogen-utilization by legume cover crop

species at 3 soil temperatures. Agronomy Journal 85:134-140.

Quemada, M., and M.L. Cabrera. 1997. Temperature and moisture effects on C and N

mineralization from surface applied clover residue. Plant and Soil 189:127-137.

Ranells, N.N., and M.G. Wagger. 1996. Nitrogen release from grass and legume cover crop

monocultures and bicultures. Agronomy Journal 88:777-782.

Rey, A., C. Petsikos, P.G. Jarvis, and J. Grace. 2005. Effect of temperature and moisture on rates

of carbon mineralization in a Mediterranean oak forest soil under controlled and field

conditions. European Journal of Soil Science 56:589-599.

Ribeiro, H.M., D. Fangueiro, F. Alves, R. Ventura, D. Coelho, E. Vasconcelos, C. Cunha-Queda,

J. Coutinho, and F. Cabral. 2010. Nitrogen mineralization from an organically managed

soil and nitrogen accumulation in lettuce. Journal of Plant Nutrition and Soil Science

173:260-267.

39

Riddle, J.A. and M. McEvoy. 2005. USDA National Organic Program rule summary outline. 22

Aug 2010. <http://www.sarep.ucdavis.edu/organic/complianceguide/national4.pdf>

Rinnofner, T., J.K. Friedel, R. de Kruijff, G. Pietsch, and B. Freyer. 2008. Effect of catch crops

on N dynamics and following crops in organic farming. Agronomy for Sustainable

Development 28:551-558.

Robertson, G. P., J. M. Blair, P. M. Groffman, D. Harris, E. Holland, K. Nadelhoffer, and D.

Wedin. 1999. Soil carbon and nitrogen availability: nitrogen mineralization, nitrification,

and soil respiration potentials. p. 258-271. In G. P. Robertson, C. S. Bledsoe et al. (eds.).

Standard Soil Methods for Long-Term Ecological Research, Oxford University Press,

New York.

Robertson, G.P. 1997. Nitrogen use efficiency in row crop agriculture: crop nitrogen use and soil

nitrogen loss. p. 347-365 in L. Jackson (ed.). Ecology in Agriculture, Academic Press,

New York.

Rosecrance, R.C., G.W. McCarty, D.R. Shelton, and J.R. Teasdale. 2000. Denitrification and N

mineralization from hairy vetch (Vicia villosa Roth) and rye (Secale cereale L.) cover

crop monocultures and bicultures. Plant and Soil 227:283-290.

Ross, S.M., J.R. King, R.C. Izaurralde, and J.T. O'Donovan. 2001. Weed suppression by seven

clover species. Agronomy Journal 93:820-827.

Ruffo, M.L., and G.A. Bollero. 2003a. Residue decomposition and prediction of carbon and

nitrogen release rates based on biochemical fractions using principal-component

regression. Agronomy Journal 95:1034-1040.

Ruffo, M.L., and G.A. Bollero. 2003b. Modeling rye and hairy vetch residue decomposition as a

function of degree-days and decomposition-days. Agronomy Journal 95:900-907.

Sainju, U.M., B.P. Singh, and W.F. Whitehead. 2000. Cover crops and nitrogen fertilization

effects on soil carbon and nitrogen and tomato yield. Canadian Journal of Soil Science

80:523-532.

Sainju, U.M., W.F. Whitehead, and B.P. Singh. 2005. Biculture legume-cereal cover crops for

enhanced biomass yield and carbon and nitrogen. Agronomy Journal 97:1403-1412.

40

Sainju, U.M., and B.P. Singh. 2008. Nitrogen storage with cover crops and nitrogen fertilization

in tilled and nontilled soils. Agronomy Journal 100:619-627.

Sarrantonio, M. 1992. Opportunities and challenges for the inclusion of soil-improving crops in

vegetable production systems. HortScience 27:754-758.

Sarrantonio, M. and E. Gallandt. 2003. The role of cover crops in North American cropping

systems. Journal of Production Agriculture 8:53-74.

Sarrantonio, M., and T. Molloy. 2003. Response of sweet corn to red clover under two tillage

methods. Journal of Sustainable Agriculture 23:91-109.

Sattell, R., R. Dick, R. Karow, D. McGrath, and E. Peachey. 1998. Common Oregon cover

crops. Oregon State University. 30 Aug 2010.

<http://smallfarms.oregonstate.edu/improving-soil-quality-crops>

Schellenberg, D.L., R.D. Morse, and G.E. Welbaum. 2009. Organic broccoli production on

transition soils: comparing cover crops, tillage and sidedress N. Renewable Agriculture

and Food Systems 24:85-91.

Seo, J.H., I.J. Meisinger, and H.J. Lee. 2006. Recovery of nitrogen-15-labeled hairy vetch and

fertilizer applied to corn. Agronomy Journal 98:245-254.

Sierra, J. 1997. Temperature and soil moisture dependence of N mineralization in intact soil

cores. Soil Biology & Biochemistry 29:1557-1563.

Sikora, L.J., and N.K. Enkiri. 2000. Efficiency of compost-fertilizer blends compared with

fertilizer alone. Soil Science 165:444-451.

Smeltekop, H., D.E. Clay, and S.A. Clay. 2002. The impact of intercropping annual 'Sava' snail

medic on corn production. Agronomy Journal 94:917-924.

Snapp, S.S., and H. Borden. 2005. Enhanced nitrogen mineralization in mowed or glyphosate

treated cover crops compared to direct incorporation. Plant and Soil 270:101-112.

Snapp, S.S., S.M. Swinton, R. Labarta, D. Mutch, J.R. Black, R. Leep, J. Nyiraneza, and K.

O'Neil. 2005. Evaluating cover crops for benefits, costs and performance within cropping

system niches. Agronomy Journal 97:322-332.

41

Soon, Y.K., and M.A. Arshad. 2004. Tillage, crop residue and crop sequence effects on nitrogen

availability in a legume-based cropping system. Canadian Journal of Soil Science 84:421-

430.

Starovoytov, A., R.S. Gallagher, K.L. Jacobsen, J.P. Kaye, and B. Bradley. 2010. Management

of Small Grain Residues to Retain Legume-Derived Nitrogen in Corn Cropping Systems.


Steenwerth, K., and K.M. Belina. 2008. Cover crops and cultivation: Impacts on soil N dynamics

and microbiological function in a Mediterranean vineyard agroecosystem. Applied Soil

Ecology 40:370-380.

Stockdale, E.A., M.A. Shepherd, S. Fortune, and S.P. Cuttle. 2002. Soil fertility in organic

farming systems - fundamental different? Soil Use and Management 18:301-308.

Sung, J.K., J.A. Jung, B.M. Lee, S.M. Lee, Y.H. Lee, D.H. Choi, T.W. Kim, and B.H. Song.

2010. Effect of incorporation of hairy vetch and rye grown as cover crops on weed

suppression related with phenolics and nitrogen contents of soil. Plant Production Science

13:80-84.

Sustainable Agriculture Network, 2007. Managing Cover Crops Profitably (2nd ed.) Sustainable

Agriculture Publications, Burlington, VT.

Teasdale, J.R., and C.L. Mohler. 1993. Light transmittance, soil-temperature, and soil-moisture

under residue of hairy vetch and rye. Agronomy Journal 85:673-680.

Teasdale, J.R., T.E. Devine, J.A. Mosjidis, R.R. Bellinder, and C.E. Beste. 2004. Growth and

development of hairy vetch cultivars in the northeastern united states as influenced by

planting and harvesting date. Agronomy Journal 96:1266-1271.

Teasdale, J.R., A.A. Abdul-Baki, and Y.B. Park. 2008. Sweet corn production and efficiency of

nitrogen use in high cover crop residue. Agronomy for Sustainable Development 28:559-

565.

Thomsen, I.K., P. Schjonning, B. Jensen, K. Kristensen, and B.T. Christensen. 1999. Turnover of

organic matter in differently textured soils - II. Microbial activity as influenced by soil

water regimes. Geoderma 89:199-218.

42

Thorup-Kristensen, K., J. Magid, and L.S. Jensen. 2003. Catch crops and green manures as

biological tools in nitrogen management in temperate zones, p. 227-302 Advances in

Agronomy, Vol 79, Vol. 79. Academic Press Inc, San Diego.

Thorup-Kristensen, K. 2006. Root growth and nitrogen uptake of carrot, early cabbage, onion

and lettuce following a range of green manures. Soil Use and Management 22:29-38.

Thorup-Kristensen, K., and D.B. Dresboll. 2010. Incorporation time of nitrogen catch crop

influences the N effect of the succeeding crop. Soil Use and Management 26: 27-35.

Tonitto, C., M.B. David, and L.E. Drinkwater. 2006. Replacing bare fallows with cover crops in

fertilizer-intensive cropping systems: a meta-analysis of crop yield and N dynamics.


Torbert, H.A., D.W. Reeves, and R.L. Mulvaney. 1996. Winter legume cover crop benefits to

corn: Rotation vs fixed-nitrogen effects. Agronomy Journal 88:527-535.

Trinsoutrot, I., S. Recous, B. Bentz, M. Lineres, D. Cheneby, and B. Nicolardot. 2000.

Biochemical quality of crop residues and carbon and nitrogen mineralization kinetics

under nonlimiting nitrogen conditions. Soil Science Society of America Journal 64:918-

926.

Tu, C., F.J. Louws, N.G. Creamer, J.P. Mueller, C. Brownie, K. Fager, M. Bell, and S. Hu. 2006.

Responses of soil microbial biomass and N availability to transition strategies from

conventional to organic farming systems. Agriculture Ecosystems & Environment

113:206-215.

U.S. Department of Agriculture. 2010. Economic Research Service. 15 Aug 2010.

<http://www.ers.usda.gov/Data/Organic/>.

U.S. Department of Agriculture. 2010. National Organic Program. 14 Aug 2010.

<http://www.ams.usda.gov/nop>.

U.S. Department of Agriculture. 2010. National Agriculture Statistics Service. 14 Aug 2010.

<http://www.agcensus.usda.gov/Publications/2007/Online_Highlights/Fact_Sheets/organi

cs.pdf>.

Vanek, S., H.C. Wien, and A. Rangarajan. 2005. Time of interseeding of lana vetch and winter

rye cover strips determines competitive impact on pumpkins grown using organic

practices. HortScience 40:1716-1722.

43

Vaughan, J.D., and G.K. Evanylo. 1998. Corn response to cover crop species, spring desiccation

time, and residue management. Agronomy Journal 90:536-544.

Vigil, M.F., and D.E. Kissel. 1991. Equations for estimating the amount of nitrogen mineralized

from cover residues. Soil Science Society of America Journal 55:757-761.

Vigil, M.F., and D.E. Kissel. 1995. Rate of nitrogen mineralized from incorporated crop residues

as influenced by temperature. Soil Science Society of America Journal 59:1636-1644.

Wagger, M.G. 1989. Time of desiccation effects on plant composition and subsequent nitrogen

release from several winter annual cover crops. Agronomy Journal 81:236-241.

Wagger, M.G., M.L. Cabrera, and N.N. Rannels. 1998. Nitrogen and carbon cycling in relation

to cover crop residue quality. Journal of Soil and Water Conservation 53:214-218.

Walz E. 2004. Fourth national organic farmers‟ survey: Sustaining organic farms in a changing

organic marketplace. Organic Farming Research Foundation, Santa Cruz, CA, pp. 69-73.

Wang, W.J., R.C. Dalal, P.W. Moody, and C.J. Smith. 2003. Relationships of soil respiration to

microbial biomass, substrate availability and clay content. Soil Biology & Biochemistry

35:273-284.

Washington Agriculture Weather Network. 2010. 15 March 2010.

<http://www.weather.wsu.edu/>

Wang, C.H., S.Q. Wan, X.R. Xing, L. Zhang, and X.G. Han. 2006. Temperature and soil

moisture interactively affected soil net N mineralization in temperate grassland in

Northern China. Soil Biology & Biochemistry 38:1101-1110.

Watson, C.A., D. Atkinson, P. Gosling, L.R. Jackson, and F.W. Rayns. 2002. Managing

fertility in organic farming systems. Soil Use and Management 18:239-247.

Watts, D.B., H.A. Torbert, Y.C. Feng, and S.A. Prior. 2010. Soil microbial community

dynamics as influenced by composted dairy manure, soil properties, and landscape

position. Soil Science 175:474-486.

Weinert, T.L., W.L. Pan, M.R. Moneymaker, G.S. Santo, and R.G. Stevens. 2002. Nitrogen

recycling by nonleguminous winter cover crops to reduce leaching in potato rotations.


44

Weston, L.A. 1996. Utilization of allelopathy for weed management in agroecosystems.


Whitmore, A.P. 1996. Modelling the release and loss of nitrogen after vegetable crops.

Netherlands Journal of Agricultural Science 44:73-86.

Whitmore, A.P., and J.J.R. Groot. 1997. The deomposition of sugar beet residues: mineralization

versus immobilization in contrasting soil types. Plant and Soil 192:237-247.

Wolf, D.C. and GH Wagner. 2005. Carbon Transformations and Soil Organic Matter Formation.

p. 285-331. In D.M. Sylvia, J.J. Fuhrmann et al. (eds.) Principles and Applications of

Soil Microbiology. Prentice Hall, Upper Saddle River, NJ.

Zemenchik, R. K.A. Albrecht, M.K Schultz. 2001. Nitrogen replacement values of kura clover

and birdsfoot trefoil in mixtures with cool-season grasses. Agronomy Journal 93:

451-458.

Zotarelli, L., L. Avila, J.M.S. Scholberg, and B.J.R. Alves. 2009. Benefits of vetch and rye cover

crops to sweet corn under no-tillage. Agronomy Journal 101:252-260.

45

CHAPTER 2

Evaluating fall cover crop blends for biomass production, residue quality and weed

suppression

1. INTRODUCTION

There is renewed interest for including cover crops in crop rotations for the purpose of

nitrogen (N) management and enhanced crop productivity, especially among organic growers

who are prohibited from using synthetic fertilizers (USDA, National Organic Program, 2010). In

the maritime Pacific Northwest, rye (Secale cereale)-hairy vetch (Vicia villosa) cover crop

blends have the potential to produce large biomass yields, enhance plant available N to

subsequent crops, and suppress winter weeds when seeded by early October (Kuo and Sainju,

1996; Kuo et al., 2002; Cogger et al., 2008). But organic vegetable growers in the region are

often challenged to find a niche for cover crops in rotations because of late season vegetable

production for niche markets and land limitations. As a consequence, growers are interested in

the effect of delayed planting, early incorporation, and rye-hairy vetch seeding ratio on cover

crop biomass yield, supply of plant available N, and winter weed control.

Winter cover crops can recycle residual soil nitrate (NO3-) that may leach below the

rooting zone (BrandiDohrn et al., 1997) and depending on the species may reduce N fertilizer

requirements in subsequent crops (Kuo et al., 1997; Cline and Silvernail, 2002). Nitrogen

availability from cover crop residues is of primary interest to organic growers in N-limited

systems. Mixing cereal and legume cover crops enhances biomass yields and carbon (C) and N

contents compared to monoculture cover crops (Sainju et al., 2005). Cereal cover crops increase

soil organic matter via increased C production (Sainju et al., 2000) while legumes increase plant

available N by atmospheric N fixation (Vaughan et al., 2000). When cereals are combined with

46

legumes, the resulting mixture typically has higher N concentration and increases plant available

N (Rannels and Wagger, 1996). A blend of legume and cereal cover crops is ideal because it can

supply sufficient C and N to soils to maintain soil quality and improve crop productivity

compared to pure stands (Rannels and Wagger, 1997; Kuo et al., 1997; Sainju et al., 2005).

The timing of fall cover crop planting is affected by harvest of the previous cash crop,

reliable establishment, and the number of growing degree days required for sufficient biomass

production. Regional research has demonstrated that cereal-hairy vetch blends should be planted

by early October to ensure successful establishment and biomass accumulation (Odhiambo and

Bomke, 2000; Kuo and Sainju, 2002; Cogger et al., 2008). Recent work at WSU Puyallup

suggests the optimal planting date for hairy vetch is early September (Cogger, personal

communication). Hairy vetch has been shown to have slow fall growth and low winter soil cover

(Holderbaum et al., 1990), possibly because its optimal temperature for root growth is relatively

high (20-25 °C) (Mosjidis and Zhang, 1995). But several studies have demonstrated that hairy

vetch has a high rate of winter survival in northern climates (Teasdale et al., 2004; Brandsaeter et

al., 2008) and rapid growth in spring as soil temperatures warm (Holderbaum et al., 1990; Kuo

and Jellum, 2000). Zachariassen and Power (1991) reported that hairy vetch dry matter

production was greatest when soil temperatures were 10 °C, when grown at temperatures ranging

from 10 to 30 °C. Contrary to hairy vetch, cereal rye has been shown to establish quickly when

planted by early October and it can effectively utilize residual soil nitrate (NO3-) because rapid

root development puts it in contact with soil N (Kuo and Jellum, 2000). Because the timing of

harvest of summer crops can vary and unfavorable weather conditions may delay planting

beyond the optimal window, improved understanding of the effect of delayed planting on stand

establishment and biomass yields is needed.

47

Cover crop N accumulation and biomass composition may be affected by spring kill date

(Clark et al., 1997; Sainju and Singh, 2001; Thorup-Kristensen and Dresboll, 2010). Several

studies show a marked increase in hairy vetch biomass by delaying the kill date 2 wk between

late April and early May, ranging from 35 to 61% (Wagger, 1989; Clark et al., 1995). In

addition, late kill may be essential when planting late in fall to ensure adequate biomass and N

accumulation (Teasdale et al., 2004). But delaying kill date may decrease residue N

concentration, increase C:N ratios, and result in higher concentrations of hemicellulose and

lignin in residue (Wagger, 1989; Cline and Silvernail, 2001), which has an important effect on N

release. For hairy vetch, this effect on residue quality may not be important if desiccated before

flowering stage because of relatively high quality until flowering (Vaughn and Evanylo, 1998).

For example, a delay in killing hairy vetch resulted in a large increase in inorganic N, likely

because of increased N content (Cook et al., 2010). But a delay in rye incorporation from early

March to late April decreased net N mineralization and availability to the subsequent crop

(Thorup-Kristensen and Dresboll, 2010). This is likely because the delay in desiccation has less

influence on hairy vetch residue quality than it does on cereal crops. Influence of climate and N

mineralization rate will affect what is an ideal kill date. Sufficient N accumulation and timely N

release from cover crop residues is essential to affect N supply to the subsequent crop.

There is little information on how rye-hairy vetch seeding ratio affects biomass

composition, residue quality, and winter weed suppression. Rye-hairy vetch cover crop blends

generally have higher residue quality than stands of pure rye and therefore higher N availability

to subsequent crops (Rannels and Wagger, 1996; Kuo and Jellum, 2002; Sainju et al., 2005). Kuo

and Sainju (1998) found that rye-hairy vetch biomass ratio should not exceed 60% to result in an

initial net increase in inorganic N. But it is unclear what seeding ratio best achieves that

48

composition and if plant and kill dates have an interactive effect. In addition winter weed

suppression is a primary interest of growers in this region. Due to the mild winter climate, weed

germination and growth in winter can increase weed management costs in summer crops. It has

been shown that rye is suitable for winter weed suppression because of rapid establishment and

competition for light (Kruidhof et al., 2008). However, there is limited research on the effect of

rye-hairy vetch blends on winter weed control.

In this study, rye-hairy vetch winter cover crops were evaluated for their ability to

provide winter ground cover, accumulate N, suppress winter weeds, and increase plant available

N in soil. Our objective was to: (i) evaluate the effect of rye-hairy vetch seeding ratio and

planting date on cover crop establishment, weed pressure, dry matter production and N

accumulation and (ii) evaluate the effect of harvest date on cover crop dry matter production and

residue quality.

2. MATERIALS AND METHODS

Site description

The Fall Cover Crop Blends field plots, located at Washington State University Puyallup

Research and Extension Center, were established in September 2004. This ground was placed in

organic transition in 2001 and has been certified organic in accordance with the National Organic

Program since 2004. The soil is classified as Briscot loam (coarse-loamy, mixed, superactive,

nonacid, mesic Fluvaquentic Endoaquepts). The average annual precipitation and temperature is

102.9 cm and 10.9°C, with mild, dry summers and cool, wet winters. Approximately 75% of

precipitation occurs between October and March. Figure 1 shows mean monthly precipitation

and temperature.

Experimental design

49

The experiment included five cover crop treatments, two planting dates, and two harvest

dates, arranged in a randomized complete block split plot design, with cover crop treatment as

the main plot and planting date as the split. Main plots measured 11 x 6.1 m and there were 4

replications for each treament. Cover crop treatments as a seeding ratio of rye-hairy vetch

included 100:0 75:25, 50:50, 25:75, and 0:100. The 75:25 rye-hairy vetch treatment was added in

2008. The two planting dates were mid-September and early-October and the two harvest dates

were late-March and late-April. A summer cover crop of sudangrass was planted in June and

harvested in August of each year. Starting in 2006, supplemental organic nitrogen (feather meal)

was applied at 89 kg N ha-1

to the 100% rye plots only before planting the sudangrass.

Management

Cover crops were planted in the fall using a 3.1 m John Deere grain drill. The rye-hairy

vetch blends were seeded at 112 kg ha-1

. All hairy vetch seed was inoculated with the appropriate

rhizobia bacteria to ensure nitrogen fixation. In the spring, cover crops were chopped and

incorporated using a rotary spader and sudangrass (Sorghum bicolor) was planted using a 3.1 m

John Deere grain drill. Supplemental feather meal nitrogen was hand broadcast on pure rye plots

at time of planting. In August, sudangrass was flail mowed and incorporated with a rotary

spader, and the plots prepared for fall cover crops. Dates of field activities are listed in Table 1.

Measurements

Cover crop stand density was evaluated on three dates during the winter of each year.

Two observers each evaluated 3 representative 0.25 m2 quadrats per plot as a percent of soil

covered by cover crop (excluding weeds) per the method of Sarrantonio (1991). In late March

and late April, plots were harvested for above ground biomass by harvesting a 6.1 x 0.91 m

swath approximately 5 cm above the soil surface with a flail mower. Cover crop heights were

50

measured along the harvest swath. A subsample of the residues was dried at 55°C and ground to

pass through a 2-mm sieve. Total C and N in residue were measured by dry combustion with a

TruSpec CN Carbon/Nitrogen Determinator (Leco, St. Joseph, MI). The remaining residue was

returned to the plots. Three additional subsamples were randomly collected from representative

0.25 m2 quadrats in each plot, and the proportion of rye, vetch, and weeds was determined

(Sarrantonio, 1991).

In June, soil samples were collected to a depth of 30 cm. Six samples were taken in each

plot with a 2.5 cm diameter tube sampler and composited. Inorganic N (NH4+ and NO3

-)-N was

extracted from 10 g soil samples with 100 mL of 2M KCl. Samples were shaken on a reciprocal

shaker for 1 h and then filtered through No. 42 Whatman filters. Aliquots were run on an

automated, continuous flow QuikChem 8000 Injection Flow Analysis System (Hach Instruments,

Loveland, CO). Ammonium-N was determined using the salicylate-nitroprusside method

(Mulvaney, 1996) and NO3--N was determined using the cadmium reduction method (Gavlak et

al., 1994).

Biochemical fractions of the residues were determined by using the neutral detergent and

acid detergent stepwise procedure developed by Van Soest et al. (1991) using an ANKOM

automated system with filter bags (ANKOM Technology Corp., Fairport, NY). Neutral detergent

fiber includes hemicellulose, cellulose, and lignin as the primary components; acid detergent

fiber consists of cellulose and lignin; and acid detergent lignin is the component remaining after

cellulose has been removed (Stubbs et al., 2010).

Statistical analysis

Analysis of variance was done on cover crop soil cover, biomass yields, crop biomass

composition, weed biomass, residue biochemical fractions, and June NO3- using the SAS

51

MIXED procedure (SAS 9.2, SAS Institute, Cary, NC, 2008). For a randomized complete block

split plot design, cover crop rye-hairy vetch seeding ratio and planting date were fixed effects

and replication was a random effect. Harvest date and year were other fixed effects included in

the analysis. The 75:25 rye-hairy vetch blend was not included in the analysis because it was not

included in all years of the study. The data for 2008 was omitted from the analysis because of

poor germination by rye, which may be attributed to bad seed. Pearson correlation coefficients

were calculated to test the relationship between cover crop biomass yields and growing degree

days elapsed between planting and harvest using the SAS CORR procedure (SAS 9.2, SAS

Institute, Cary, NC, 2008). Growing degree days were calculated per the Baskerville-Emin

method (Andresen, 2010), using base temperature of 4 °C.

53

Table 2. Analysis of variance for cover crop biomass, nitrogen (N)

concentration, N content, and C:N ratio as affected by experiment year,

harvest date, planting date, and cover crop seeding ratio.

Effect Biomass N concentration N Content C:N Ratio

Probability > F

Year (Y) <.0001 <.0001 <.0001 <.0001

Harvest (H) <.0001 <.0001 <.0001 <.0001

Y x H <.0001 <.0001 <.0001 0.0009

Plant (P) <.0001 0.0002 <.0001 <.0001

Y x P <.0001 0.0001 <.0001 <.0001

H x P 0.0156 0.8059 <.0001 0.0492

Y x H x P 0.1962 0.7641 0.099 0.1874

Cover crop (C) <.0001 <.0001 0.0346 <.0001

Y x C <.0001 <.0001 <.0001 <.0001

H x C <.0001 <.0001 0.1391 <.0001

Y x H x C 0.0982 0.6234 0.8734 0.0012

P x C <.0001 0.0037 <.0001 <.0001

Y x P x C 0.0074 0.0437 0.261 0.0001

H x P x C 0.0297 0.3084 0.246 0.2987

Y x H X P x C 0.884 0.5695 0.1602 0.301

54

Table 3. Cover crop biomass as a function of growing degree days

Cover crop Slope Y-intercept R2 P-value

Rye 11.22 a1 -5377 b 0.712 < 0.0001

R50V50 8.50 b -3640 b 0.616 < 0.0001

R25V75 7.38 b -3026 b 0.604 < 0.0001

Vetch 2.79 c -567 a 0.220 < 0.05 1Values followed by same letter are not signficantly different (P <

0.05)

Table 4. Cover crop biomass yield and total C and N content as affected by planting

and harvest date and rye-hairy vetch seeding ratio (% rye)

Rye-hairy vetch Biomass yield N conc. N content C:N

Plant Harvest seeding ratio kg ha-1

g kg-1

kg ha-1

ratio

Sept Early 0:100 1354 h1 44 a 55 e 10 i

Sept Early 25:75 2224 f 35 c 77 c 13 g

Sept Early 50:50 2384 f 32 d 73 cd 14 f

Sept Early 100:0 2820 e 29 e 77 c 15 e

Sept Late 0:100 2271 f 39 b 86 b 11 h

Sept Late 25:75 4183 c 25 g 99 a 19 c

Sept Late 50:50 4758 b 23 h 105 a 20 b

Sept Late 100:0 5518 a 18 i 98 a 25 a

Oct Early 0:100 714 j 44 a 29 f 10 i

Oct Early 25:75 923 ij 35 c 32 f 13 g

Oct Early 50:50 1055 i 34 cd 36 f 13 g

Oct Early 100:0 1036 i 30 e 29 f 15 e

Oct Late 0:100 1853 g 38 b 69 d 12 gh

Oct Late 25:75 2960 e 26 f 77 c 17 de

Oct Late 50:50 3039 e 25 fg 75 cd 18 d

Oct Late 100:0 3311 d 19 i 62 de 24 a 1Values followed by same letter within a column are not significantly different (P <

0.05)

55

Table 5. Analysis of variance for fiber fractions as

affected by cover crop, planting date, harvest date,

and year

Effect NDF1

ADF ADL

Cover crop (C) <.0001 <.0001 <.0001

Plant (P) <.0001 <.0001 0.0321

C x P 0.0062 0.0635 0.1874

Harvest (H) <.0001 <.0001 0.8354

C x H 0.007 0.0133 0.0503

P x H 0.0514 0.0020 0.6645

C x P x H 0.0443 0.2954 0.9958

Year (Y) <.0001 <.0001 <.0001

C x Y 0.0588 <.0001 0.066

P x Y 0.0008 <.0001 0.0116

C x P x Y 0.4973 0.0235 0.0034

H x Y 0.0726 <.0001 <.0001

C x H x Y 0.0059 <.0001 0.1495

P x H x Y 0.4719 0.0083 0.4559

C x P x H x Y 0.8506 0.003 0.3935 1Neutral detergent fiber, NDF; acid detergent fiber,

ADF; acid detergent lignin, ADL

Table 6. Neutral detergen fiber (NDF), acid detergent fiber

(ADF), and acid detergent lignin (ADL) by harvest date, and rye-

hairy vetch seeding ratio

Rye-hairy vetch NDF ADF ADL

Harvest date seeding ratio g kg-1

Early 0:100 374 e1 237 c 66.4 b

Early 25:75 401 de 230 d 57.6 c

Early 50:50 408 d 226 d 56.3 c

Early 100:0 420 cd 224 d 56.6 c

Late 0:100 426 c 325 a 74.5 a

Late 25:75 500 b 330 a 57.2 c

Late 50:50 508 b 324 a 59.7 c

Late 100:0 525 a 305 b 47.2 d

1Values followed by same letter within a column are not

significantly different (P < 0.05)

56

3. RESULTS AND DISCUSSION

Cover crop establishment

Cover crop establishment was monitored over each winter as a percent ground cover

excluding weed species. As shown in Figure 2, planting date had a significant effect on cover

crop establishment. At the October planting, there were considerable reductions in percent

ground cover across all treatments in comparison to the September planting. The differences

between treatments at the October planting were not large. In contrast, there were significant

differences between treatments at the September planting date. Rye treatments had the highest

ground cover at the November rating date, whereas the rye-hairy vetch blends provided the most

ground cover at the later two rating dates. These differences are not surprising, given the growth

habits of rye and hairy vetch. Cereal rye is a standard winter cover crop in many regions because

it establishes quickly and thrives in cool conditions (Sustainable Agriculture Network, 2007).

Hairy vetch has been shown to be a hardy winter legume, but it prefers warm soil temperatures

and therefore establishes more slowly in cool conditions (Mosjidis and Zhang, 1995). Increased

ground cover at the last two rating dates in the rye-hairy vetch blend treatments suggest that the

rye may act as a nurse crop to the hairy vetch, as has been observed in other experiements

(Bjorkman and Shail, 2008; Grubinger, 2010). There is evidence that cover crops grown in

biculture have a wider range of tolerance to adverse environmental conditions than grown in

monoculture (Creamer et al., 1997; Gaskell, 2006).

Cover crop biomass yield

Cover crop biomass yield was significantly affected by planting date, harvest date, rye-

hairy vetch seeding ratio, and experiment year (Table 2). The benefit of increased biomass yield

of hairy vetch when combined with rye was evident in our study (Figure 3). On average, the

57

50:50 rye-hairy vetch blends yielded 66 to 81% (1.02 to 1.26 Mg ha-1

) higher biomass than pure

hairy vetch. Other studies have reported similar findings, but also demonstrate that rye-hairy

vetch blends may produce equal or more biomass than pure rye stands (Clark et al., 1994;

Teasdale and Abdul-Baki, 1998; Sainju et al., 2005). In contrast, the rye-hairy vetch blends in

our study yielded up to 19% (0.59 Mg ha-1

) less biomass than pure rye, depending on planting

and harvest date. There is little published data on rye-hairy vetch biomass yields in the maritime

Pacific Northwest that include seeding ratios similar to ours. The studies cited were conducted in

Maryland and Georgia, states with warmer fall and spring conditions that favor the growth of

hairy vetch. Given the cool climate in the maritime Pacific Northwest, it is not surprising that

lowering the seeding ratio of rye in favor of hairy vetch may decrease biomass yields. Cool fall

and spring temperatures are likely to support rye growth more than hairy vetch. Results from a

long-term study in Puyallup, WA support this hypothesis, demonstrating that on average, hairy

vetch biomass was 32% (0.85 Mg ha-1

) lower than rye (Kuo and Jellum, 2000).

The interaction between planting and harvest date on cover crop biomass yield

demonstrates that on average, early harvest reduced biomass yields more (1.92 Mg ha-1

) than late

planting (1.33 Mg ha-1

) when compared cover crops planted early and harvested late. But when

analyzed according to rye-hairy vetch seeding ratio, planting and harvest dates affected biomass

yields differently. For late planted treatments, biomass was reduced 0.53 and 2.00 Mg ha-1

for

hairy vetch and rye, respectively, compared to 1.03 and 2.49 Mg ha-1

at early harvest. These

figures demonstrate that although hairy vetch growth is slow in fall, it experiences a period of

rapid growth in spring as the temperature increases.

The effect of planting date, harvest date, and experiment year on cover crop biomass

yields can be explained by variation in growing degree days accumulated between planting and

58

harvest. Teasdale et al. (2004) have demonstrated that hairy vetch cover crop biomass yield is

linearly related to growing degree days accumulated between planting and harvest dates. In our

experiment, differences in growing degree days between planting and harvest across all rye-hairy

vetch seeding ratios could explain variation in biomass yields (Table 3). The relationship was

much stronger for pure rye and rye-hairy vetch bicultures than pure hairy vetch, and therefore

growing degree days is not a good indicator of hairy vetch biomass. It is possible that winter

injury from cold temperatures could affect hairy vetch growth and biomass yield. Absolute

minimum temperatures reached -12°C on three occasions in 2009-10 and -8 to -10°C in 2008-09.

Teasdale et al. (2004) have observed winter injury to hairy vetch foliage when absolute winter

temperatures reached -11 to -13°C. In that study, winter injury was highest on late planted hairy

vetch.

Cover crop dry matter composition and weed biomass

The contribution of rye and hairy vetch to total dry matter varied by planting date and

rye-hairy vetch seeding ratio (Figure 4). Rye dominated dry matter composition regardless of

seeding ratio and planting date. For early planted cover crops, a 50:50 rye-hairy vetch seeding

ratio had 67% rye in dry matter, while a 25:75 rye-hairy vetch blend had 59%. Rye established

quickly in the cool conditions typical in this region in the fall, and therefore it may have a

competitive advantage over hairy vetch when planted early. At late planting, the percent rye in

total dry matter is lower than for early planted cover crops (52 and 40% for 50:50 and 75:25 rye-

hairy vetch seeding ratios, respectively). Although weeds make up a slightly larger fraction of

the total dry matter (13% compared to 20 to 21% for early and late planting, respectively), the

hairy vetch component is larger at the late planting date. Hairy vetch seems to be more

competitive with rye when planted late because most growth and biomass production occurs in

59

spring when warm temperatures favor more rapid growth of hairy vetch. Hairy vetch is slow to

establish regardless of planting date. Rye has a competitive advantage when planted early

because of its ability to establish quickly. The dry matter composition of cereal-legume cover

crop mixtures has important implications on N availability because of its affect on biomass yield,

N concentration, and residue quality.

The weed component of the total dry matter was significantly lower when rye and hairy

vetch were combined than for either species alone (Figure 4). Winter cover crops may affect

winter weed germination and growth by competition for light (Kruidhof et al., 2008). As

reported above, rye-hairy vetch bicultures had higher ground cover than either species alone

when planted early. It is likely that increased competition for light from the rye-hairy vetch blend

treatments reduced weed pressure compared to monocultures. Planting date significantly affected

the percentage of weeds in total dry matter, regardless of rye-hairy vetch seeding ratio. This

suggests that cover crops are less effective at suppressing weed growth when planting date is

delayed.

Total weed biomass was lower for rye-hairy vetch blends than for stands of pure rye

(Figure 5). This is consistent with our discussion above concerning ground cover and light

interception. Only the 25:75 rye-hairy vetch seeding ratio at early planting lowered weed

biomass compared to pure hairy vetch. Given the higher biomass and greater ground cover of rye

compared to hairy vetch, it is surprising that weed biomass was greater under rye than hairy

vetch. Because of its marked growth response to warm spring temperatures and sprawling nature,

it is possible that hairy vetch better competed with weeds late in the season.

Cover crop N concentration and N content

60

Residue N concentration was largely affected by rye-hairy vetch seeding ratio and harvest

date (Table 2). The effect of planting time was significant but differences were not large.

Nitrogen concentration decreased from early to late harvest for all rye-hairy vetch treatments,

with the change being most drastic for pure rye (Table 4). While rye had the lowest N

concentration, hairy vetch had the highest, and both blends were intermediate. The N

concentration of the rye-hairy vetch bicultures was not significantly different, which was likely

because rye-hairy vetch biomass composition was similar for both seeding ratios. There were

significant differences in N concentrations between pure rye and hairy vetch treatments and rye-

hairy vetch bicultures. On average the N concentration of the rye-hairy vetch bicultures was 11.5

g kg-1

less than hairy vetch but 5.5 g kg-1

greater than rye. Other studies report that the N

concentration of rye-hairy vetch mixtures range between the N concentration of pure hairy vetch

and pure rye, and the ratio of the components has a large effect (Clark et al., 1994).

The interaction between cover crop treatment and harvest date was significant across all

years (Figure 6). The N concentration decreased from early to late harvest by an average of 5 g

kg-1

for pure hairy vetch, compared to 10 and 11 g kg-1

for rye-hairy vetch bicultures and pure

rye, respectively. Hairy vetch was in a vegetative stage at both harvests, and therefore a smaller

decrease is expected (Teasdale et al., 2004). Planting date had a small but significant effect on

residue N concentration (Table 4). On average, late planting increased N concentration 1 g kg-1

for rye-hairy vetch biculture and pure rye treatments.

The total N content (kg N ha-1

) of rye-hairy vetch bicultures was equal to or greater than

the N contents of either cover crop grown in monoculture. Surprisingly, mean N content of pure

rye was greater than pure hairy vetch (Table 4). Research shows that rye N uptake is increased

by residual soil N (McCracken et al., 1994). In our study, a summer crop of sudangrass was

61

incorporated 3 to 6 weeks prior to cover crop planting, which may have provided a slow-release

N supply for N uptake during fall and spring. In an intensively cropped system where post-

harvest residual soil N is low, hairy vetch and rye-hairy vetch blends may have higher N content

than pure rye because hairy vetch fixes N (Rannels and Wagger, 1996; Teasdale and Abdul-Baki,

1998; Sainju et al., 2005).

For cover crops planted late and harvested early there was no difference in total N

content (29 to 36 kg N ha-1

) (Table 4). Such a small amount of cover crop N is not significant

enough to impact N dynamics in a subsequent cash crop. Nitrogen content was highest when

cover crops were planted early and harvested late (86 to 105 kg N ha-1

), which was likely

because the highest number of growing degree days were accumulated between these dates. On

average there was a 32 kg ha-1

decrease in N content when planting date was late and a 33 kg ha-1

increase in N content when harvest was late. The interaction between cover crop and planting

and harvest dates demonstrated that rye and hairy vetch N content was affected by planting and

harvest dates differently. Nitrogen uptake in hairy vetch was higher for late planting/late harvest

than early planting/early harvest. This is not surprising because hairy vetch goes through a period

of rapid growth in N fixation in spring as temperatures increase. In contrast, rye accumulated

more N for early planting/early harvest than late planting/late harvest. Unlike hairy vetch, rye

established quickly in fall and is well-adapted to take up residual fall soil N. Soil inorganic N is

low in spring after winter precipitation and therefore may limit N uptake in rye at that time.

Residue quality

The release of N from cover crop residues to a subsequent cash crop is largely dependent

on residue quality (Myrold and Bottomley, 2008). Cover crop C:N ratio, which is a simple

measure of residue quality, has been negatively correlated to N release (Vigil and Kissel, 1991;

62

Quemada and Cabrera, 1995; Chaves et al., 2004). Our data demonstrated that rye combined

with hairy vetch had a lower C:N ratio than pure rye treatments (Table 4), which is consistent

with what others have reported (Rannels and Wagger, 1996; Kuo and Jellum, 2002; Sainju et al.,

2005). But rye-hairy vetch seeding ratio of the biculture treatments did not have a large impact

on C:N ratio, as we had hypothesized. Similarity in the portions of rye and hairy vetch in the

total biomass for the two bicultures offers a likely explanation. Harvest date had a large impact

on C:N ratio while planting date did not. The interaction between cover crop treatment and

harvest date demonstrated that the C:N ratio of rye was more affected by harvest date than hairy

vetch. On average, delaying harvest increased C:N ratio by 1.1, 1.4, and 1.7 times for hairy

vetch, rye-hairy vetch bicultures, and rye, respectively. This is likely because rye went from a

vegetative to heading stage while hairy vetch remained in a vegetative stage. The growth stage of

plant residues at kill date has been shown to affect residue quality (Handayanto et al., 1997).

Vaughan and Evanylo (1998) reported a similar trend, demonstrating that a three week delay in

spring kill date increased C:N ratio of rye but not hairy vetch. All cover crop C:N ratios were

below 25, which is often considered the breakeven point between net mineralization and

immobilization (Myrold and Bottomley, 2008).

The fiber content of plant residues has been shown to influence residue decomposition

and N release (Ruffo and Bollero, 2003; Jensen et al., 2005; Stubbs et al., 2009). Therefore, it is

important to understand how management and cereal-legume mixture affects fiber content. We

found that planting date, harvest date, and rye-hairy vetch seeding ratio significantly affected

residue fiber (Table 5). On average, hairy vetch had the lowest NDF (386 g kg-1

) and rye the

lowest ADF (257 g kg-1

) and ADL (51.5 g kg-1

). There were large differences in NDF between

hairy vetch and rye (386 to 462 g kg-1

) but only small differences in ADF (257 to 265 g ka-1

).

63

This is consistent with the literature, which has shown that hemicellulose content may vary

widely between rye and hairy vetch residues while cellulose portions were typically similar

(Rannels and Wagger, 1996; Magid et al., 2004). These findings are in agreement with our

results because NDF includes hemicellulose, cellulose, and lignin and ADF contains cellulose

and lignin but not hemicellulose. In addition, our results demonstrated that ADL was relatively

low for all cover crop residues (51.9 to 70.5 g kg-1

). Other studies with rye and hairy vetch cover

crop residues reported similar lignin contents, ranging from 27 to 92 g kg-1

(Rannels and

Wagger, 1996; Kuo and Sainju, 1998). Research has shown that even small amounts of lignin

can significantly affect residue decomposition and N release (Vigil and Kissel, 1991; Quemada

and Cabrera, 1995; Hadas et al., 2004).

Rye-hairy vetch biculture treatments were not significantly different in NDF (441 g kg-1

),

ADF (265 g kg-1

), or ADL (52.3 g kg-1

) content in our study. This was likely due to the similarity

in the portions of rye and hairy vetch in total biomass of the biculture treatments. In general,

fiber in rye-hairy vetch bicultures resembled the rye treatments more closely than hairy vetch.

This is likely because of the high portion of rye in the total biomass yield for both treatments.

Cover crop planting and harvest date significantly affected fiber across all cover crop

treatments (Table 5). But planting date had a much smaller affect on residue fiber than harvest

date. Overall, late planting date decreased NDF, ADF, and ADL by an average of 17, 14, and 7.6

g kg-1

(data not shown). There was only a minor effect of planting date on residue fiber likely

because planting date had a small effect in plant development of rye and hairy vetch.

Alternatively, fiber content, NDF, ADF, ADL was significantly affected by harvest date and

cover crops (Table 5). Delaying harvest date had a small but significant affect on the NDF and

ADF contents of hairy vetch (68 and 77 g kg -1

increase) relative to rye and rye-hairy vetch

64

blends (100 to 121 and 96 to 107 g kg-1

increase, respectively) (Figure 7). As previously

described, this may be because rye went from a vegetative to heading stage between early to late

harvest dates while hairy vetch remained in a vegetative stage. Other research has shown that

NDF, ADF, and ADL have been found to increase with crop maturity (Cherney et al., 1993;

Elizade et al., 1999). Therefore, the benefits of increased N content at the late harvest date must

be weighed against the increase in fiber content when considering N release dynamics.

Mid-June soil nitrates

The N availability from the incorporated cover crop residues was monitored via mid-June

soil NO3--N analysis. We compared the effects of planting date and rye-hairy vetch seeding ratio

on the soil N response (early harvested cover crops were not incorporated until time of late

harvest). Soil NO3--N data from 2010 is not included in this analysis. On average, NO3

--N was

approximately double in pure hairy vetch treatments relative to pure rye. This trend is not

surprising given the high N concentration of hairy vetch compared to rye. There was a significant

increase in NO3--N in the rye-hairy vetch blends compared to pure rye. We hypothesize that a

slower release of NO3--N from rye-hairy vetch blends may be better timed for crop N uptake in

comparison to pure hairy vetch.

As shown in Figure 8, the interaction between rye-hairy vetch seeding ratio and

experiment year was significant. In general, the soil NO3--N response was similar between years.

But lower biomass yields in 2007 resulted in reduction of NO3--N in hairy vetch and rye-hairy

vetch blends than other years. Growers relying on cover crop stands as a source of N for

subsequent grown crops may be faced with poor stand establishment and N accumulation every

few years and therefore insufficient supply of plant available N. In those circumstances, it may

be appropriate to supplement N fertility needs with a commercial organic N fertilizer. In this

65

study, rye-hairy vetch cover crops accumulated sufficient biomass to significantly increase soil

NO3--N relative to pure rye in three out of four years. Therefore, winter-grown rye-hairy vetch

cover crop blends appear to be a reliable means of increasing soil NO3--N.

66

Figure 1. Mean monthly precipitation and mean monthly maximum (max.), minimum (min.) and

daily temperatures from 1995-2010

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Pre

cip

ita

tio

n, cm

Tem

per

atu

re, °C

Month

Mean precipitation

Mean max. temp.

Mean temp.

Mean min. temp.

67

Figure 2. Cover crop establishment measured as a percent ground cover excluding weeds for

early (a) and late (b) planted cover crops. Cover crop treatments are hairy vetch (Vetch), 25:75

rye-hairy vetch blend (R25V75), 50:50 rye-hairy vetch blend (R50V50), and pure rye (Rye)

(P < 0.0001)

0

10

20

30

40

50

60

70

80

90

Nov Jan Mar

Gro

un

d c

ov

er, %

Rating date

Vetch

R25V75

R50V50

Rye

0

10

20

30

40

50

60

70

80

Nov Jan Mar

Gro

un

d c

ov

er, %

Rating date

Vetch

R25V75

R50V50

Rye

(a)

(b)

68

Figure 3. Cover crop biomass yields as affected by planting date, harvest date, and rye-hairy

vetch seeding ratio (P < 0.05)

0

1000

2000

3000

4000

5000

6000

0:100 25:75 50:50 100:0

Bio

mas

s yi

eld

, kg

ha

-1

Rye-hairy vetch seeding ratio

Late planting, early harvest

Early planting, early harvst

Late planting, late harvest

Early planting, late harvest

69

Figure 4. Percentage of above ground biomass from rye, hairy vetch, and weeds at four rye-hairy

vetch seeding ratios (Rye, %) at early (a) and late (b) planting dates (P < 0.05)

5967

8171

2820

29

13 13 19

0%

20%

40%

60%

80%

100%

0:100 25:75 50:50 100:0

Ab

ov

e g

rou

nd

bio

ma

ss,

%


Weeds

Vetch

Rye

4052

7366

4024

3420 21 27

0%

20%

40%

60%

80%

100%

0:100 25:75 50:50 100:0

Ab

ov

e g

ro

un

d b

iom

ass

, %


Weeds

Vetch

Rye

(a)

(b)

70

Figure 5. Weed biomass yield as affected by planting date and rye-hairy vetch seeding ratio (P <

0.05)

Figure 6. Cover crop residue N concentration as affected by harvest date and rye-hairy vetch

seeding blend (P < 0.0001)

0

100

200

300

400

500

600

700

800

900

0:100 25:75 50:50 100:0

Wee

d b

iom

ass

, k

g h

a-1


Sept Planting

Oct Planting

0

5

10

15

20

25

30

35

40

45

50

0:100 25:75 50:50 100:0

N c

on

cen

tra

tio

n, g

kg

-1


Early Harvest

Late Harvest

71

Figure 7. Neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin

(ADL) by rye-hairy vetch seeding ratio and harvest date. Values within the same group for each

seeding ratio treatment followed by the same letter are not significantly different (P < 0.05)

e

d d cd

d e f f

cc c b

c

b ba

ca b c

b b a a

0

100

200

300

400

500

600

0:100 25:75 50:50 100:0 0:100 25:75 50:50 100:0 0:100 25:75 50:50 100:0

NDF . ADF . ADL

g kg

-1

Early harvest

Late harvest

72

Figure 8. Mid-June soil NO3--N as affected by rye-hairy vetch seeding ratio and experiment year

(P < 0.001)

0

10

20

30

40

50

60

0:100 25:75 50:50 100:0

So

il (

NO

3- )

-N, m

g k

g-1


2005

2006

2007

2009

73

4. CONCLUSIONS

If planted by early-October, the latest planting date in our study, rye-hairy vetch cover

crop blends can accumulate sufficient biomass and N to provide inorganic N to support a

subsequent cash crop. Both planting and harvest date impact cover crop biomass yields, total N

content, and residue quality. While late harvest favors larger biomass production, we report an

increase in greater NDF, ADF, and ADL. It is unclear whether the increase in N content is

enough to offset the effect of more recalcitrant C on N release dynamics. Our data suggests that

insufficient biomass and N is accumulated when cover crops are planted late and harvested early

to impact N supply to subsequent cash crop.

Rye-hairy vetch seeding ratio of mixed species treatments did not have a large affect on

cover crop biomass yield or composition. We noticed an advantage in winter weed suppression

under rye-hairy vetch bicultures relative to monoculture rye. But this benefit was not consistently

different for hairy vetch. Rye established more quickly than hairy vetch in cool fall conditions,

which makes it a favorable winter cover crop in the maritime Pacific Northwest. Although hairy

vetch is slow to establish, it goes through a period of rapid growth in the spring and has a higher

potential to supply large amounts of N to subsequent crops. The soil inorganic N response to

incorporated cover crops demonstrates that rye-hairy vetch blends can increase N availability to

subsequent cash crops compared to pure rye. We hypothesize that slower N release from rye-

hairy vetch blends may be better timed for crop N uptake than pure hairy vetch. Given the

similarities between the two rye-hairy vetch seeding blends, we recommend using a 50:50 rye-

hairy vetch seeding ratio to optimize biomass yields, N accumulation, winter weed suppression,

and N supply to crops in rotation.

74

5. LITERATURE CITED

Andresen, J. 2010. Calculation of Baskerville-Emin (“BE”) growing degree days. Michigan State

University. 3 April 2010. <http://www.maes.msu.edu/nwmihort/be_method.pdf>

Björkman, T. and J.W. Shail. 2008. Cornell cover crop guide for hairy vetch. Cornell University.

Ver. 1.100716.



188.








Cherney, D.J.R., J.H. Cherney, and R.F. Lucey. 1993. In vitro digestion kinetics and quality of

perennial grasses as influenced by forage maturity. Journal of Dairy Science 76:790-

797.

Clark, A.J., A.M. Decker, and J.J. Meisinger. 1994. Seeding rate and kill date effects on hairy

vetch cereal rye cover crop mixtures for corn production. Agronomy Journal 86:1065-

1070.

Clark, A.J., A.M. Decker, J.J. Meisinger, F.R. Mulford, and M.S. McIntosh. 1995. Hairy vetch

kill date effects on soil-water and corn production. Agronomy Journal 87:579-585.


vetch-rye mixture. 1. Cover crop and corn nitrogen. Agronomy Journal 89:427-434.



11:219-225.

75




Washington State University Puyallup Research and Extension Center, Puyallup, WA.

Cook, J.C., R.S. Gallagher, J.P. Kaye, J. Lynch, and B. Bradley. 2010. Optimizing Vetch

Nitrogen Production and Corn Nitrogen Accumulation under No-Till Management.



in vegetable production systems. Hortscience 32:866-870.

Elizalde, J.C., N.R. Merchen, and D.B. Faulkner. 1999. Fractionation of fiber and crude protein

in fresh forages during the spring growth. J. Anim Sci. 77:476-484.

Gaskell, M. 2006. Organic nitrogen sources for vegetable crops. Hortscience 41:957-957.

Galvak R.G., Horneck D.A., and Millier R.O. 1994. Plant, soil, and water reference methods for

the western region. Western Regional Extension Publ., 125, Univ. of Alaska-Fairbanks.

Grubinger, V. 2010. Winter rye: a reliable cover crop. University of Vermont Extension. 5 Nov

2010. <http://www.uvm.edu/vtvegandberry/factsheets/winterrye.html>

Hadas, A., L. Kautsky, M. Goek, and E.E. Kara. 2004. Rates of decomposition of plant residues

and available nitrogen in soil, related to residue composition through simulation of

carbon and nitrogen turnover. Soil Biology & Biochemistry 36:255-266.

Handayanto E., G. Cadisch, and K.E. Giller. Regulating N Mineralziation from Plant Residues

by Manipulation of Quality. p. 175-185. In Cadisch G. and K.E. Giller (eds.), Driven by

Nature Plant Litter Quality and Decomposition. Cab International, Wallingford, UK.

Holderbaum, J.F., A.M. Decker, J.J. Meisinger, F.R. Mulford, and L.R. Vough. 1990. Fall-

seeded legume cover crops for no-tillage corn in the humid east. Agronomy Journal

82:117-124.




76

Kruidhof, H.M., L. Bastiaans, and M.J. Kropff. 2008. Ecological weed management by cover

cropping: effects on weed growth in autumn and weed establishment in spring. Weed

Research 48:492-502.



Kuo, S., and E.J. Jellum. 2002. Influence of winter cover crop and residue management on soil

nitrogen availability and corn. Agronomy Journal 94:501-508.



Soils 22: 310-317.



Magid, J., O. Henriksen, K. Thorup-Kristensen, and T. Mueller. 2001. Disproportionately high

N-mineralisation rates from green manures at low temperatures - implications for

modeling and management in cool temperate agro-ecosystems. Plant and Soil 228:73-82.

McCracken, D.V., M.S. Smith, J.H. Grove, C.T. Mackown, and R.L. Blevins. 1994. Nitrate

leaching as influenced by cover cropping and nitrogen-source. Soil Science Society of

America Journal 58:1476-1483.

Mosjidis, J.A., and X. Zhang. 1995. Seed germination and root growth of several Vicia species at

different temperatures. Seed Science and Technology 23:749-759.

Mulvaney R.L. 1996. Nitrogen – Inorganic forms. In D.L. Sparks et al. eds. Methods of Soil

Analysis. Part 3. SSSA Book Ser. 5. ASA and SSSA, Madison, WI.


immobilization. In J.S. Schepers and W.R. Raun (eds.) Nitrogen in Agricultural Systems.





77

Quemada, M., and M.L. Cabrera. 1995. Carbon and nitrogen mineralized from leaves and steams

of 4 cover crops. Soil Science Society of America Journal 59:471-477.



Ranells, N.N., and M.G. Wagger. 1997. Grass-legume bicultures as winter annual cover crops.


Ruffo, M.L., and G.A. Bollero. 2003. Residue decomposition and prediction of carbon and



Sainju, U.M., and B.P. Singh. 2001. Tillage, cover crop, and kill-planting date effects on corn

yield and soil nitrogen. Agronomy Journal 93:878-886.

Sainju, U.M., B.P. Singh, and W.F. Whitehead. 2000. Cover crops and nitrogen fertilization

effects on soil carbon and nitrogen and tomato yield. Canadian Journal of Soil Science

80:523-532.



Sarrantonio, M. 1991. Soil-Improving Legumes. Rodale Institute, Kutztown, PA.

Stubbs, T.L., A.C. Kennedy, P.E. Reisenauer, and J.W. Burns. 2009. Chemical Composition of

Residue from Cereal Crops and Cultivars in Dryland Ecosystems. Agronomy Journal

101:538-545.

Stubbs, T.L., A.C. Kennedy, and A.M. Fortuna. 2010. Using NIRS To Predict Fiber and Nutrient

Content of Dryland Cereal Cultivars. Journal of Agricultural and Food Chemistry 58:398-

403.

Sustainable Agriculture Network, 2007. Managing Cover Crops Profitably (2nd ed.) Sustainable

Agriculture Publications, Burlington, VT.

Teasdale, J.R., and A.A. Abdul-Baki. 1998. Comparison of mixtures vs. monocultures of cover

crops for fresh-market tomato production with and without herbicide. Hortscience

33:1163-1166.

78




Thorup-Kristensen, K., and D.B. Dresboll. 2010. Incorporation time of nitrogen catch crop

influences the N effect of the succeeding crop. Soil Use and Management 26: 27-35.



Van Soest, P.J., J.B. Robertson, and B.A. Lewis. 1991. Methods for dietary fiber, neutral

detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. Journal of

Dairy Science 74:3583-3597.



Vaughan, J.D., G.D. Hoyt, and A.G. Wollum. 2000. Cover crop nitrogen availability to

conventional and no-till corn: Soil mineral nitrogen, corn nitrogen status, and corn yield.

Communications in Soil Science and Plant Analysis 31:1017-1041.


from crop residues. Soil Science Society of America Journal 55:757-761.



Zachariassen, J.A., and J.F. Power. 1991. Growth-rate and water-use by legume species at 3 soil

temperatures. Agronomy Journal 83:408-413.

79

CHAPTER 3

Nitrogen release from rye-hairy vetch cover crop residues with and without a semi-fast

release organic fertilizer in a laboratory incubation

1. INTRODUCTION

One of the challenges in organic crop production is synchronizing plant available

nitrogen (N) with crop uptake (Pang and Letey, 2000). Because synthetic fertilizers cannot be

used in organic systems (USDA, National Organic Program, 2010), immediate release of

inorganic (NH3++NO4

-)-N is not possible. Systems that utilize cover crops have the potential to

accumulate large amounts of plant available N, but release of inorganic N must be carefully

timed with subsequent crop uptake (Cherr et al., 2006). In general, legumes have been

considered superior cover crops compared to nonleguminous crops because of their ability to fix

atmospheric N (Fageria, 2007). But mixing cereal cover crops with legumes can enhance N

cycling because cereal crops can take up residual soil nitrate (NO3-) after fall harvest

(BrandiDohrn et al., 1997). When cereal and legume species are grown as a biculture, the

combined cover crops typically have larger total N content, lower C:N ratios, and increase plant

available N relative to cereals in monoculture (Rannels and Wagger, 1996; Kuo and Sainju,

1998; Sainju et al., 2005). But it is unclear how the portions of cereal and legume residues in

total dry matter of the blend affect N release. There is a need to better understand and predict N

release so that fertility recommendations can be accurately made (Granatstein et al., 2010).

Due to variations in cover crop N content between years (Lawson, 2010), addition of

organic N fertilizers in combination with cover crops may be necessary to provide supplemental

N. A range of approved organic fertilizers are commercially available, most of which are

composed of by-products of fish, livestock, and food processing industries (Gaskell and Smith,

80

2007). A few common examples include sea bird guano, fish powder, feather meal, and blood

meal, which have N concentrations ranging from 9 to 12 % (Gaskell et al., 2006) Although these

fertilizers can be expensive, the value of these products is high in situations where cover crop N

supply is insufficient for an upcoming cash crop. These organic fertilizers have been shown to

have rapid N availability, ranging from 48 to 67 % of total N released over 4 weeks at 25 °C

(Gaskell et al., 2006; Hartz and Johnstone, 2006). Some research has shown that the application

a semi-rapid release organic N fertilizer in combination with organic residues can increase

apparent N mineralization (Sikora and Enkiri, 2000). In one study, granulated poultry manure

applied in combination with compost enhanced the net N mineralization compared to the sum of

each component separately (Ribeiro et al., 2010). But application of N fertilizers in combination

with residues with low N concentration can temporarily immobilize N and have an overall

negative impact on net N mineralization (McSwiney and Snapp, 2010). It is unclear how N

mineralization of cover crop residues is affected by the application of a semi-rapid release

organic N fertilizer, such as feather meal.

Under constant environmental conditions, N release from plant residues is primarily a

function of the relative availability of carbon (C) and N in residues (Myrold and Bottomley,

2008). A measure of residue quality can be used to describe the availability of C and N from

plant residues and has been correlated to residue decomposition and release of plant available N

(Palm and Rowland, 1997). Several studies have demonstrated correlation of plant

decomposition and N release with residue quality fractions such as polyphenols, lignin, and N

concentration (Constantinides and Fownes, 1994; Rannels and Wagger, 1996; Nakhone and

Tabatabai, 2008). Others have found that C:N and lignin:N ratios are useful indices of N release

(Vigil and Kissel, 1991; Gilmour et al., 1998; Chaves et al., 2004). But there is no clear

81

consensus of which quality variables are best correlated with N release from cover crop residues.

For example, the C:N ratio of organic residues has been well related to N mineralization in many

studies. But some have found that it is only initially correlated with N release because residue

quality changes as decomposition and nutrient release progress (Chaves et al., 2004). Others

have demonstrated that it is neither an adequate measure of residue quality (Ruffo and Bolloro,

2003) nor a useful parameter for estimating N mineralization (Vigil and Kissel, 1995).

Mckenney et al. (1995) hypothesize that C:N ratio is not a good predicator of plant residue N

mineralization because it does not adequately describe the nutrient availability for microbial

growth.

Mineralization of organic residues transforms organic N to ammonium (NH4+). In N-rich

agricultural soils, the consequence of most NH4+ is thought to be nitrification (Robertson, 1997).

Nitrification potentials are a measure of the ability of nitrifying bacteria to transform NH4+ to

NO3-. Cropping systems that result in high NH4

+ levels often increase rates of nitrification

(Chantigny et al., 1996; Fortuna et al., 2003). Likewise, seasonal immobilization events, such as

incorporation of wheat straw, lower soil inorganic N pool and decrease nitrification rates

(Recous et al., 1999). Nitrification potentials are often used in assessments of soil quality

because it may be a useful indicator of the effect of management to improve N use efficiency and

soil quality (Stamatiadis et al., 1999; Fortuna et al., 2003).

It is difficult to predict N release and availability from field studies due to variability in

climate and soils (Cabrera et al., 2005). Laboratory incubations that are conducted at ideal

moisture and temperature conditions provide a method for comparing N availability across

treatments and systems, which is not possible in the field (Robertson et al., 1999). A laboratory

incubation study was set up to measure N availability from cover crop blends applied with and

82

without a relatively fast release organic fertilizer. The objective was to (i) determine the timing

of N release from rye-hairy vetch cover crop blends both with and without organic feather meal

fertilizer in a Puyallup fine sandy loam soil, (ii) relate rye-hairy vetch biochemical characteristics

to N availability as measured in the incubation, and (iii) and assess changes in nitrification

potentials for cover crops and cover crop-fertilizer combinations in the incubation to be used as a

soil quality indicator.


Field plots

The Fall Cover Crop Blends study is located at Washington State University Puyallup

Research and Extension Center, Puyallup, WA. This ground was placed in organic transition in

2001 and has been certified organic in accordance with the National Organic Program since

2004. The study was established in September 2004 to determine the effect that planting and

harvest date and rye-hairy vetch seeding ratio has on cover crop biomass yield and N content.

Cover crop samples were harvested from field plots that were planted in mid-September and

harvested in late-April. Residues for pure rye and pure vetch were taken from respective field

plots while residues for the rye-hairy vetch blends were taken from field plots that had been

seeded at a 50:50 seeding ratio. After harvest of above ground cover crop biomass, residues were

dried at room temperature.

Because there was no control plot in Cover Crop Blends, soil was collect from the 0 to 30

cm depth from the control plots of an adjacent study Cover Crops-2, also located at the Puyallup

station. This ground has been under organic management practices since 2004. The entire field

received compost at approximately 34 Mg ha-1

dry matter in July 2008, but control plots had no

subsequent amendments or cover crops. The soil is classified as Puyallup fine sandy loam

83

(coarse-loamy over sandy or sandy-skeletal, isotic over mixed, mesic Vitrandic Haploxerolls).

Soil and cover crop residues were collected on April 27, 2009.

Laboratory incubation

The release of inorganic (NH4+ + NO3

-)-N from cover crop residues was estimated via a

laboratory incubation. The experiment included four rye-hairy vetch cover crop blends. As a

percent rye biomass, these were 0 (pure hairy vetch), 50 (r50v50), 75 (r75v25), and 100% (pure

rye). A no cover crop soil control was included. Application rates for cover crop treatments were

equivalent to 2.75, 4.50 and 4.75 Mg biomass ha-1

for pure vetch, pure rye, and both rye-vetch

blends, respectively, based on yields observed in the Cover Crop Blends study. Certified organic

feather meal fertilizer was amended to half of the vessels at a rate equivalent to 120 kg N ha-1

. It

contains 12% N and approximately 75% is available in a growing season, which is equivalent to

90 kg N ha-1

. In total there were 10 treatments (5 cover crops x 2 fertilizer levels), each with

three replicates, and 9 sample dates, a total of 270 incubation vessels. Table 1 lists the cover

crop-feather meal treatments and the application rates.

Cover crops and feather meal were analyzed for total C and N concentration and cover

crops for fiber contents. A subsample of the residues was dried at 55°C and ground to pass

through a 2-mm sieve. Total C and N in residue were measured by dry combustion with a

TruSpec CN Carbon/Nitrogen Determinator (Leco, St. Joseph, MI). Biochemical fractions of the

residues were determined by using neutral detergent and acid detergent stepwise procedure

developed by Van Soest et al. (1991) using an ANKOM automated system with filter bags

(ANKOM Technology Corp., Fairport, NY). Neutral detergent fiber includes hemicellulose,

cellulose, and lignin as the primary components; acid detergent fiber consists of cellulose and

84

lignin; and acid detergent lignin is the component remaining after cellulose has been removed

(Stubbs et al., 2010).

The method for set up of the laboratory incubation was similar to that reported by

Fortuna et al. (2003). Prior to construction of the vessels, soil was passed through a 2 mm sieve

and pre-incubated at room temperature for 7 days. Each incubation vessel contained the

equivalent of 50 g of oven dry soil, which was packed to a bulk density of 1.2 g cm-3

, based on

field measurements. Soils were weighed into specimen vials and packed prior to addition of

distilled water (dH2O), residue (where applicable), and simulation of rotary spading. Residues

had been cut into 5 to 7 cm lengths and were mixed into the soil such that less than 10% was

visible from the surface.

Incubations were maintained at 40% water filled pore space (WFPS). To calculate the

percent gravimetric water content of microcosms and the amount of dH2O to add per specimen

vial, the following equation (1) was used:

[1]

where 40% is WFPS, 2.65 g/cm3 is the bulk density of the soil mineral constituent, and 1.2 g/cm

3

is the bulk density of the soil (Elliot et al., 1999). The field moist soil had a gravimetric water

content of 15.4%. Therefore, 57.7 g field moist soil and 1.3 g of dH2O was weighed into each

vial to achieve 40% WFPS. Distilled water was added to the incubation vessels weekly to

maintain 40% WFPS. The caps were not tightly sealed, which allowed gas exchange and

prevented microcosms from drying. Temperature was maintained at 25 °C.

85

Specimen vials were removed and sampled 0, 7, 15, 28, 50, 70, 106, and 157 days after

set up. Inorganic N (NH4+ and NO3

-)-N was extracted from 10 g soil samples with 100 mL of 2

M KCl at each time point. Samples were shaken on a reciprocal shaker for 1 h and then filtered

through No. 42 Whatman filters. Aliquots were run on an automated, continuous flow QuikChem

8000 Injection Flow Analysis System (Hach Instruments, Loveland, CO). Ammonium-N was

determined using a salicylate-nitroprusside method (Mulvaney, 1996) and nitrate-N using the

cadmium reduction method (Gavlak et al., 1994). At the same time, nitrification potentials were

measured by the shaken slurry method described by Hart et al. (1994). A 15 g sample of soil was

taken from each microcosm and placed in a 250 mL Erlenmeyer flask, which contained a 100

mL mixture of 1.5 mM NH4+ and 1 mM PO4

-. Substrate concentration was not limiting because

excess NH4+ was available. Samples were shaken on an orbital shaker at 180 rpm for a 24 hours

incubation period at 22˚C. Each flask was sampled four times during that period at 2, 4, 22, and

24 hours. Nitrate was measured on an automated, continuous flow QuikChem 8000 Injection

Flow Analysis System (Hach Company, Loveland, CO), as described above.

Data analysis

Net N release from cover crop and cover crop-feather meal residues in the laboratory

incubation was calculated by subtracting inorganic N content of control soil from total inorganic

N content of each cover crop-feather meal treatment. The percent N release was calculated by

dividing net N released from cover crop residue by total N content of residue applied. Net N

mineralization data was fitted to a simple exponential model [Eq. 2] (Curtin and Campbell,

2008), which assumes a single pool of potentially mineralizable N, mineralized at a rate

proportional to its concentration:

[2]

86

where Nm is mineralized N at time t, t is incubation time, No is the potentially mineralizable N

pool, and k is the mineralization rate constant. Curve fitting of N mineralized was approximated

by least-squares iteration with the SAS NLIN procedure (SAS 9.2, SAS Institute, Cary, NC

2008). Analysis of variance was done with a mixed model procedure to determine the effect of

rye-vetch biomass ratio and feather meal amendment on N mineralization and nitrification

potential using SAS statistical software (SAS 9.2, SAS Institute, Cary, NC 2008). Correlations

between net N mineralization and residue quality were conducted using Pearson correlation

coefficients using the SAS CORR procedure (SAS 9.2, SAS Institute, Cary, NC, 2008).

87

Table 1. Cover crop-feather meal treatments used in (nitrogen) N mineralization incubation

study, including the equivalent rates of cover crop biomass application and total applied N.

Cover crop FM1 Total N

Treatment Mg biomass ha-1

kg N ha-1

kg N ha-1

kg N ha-1

Control None 0 0 0 0

Vetch Hairy vetch 2.75 99 0 99

Rye Rye 4.50 73 0 73

R50V502

50:50 R-HV 4.60 137 0 137

R75V253

75:25 R-HV 4.75 113 0 113

FM None 0 0 120 120

FM & Vetch Hairy vetch 2.75 99 120 219

FM & Rye Rye 4.50 73 120 193

FM & R50V50 50:50 R-HV 4.60 137 120 257

FM & R75V25 75:25 R-HV 4.75 113 120 233 1Feather meal, FM; 250:50 rye-hairy vetch blend, R50V50; 375:25 rye-hairy vetch blend,

R75V25

88

Table 2. Total carbon (C) and nitrogen (N) concentration of residue and soil, and

residue quality

N C C:N NDF1 ADF ADL

Residue (g kg-1

) (g kg-1

)

Rye 17 e2 442 c 26 f 457 a 253 c 21 c

R75V253 24 d 446 bc 21 e 444 ab 263 bc 42 b

R50V50 30 c 447 b 18 d 426 b 271 b 49 ab

Hairy vetch 36 b 451 b 13 c 392 c 302 a 63 a

Feather meal 118 a 493 a 4.2 a

Soil 1.5 f 17 d 12 b 1NDF, neutral detergent fiber; ADF, acid detergent fiber; ADL, acid detergent lignin 2Numbers followed by same letter within row not different (P < 0.01) 3R75V25, 75:25 rye-hairy vetch blend; R50V50, 50:50 rye-hairy vetch blend

Table 3. Parameters of first-order model fitted to net N mineralization from

cover crop residues.

Residue No1

k Nok R2

kg ha-1

day-1

kg ha-1

day-1

R100 36.4 d2 0.027 c 1.0 e 0.931

R75V253 63.5 c 0.038 c 2.4 c 0.949

R50V50 78.9 b 0.088 b 7.0 b 0.957

V100 62.5 c 0.130 a 8.1 a 0.970

SOIL 124.2 a 0.014 d 1.7 d 0.979 1To calculate the net pool of potentially mineralizale N from residue only,

soil (NH3++NO4

-)-N has been subtracted from treatments with residues

2Numbers followed by same letter within column not significantly different

(P < 0.001) 375:25 rye-hairy vetch blend (R75V25), 50:50 rye-hairy vetch blend

(R50V50)

90


Residue quality

As shown in Table 2, hairy vetch had the highest N concentration, approximately double

that of rye. Some research has shown that residues of cover crops grown in biculture may have

higher N concentration than when grown alone (Rannels and Wagger, 1996; Elgersma and

Schlepers, 2000; Ndakidemi, 2006). We found that the rye component of the rye-hairy vetch

blends had only slightly greater N concentration than pure rye (+1.8 g kg-1

), while hairy vetch

from mixture was much greater in N concentration than from pure hairy vetch (+5.2 g kg-1

).

Increased competition for residual N by the cereal may enhance N fixation by legumes and

increase residue N concentrations (Hardarson and Atikins, 2003). Alternatively, mineralization

of decomposing legume roots can enhance soil (NH4+ + NO3

-)-N pool for uptake by cereal grown

simultaneously (Evans et al., 2001).

Cover crop C:N ratios ranged from 13 (hairy vetch) to 26 (rye) (Table 2). The C:N ratios

for hairy vetch and the rye-hairy vetch bicultures were below 25, which has typically been

considered the break-even point between N mineralization and immobilization (Myrold and

Bottomley, 2008). The fiber data for cover crop residues demonstrated that hairy vetch had the

lowest NDF (392 g kg-1

), while rye had the lowest ADF (253 g kg-1

) and ADL (21 g kg-1

). The

fiber data for the cover crop residues in this study were similar to what has been reported in the

Fall cover crop blends study at Puyallup, WA (Lawson, 2010).

Nitrogen release from cover crop residues

As shown in Figure 1, (NH4++NO3

-)-N was higher for cover crop treatments at all sample

dates relative to the soil control. The net release of N from cover crop residues was calculated by

subtracting (NH4++NO3

-)-N accumulated in control soil from the cover crop treatments. Nitrogen

91

mineralization from soil fit a linear relationship for the duration of the incubation (R2 = 0.973, P

< 0.05). But the rate of net N release for cover crop treatments decreased with time, shown in

Figure 2. The curves demonstrate that there was a rapid phase of N mineralization followed by a

plateau for all cover crop treatments. Our data for N release from legume and cereal-legume

residues are comparative to other studies with cover crop residues (Quemada and Cabrera, 1995;

Kuo and Sainju, 1998; Odihambo and Bomke, 2000). We did not observe net N immobilization

at any time during the incubation for pure rye, as has been reported. In our study, the N

concentration for pure rye was higher than the critical value for net N mineralization as observed

by Odhiambo and Bomke (2000) (14.1 g kg-1

), but lower than that reported by Kuo et al. (1997)

(17.6 g kg-1

). The literature demonstrates wide variation in the critical N concentration necessary

for net N mineralization, ranging as low as 11.0 g kg-1

(Nourbakhsh and Dick, 2005). Variation

in microbial biomass N and residue quality may account for differences. For example, Deng et

al. (2000) demonstrate a significant relationship between potential N mineralization and

microbial biomass N, which may account for variation in N mineralization dynamics of cover

crop residues. When plant residues are added to soil, microbial growth is stimulated because of

available C (Wang et al., 2003; Tu et al., 2006). But the microbial biomass must assimilate a

certain amount of N, which is determined by microbial C:N ratio (Kaye and Hart, 1997). If the N

concentration available from the residue is greater than what is needed by microbial biomass,

there will be net N mineralization (Myrold and Bottomley, 2008). Other studies have

demonstrated that cellulose, hemicellulose, and lignin fractions can affect residue decomposition

and N release (Vigil and Kissel, 1991; Hadas et al., 2004; Jensen et al., 2005). Therefore, the

critical N concentration value may not be an indicator of N release from plant residues.

92

The rye-hairy vetch blend ratio had a significant impact on net N mineralization from the

residues. As the proportion of rye increased from 50 to 100% there was a trend of less (NH4+ +

NO3-)-N release. The pure hairy vetch treatment released less N than r50v50 after day 50, which

is likely because of the lower amendment rate of hairy vetch residue. However, pure vetch and

r50v50 released a similar percent of residue N from day 70 to 158 (Figure 2). After 70 days pure

vetch, r50v50, r75v25, and pure rye had released 64.9, 56.8, 50.0, and 39.9% of total residue N,

respectively. This timeframe is representative of a typical growing season (May-September) in

the maritime Pacific Northwest when calculated on a growing degree basis. The release of N as a

percent of total residue N was not different for pure hairy vetch and r50v50 treatments. Our data

demonstrate that even a small amount of hairy vetch residue (25% of blend total) in combination

with rye will significantly increase N release in comparison to pure rye, which is consistent with

other findings (Kuo and Sainju, 1998).

Net N release from feather meal-cover crop combinations

The cumulative N release curves for feather meal-cover crop treatments demonstrate that

there was a rapid phase of N mineralization over the first 21 days followed by slow linear phase

after day 50 (Figure 3). Net N release from feather-meal cover crop treatments were calculated

by subtracting (NH4++NO3

-)-N accumulated in control soil from these treatments (Figure 4).

Feather meal-cover crop combinations released more N than cover crop residues alone, which

was likely because of higher total N content of the combined materials. The N release curves for

feather meal-cover crop treatments reflected the pattern observed for feather meal without cover

crops. In total, 65% of feather meal N was released over the first 21 days of the incubation. Other

studies have reported slower N release from feather meal over two weeks after incorporation (48

to 55% of applied N) (Hadas and Kautsky, 1994; Hartz and Johnstone, 2006). In our study,

93

feather meal pellets were cut into pieces to scale down for microcosms. Fragmenting the feather

meal pellets could increase microbial access and therefore enhance N mineralization. Several

studies have demonstrated that decreasing particle size facilitated microbial activity and

decomposition of organic residues (Ambus and Jensen, 1997; Angers and Recous, 1997), which

may enhance N mineralization.

A much more rapid increase in inorganic N was observed in the first 21 days in feather

meal-cover crop treatments than cover crops alone. The higher initial N release rate from feather

meal and greater total N content of combined materials offers a likely explanation. Nitrogen

release for feather meal combinations with r50v50, r75v25, and pure hairy vetch was not

different after 14 d. These treatments were applied at approximately the same N rate. The pure

rye-feather meal treatment released more N than feather meal only after day 50, which is

expected because of lower N content of feather meal-rye treatment and slow release pattern of

pure rye. Cumulative (NH4+ + NO3

-)-N feather meal-cover crop treatments did not change

significantly after day 21.

The feather meal-cover crop treatments accumulated less (NH4+ + NO3

-)-N than the sum

of the individual component residues. Several studies have shown that low quality residue (low

N concentration, high cellulose and hemicellulose concentrations) applied in combination with

other N amendments can immobilize fertilizer-derived N (Gentile et al., 2008; McSwiney and

Snapp, 2010; Starovoytov et al., 2010). But the cover crop residues in this study were of

relatively high quality (C:N ratio < 26.2). The N mineralization curves for cover crop residues

without feather meal demonstrate that there was not N immobilization for any of the residues at

any time in the incubation. Because NO3--N leaching was not possible, N immobilization in

microbial biomass or gaseous N loss must account for the decrease in (NH4+ + NO3

-)-N in the

94

feather meal treatment. Immobilization of N in microbial biomass is not likely given the high

C:N ratio of the feather meal. We did not observe remineralization of immobilized N later during

the incubation, which would be likely given the length of our microcosm study (Zagal and

Persson, 1994). Gaseous N loss in the form of nitrous oxide (N2O) or ammonia (NH3) may

account for decrease in the (NH4+ + NO3

-)-N. But conditions were not favorable for high rates of

denitrification in this study (Coyne, 2008). Senbayram et al. (2009) reported that N2O emissions

from biogas waste and mineral ammonium sulfate fertilizer were insignificant for soil at 65%

water-filled pore space, but that emissions increased approximately 5-fold for soil at 85% water-

filled pore space. In this study, soil moisture was maintained at 40% water-filled pore space, and

although some denitrification is possible, N2O loss is not likely to account for the magnitude of

N loss we observed. Although ammonia volatilization is minimal when N source is incorporated

into soil, a 5 to 10 cm depth is reported as necessary to minimize NH3 loss (Hargrove, 1988).

One study measured 16% of applied urea N was lost to NH3 volatilization when incorporated to a

depth of 0-5 cm (Rochette et al., 2009). In our study, feather meal was incorporated to a depth of

approximately 2 cm. No research has been done to look at NH3 loss from feather meal fertilizer,

but the literature suggests that significant N loss from NH3 volatilization is possible from urea

fertilizer under moisture and pH conditions (Bayrakli and Gezgin, 1996; Fox et al., 1996; Ping et

al, 2000). Further research is necessary to quantify NH3 volatilization potential from shallow

incorporated feather meal fertilizer.

Fitting net N mineralization data to kinetics model

Net N mineralization from cover crop residues fit a single first-order kinetics model well

(R2 = 0.931 to 0.970). Parameters of the model are given in (Table 3). The size of the

mineralizable N pool No for r50v50 was more than double pure rye. The other treatments, r75v25

95

and pure hairy vetch, had similar No values, which were slightly smaller than r50v50. In general,

No reflects the total N content of the cover crop residues applied. The rate constant k was highest

for pure hairy vetch and decreased as the rye component in the blends increased. Although No

was not different for pure hairy vetch and r75v25, the rate constant k was significantly smaller

for r75v25. This suggests that although similar N release is expected for these treatments over

157 d, the timing of release is much more rapid for the pure hairy vetch. The slower N release

from r75v25 residues may be better timed with the critical period of crop N uptake and therefore

enhance N use efficiency. The initial potential mineralization rate Nok of pure hairy vetch and

r75v25 support this hypothesis. Net N mineralization from cover crops applied in combination

with feather meal did not fit a single first-order kinetics model. A large portion of the N

contained in the feather meal was immediately available. Therefore, fitting a single first-order

kinetics model was not appropriate for that data.

Correlation of cover crop properties and net N mineralization

Total C and N concentrations and fiber data for the cover crop residues (Table 2) were

correlated to net N release from the residues at each time interval of the incubation. Our results

demonstrated that residue N concentration and C:N ratio were well correlated to net N release

from rye-hairy vetch cover crops for the first 70 days of the incubation (Table 4). Many studies

have confirmed that the timing and rate of N release from plant residues incorporated into soil

are primarily related to the initial N concentration and C:N ratio of the residues (Vigil and

Kissel; 1991; Constantinides and Fownes, 1994; Trinsoutrot et al., 2000; Justes et al., 2009). But

some have demonstrated that C:N ratio is only correlated with N mineralization over certain

stages of decomposition because residue biochemical composition changes as residues

decompose and release nutrients (Heal et al., 1997). Others have demonstrated that it is neither

96

an adequate measure of residue quality (Ruffo and Bollero, 2003), nor a useful parameter for

measuring N mineralization dynamics (Vigil and Kissel, 1995).

The relationship between N mineralization and residue fiber content has been used to

improve models that predict N release from residues (Vigil and Kissel, 1991; Kumar and Goh,

2003). In particular, the amount of lignin and other recalcitrant C in plant residues may slow N

release from plant materials (Vigil and Kissel, 1991; Quemada and Cabrera, 1995; Hadas et al.,

2004). But the research has demonstrated that no single residue quality criterion has been

correlated to N release across a range of plant types (Handayanto et al., 1997). Special emphasis

has been placed on linking N mineralization to cellulose, hemicellulose, and lignin contents,

which are insoluble compounds of the cell wall (Wagger et al., 1998). These components have

slower rates of decomposition than soluble compounds (Kumar and Goh, 2000), which may have

a negative effect on N mineralization (Muller et al., 1988).

In this study, residue fiber content was reported as NDF, ADF, and ADL, which is the

standard way of reporting fiber that was determined using the Van Soest et al. (1991) procedure.

We found that NDF was well negatively correlated with net N mineralization through the first 70

days of the incubation and ADF between days 21 and 50 (Table 4). These results are in

agreement with the literature, which has shown that NDF and ADF contents are negatively

correlated to residue decomposition (Stubbs et al., 2009) and N availability (Ruffo and Bollero,

2003). In one study, the inclusion of hemicellulose content (a component of NDF) bolstered the

Pearson correlation coefficient for a model of net N mineralization from plant residues (Johnson

et al., 2007). However, Ruffo and Bollero (2003) suggested that NDF and ADF fractions be

considered in combination with neutral and acid detergent soluble N as a measure N availability,

97

which was shown to be a more critical factoring in N release than total N concentration or C:N

ratio.

Residue lignin content has been negatively correlated with net N mineralization in a

range of studies (Vigil and Kissel, 1991; Constantinides and Fownes, 1994; Kumar and Goh,

2003). But ADL was positively correlated to N release through the first 106 days of this study.

We found a strong correlation between ADL and total N concentration of cover crop residues (R2

= 0.90, P < 0.0001), which suggests that this relationship was likely incidental. Although ADL

was higher in hairy vetch (63 g kg-1

) than rye (21 g kg-1

), the structural linkages in lignin have

been shown to differ between legumes and cereals, with the lignin in cereal residues being more

resistant to decomposition than legumes (Gordon et al., 1983). Additionally, lignin typically

affects residue mineralization in the late stages of decomposition (McClaugherty and Berg,

1987), which is in contrast with our results. Therefore, the relationship between ADL and net N

mineralization in this study is not a meaningful one.

Nitrification potentials

Nitrification potentials were significantly higher for treatments receiving cover crop

residue than control soil (Figure 5). Treatments with feather meal fertilizer in combination with

cover crop residues had greater nitrification potentials than cover crop treatments without feather

meal. For treatments without feather meal, r50v50 had the highest nitrification potential and pure

rye the lowest (5.78 vs. 4.99 μg N g-1

soil per day). Nitrification potentials for pure vetch and

r75v25 without feather meal were not significantly different. Regardless of cover crop treatment,

nitrification potentials were consistently greater when feather meal was applied than without

(5.93 vs. 5.24 μg N g-1

soil per day). Mean nitrification potentials for cover crop treatments over

the 70 day laboratory mineralization study were well correlated with total (NH4+ +

NO3

-)-N

98

accumulated from residues and soil over that time (R2 = 0.975, P = 0.05). But mean nitrification

potentials for feather meal-cover crop treatments over that time were not significantly correlated

with total inorganic N accumulation. Similarity in nitrification potentials across cover crop

treatments indicates that substrate availability is driver in nitrifier response to cover crop

incorporation.

Change in nitrification potential over time is shown in Figure 6. Nitrification potential for

all treatments increased with time until a maximum rate was reached. For treatments not

receiving feather meal, the maximum rate was achieved on day 28 (6.94 μg N g-1

soil per day).

Treatments containing feather meal achieved highest nitrification potential on day 50 (8.81 μg N

g-1

soil per day). By day 70, nitrification potentials had decreased to rates similar to or below

those measured on day 7. Therefore, nitrification potentials were not measured after that date.

The increase in nitrification potential over the first 28 d after cover crop incorporation is likely

due to N release from cover crop residues. The return of nitrification potentials to rates below

those measured on day 7 indicate that the temporary increase in nitrification potential is not

likely to contribute to potential nitrate leaching because highest rates are achieved at the time of

high crop N uptake.

99

Figure 1. Cumulative N release from cover crops residues and soil over 157 d incubation

(P < 0.05)

Figure 2. Cumulative net N release from cover crop residues (soil (NH4++NO3

-)-N has been

subtracted) over 157 d incubation (P < 0.05)

0

50

100

150

200

0 50 100 150

(NH

4+

+ N

O3- )

-N, k

g h

a-1

Time, days

VetchR50V50R75V25RyeSoil

0

20

40

60

80

100

120

0 50 100 150

(NH

4++

NO

3- )-N

, kg

ha-1

Time, days

Vetch

50:50 Rye-Vetch

75:25 Rye-Vetch

Rye

100

Figure 3. Cumulative N release from cover crops and feather meal residues and soil over 157 d

incubation (P < 0.05)

Figure 4. Cumulative net N release from feather meal (FM) and cover crop residues (soil

(NH4++NO3

-)-N has been subtracted) over 157 d incubation (P < 0.05)

0

50

100

150

200

0 50 100 150

(NH

4+

+ N

O3- )

-N, k

g h

a-1

Time, days

FM & Vetch

FM & R50V50

FM & R75V25

FM & Rye

FM

0

20

40

60

80

100

120

140

0 50 100 150

(NH

4++

NO

3- )-N

, kg

ha-1

Time, days

FM & VetchFM & 50:50 Rye-VetchFM & 75:25 Rye-VetchFM & Rye

FM

101

Figure 5. The effect of cover crop residue and feather meal (FM) on mean nitrification potentials

over 70 day laboratory study (P < 0.05)

1Rye-Vetch (RV)

Figure 6. The effect of time and feather meal (FM) on nitrification potentials (rates averaged

across all cover crop treatments) (P < 0.05).

0

1

2

3

4

5

6

7

8

50:50 RV 75:25 RV Rye Vetch Soil

μg

N g

-1so

il d

-1

Cover crop residue

No-FM

FM

1

0

1

2

3

4

5

6

7

8

9

10

0 7 14 21 28 50 70

μg

N g

-1so

il d

-1

Time, days

No-FM

FM

102

4. CONCLUSIONS

Rye-hairy vetch cover crop residues of relatively high quality can release significant

amounts of N if sufficient biomass yield is accomplished. Our results indicate that a biculture of

cereal and legume cover crops can enhance the N concentration of the mixture compared to

either component alone, which has implications for N release dynamics. A 50:50 rye-hairy vetch

blend released a similar percent of residue N compared to pure hairy vetch over the course of a

70 day incubation. The 50:50 rye-hairy vetch blend may supply greater amounts of (NH4++NO3

-

)-N to subsequent cash crops than hairy vetch due to higher biomass and N content. A 75:25 rye-

hairy vetch blend released a significantly lower portion of the total residue N compared to hairy

vetch but comparable total (NH4++NO3

-)-N because of higher biomass yield. Although hairy

vetch and the75:25 rye-hairy vetch blend released similar amounts of N over 70 incubation days,

the initial rate of N release was nearly 3-fold greater for the hairy vetch treatment. The slower

rate of N release from the 75:25 rye-hairy vetch blend may result in N release that is better timed

with crop N uptake and therefore increase crop N use efficiency. When cover crops were

combined with organic feather meal fertilizer, the combined net N release was less than the sum

of the individual components. The cause of the negative interaction was not well understood and

therefore deserves further research.

Residue quality was relatively well correlated to N release from cover crop residues, and

therefore may be used to predict N release from rye-hairy vetch cover crop blends. In particular,

residue N concentration and C:N ratio were well correlated to net N mineralization over the first

70 incubation days. Neutral detergent fiber and ADF were negatively correlated to net N

mineralization during the first 70 days and between days 21 and 50, respectively. Therefore,

inclusion of these fractions in a model to predict N release could increase the accuracy of the

103

model. The recent development of the near-infrared spectroscopy method to determine the fiber

content of plant residues offers farmers an inexpensive alternative to the time-consuming, wet

chemistry methods currently used, which makes the practical application of these findings

relevant.

Nitrification potentials for cover crop treatments were significantly higher than bare soil

over the first 70 incubation days. Rates averaged across cover crop treatments increased until day

28 and returned to rates below those measured on day 7 by day 70. Our results indicate that the

increase in nitrification potentials over the first 28 days is likely due to increased (NH4++NO3

-)-N

and that nitrification potentials were not largely different between cover crop treatments. The

decrease in nitrification potentials to rates below those measured on day 7 by day 70

demonstrates that higher nitrification potentials are not likely to contribute to nitrate leaching

because the highest rates are timed with crop N uptake.

104

5. LITERATURE CITED

Ambus, P., and E.S. Jensen. 1997. Nitrogen mineralization and denitrification as influenced by

crop residue particle size. Plant and Soil 197:261-270.

Angers, D.A., and S. Recous. 1997. Decomposition of wheat straw and rye residues as affected

by particle size. Plant and Soil 189:197-203.

Bayrakli, F., and S. Gezgin. 1996. Controlling ammonia volatilization from urea surface applied

to sugar beet on a calcareous soil. Communications in Soil Science and Plant Analysis

27:2443-2451.



188.

Cabrera, M.L., D.E. Kissel, and M.F. Vigil. 2005. Nitrogen mineralization from organic

residues: Research opportunities. Journal of Environmental Quality 34:75-79.

Chantigny, M.H., D. Prevost, D.A. Angers, L.P. Vezina, and F.P. Chalifour. 1996. Microbial

biomass and N transformations in two soils cropped with annual and perennial species.

Biology and Fertility of Soils 21:239-244.






Constantinides, M., and J.H. Fownes. 1994. Nitrogen mineralization from leaves and litter of

tropical plants - relationship to nitrogen, lignin and soluble polyphenol concentrations.

Soil Biology & Biochemistry 26:49-55.

Coyne, M.S. 2008. Biological denitrification. p. 201-254. In J.S. Schepers and W.R. Raun (eds.).

Nitrogen in Agricultural Systems. American Society of Agronomy, Madison, WI.

Curtin D. and Campbell C.A. 2008. Mineralizable nitrogen. pp. 599-606. In M.R. Carter and

E.M. Gregorich (eds.). Soil Sampling and Methods of Analysis. CRP Press, Boca Raton,

FL.

105

Deng, S.B., J.M. Moore, and M.A. Tabatabai. 2000. Characterization of active nitrogen pools in

soils under different cropping systems. Biology and Fertility of Soils 32:302-309.

Elgersma, A., H. Schlepers, and M. Nassiri. 2000. Interactions between perennial ryegrass

(Lolium perenne L.) and white clover (Trifolium repens L.) under contrasting nitrogen

availability: productivity, seasonal patterns of species composition, N-2 fixation, N

transfer and N recovery. Plant and Soil 221:281-299.

Elliot, E.T., J.W. Heil, E.F.Kelly, and H.C. Monger. 1999. Soil structural and other physical

properties. p. 74-85. In G. P. Robertson, C. S. Bledsoe et al. (eds.). Standard Soil

Methods for Long-Term Ecological Research, Oxford University Press, New York.

Evans, J., A.M. McNeill, M.J. Unkovich, N.A. Fettell, and D.P. Heenan. 2001. Net nitrogen

balances for cool-season grain legume crops and contributions to wheat nitrogen uptake:

a review. Australian Journal of Experimental Agriculture 41:347-359.

Fageria, N.K. 2007. Green manuring in crop production. Journal of Plant Nutrition 30:691-719.

Fortuna, A., R.R. Harwood, G.P. Robertson, J.W. Fisk, and E.A. Paul. 2003. Seasonal changes in

nitrification potential associated with application of N fertilizer and compost in maize

systems of southwest Michigan. Agriculture Ecosystems & Environment 97:285-293.

Fox, R.H., W.P. Piekielek, and K.E. Macneal. 1996. Estimating ammonia volatilization losses

from urea fertilizers using a simplified micrometeorological sampler. Soil Science


Gaskell, M. and R. Smith. 2007. Nitrogen sources for organic vegetable crops. HortTechnology

17:431-441.

Gaskell, M., R. Smith, J. Mitchell, S.T. Koike, C.Fouche, T. Hartz, W. Horwath and L. Jackson.

2006. Soil fertility management for organic crops. University of California Division of

Agriculture and Natural Resources. Publication 7249.



Gentile, R., B. Vanlauwe, P. Chivenge, and J. Six. 2008. Interactive effects from combining

fertilizer and organic residue inputs on nitrogen transformations. Soil Biology &

Biochemistry 40:2375-2384.

106

Gilmour, J.T., A. Mauromoustakos, P.M. Gale, and R.J. Norman. 1998. Kinetics of crop residue

decomposition: Variability among crops and years. Soil Science Society of America

Journal 62:750-755.

Gordon, A.H., J.A. Lomax, and A. Chesson. 1983. Glycosidic linkages of legume, grass and

cereal straw cell walls before and after extensive degradation by rumen microorganisms.

Journal of the Science of Food and Agriculture 34:1341-1350.

Granatstein, D., A. Stone, C. Williams, C. Miles, D. Bezdicek, and C. Perillo. 2010. Organic

Farming Research in the Pacific Northwest. 14 Aug 2010.

<http://www.sarep.ucdavis.edu/organic/complianceguide/intro3.pdf>.

Hadas, A. and L. Kautsky. 1994. Feather meal, a semi-slow release nitrogen fertilizer for organic

farming. Fertilizer Research 38: 165-170.

Hadas, A., L. Kautsky, M. Goek, and E.E. Kara. 2004. Rates of decomposition of plant residues

and available nitrogen in soil, related to residue composition through simulation of

carbon and nitrogen turnover. Soil Biology & Biochemistry 36:255-266.

Handayanto E., G. Cadisch, and K.E. Giller. Regulating N Mineralziation from Plant Residues

by Manipulation of Quality. p. 175-185. In Cadisch G. and K.E. Giller (eds.), Driven by

Nature Plant Litter Quality and Decomposition. Cab International, Wallingford, UK.

Hardarson, G., and C. Atkins. 2003. Optimising biological N-2 fixation by legumes in farming

systems. Plant and Soil 252:41-54.

Hargrove, W.L. 1988. Evaluation of ammonia volatilization in the field. Journal of Product

1:104-111.

Hart, S.C., J.M. Stark, E.A. Davidson, and M.K. Firestone. 1994. Nitrogen mineralization,

immobilization, and nitrification. p. 1011-1018. In Weaver, R.W. and J.S. Angle et al.

(eds.), Methods of Soil Analysis. Part 2. Microbiology and Biochemical Properties.

SSSA Book Series, No. 5. SSSA, Madison, WI.

Hartz, T.K., and P.R. Johnstone. 2006. Nitrogen availability from high-nitrogen-containing

organic fertilizers. Horttechnology 16:39-42.

Heal, O.W., F.M. Anderson, and M.F. Swift. 1997. Plant litter quality and decomposition: an

historical overview. p. 3-32. In Cadisch, G. and K.E. Giller, Driven by Nature Plant Litter

Quality and Decomposition. Cab International, Wallingford, UK.

107




Johnson, J.M.F., N.W. Barbour, and S.L. Weyers. 2007. Chemical composition of crop biomass

impacts its decomposition. Soil Science Society of America Journal 71:155-162.

Justes, E., B. Mary, and B. Nicolardot. 2009. Quantifying and modelling C and N mineralization

kinetics of catch crop residues in soil: parameterization of the residue decomposition

module of STICS model for mature and non mature residues. Plant and Soil 325:171-185.

Kaye, J.P., and S.C. Hart. 1997. Competition for nitrogen between plants and soil

microorganisms. Trends in Ecology & Evolution 12:139-143.

Kumar, K., and K.M. Goh. 2003. Nitrogen release from crop residues and organic amendments

as affected by biochemical composition. Communications in Soil Science and Plant

Analysis 34:2441-2460.



353.



Lawson, 2010. Evaluating fall cover crop blends for biomass production, residue quality, and

weed suppression. M.S. Thesis. Washington State University, Pullman, WA.

McClaugherty, C., and B. Berg. 1987. Cellulose, lignin and nitrogen concentrations as rate

regulating factors in late stages of forest litter decomposition. Pedobiologia 30:101-112.

McKenney, D.J., S.W. Wang, C.F. Drury, and W.I. Findlay. 1995. Denitrification,

immobilization, and mineralization in nitrate limited and nonlimited residue-amended

soil. Soil Science Society of America Journal 59:118-124.

McSwiney, C.P., S.S. Snapp, and L.E. Gentry. 2010. Use of N immobilization to tighten the N

cycle in conventional agroecosystems. Ecological Applications 20:648-662.

Muller, M.M., V.Sundman, O. Soininvaara, and A. Merilainen. 1988. Effect of chemical

composition on the release of nitrogen from agricutlural paltn materials during

decomposing in soil under field conditions. Biology and Fertility of Soils 6:78-83.

108

Mulvaney R.L. 1996. Nitrogen – Inorganic forms. In D.L. Sparks et al. eds. Methods of Soil

Analysis. Part 3. SSSA Book Ser. 5. ASA and SSSA, Madison, WI.


immobilization. In J.S. Schepers and W.R. Raun (eds.). Nitrogen in Agricultural Systems.


Nakhone, L.N. and M.A. Tabatabai. 2008. Nitrogen mineralization of leguminous crops in soils.

Journal of Plant Nutrition and Soil Science 171:231-241.

Ndakidemi, P.A. 2006. Manipulating legume/cereal mixtures to optimize the above and below

ground interactions in the traditional African cropping systems. African Journal of

Biotechnology 5:2526-2533.

Nourbakhsh, F., and R.P. Dick. 2005. Net nitrogen mineralization or immobilization potential in

a residue-amended calcareous soil. Arid Land Research and Management 19:299-306.




Palm, C.A., and A.P. Rowland. (1997) A minimum dataset for characterization of plant quality

for decomposition. p. 379-392. In Cadisch, G. and K.E. Giller (eds.), Driven by Nature:

Plant Litter Quality and Decomposition. CAB International Publishing, Wallingford, UK.



Ping, J.L., E. Bremer, and H.H. Janzen. 2000. Foliar uptake of volatilized ammonia from

surface-applied urea by spring wheat. Communications in Soil Science and Plant

Analysis 31:165-172.

Quemada, M., and M.L. Cabrera. 1995. Carbon and nitrogen mineralized from leaves and stems

of 4 cover crops. Soil Science Society of America Journal 59:471-477.



Recous, S., C. Aita, and B. Mary. 1999. In situ changes in gross N transformations in bare soil

after addition of straw. Soil Biology & Biochemistry 31:119-133.

109

Ribeiro, H.M., D. Fangueiro, F. Alves, R. Ventura, D. Coelho, E. Vasconcelos, C. Cunha-Queda,

J. Coutinho, and F. Cabral. 2010. Nitrogen mineralization from an organically managed

soil and nitrogen accumulation in lettuce. Journal of Plant Nutrition and Soil Science

173:260-267.

Robertson, G.P. 1997. Nitrogen use efficiency in row crop agriculture: crop nitrogen use and soil

nitrogen loss. pp. 347-365 in L. Jackson (ed.). Ecology in Agriculture, Academic Press,

New York.

Robertson, G. P., J. M. Blair, P. M. Groffman, D. Harris, E. Holland, K. Nadelhoffer, and D.

Wedin. 1999. Soil carbon and nitrogen availability: nitrogen mineralization, nitrification,

and soil respiration potentials. p. 258-271. In G. P. Robertson, C. S. Bledsoe et al. (eds.).

Standard Soil Methods for Long-Term Ecological Research, Oxford University Press,

New York.

Rochette, P., J.D. MacDonald, D.A. Angers, M.H. Chantigny, M.O. Gasser, and N. Bertrand.

2009. Banding of urea increased ammonia volatilization in a dry acidic soil. Journal of

Environmental Quality 38:1383-1390.

Ruffo, M.L., and G.A. Bollero. 2003. Residue decomposition and prediction of carbon and





Senbayram, M., R.R. Chen, K.H. Muhling, and K. Dittert. 2009. Contribution of nitrification and

denitrification to nitrous oxide emissions from soils after application of biogas waste and

other fertilizers. Rapid Communications in Mass Spectrometry 23:2489-2498.

Sikora, L.J., and N.K. Enkiri. 2000. Efficiency of compost-fertilizer blends compared with

fertilizer alone. Soil Science 165:444-451.

Stamatiadis, S., J.W. Doran, and T. Kettler. 1999. Field and laboratory evaluation of soil quality

changes resulting from injection of liquid sewage sludge. Applied Soil Ecology 12:263-

272.

Starovoytov, A., R.S. Gallagher, K.L. Jacobsen, J.P. Kaye, and B. Bradley. 2010. Management

of Small Grain Residues to Retain Legume-Derived Nitrogen in Corn Cropping Systems.


110

Stubbs, T.L., A.C. Kennedy, and A.M. Fortuna. 2010. Using NIRS To Predict Fiber and Nutrient

Content of Dryland Cereal Cultivars. Journal of Agricultural and Food Chemistry 58:398-

403.

Trinsoutrot, I., S. Recous, B. Bentz, M. Lineres, D. Cheneby, and B. Nicolardot. 2000.

Biochemical quality of crop residues and carbon and nitrogen mineralization kinetics

under nonlimiting nitrogen conditions. Soil Science Society of America Journal 64:918-

926.

Tu, C., F.J. Louws, N.G. Creamer, J.P. Mueller, C. Brownie, K. Fager, M. Bell, and S. Hu. 2006.

Responses of soil microbial biomass and N availability to transition strategies from

conventional to organic farming systems. Agriculture Ecosystems & Environment

113:206-215.



Van Soest, P.J., J.B. Robertson, and B.A. Lewis. 1991. Methods for dietary fiber, neutral

detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. Journal of

Dairy Science 74:3583-3597.



Vigil, M.F., and D.E. Kissel. 1995. Rate of nitrogen mineralized from incorporated crop residues

as influenced by temperature. Soil Science Society of America Journal 59:1636-1644.

Wagger, M.G., M.L. Cabrera, and N.N. Rannels. 1998. Nitrogen and carbon cycling in relation

to cover crop residue quality. Journal of Soil and Water Conservation 53:214-218.

Wang, W.J., R.C. Dalal, P.W. Moody, and C.J. Smith. 2003. Relationships of soil respiration to

microbial biomass, substrate availability and clay content. Soil Biology & Biochemistry

35:273-284.

Zagal, E., and J. Persson. 1994. Immobilization and remineralization of nitrate during glucose

decomposition at 4 rates of nitrogen addition. Soil Biology & Biochemistry 26:1313-

1321.

111

CHAPTER 4

Response of organic sweet corn to a fall planted 50:50 rye-hairy vetch cover crop blend

1. INTRODUCTION

Organic cropping systems are often limited by the timely supply of plant available N

(Pang and Letey, 2000; Berry et al., 2002). In the Puget Sound region of Western Washington,

organic farmers have expressed concerns over yield reduction due to N deficiency (Cogger,

personal communication). Because organic production prohibits the use of mineral fertilizers, a

variety of organic materials are used to supply N to crops, including animal manure, compost,

cover crops, and specialty products (Cogger, 2000; Watson et al., 2002; Gaskell, 2006).

Specialty organic products are expensive while compost and manures are bulky and costly to

import and apply (Gaskell and Smith, 2007). Legumes and cereal-legume cover crop blends are

often used in rotation as a source of short-term N fertility (Rannels and Wagger, 1996; Burket et

al., 1997; Griffin et al., 2000; Sarrantonio and Malloy, 2003; Tonitto et al., 2006; Sainju and

Singh, 2008; Teasdale et al., 2008). But it is difficult to predict N availability to subsequent crops

because N mineralization is controlled by many factors, including residue composition (Vigil

and Kissel, 1991; Rannels and Wagger, 1996; Kuo and Sainju, 1998; Jensen et al., 2005) and

environmental parameters such as temperature and soil moisture (Quemada and Cabrera, 1997;

Ruffo and Bolero, 2003). Regional information on cover crop N supply to subsequent cash crops

is needed in organic cropping systems.

Mixed cereal-legume cover crop blends are considered to be a better management option

than growing cover crops in monoculture because it can reduce the risk of stand failure (Creamer

et al., 1997; Gaskell, 2006), enhance biomass productivity (Sainju et al., 2005), and prevent N

immobilization after spring incorporation (Rannels and Wagger, 1996; Kuo and Sainju, 1998).

112

Cover crop blends that include both cereal and legume species synchronize plant available N

with subsequent cash crop needs. Cereals are capable of taking up residual soil NO3- after fall

harvest to minimize leaching (BrandiDohrn et al., 1997; Moller and Reents, 2009, Thorup-

Kristensen and Dresboll, 2010). In contrast, legumes fix atmospheric N, which increases residue

N concentration, and therefore represents an N input into the system (Clark et al., 1997). In some

cases, the N concentration of cereal in mixture with legume is higher than when it is grown alone

(Rannels and Wagger, 1996; Burket et al., 1997). While monocropped cereals such as rye can

immobilize N following incorporation, cereal-legume bicultures can supply N to subsequent

crops because of increased residue N concentration (Kuo and Sainju, 1998).

Past research at the WSU Research and Extension Center in Puyallup, WA demonstrates

that rye-hairy vetch cover crops blends are well suited for the climate and cropping systems of

the maritime Pacific Northwest (Kuo et al., 1997; Kuo and Jellum, 2000; Cogger et al., 2008).

Cereal rye establishes rapidly when planted by early October, and it is an effective N scavenger

(Kuo and Jellum 2000; Thorup-Kirstensen et al., 2003; Feaga et al., 2010). Although hairy vetch

is characterized by slow fall growth and low soil cover (Holderbaum et al., 1990), it has been

found to have high winter survival in northern temperate climates (Teasdale et al., 2004;

Brandsaeter et al., 2007) and accumulates biomass and fixes N rapidly in the spring as soil

temperatures increase (Holderbaum et al., 1990; Kuo and Jellum, 2000). Research has

demonstrated that a 50:50 (seeding ratio) rye-hairy vetch cover crop blend planted by early

October and killed in late April optimized N accumulation and residue quality in this region

(Lawson, 2010a).

Cover crops influence subsequent crop yield primarily via their affect on N availability

(Torbert et al., 1996; Vaughan and Evanylo, 1998; Kuo and Jellum, 2000; Cherr et al., 2006).

113

Crop yields can be maintained by replacing or supplementing N fertilizer application with winter

legume or cereal-legume cover crop residues (Sainju et al., 2005; Fortuna et al., 2008). But there

must be sufficient biomass and N accumulation, and timely N mineralization for cover crops to

supply sufficient N to crops (Griffin et al., 2000; Teasdale et al., 2008). Several studies have

examined sweet corn performance after legume and mixed cereal-legume cover crops because of

its marked response to N fertility. Some have shown that it can produce yields as good as N-

fertilizer treatments when grown in rotation with hairy vetch (Griffin et al., 2000; Cline and

Silvernail, 2002; Carrera et al., 2004). But often crop yield potential may be optimized when

cover crops are combined with low supplemental N fertilizer rates. Schellenberg et al. (2009)

recommended that legume-based cover crops systems be combined with modest sidedress N

fertilizer to maximize organic broccoli yield.

Lack of synchrony between N supply from cover crop residue and crop N uptake may

influence efficiency of crop N use (Teasdale et al., 2008). But this depends on timing of field

events and types of crops grown. For instance, a delay in spring cover crop desiccation may

result in a late flush of N release, which is better timed with crop N uptake (Cline and Silvernail,

2001). There are mixed results for crop N use efficiency of cover crop-derived N (Sarranotonio

and Malloy, 2003; Haas et al., 2007; Teasdale et al., 2008). In some cases crop N use efficiency

of cover crop-derived N is low but overall efficiency is high because of high N recovery in soil

(Seo et al., 2006). Pang and Letey (2000) suggest that crops with high maximum uptake rates

have low utilization efficiencies because it is difficult to meet peak N crop demand with

relatively slow release materials. The research focus needs to shift from maximum N supply to

more timely N release.

114

A laboratory incubation study was previously conducted to measure N release from rye-

hairy vetch cover crop blends under controlled environmental conditions (Lawson, 2010b). This

field study was designed to determine N release under field conditions from one rye-hairy vetch

cover crop blend treatment, which was included in the incubation study. Because the rate of N

release from organic residues is influenced by soil moisture and temperature, it is necessary to

test the legitimacy of the N release patterns observed in the incubation under field conditions. A

fertility trial was devised with cover crops and organic fertilizer, and sweet corn yield and N

uptake were measured. The objective was to: (i) evaluate the response of organically grown

sweet corn to a 50:50 rye-hairy vetch cover crop blend and an organic feather meal fertility

regime, (ii) assess sweet corn N use efficiency from a a 50:50 rye-hairy vetch cover crop blend

planted over two fall dates and in combination with feather meal fertilizer, and (iii) use sweet

corn yield and N recovery data to validate results from a related N mineralization laboratory

incubation study.


Site description

The Cover Crops-2 field plots, located at Washington State University Puyallup Research

and Extension Center, Puyallup, WA, were established in September 2007. This ground has not

been certified organic, but has been under organic management practices since 2004. The soil is

classified as Puyallup fine sandy loam (coarse-loamy over sandy or sandy-skeletal, isotic over

mixed, mesic Vitrandic Haploxerolls). The average annual precipitation and temperature is 102.9

cm and 10.9°C, respectively, with mild, dry summers and cool, wet winters. Approximately 75%

of precipitation occurs between October and March.

Experimental design

115

This study was two years in duration starting in September 2008. The experiment was

designed to evaluate the N contribution of a 50:50 rye-hairy vetch blend to organically grown

sweet corn. Additionally, results from this study were used to validate a related N incubation

study. Treatments include two fall planting dates, a no-cover crop control, and four N fertilizer

rates, including one zero-N check. The study was arranged in a randomized complete block split

plot design with cover crop planting date (early, late, or no cover) as the main plots and N-

fertilizer rate as the split. Main plots measure 24.4 x 6.1 m, split plots measure 6.1 x 6.1 m, and

there are four replications. Early and late planting dates were mid-September and early-October

each year and the 50:50 rye-hairy vetch treatments were a blend by seed weight ratio. The N

source is feather meal, a relatively fast release commercially available organic material. It has

12% N and approximately 75% is available over a growing season, according to the

manufacturer (California Organic Fertilizers, Inc., Fresno, CA). A summer crop of organically

grown sweet corn was planted in June and harvested at maturity. After harvest, sweet corn stover

was flail mowed and incorporated with a rotary spader, and the plots were prepared for cover

crops. Dates of sampling and field activities are listed in Table 1.

Management

Cover crops were planted in the fall using a 3.1 m John Deere grain drill and chopped and

incorporated in the spring using a rotary spader. Seeding rate for the rye-hairy vetch blend was

112 kg ha-1

; all vetch seed was inoculated with the appropriate rhizobia bacteria to ensure

nitrogen fixation. Field plots were fertilized by hand broadcasting feather meal at four rates prior

to planting: 0, 56, 112, and 168 kg N ha-1

. „Golden jubilee‟ sweet corn was seeded with a Cole

Planter on 1.5 m beds with 0.76 m between-row and 0.1-0.15 m in-row spacing at rate of 86,100

seeds ha-1

. Each plot is 8 rows wide. Weeds were controlled as necessary via cultivation (basket-

116

weeder, tine-weeder, and sweeps) and hilling. Irrigation was supplied as needed beginning in

early July via sprinklers on 2.4 m risers. Approximately 1 inch of water was applied every 10

days through harvest.

Field measurements

In late April, plots were harvested for above ground biomass by harvesting a 6.1 x 0.91 m

swath approximately 5 cm above soil surface with a flail mower and fresh weights recorded. A

subsample of cover crop residue from each plot was collected for total C and N and moisture

content determined. The remaining residue was returned to the plots. Three additional

subsamples were collected from representative 0.25 m2 quadrats in each plot, and proportions of

rye, vetch, and weeds were determined (Sarrantonio, 1991).

Soils were sampled for total NO3--N analysis on three occasions: after cover crop

incorporation, at the time of pre-sidedress soil nitrate testing (sweet corn approximately 0.15 m

tall), and post-harvest (prior to stover incorporation). Soil samples were collected to a depth of

30 cm; 10 samples were taken in each plot with a 2.5 cm diameter tube sampler and composited.

Soil was immediately dried at 30°C to stop microbial activity and soil moisture was determined.

Dried soil was passed through a 2-mm diameter screen opening. Nitrate-N was extracted from 10

g soil samples with 100 mL of 2M KCl. Samples were shaken on a reciprocal shaker for 1 h and

then filtered through No. 42 Whatman filters. Aliquots were run on an automated, continuous

flow QuikChem 8000 Injection Flow Analysis System (Hach Instruments, Loveland, CO).

Nitrate-N was determined using the cadmium reduction method (Gavlak et al., 1994).

In-season N status of the sweet corn crop was measured at silking on ear leaves. We

measured chlorophyll content using a chroma meter (CR-400, Konica Minolta Holding, Inc.).

Leaf chlorophyll concentration has been correlated to leaf N concentration (Schepers et al.,

117

1992). Therefore, a non-destructive measure of leaf chlorophyll concentration, or leaf greenness,

can be used as a measure of crop N status (Varvel et al., 1997). Research has demonstrated that a

chroma meter can accurately measure chlorophyll content of plant leaves (Madeira et al., 2003;

Leon et al., 2007). Amarante et al. (2008) found that the ho/(LxC) ratio was best correlated to

chlorophyll content. Readings were taken at silking using the ear leaf from a subsample of 10

leaves per plot. At the same time, ear leaves were pulled for total C and N analysis. Ear leaves

from 10 plants from the middle four rows of each plot were removed, dried at 55°C, ground to

pass through 2-mm screen opening, and moisture content determined.

Sweet corn population was assessed at harvest by counting the number of plants in a 6.1

m length of an inner row. One ear of sweet corn per plant was harvested within a 6.1 m section

of a middle row in each plot and fresh weight recorded. Total aboveground biomass of sweet

corn plants in a 6.1 m section of middle row was removed and fresh weight recorded. A

subsample of ten plants was chopped, dried at 55°C, and ground to pass through a 2-mm screen

opening for total C and N analysis. Water content of total biomass was determined and used to

calculate dry weight. All plant residues (cover crop, sweet corn ear leaves, and sweet corn silage)

were analyzed for total C and N by dry combustion with a TruSpec CN Carbon/Nitrogen

Determinator (Leco, St. Joseph, MI).

Data analysis

Analysis of variance was conducted on cover crop biomass, portion of rye and hairy

vetch in total biomass, and N accumulation using the SAS Mixed procedure (SAS 9.2, SAS

Institute, Cary, NC, 2008). For a randomized complete block design, planting date and feather

meal were fixed effects and replication was a random effect. Sweet corn in-season N status, ear

and biomass yield, and N uptake were analyzed in the same procedure. Cover crop planting date,

118

feather meal, and sample date were fixed effects and replication a random effect in the analysis

of variance of soil NO3--N levels, done using a mixed model procedure. Sweet corn N uptake

was fitted to a linear regression using the SAS GLM procedure (SAS 9.2, SAS Institute, Cary,

NC, 2008). The significance of cover crop treatment effect from the above procedure was the

primary consideration for development of linear regression equations.

Apparent N recovery of cover crop derived N in sweet corn was calculated according to

the method used by Sullivan et al., (2002). Equation [1] estimates the increase in sweet corn N

uptake that is attributed to cover crops:

[1] Apparent N recovery (ANR, kg ha-1

) = A - B

where A is the y-intercept for cover crop treatment and B is the y-intercept for the no cover crop

control treatment. We estimated the reduction in the requirement of feather meal fertilizer N

attributed to cover crops using equation [2]:

[2] Reduction in fertilizer N requirement = ANR/ef

where ANR is apparent N recovery from equation [1] and ef is fertilizer N uptake efficiency,

estimated from the slope of the line for sweet corn N uptake vs. feather meal available N.

Nitrogen use efficiency was calculated by dividing sweet corn dry matter by total N supply. We

estimated the N contribution from soil as total N uptake in sweet corn in the zero-feather meal

control plot.

119

Table 1. Dates of sampling and field activities

2008-09

Early Planting 17 Sep

Late Planting 2 Oct

Harvest 27 Apr

Field chopped 5 May

Residue incorporated 7 May

Soil sampled for NO3-N 2 Jun

Fertilized 2 Jun

Corn planted 4 Jun

Soil sampled for NO3-N 26 Jun

Ear leaf sampled 4 Aug

Corn Harvest 27 Aug

Soil sampled for NO3-N 9 Sep

Residue incorporated 10 Sep

Table 2. Cover crop dry matter production, nitrogen (N) concentration, total N content and

dry matter composition in 2009

Dry matter N conc. Total N C:N Dry matter composition

Planting Date kg ha-1

mg kg-1

kg ha-1

Ratio Rye, % Vetch, %

Early 3121 a1 22 c 70 a 19 a 76 b 21 a

Late 1718 b 23 b 39 b 18 a 84 a 13 b

None 30 c 29 a 1 c 15 b 1Values followed by same letter within column are not significantly different (P < 0.05)

120

Table 4. Degree day elapsed between cover crop incorporation and soil

sampling

Field Trial Laboratory Incubation

Sample date Days

Degree

Days

Degree

Days1 Days

2-Jun-09 26 249 14 288

26-Jun-09 50 546 28 576

9-Sep-09 124 1579 70 1439 1Degree days based on base temperature of 4.4˚C

Table 3. The effect of cover crop and sample

date on soil nitrate (NO3-)-N concentration.

Total nitrogen (N) content of early and late

cover crops was 70 and 39 kg N ha-1

Soil (NO3-)-N

Planting Date Date kg ha-1

Early June 2 29 c1

Early June 26 67 a

Early Sept 9 10 d

Late June 2 27 c

Late June 26 59 b

Late Sept 9 7 d

None June 2 25 c

None June 26 52 b

None Sept 9 9 d

1Values followed by same letter not different

(P < 0.01)

121

Table 5. The effect of cover crop and feather

meal on post-harvest soil (NO3-)-N

Feather meal

available N Soil (NO3-)-N

Planting Date kg ha-1

kg ha-1

Early 0 10 c1

Early 56 18 c

Early 112 28 bc

Early 168 59 a

Late 0 7 c

Late 56 9 c

Late 112 27 bc

Late 168 29 bc

None 0 9 c

None 56 9 c

None 112 14 c

None 168 36 b

1Values followed by same letter not significantly

different (P < 0.05)

Table 6. Sweet corn fresh ear yield and dry

matter as affected by feather meal

Feather meal Ears Plant

available N fresh weight dry matter

kg ha-1

Mg ha-1

Mg ha-1

0 8.66 c 7.79 b

56 9.53 b 8.28 b

112 10.51 a 8.54 ab

168 11.02 a 9.04 a 1Values followed by same letter not

signficantly different (P < 0.05)

122

Table 7. Effect of cover crop and available feather meal nitrogen (N) on ear leaf

N status at silking and total plant N uptake. The interaction between cover crop

and feather meal was not significant at P = 0.05

Ear leaf Ear leaf Plant

Main plot or split color N concentration N uptake

treatment ho/(LxC) g kg

-1 kg ha

-1

Cover crop

Early 0.222 a1 28.7 a 159 b

Late 0.218 a 27.4 b 148 c

None 0.212 b 26.0 bc 141 c

Feather meal N, kg ha-1

0 0.197 d 25.0 c 112 d

56 0.214 c 27.3 b 142 c

112 0.222 b 28.5 ab 161 b

168 0.235 a 29.4 a 183 a 1Values followed by same letter are not significantly different (P < 0.05)

Table 8. Linear regression equations for sweet corn nitrogen (N) uptake as a function of

feather meal available N. Effect of cover crop on apparent N recovery and calculated

reduction in feather meal N requirement.

Apparent Reduction in feather

Cover crop Y-intercept Slope N recovery meal N requirement

treatment Value Std Error Value Std Error kg ha-1

kg ha-1

EarlyCC1

131 9 0.38 0.07 33 57

LateCC 114 8 0.47 0.09 16 27

NoCC

98 8 0.57 0.09 1EarlyCC = early cover crops, LateCC = late cover crops, NoCC = no cover crops

123


Cover crops

This chapter cover data collected in the first year of a two year study. In 2009, early

planted cover crops yielded almost twice as much dry matter as late planted cover crops (Table

2), while weed biomass was insignificant in no cover crop treatments. Yields across both

planting dates were significantly lower than dry matter yields measured in the fall cover crop

blends study at WSU Puyallup conducted the same year. In the other study, a similar 50:50 rye-

hairy vetch cover crop blend planted in mid-September and harvested in late-April yielded 4240

kg ha-1

dry matter, which was slightly lower than the six year mean in that study (4760 kg ha-1

)

(Lawson, 2010a). There is evidence that some crop residues may release allelopathic chemicals,

which can negatively impact germination of subsequent crops and weed seeds (Singh et al.,

2003). In the continuous corn rotations of the Midwest, allelopathic chemicals released from

corn stover have been linked to decreased corn germination in a laboratory incubation study

(Elmore and Abendroth, 2007). In our study, corn stover was tilled into the soil just prior to

seeding cover crops, which may have created an allelopathic effect, decreasing cover crop

germination and early season vigor, accounting for low relative cover crop dry matter yields in

comparison to the other study that did not include corn stover.

The N concentration of cover crop residues was not largely affected by planting date.

This is consistent with data collected at WSU Puyallup in the fall cover crop blends study, which

has shown that a 50:50 rye-hairy vetch cover crop blend harvested in late-April has a mean N

concentration of 23.8 mg kg-1

, regardless of planting date (Lawson, 2010a). In the same study,

total N content was significantly higher (93 and 74 kg ha-1

) than what we observed for early and

late planting dates, respectively (70 and 39 kg ha-1

). Lower cover crop biomass production in this

124

study is likely to account for the difference. The biomass composition for the early planted cover

crops was approximately 75:25 rye-hairy vetch, which is consistent with the previously cited

study. The hairy vetch component of the late planted cover crops was slightly lower than what

was observed in that study (22% vetch) (Lawson, 2010a). In fact, delaying planting date has been

shown to increase hairy vetch biomass composition in that study. It is unclear what caused the

decrease in hairy vetch biomass in the late planting.

Parameters of cover crop N concentration, C:N ratio, and dry matter composition were

similar to one of the treatments in a related N mineralization laboratory incubation study, which

is tested in this study (Lawson, 2010b). Although total N content is lower than what was applied

in the incubation study, net N release as a percent of total residue N should be not affected by N

content. Residue N concentration and quality are the drivers of N mineralization for a given

climate (Wagger, 1989; Rannels and Wagger, 1996; Kuo and Sainju, 1998; Magid et al., 2001).

Soil nitrates

Soil was sampled for NO3- over three dates as a gauge of N release from cover crop

residues in the field (Table 3). Field NO3- was highest on June 26, approximately 8 weeks after

cover crop incorporation and lowest on September 9, 2 weeks after sweet corn harvest. On June

26, soil NO3- was highest for early planted cover crops. Nitrates in the late planted cover crop

treatment were not different from the control. We expected a higher soil NO3- response from

cover crop residues in the field, based on data from a related laboratory incubation study

(Lawson, 2010b). Sample times in the incubation were correlated to field dates based on growing

degree days elapsed between cover crop residue incorporation and soil sampling (Table 4),

which allowed for comparison between the studies. Moisture was not limiting in the field

because over-head irrigation was provided in July and August. Based on the incubation data,

125

cover crop residue should have released 27 and 15 kg N ha-1

by June 26 in the field. But the soil

response in the field was approximate half of what was expected. Sweet corn had been planted

almost 4 weeks prior to sampling. Therefore crop N uptake may account for the discrepancy. In

addition, we did not measure NH4+ in the soil samples. Sarrantonio and Malloy (2003) noted

slow conversion of NH4+ to NO3

- in a cool, wet year in a similar cover crop study. Cool, wet

conditions are typical of the region in May and June, which suggests that N in the NH4+ form

may account for lower than expected NO3- on June 26.

Post-harvest soil NO3- was low across treatments receiving 0 and 56 kg ha

-1 feather meal

N (Table 5), which indicated that N was limiting. At the 112 kg ha-1

feather meal N rate, early

and late planted cover crop treatments had significantly higher NO3- than the no cover crop

treatment, demonstrating that N was limiting when cover crops were not included. At the highest

feather meal N rate, soil NO3- was high across all cover crop treatments. But soil NO3

- was

nearly double in the early cover crop treatments than in late or no cover crop treatments at that

rate, which indicates a large surplus of N.

Sweet corn in-season N status, fresh ear yield, and dry matter production

The effect of cover crops on sweet corn fresh ear yield and plant dry matter production

was not statistically significant. We noticed a trend of increased fresh ear yield (7.76 to 9.77 Mg

ha-1

) and dry matter production (7.53 to 8.13 Mg ha-1

) in the early cover crop treatment

compared to the control when no feather meal was applied. But this effect was not significant,

likely because of high variability in fresh ear yield data and plant dry matter production. Based

on the related N incubation study, only 56% of total residue N is available in a growing season

from a similar rye-hairy vetch cover crop blend (Lawson, 2010b), which is equivalent to

approximately 38 kg N ha-1

in this study. It is possible that the cover crop N contribution did not

126

significantly increase sweet corn yield because the N supply was dominated by a relatively large

N contribution from the soil (approximately 100 kg N ha-1

) and feather meal. Feather meal

available N had a strong affect on fresh ear yield and dry matter production, demonstrating an

increase with feather meal from 8.66 to 11.02 Mg ha-1

and from 7.79 to 9.04 Mg ha-1

,

respectively (Table 6).

Other studies have demonstrated a significant sweet corn ear yield and plant dry matter

response to hairy vetch and rye-hairy vetch cover crop residues (Cline and Silvernail, 2002;

Sarrantonio and Malloy, 2003; Zotarelli et al., 2009). In those studies, sweet corn planted after

cover crops had double the biomass as winter fallow treatments without fertilizer. We had a

much larger N contribution from soil than either of those studies, which could have reduced the

relative impact of cover crops on available N. Teasdale et al. (2008) reported large N

contribution from soil (78 kg ha-1

), demonstrating a smaller but significant response in sweet

corn biomass from rye-hairy vetch cover crops. In that study, cover crop N contents were much

higher than in our study (197 to 259 kg N ha-1

), which may explain why a response was observed

in that study and not ours.

Despite non-significant sweet corn yield response to cover crops, in-season plant N status

indicated that cover crops benefited sweet corn via N contribution (Table 7). As the crop begins

its reproductive cycle, N is allocated for grain production, and therefore the ear leaf is a good

indicator of in-season plant N status (Plenet and Lemaire, 1999). We found that early cover crops

had higher ear leaf N concentrations at silking than no cover crop treatments (28.6 and 26.0 g kg-

1, respectively). An extension publication from Oregon State has reported that sweet corn is N

deficient when ear leaf N concentrations are below 28 g kg-1

(Anonymous, 2004). According to

this standard, sweet corn in early planted cover crop treatments was N sufficient at silking, while

127

the no cover crop treatments were not. Our data indicated that early planted cover crops may

have provided N benefits during growth stages leading up to silking. There was a response in ear

leaf N concentration to feather meal available N (Table 7), demonstrating that sweet corn was N

deficient when feather meal available N was below 112 kg N ha-1

. The interaction between cover

crop and feather meal was not significant, which was likely due to the relatively small

contribution of N from cover crop residues compared to the soil N pool.

Chroma meter measurements of ear leaf chlorophyll content at silking demonstrate that

cover crops had a small N benefit to sweet corn. The ho/(LxC)ratio, which has been best

correlated to leaf chlorophyll content for chroma meter measurements (Amarante et al., 2008),

was slightly higher for early planted cover crops than no cover crop treatments. But the effect of

feather meal N rate on the ho/(LxC)ratio was much greater. Together, in-season N status at

silking and sweet corn yield data demonstrated that feather meal N rate had a signficant effect on

sweet corn. In-season N status at silking suggests that sweet corn had taken up some N at silking

from cover crops. But the N contribution from cover crops may have been small enough in

comparison to soil and feather meal N that it did not significantly affect sweet corn yield.

Sweet corn total N uptake and efficiency of N use

Sweet corn total N uptake in above ground biomass was significantly affected by cover

crops and feather meal (Table 7). Total N uptake increased as feather meal N rate increased,

ranging from 112 to 183 kg N ha-1

. For cover crops, N uptake was highest in early planted cover

crops and lowest in the no cover crop treatments. The interaction between cover crops and

feather meal was not significant. Regional guidelines suggest that sweet corn yield is maximized

when 196 to 224 kg N ha-1

is available (Anonymous, 2004). We estimated the size of the

available soil N pool from the total N uptake in the zero-feather meal control plots

128

(approximately 100 kg N ha-1

). When feather meal was applied at the highest two rates (112 and

168 kg available N ha-1

), available N was adequate or in excess of what was required by the

sweet corn crop if inorganic N from soil was accounted for. Post-harvest soil NO3- levels at the

highest two feather meal N rates (Table 5) also demonstrated that available N was in excess of

what was used by the crop. Therefore, it is not surprising that the interaction between cover crops

and feather meal was not significant because the available N pool was sufficient or in excess of

the crop requirement at the highest two feather meal N rates and cover crops supplied only a

small portion of the total available N to sweet corn.

We estimated ANR from the y-intercepts in the regression models for N uptake (Figure 1,

Table 8). Apparent N recovery for early and late planted cover crops was 31 and 14 kg N ha-1

,

respectively (Table 8). The slope of the line for N uptake in the regression models provided an

estimate of feather meal N uptake efficiency, which were 38, 47, and 49% for early, late and no

cover crop treatments, respectively (Table 8). Based on the standard deviation of these values in

each regression model, there were not significant differences in N uptake efficiency between

cover crop treatments. Cover crop N uptake efficiency in our study was similar to what has been

reported by others in cover crop-vegetable rotations (Sarranotonio and Malloy, 2003; Haas et al.,

2007; Collins et al., 2008). In those studies, N uptake efficiency ranged from 29 to 62% of total

cover crop N content. These values were comparable to estimates of mineral fertilizer N uptake

by corn, which averaged approximately 50% in one study (Karlen et al., 1998). Some research

has shown high N recovery of cover crop derived N in soil organic fractions and soil microbial

biomass when compared to mineral fertilizers (Harris et al., 1994; Seo et al., 2006; Collins et al.,

2007, Holness et al., 2008). Therefore, it is possible that some cover crop derived N will persist

in soil and become available to future crops.

129

We calculated N use efficiency as kg sweet corn dry matter per kg N input (Huggins and

Pan, 1993). This calculation was formulated in terms of dry matter production instead of ear

yield because our objective was to evaluate total N contribution from cover crops to subsequent

cash crops. At the lowest two feather meal N rates, N use efficiency was highest without cover

crops (Figure 2). This is likely because only a portion of the total N contained in cover crop

residue was available over a single growing season. In a related incubation study, 56% of total

residue N was released from a rye-hairy vetch cover crop blend similar to the one in this study.

We observed a significant decline in N use efficiency as the feather meal N rate increased.

Teasdale et al. (2008) reported similar findings, demonstrating higher N use efficiency for hairy

vetch and rye-hairy vetch cover crops without a mineral fertilizer application. In that study, cover

crops accumulated much higher N content (197 to 259 kg N ha-1

) than in this study. Therefore, N

supply was likely in large excess of what sweet corn requirement when cover crops were

combined with fertilizer. A couple studies have reported increased corn root density and length

under N deficient conditions, which could increase corn N uptake efficiency (Bonifas et al.,

2005; Bonifas and Lindquist, 2009). Therefore, lower dry matter production per N input

efficiency as feather meal N rate increased was likely related to the size of the available N pool.

Cover crop fertilizer N replacement values and validation of N release in a related N

mineralization study

The increase in sweet corn N uptake with cover crops was used in combination with

sweet corn N uptake efficiency to estimate of the amount of plant available N supplied by cover

crops. We calculated fertilizer N replacement values of 57 and 27 kg N ha-1

for early and late

cover crops, respectively (Table 8). The N provided by cover crop, expressed as a portion of the

total N content, was 81 and 69% for early and late planted cover crops. These values are higher

130

than what was observed in a related N mineralization laboratory incubation study with a similar

50:50 rye-hairy vetch cover crop blend (56% of total N content was released). But other field

studies have reported high percent N release from similar cover crop residues (Kuo et al., 1996;

Rannels and Wagger, 1996; Griffin et al., 2000; Sainju et al., 2006; Teasdale et al. 2008).

Nitrogen release from cereal-hairy vetch cover crops as a percent of cover crop N content ranged

from 66 to 112% in a range of similar field studies (Rannels and Wagger, 1996; Griffin et al.,

2000; Odihambo and Bomke, 2000; Teasdale et al., 2008). But it is unclear how the ratio of rye

and hairy vetch biomass and residue quality in those studies compared to ours.

Very few studies have directly compared N release from cover crop residues in

laboratory incubation to N release under field conditions. One study has found that N

mineralization of hairy vetch in a laboratory incubation study was consistent with results from

related field trail (Honeycutt, 1999). De Neve and Hoffman (1996) were also able to confirm N

mineralization results collected in the lab with field trials. We found that N release from cover

crop residues in the laboratory incubation were lower than what was observed in the field. But

our laboratory incubation did not include root biomass from cover crop residues. Shipley et al.

(1992) estimated root biomass of rye and hairy vetch as 25 and 10% of total above ground

biomass, respectively. Similarly, Kuo et al., (1997) measured root biomass of rye and hairy vetch

cover crops as 32 and 8% of above ground biomass, respectively. In our study, roots could have

contributed as much as 15 kg N ha-1

, based on those estimates. The contribution of N from root

biomass may account for some of the discrepancy.

131

Figure 1. Sweet corn total nitrogen (N) uptake as a linear function of available feather meal N.

Unique regression models plotted for each cover crop treatment because cover crop treatments

were significantly different at P = 0.05.

EarlyCC, early cover crops; LateCC, late cover crops; NoCC, no cover crops

Figure 2. Nitrogen (N) use efficiency of sweet corn dry matter production per unit N supply,

which includes soil N (P < 0.01)

EarlyCC, early cover crops; LateCC, late cover crops; NoCC, no cover crops

50

70

90

110

130

150

170

190

0 50 100 150

N u

pta

ke, k

g h

a-1

Feather meal available N, kg ha-1

EarlyCC

LateCC

NoCC

0

10

20

30

40

50

60

70

80

90

0 56 112 168

kg d

ry m

atte

r kg

-1N

su

pp

ly

Feather meal avaible N, kg ha-1

EarlyCC

LateCC

NoCC

132

4. CONCLUSIONS

The results indicate that a 50:50 rye-hairy vetch blend may benefit a subsequent cash

crop via increased plant available N, based on one year of data. In-season N status of sweet corn

demonstrated that cover crops had provided N for crop uptake at the time of maximum N

requirement for corn. A trend of increased ear yield and biomass was noticeable for sweet corn

fertilized with early planted cover crops compared to no cover crop treatments when no feather

meal was applied. But there were not significant differences in sweet corn ear yield and dry

matter production between cover crop treatments, likely due to large variation in sweet corn

yield and dry matter production between treatments. There was a large N contribution from the

soil N pool, which made it difficult to separate sweet corn N and yield responses from cover crop

residue additions relative to soil N.

Sweet corn N uptake was significantly different between cover crop and feather meal

treatments. Nitrogen uptake fit a linear regression over feather meal N rates. Apparent N

recovery and N uptake efficiency, estimated from the N uptake regression models, were used to

calculate an indirect N fertilizer replacement value. We estimated the N fertilizer replacement

value to be approximately 57 and 27 kg N ha-1

for early and late planted cover crops. When

expressed as a portion of the total N content of cover crops, these were 81 and 69%, much

greater than the related N mineralization incubation study. The incubation study did not include

N contribution from cover crop root biomass, which may account for some of the discrepancy. It

is not possible to make broad conclusions about the validity of the N mineralization incubation

study based on just one year of field data.

133

5. LITERATURE CITED

Anonymous. 2010. Sweet corn for processing. Commercial Vegetable Production Guide. Oregon

State University Extension Service, Corvalis, OR.

Amarante, C.V.T. do, D.A. Bisognin, C.A. Steffens, O.Z. Zanardi, and E.O. Ahmed. 2008. Non-

destructive quantification of chlorophyll in leaves by means of a colorimetric method.

Horticultura Brasileira 26: 471-475.

Berry, P.M., R. Sylvester-Bradley, L. Philipps, D.J. Hatch, S.P. Cuttle, F.W. Rayns, and P.

Gosling. 2002. Is the productivity of organic farms restricted by the supply of available

nitrogen? Soil Use and Management 18:248-255.

Bonifas, K.D., and J.L. Lindquist. 2009. Effects of nitrogen supply on the root morphology of

corn and velvetleaf. Journal of Plant Nutrition and Soil Science 32:1371-1382.

Bonifas, K.D., D.T. Walters, K.G. Cassman, and J.L. Lindquist. 2005. Nitrogen supply affects

root : shoot ratio in corn and velvetleaf (Abutilon theophrasti). Weed Science 53:670-

675.



188.





Burket, J.Z., D.D. Hemphill, and R.P. Dick. 1997. Winter cover crops and nitrogen management

in sweet corn and broccoli rotations. Hortscience 32:664-668.

Carrera, L.M., A.A. Abdul-Baki, and J.R. Teasdale. 2004. Cover crop management and weed

suppression in no-tillage sweet corn production. Hortscience 39:1262-1266.




vetch-rye mixture. 1. Cover crop and corn nitrogen. Agronomy Journal 89:427-434.

134



11:219-225.



Cogger, C.G. 2000. Soil management for small farms. EB 1895. Washington State University

Cooperative Extension, Oregon State University Extension Service, University of Idaho

Cooperative Extension System, US Department of Agriculture.


Washington State University Puyallup Research and Extension Center, Puyallup, WA.

Collins, H.P., J.A. Delgado, A.K. Alva, and R.E. Follett. 2007. Use of nitrogen-15 isotopic

techniques to estimate nitrogen cycling from a mustard cover crop to potatoes. Agronomy

Journal 99:27-35.


in vegetable production systems. Hortscience 32:866-870.

De Neve, S., and G. Hofman. 1996. Modelling N mineralization of vegetable crop residues

during laboratory incubations. Soil Biology & Biochemistry 28:1451-1457.

Elmore, R. W. and L. J. Abendroth. 2007. Allelopathy: a cause for yield penalties in corn

following corn? Integrated crop management newsletter. Iowa State University. 25 Oct

2010. <http://www.agronext.iastate.edu/corn/production/management/cropping/corn

followcorn.html>

Feaga, J.B., J.S. Selker, R.P. Dick, and D.D. Hemphill. 2010. Long-Term Nitrate Leaching

Under Vegetable Production with Cover Crops in the Pacific Northwest. Soil Science


Fortuna, A., R.L. Blevins, W.W. Frye, J. Grove, and P. Cornelius. 2008. Sustaining soil quality

with legumes in no-tillage systems. Communications in Soil Science and Plant Analysis

39:1680-1699.

Gaskell, M. 2006. Organic nitrogen sources for vegetable crops. Hortscience 41:957-957.

135

Gaskell, M., R. Smith, J. Mitchell, S.T. Koike, C.Fouche, T. Hartz, W. Horwath and L. Jackson.

2006. Soil fertility management for organic crops. Publication 7249. University of

California Division of Agriculture and Natural Resources.



Griffin, T., M. Liebman, and J. Jemison. 2000. Cover crops for sweet corn production in a short-

season environment. Agronomy Journal 92:144-151.

Haas, G., H. Brand, and M.P.d.l. Vega. 2007. Nitrogen from hairy vetch (Vicia villosa) as winter

green manure for white cabbage in organic horticulture. Biological Agriculture &

Horticulture 25:37-53.

Harris, G.H., O.B. Hesterman, E.A. Paul, S.E. Peters, and R.R. Janke. 1994. Fate of legume and

fertilizer nitrogen-15 in a long-term cropping systems experiment. Agronomy Journal

86:910-915.

Holderbaum, J.F., A.M. Decker, J.J. Meisinger, F.R. Mulford, and L.R. Vough. 1990. Fall-

seeded legume cover crops for no-tillage corn in the humid east. Agronomy Journal

82:117-124.

Holness, R.L., M.R. Reddy, C.R. Crozier, and C.E. Niedziela. 2008. Evaluating inorganic

nitrogen and rye-crimson clover mixture fertilization of spring broccoli and lettuce by

(15)nitrogen tracing and mass balance. Journal of Plant Nutrition 31:1033-1045.

Honeycutt, C.W. 1999. Nitrogen mineralization from soil organic matter and crop residues: Field

validation of laboratory predictions. Soil Science Society of America Journal 63:134-141.

Huggins, D.R., and W.L. Pan. 1993. Nitrogen efficiency component analysis - an evaluation of

cropping system differences in productivity. Agronomy Journal 85:898-905.




Karlen, D.L., A.A. Kramer, and D.S. Logsdon. 1998. Field-scale nitrogen balances associated

with long-term continuous corn production. Agronomy Journal 90:644-650.



136



353.



Soils 22: 310-317.



Lawson, A. 2010a. Evaluating fall cover crop blends for biomass production, residue quality, and

weed suppression. M.S. Thesis. Washington State University, Pullman, WA.

Lawson, A. 2010b. Nitrogen release from rye-hairy vetch cover crop residues with and without a

semi-fast release organic fertilizer in a laboratory incubation. M.S. Thesis. Washington

State University, Pullman, WA.

Leon, A.P., S.Z. Vina, D. Frezza, A. Chaves, and A. Chiesa. 2007. Estimation of chlorophyll

contents by correlations between SPAD-502 meter and chroma meter in butterhead

lettuce. Communications in Soil Science and Plant Analysis 38:2877-2885.

Madeira, A.C., A. Ferreira, A.d. Varennes, and M.I. Vieira. 2003. SPAD meter versus tristimulus

colorimeter to estimate chlorophyll content and leaf color in sweet pepper.

Communications in Soil Science and Plant Analysis 34:2461-2470.

Magid, J., O. Henriksen, K. Thorup-Kristensen, and T. Mueller. 2001. Disproportionately high

N-mineralisation rates from green manures at low temperatures - implications for

modeling and management in cool temperate agro-ecosystems. Plant and Soil 228:73-82.

Moller, K., and H.J. Reents. 2009. Effects of various cover crops after peas on nitrate leaching

and nitrogen supply to succeeding winter wheat or potato crops. Journal of Plant

Nutrition and Soil Science-Zeitschrift Fur Pflanzenernahrung Und Bodenkunde 172:277-

287.




137



Plenet, D., and G. Lemaire. 1999. Relationships between dynamics of nitrogen uptake and dry

matter accumulation in maize crops. Determination of critical N concentration. Plant and

Soil 216:65-82.

Quemada, M., and M.L. Cabrera. 1997. Temperature and moisture effects on C and N

mineralization from surface applied clover residue. Plant and Soil 189:127-137.



Ruffo, M.L., and G.A. Bollero. 2003. Modeling rye and hairy vetch residue decomposition as a

function of degree-days and decomposition-days. Agronomy Journal 95:900-907.

Sainju, U.M., and B.P. Singh. 2008. Nitrogen storage with cover crops and nitrogen fertilization

in tilled and nontilled soils. Agronomy Journal 100:619-627.



Sarrantonio, M., and T. Molloy. 2003. Response of sweet corn to red clover under two tillage

methods. Journal of Sustainable Agriculture 23:91-109.

Sarrantonio, M. 1991. Methodologies for screening soil improving legumes. Rodale Institute,

Kutztown, PA.

Schellenberg, D.L., R.D. Morse, and G.E. Welbaum. 2009. Organic broccoli production on

transition soils: comparing cover crops, tillage and sidedress N. Renewable Agriculture

and Food Systems 24:85-91.

Schepers, J.S., D.D. Francis, M. Vigil, and F.E. Below. 1992. Comparison of corn leaf nitrogen

concentrations and chlorophyll meter readings. Communications in Soil Science and

Plant Analysis 23:2173-2187.

Seo, J.H., I.J. Meisinger, and H.J. Lee. 2006. Recovery of nitrogen-15-labeled hairy vetch and

fertilizer applied to corn. Agronomy Journal 98:245-254.

138

Shipley, P.R., J.J. Meisinger, and A.M. Decker. 1992. Conserving residual corn fertilizer

nitrogen with winter cover crops. Agronomy Journal 84:869-876.

Singh, H.P., D.R. Batish, and R.K. Kohli. 2003. Allelopathic interactions and allelochemicals:

New possibilities for sustainable weed management. Critical Reviews in Plant Sciences

22:239-311.

Sullivan, D.M., A.I. Bary, D.R. Thomas, S.C. Fransen, and C.G. Cogger. 2002. Food waste

compost effects on fertilizer nitrogen efficiency, available nitrogen, and tall fescue yield.


Teasdale, J.R., A.A. Abdul-Baki, and Y.B. Park. 2008. Sweet corn production and efficiency of

nitrogen use in high cover crop residue. Agronomy for Sustainable Development 28:559-

565.




Thorup-Kristensen, K., and D.B. Dresboll. 2010. Incorporation time of nitrogen catch crops

influences the N effect for the succeeding crop. Soil Use and Management 26:27-35.

Thorup-Kristensen, K., J. Magid, and L.S. Jensen. 2003. Catch crops and green manures as

biological tools in nitrogen management in temperate zones, p. 227-302 Advances in

Agronomy, Vol 79, Vol. 79. Academic Press Inc, San Diego.

Tonitto, C., M.B. David, and L.E. Drinkwater. 2006. Replacing bare fallows with cover crops in

fertilizer-intensive cropping systems: a meta-analysis of crop yield and N dynamics.


Torbert, H.A., D.W. Reeves, and R.L. Mulvaney. 1996. Winter legume cover crop benefits to

corn: Rotation vs fixed-nitrogen effects. Agronomy Journal 88:527-535.

Varvel, G.E., J.S. Schepers, and D.D. Francis. 1997. Ability for in-season correcction of nitrogen

deficiency corn using chlorophyll meters. Soil Science Society of America Journal

61:1233-1239.



139





Watson, C.A., D. Atkinson, P. Gosling, L.R. Jackson, and F.W. Rayns. 2002. Managing soil

fertility in organic farming systems. Soil Use and Management 18:239-247.

Zotarelli, L., L. Avila, J.M.S. Scholberg, and B.J.R. Alves. 2009. Benefits of vetch and rye

cover crops to sweet corn under no-tillage. Agronomy Journal 101:252-260.

140

CHAPTER 5

General conclusions and recommendations

Organic vegetable growers may use rye-hairy vetch cover crop blends to enhance plant

available nitrogen (N) to subsequent cash crops. Our research was designed to address grower

uncertainty about how cover crops affect crop rotations and how to optimize N availability from

cover crop residues in western Washington. We devised two field studies and one laboratory

incubation to evaluate the effect of planting date, harvest date, and seeding ratio on cover crop

growth, residue quality, and N availability.

1. SUMMARY OF FINDINGS

If planted by early-October, rye-hairy vetch cover crop blends may accumulate sufficient

biomass and N to influence N dynamics to subsequent cash crops. We found that planting date

and harvest date significantly impacted cover crop establishment, biomass production, total N

content, and residue quality. Rye-hairy vetch seeding ratio of the biculture treatments did not

have a large effect on cover crop biomass yield or composition, as we had hypothesized. Rye

established more quickly than hairy vetch in cool fall conditions, which makes it a favorable

winter cover crop species in the region. Although hairy vetch is slow to establish, it went through

a period of rapid growth in the spring and has a higher potential to supply large amounts of N to

subsequent crops. Cover crop biomass and N content were optimized when cover crops were

planted early and harvested late. While late harvest favored larger biomass production, we

measured a significant increase in C:N ratio and higher neutral detergent fiber (NDF), acid

detergent fiber (ADF), and acid detergent lignin (ADL). It is seems likely that the increase in N

content at the late harvest is enough to offset the affect of more recalcitrant carbon (C) on N

release dynamics. The soil N response to incorporated cover crop residues demonstrated that rye-

141

hairy vetch blends can increase N availability to subsequent cash crops compared to pure rye.

Our data suggests that insufficient biomass and N is accumulated to impact N supply to

subsequent cash crops when cover crops are planted late and harvested early.

Cover crop residue quality was well correlated to N release patterns for rye-hairy vetch

residues. Nitrogen concentration and C:N ratio of the cover crop blends was well correlated with

net N mineralization over the first 70 days. Neutral detergent fiber and ADF were negatively

correlated with net N mineralization over the first 70 days and between days 21 and 50. The

inclusion of these fractions in a model to predict N release from cover crop residues may

improve the accuracy of the model.

A 50:50 rye-hairy vetch blend released a similar percentage of total residue N over 70 d

compared to pure hairy vetch. This blend may supply larger amounts of plant available N to

subsequent cash crops because of higher biomass production. A 75:25 rye-hairy vetch blend

released a significantly lower percentage of total residue N than pure hairy vetch. But the total

inorganic N release was similar between the two treatments because of higher N content of the

75:25 rye-hairy vetch treatment. Although hairy vetch and the75:25 rye-hairy vetch blend

released similar amounts of N over 70 d, the initial rate of N release was nearly 3-fold greater for

the hairy vetch treatment. The slower rate of N release from the 75:25 rye-hairy vetch blend may

result in N release that is better timed with crop N uptake and therefore increase crop N uptake

efficiency. When cover crops were combined with feather meal, the combined net N release was

less than the sum of the individual components. The cause of the negative interaction was not

well understood and therefore deserves further research. Growers are not likely to apply feather

meal at the time of cover crop incorporation. Further research should explore the effect of

organic fertilizer application many weeks after cover crop incorporation.

142

A measure of in-season N status in sweet corn demonstrated that cover crops had

provided N benefits to sweet corn by the time of silking. We observed a trend of increased ear

yield and biomass for early planted cover crops compared to no cover crop treatments when no

feather meal was applied. But these differences were not statistically different. There was a large

contribution from the soil N pool (100 kg N ha-1

) in comparison to cover crops (20 to 35 kg N ha-

1), which made it difficult to separate the N contributions from cover crops and soil according to

the sweet corn yield response. Sweet corn N uptake was significantly increased by early planted

cover crops. Nitrogen uptake in sweet corn fit a linear regression over feather meal N rates.

Apparent N recovery and N uptake efficiency, estimated from the N uptake regression models,

were used to calculate an indirect N fertilizer replacement value. We estimated the N fertilizer

replacement value to be approximately 64 and 28 kg N ha-1

for early and late planted cover

crops. When expressed as a portion of the total N content of cover crops, these were 91 and 72%,

much greater than the related N mineralization incubation study. The incubation study did not

include N contribution from cover crop root biomass, which may account for some of the

discrepancy. It is not possible to make broad conclusions about the validity of the N

mineralization incubation study based on just one year of field data.

2. RECOMMENDATIONS

Given the similarities between the two rye-hairy vetch biculture seeding ratios, we

recommend using a 50:50 rye-hairy vetch seeding ratio to optimize biomass yield, N

accumulation and N supply to subsequent cash crops. There was not significant enough an

increase in hairy vetch biomass for the hairy vetch dominated rye-hairy vetch seeding ratio to

offset the high cost of hairy vetch seed. Our data indicated that harvest date has a larger impact

on cover crop biomass than planting date. If cover crops are planted by early October, we

143

recommend incorporation at the end of April to optimize biomass and N accumulation. At that

time, cover crops are still in a vegetative stage and residue quality will not significantly affect the

quantity of inorganic N mineralized.

Growers may estimate N release from cover crop stands by measuring biomass,

estimating total N content, and calculating the percent of total residue N that will become

available. Biomass can be accurately measured by harvesting the above ground biomass in

representative quadrats. Cover crop residues can be sent away for analysis of total C and N and

results may be used to calculate total N content. Our results indicate that residue C:N ratio can be

used to estimate the portion of total residue N that will become available over a single growing

season. A measurement of total C and N concentrations in plant residue is a routine analysis that

can be conducted between the time of incorporation of cover crops in spring and planting of a

subsequent cash crop. An estimation of N supply from cover crop stands would allow growers to

better manage fertilizer application needs and promote more efficient use of N.

cover crops to enhance soil productivity in organic

Documents