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THESlS

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193 01570 6934

This is to certify that the

dissertation entitled
MEDICS AND CLOVERS IN WHEAT-NO-TILLAGE CORN ROTATIONS
WITH INSIGHTS INTO THEIR USE BY FARMERS

presented by

JOHN WINFIELD FISK

has been accepted towards fulfillment
of the requirements for

Ph . D degree in W1 Sciences

 

    

Major professor

Date August 22, 1997

 

MSU i: an Affirmative Action/Equal Opportunity Insrirution 0-12771

 

 

 

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university

 

 

 

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TO AVOID FINES Mum on or More data duo.

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Wan-9.1

 

MEDICS AND CLOVERS IN WHEAT-NO-TILLAGE CORN ROTATIONS WITH
INSIGHTS INT 0 THEIR USE BY FARMERS

By

John Winfield Fisk

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY
Department of Crop an Soil Sciences
1997

ABSTRACT

MEDICS AND CLOVERS IN WHEAT-NO-TILLAGE CORN ROTATIONS
WITH INSIGHTS INTO THEIR USE BY FARMERS

By

John Winfield Fisk

Forage legumes can be beneficial as cover crops in grain crop rotations typical of
the north central USA. This research was conducted to investigate the potential of
Medicago (annual medics) species and clovers as cover crops for no-tillage corn (Zea
mays L.). Specific objectives were 1) determine legume biomass, tissues nitrogen (N)
concentration, biomass N, and dinitrogen fixation ability when frost-seeded into winter
wheat or planted after wheat harvest, 2) measure the effect of cover crops in the rotation
in terms of plant available soil N, corn grain yield and biomass, fertilizer replacement
value, and uptake of annual legume 15N, 3) determine the effect of fall seeded legumes
on weed suppression 4) investigate whether participatory approaches to the generation
and dissemination of information and technologies around sustainable agriculture,
specifically cover crops, may be more appropriate than conventional methods.

Annual legume cover crops established after wheat harvest demonstrated
excellent potential for N2 fixation (15.7 to 64.9 % of biomass N) and biomass N
accumulation (48 to 206 kg N ha'l) and were comparable to fall and frost-seeded red
clover (T rifolium pratense L). Soil inorganic N levels were ofien higher following
legumes than the no cover control. Fertilizer replacement values were between 24 and
112 kg N ha'1 for legumes, whereas, actual legume 15N recovery in a following crop was

between 9 and 16 % indicating rotation effects beyond N contribution.

Density and dry weight of winter annual weeds as well as dry weight of perennial
weeds following, fall—planted cover crops, were almost always lower then when
following the no cover crop control. The effect of cover crops on the density of summer
annual and perennial weeds was not as pronounced as for spring annuals. Summer weed
density and dry weight were significantly lower where cover crop residue was retained
compared to when it was removed.

Evidence that participatory approaches would be effective in facilitating the
generation and dissemination of sustainable agriculture technologies was found,
including: a desire by farmers for more farmer-to-farmer interaction indicating an ’
attraction to the participatory learning process, a desire by knowledge brokers for greater
skills in facilitating participatory methods, and that a limited number of farmers are

currently learning to integrate their farms with participatory approaches.

To my children, Tyler Fredrick and Liam Cole.

iv

ACKNOWLEDGMENTS

It is my feeling that nothing is accomplished alone, by one single person, and
therefore I owe thanks, not only to those who assisted and supported me during my
graduate studies, but also to those who taught me many lessons throughout life. To Dr.
Oran Hesterman, for his guidance, vision, friendship, and for illustrating the dynamic
quality of seemingly static things. To Dr. Richard Harwood, for the inspiration I receive
from him on a daily basis, for his guidance, and for providing a CS Mott Foundation
fellowship for sustainable agriculture in financial support of my graduate studies. To Dr.
Steve Kaagan, for allowing this agronomist into his heart, for teaching me about writing
and working with groups. To Dr. Eldor Paul, for teaching me soil microbiology and how
to be a scientist.

For technical help, thanks go to Joe Paling, Greg Parker, Brian Graff, Dave
Harris, Elaine Parker, Tom Wilson, Kim Cassida, Glen Harris, Craig Sheafl‘er and
Michael Russelle. A special thanks goes to Dr. Anil Shrestha and John Baboola for their
continued friendship and assistance.

Special gratitude and thanks go to my parents, Fred and Olga Fisk, for always
being there and believing in me.

In acknowledgment and honor of my past teachers; Hank Mayer, Drs. Walter
Manech, Steve Gliessman, Martha Rosemeyer, Rob Kluson, Matt Werner, and Rob
Myers.

Most importantly, I thank my wife, Ruth, for her continual support, love, and
light that she brings to my life. I thank my boys, Tyler and Liam, for their joy and love.

PREFACE

Chapter 1 in this dissertation was written in the style required for publication in
the Agronomy Journal. Significant contributions were made by Dr. Oliver
Shabenburger. His contribution was in analysis of data collected by the author. More
specifically: a statistical code of a higher order for the analysis of and trend description
for legume biomass, tissue N, biomass N, and soil inorganic N; figures describing
legume and soil N trends over time; sub-soil N analysis.

Chapter 2 in this dissertation was written in the style required for publication in
the Agronomy Journal. Chapter 3 in this dissertation was written in the style required for

publication in the American Journal of Alternative Agriculture.

vi

TABLE OF CONTENTS

Page
LIST OF TABLES ...................................................................................... ix
LIST OF FIGURES ..................................................................................... xii
CHAPTER ONE: GROWTH TRENDS 0F MEDICS AND CLOVERS
AND THEIR EFFECT ON YIELD AND NITROGEN UPTAKE BY
NO-TILLAGE CORN ................................................................................. 1
ABSTRACT ................................................................................................ 1
INTRODUCTION ........................................................................................ 2
MATERIALS AND METHODS ................................................................. 4
Cover crop management ................................................................... 5
Corn management ............................................................................ 6
Plant and soil sampling and nutrient analysis .................................... 7
Dinitrogen fixation ........................................................................... 8
Tracer experiment with 15N labeled legume biomass ........................ 9
experimental design and analysis ...................................................... 10
RESULTS AND DISCUSSION .................................................................... 12
Legume biomass ................................................................................ 12
Legume tissue nitrogen ...................................................................... l3
Biomass nitrogen yield and dinitrogen fixation .................................. 14
Spring regrowth of red clover ............................................................ 15
Soil inorganic nitrogen following cover crop treatments .................... 16
Corn grain and total biomass yield .................................................... l7
Fertilizer replacement values ............................................................. 19
Recovery of legume l5N .................................................................... 20
CONCLUSIONS ........................................................................................... 22
REFERENCES .............................................................................................. 24
CHAPTER TWO: WEED SUPPRESSION BY ANNUAL LEGUME
COVER CROPS IN NO-TILLAGE CORN ............................................... 48
ABSTRACT ................................................................................................... 48
INTRODUCTION ......................................................................................... 49
MATERIALS AN METHODS ...................................................................... 51
RESULTS AND DISCUSSION ...................................................................... 55
Spring annual weed density and dry weight ......................................... 55
Summer annual weed density and dry weight ...................................... 56
Residue effect on summer annual weeds .............................................. 58
Perennial weed density and dry weight ................................................ 58
Residue effect on perennial weeds ....................................................... 60

vii

CONCLUSIONS ............................................................................................ 60
REFERENCES ............................................................................................... 63
APPENDD( .................................................................................................... 100

CHAPTER 3: THE VALUE OF A PARTICIPATORY APPROACH IN

SUSTAINABLE AGRICULTURE RESEARCH ........................................ 75
ABSTRACT ................................................................................................... 75
INTRODUCTION .......................................................................................... 77
METHODS ..................................................................................................... 82
RESULTS AND DISCUSSION ...................................................................... 83
Knowledge about cover crops .............................................................. 83
Desired information about cover crops ................................................ 84
Sources of information for crop production and cover crop use. ........ 86
Generation and transfer of cover crop information ............................... 87
Current generation and transfer of information ......................... 87

Participatory approach to information generation and transfer .. 88
CONCLUSIONS ............................................................................................ 89
FUTURE RESEARCH ................................................................................... 92
REFERENCES ............................................................................................... 93

viii

LIST OF TABLES

Page

CHAPTER ONE: GROWTH TRENDS OF MEDICS AND CLOVERS
AND THEIR EFFECT ON YIELD AND NITROGEN UPTAKE BY
NO-TILLAGE CORN
Table 1. Monthly precipitation and mean air temperature during the

growing seasons of 1994-1996 at EL and KBS, MI. ................... 27
Table 2. Legume cover crop biomass, tissue N, biomass N, and dinitrogen

fixation at maximum fall biomass at EL ..................................... 28
Table 3. Legume cover crop biomass, tissue N, biomass N, and dinitrogen

fixation at maximum fall biomass at KBS .................................. 29
Table 4. Biomass, tissue N, and biomass N for spring regrowth of red

clover prior to burndown application. ........................................ 30
Table 5. Soil inorganic N following cover treatments combined over

location and sample date in 1995 and 1996. ............................... 31
Table 6. Soil NO at three depths (cm) following cover treatments

averaged over two locations in MI .............................................. 31
Table 7. Repeated measures analysis for legume biomass, tissue N,

biomass N, and soil inorganic N. ............................................... 32
Table 8. Response of no-till corn grain to cover treatments averaged

over applied N levels. ................................................................. 33
Table 9. Response of no-till corn total biomass to cover treatments

averaged over applied N levels. .................................................. 33
Table 10. Regression equations for corn grain yield (Y) as a function

of applied N (x) following cover treatments. .............................. 34
Table 11. Nitrogen fertilizer replacement values (FRI) based on corn

yield and N uptake. .................................................................... 35

Table 12. Recovery of annual legume N applied to soil surface in selected
soil pools and in surface residue in 1996 at EL and KBS, MI. 36

Table 13. Recovery and loss of annual legume N applied to soil surface in
1996 at EL and KBS, MI. ........................................................... 36

ix

CHAPTER TWO: WEED SUPPRESSION BY ANNUAL LEGUME COVER

CROPS IN NO-TILLAGE CORN
Table 1. Density and dry weight of winter annual weeds following

legume cover crops and no cover control prior to corn planting. 66
Table 2. Density and dry weight of summer annual weeds following

legume cover crops and no cover control approximately

45 days after corn planting. ....................................................... 67
Table 3. Density and dry weight of summer annual weeds with and

without legume residue removed. .............................................. 68
Table 4. Perennial weed density and dry weight following legume cover

crops and a no cover control just prior to corn planting. ............. 69
Table 5. Perennial weed density and dry weight following legume cover

crops and a no cover control approximately 45 days after

corn planting. ............................................................................ 70
Table 6. Density and dry weight of perennial weeds with and without

legume residue removed. ........................................................... 71
Table 7. Density and dry weight of the dominant weed species in

the no cover control just prior to corn planting. .......................... 72
Table 8. Density and dry weight of the dominant weed species in the

control 45 days after corn planting. ............................................ 73
Table 9. Soil temperatures at 5 cm depth on selected dates following

legume cover crops and a no cover control. ................................ 74
Table A. 1. Density of all weed species prior to burndown application in

1995 at EL and KBS. ................................................................. 100
Table A2. Dry weight of all weed species prior to burndown application in

1995 at EL and KBS. ................................................................. 101
Table A3. Density of all weed species prior to burndown application in

1996 at EL and KBS. ................................................................. 102
Table A4. Dry weight of all weed species prior to burndown application in

1996 at EL and KBS. ................................................................. 103
Table A5. Density of all weed species prior to postemergence application in

1995 at EL and KBS. ................................................................. 104
Table A6. Dry weight of all weed species prior to postemergence application

in 1995 at EL and KBS. ............................................................ 105
Table A7. Density of all weed species prior to postemergence application in

1996 at EL and KBS. ................................................................. 106

Table A8. Dry weight of all weed species prior to postemergence application
in 1996 at EL and KBS. ............................................................ 107

CHAPTER 3: THE VALUE OF A PARTICIPATORY APPROACH IN
SUSTAINABLE AGRICULTURE RESEARCH

Table 1. Comparison of outcomes of participatory research with factors

limiting the adoption of sustainable agriculture practices. ......... 95
Table 2. Questions presented for discussion during the focus

group interviews. ..................................................................... 96
Table 3. Desired information about cover crops generated by each

focus group. .............................................................................. 99

xi

LIST OF FIGURES

CHAPTER ONE: GROWTH TRENDS OF MEDICS AND CLOVERS
AND THEIR EFFECT ON YIELD AND NITROGEN UPTAKE BY

NO-TILLAGE CORN
Figure l. Fitted dry matter yield of legume cover crops in 1994

at EL and KBS. ...........................................................................
Figure 2. Fitted dry matter yield of legume cover crops in 1995

at EL and KBS. ...........................................................................
Figure 3. Fitted nitrogen concentration in legume tissue in 1994

at EL and KBS. ................................... q ........................................
Figure 4. Fitted nitrogen concentration in legume tissue in 1995

at EL and KBS. ...........................................................................
Figure 5. Fitted total N accumulated in legume cover crops in 1994

at EL and KBS. ...........................................................................
Figure 6. Fitted total N accumulated in legume cover crops in 1995

at EL and KBS. ...........................................................................
Figure 7. Fitted total soil mineral N + NO ) in sp pring and summer

following cover treatments es lrshed3 in 1994 at EL and KBS.
Figure 8. Fitted total soil mineral Nes + NO) )in spring and summer

following cover treatments lished3 in 1995 at EL and KBS.
Figure 9. Corn grain yield response to applied N following cover

treatments in 1995 at KBS. .........................................................
Figure 10. Corn grain yield response to applied N following cover

treatments in 1996 at EL. ...........................................................
Figure 11. Uptake of 15N by sorghum sudangrass from annual medic

biomass placed on the soil surface. .............................................

xii

Page

37

38

39

40

41

42

43

44

45

46

47

Chapter 1

GROWTH TRENDS OF MEDICS AND CLOVERS AND THEIR EFFECT ON
YIELD AND NITROGEN UPTAKE BY NO-TILL CORN

ABSTRACT

There is need for increased cover crop options which avoid depleting available
soil moisture, reduce the need for chemical control, significantly contribute N to a
following crop and demonstrate positive yield effects. The goal of this research was to
determine the potential of two annual medic species, Berseem clover, and red clover as
fall seeded cover crops followed in rotation with no-tillage corn. Specific objectives
were to i) quantify biomass, tissue N, and biomass N of the legumes over the course of
growth, ii) measure legume N2 fixing capacity, iii) measure the effect of legumes on soil
inorganic N, iv) measure yield effects in terms of fertilizer replacement value (FRI), and
v) measure the recovery of legume N by a following crop and in selected soil pools. The
annual legume species generally reached maximum predicted biomass by mid-to late-
Oct. which is equivalent to 65 to 80 days after planting. Annual legumes demonstrated
excellent potential for N2 fixation (15.7 to 64.9 % of biomass N) and biomass N
accumulation (48 to 206 kg N ha'l). Soil inorganic N levels were higher following all
legumes in 1995 than in the no cover control, and higher following only red clover in
1996. Early season sub-soil NO3-N following cover treatments were increased at the 30-
60 cm depth in 1995, however, there were no significant differences at 60 to 90 cm
depth. Fertilizer replacement values were between 24 and 112 kg N ha'1 for annual
legumes. Legume l5N recovery in a following crop was between 9 and 16 % of input

with soil retention between 47 and 65 %.

2

INTRODUCTION

Legume cover crops used in no-till corn systems can supply biologically fixed N
to a succeeding corn crop (Decker et al., 1994; Ebelhar et al., 1984; Holderbaum et al.,
1990;). Cover crops may also provide positive rotation effects (Hesterman et al. 1986).
Rotation effects are yield increases which are not attributable to N from the cover crop.
Long-term use of cover crops has been shown to enhance soil productivity by changing
physical and chemical properties (Smith eta] 1987).

Most legume cover crops which have been evaluated are considered winter
annuals since they are established in the fall and survive the winter, with spring regrowth
being chemically controlled prior to crop planting. Cover crops can be established by
seeding afier crop harvest, inter-seeding into a standing crop, or spring frost-seeding into
an over-wintering crop (Hesterman, 1988, Stute et al. 1993). In northern parts of the
mid-west and the eastern USA, it can be difficult to fit cover crops into established
cropping systems. The length of the growing season may not allow fall planted cover
crops to survive the harsh winters or protect the soil during the fall and early spring. To
maximize time for growth, frost-seeding legumes and full-year rotations have
traditionally been used. Frost-seeding red clover (T rifolium pratense L.) into winter
wheat, by broadcasting seed onto the soil surface in late-winterbefore the soil warms, is
a traditional means of establishing a red clover cover crop. A full-year rotation means
that crops such as alfalfa (Medicago sativa L.) or red clover, once established, are
allowed to occupy the field for an entire year or longer. These crops can be cut for hay
or grazed and followed by a grain crop the next year to take advantage of rotation effects

and N contribution. These traditional methods are reliable but have their drawbacks.
‘ One barrier to the successful use of cover crops may be soil moisture depletion in
the spring of years with low precipitation (Badaruddin and Meyer, 1989; Frye et al.
1988; Hesterman et al. 1992; Tiffin, 1994). When cover crops are fall-ploughed to

remove the risk of spring moisture depletion, the soil is left uncovered and susceptible to

3

erosion. In cropping systems where a goal is herbicide reduction, killing the cover crop
may present a problem. Even the use of cultivation may not completely kill some of the
more vigorous species such as red clover and hairy vetch (Vicia villosa Roth).

There is a need for cover crops which do not deplete available soil moisture,
which minimize the use of herbicides to terminate growth, and which contribute N and
demonstrate positive yield effects on a succeeding crop. True annual legume species will
not over-winter in northern regions of the USA. As a result, they may be able to provide
the benefits which have been demonstrated for winter annuals without either reducing
available soil moisture or requiring a burndown herbicide. This research was carried out
to determine the suitability of annual legume species as cover crops in a cropping system
common to the northern mid-west region of the USA.

Annual species of Medicago (annual medics), originating in North Africa and the
Middle East, are adapted to a range of environmental conditions (Ewing, 1983., Lesins
and Lesins, 1979). First introduced for grazing purposes into Australia and New
Zealand, they are now a common component of sheep pastures and are used in ley
cropping systems rotated with cereal crops (Puckridge and French, 1983). In these
systems, medics provide high quality forage, contribute nitrogen and improve physical
structure of the soil (Crawford et al., 1989). Ladd et al. (1983) studied N cycling in a
wheat-medic-wheat rotation in Australia. Wheat recovered between 20 and 28% of the
applied residue N when medic had been placed in the soil 7 months prior to planting
wheat. Estimated dinitrogen fixation by annual medic pastures in Cyprus has been as
high as 122 kg N ha'1 (Papastylianou, 1987).

In Montana, small grain yields were doubled following medic compared to
following fallow in rotation (Sims and Slinkerd, 1991). As a green manure crop before
wheat in North Dakota, black, snail and barrel medics yielded 37, 85, and 79 kg N ha'1
(Gardener et al., 1991). Although N accumulation was lower than in hairy vetch, vetch
reduced soil moisture significantly more than the medics. Annual medic biomass yields

4

in the north-central USA planted as a forage legume or green manure have ranged
between 1.2 and 6.2 Mg ha'1 with biomass N up to 140 kg N ha"1 (Moynihan et al.,
1996; Shrestha, 1996; Zhu et al., 1996).

In addition to annual medic species, Berseem clover ( T rifolium alexandrinum L.)
was investigated in this study. Berseem clover is an annual legume used as a forage plant
in India and in areas with Mediterranean climates. As a hay crop it has the potential to
produce large amounts of biomass rapidly and can be out several times a year. Wescott et
a1. (1995) reported biomass N of 125 to 200 kg N ha'l.

The goal of this research was to determine the potential of two annual medic
species, berseem clover, and red clover as fall seeded cover crops followed in rotation by
no tillage corn. Specific objectives were to:

1) Characterize the biomass, tissue N, and biomass N of the legume cover crops

over the course of growth.

2) Measure legume N2 fixing capacity.

3) Measure the effect of legumes on soil inorganic N.

4) Determine the effect of legumes on no-till corn yield.

5) Measure the recovery of legume N by a following crop and in selected soil

pools.

MATERIALS AND METHODS
Experiments were conducted in the 1994-5 and 1995-6 growing seasons at the
Michigan State University Crop and Soil Sciences Research Farm in East Lansing (EL),
MI and at the Kellogg Biological Station (KBS) in Hickory Corners, MI. Separate sites
were used each year at each location. Soils were a Capac loam (fme-loamy, mixed,
mesic Aeric Ochraqualt) at EL and a Kalamazoo loam (fine-loamy, mixed, mesic Typic
Hapludalt) at KBS. The experiment consisted of five cover crop treatments in a

randomized complete block design with 4 replications at each location.

5

The cropping system in this study was winter wheat ( T riricum aestivum L. )/
cover crop / no-till corn (Zea mays L.) rotation. The cover crops were either frost seeded
into wheat or planted after wheat harvest. Annual legume species winter killed and red

clover was killed with a pre-plant herbicide in the spring prior to planting no-till corn.

Cover Crop Management

Cover crop treatments included two annual medic species; Santiago burr medic
(Medicago polymorpha L. cv. Santiago) and Mogul barrel medic (M truncatula Gaertn.
cv. Mogul), as well as Bigbee berseem clover (T rifolium alexandrinum L.), Michigan red
clover , and a no-cover crop control. White winter wheat (Chelsa) was fall planted in the
year preceding cover crop planting at 2.8 kg ha'l. Fertilizer was applied according to
soil test results. i In 1993 at EL, liquid manure containing 133 kg N ha'1 was applied.
Cover crops were no-till drilled into wheat stubble (straw removed) on 8 August and 9
August in 1994 at EL and KBS, respectively, and on 9 August and 11 August in 1995 at
EL and KBS, respectively. Legume plot size at EL was 3 m by 33.4 m and at KBS was
4.5 m by 33.4 m. Planting was done with a John Deere Power-Till No-Till Drill in rows
20 cm apart to a depth of l to 2 cm. Annual medics were seeded at a rate of 269 live
seeds m2. This translated into seeding rates of 13.4 kg ha"1 for Santiago medic and 15.7
kg ha'1 for Mogul medic. Red and berseem clover were planted at 16.8 kg ha’1 which is
the commonly used rate for red clover in MI. Annual medics were inoculated with a 50 -
50 mixture of Medicago "A" and Medicago "N" (Liphatech, Inc. Milwaukee, WI).
Berseem clover did not establish at EL in 1995 due to a clogged planter. When Berseem
was reseeded several weeks later it failed to produce consistent stands.

Prior to cover crop planting each field received a pre-plant herbicide application
of glyphosate CN-(phosphonomethyl)glycine) at 1.68 kg a.i. ha"l with .1% non-ionic
surfactant (NIS). In addition, sethoxydim (2-[1-(ethoxyimino)butyl]-5-[2-

(ethylthio)propyl]-3 -hydroxy-2-cyclo-hexen-1-one) was applied at .32 kg a.i. ha"l with

6

2.31 L h"1 COC: at EL on 19 August 1994 to control volunteer wheat and at KBS 12
September in 1995 to control large crabgrass (Digitaria sanguinalis L.) and quackgrass
(Elytrigr'a repens (L.) Beauv.).

Prior to corn planting in the spring of the year following cover crop planting,
each field received a burndown application of glyphosate at 1.68 kg a.i. ha'l with .1°/o
non-ionic surfactant (NIS); 2,4-D ester (2,4-dichlorophenoxyacetic acid,
butoxyethylester) at .532 kg a.i ha'1 and .5 % NIS. At both locations in 1994, red clover
was not killed by the burndown herbicides. As a result, red clover plots were mowed by
hand at EL, avoiding the corn seedlings, followed by an application of dicamba (3,6-
dichloro-Z-methoxybenzoic acid) at .56 kg a.i_ha’l to red clover re-growth which resulted
in complete kill. Also in 1994 at EL, bentazon (3-(1-methylethyl)-(1_I_I)-2,1,3-
benzothiadiazin-4(3_li)—one2,2-dioxide) at .84 kg a.i. ha“l with 2.31 L h'1 COC was spot-

sprayed for nutsedge (Cmrus esculentus L.) control on 3 June.

Corn Management

Corn (Pioneer 3751) was planted using no-till equipment in mid-May of each
year at 62,220 seeds ha'1 at a row spacing of 0.76m. Main plots were split into four
subplots, each 6.1 and 7.6 m in length in 1995 and 1996, respectively. Subplots received
either 0, 67, 134 or 202 kg N ha'1 as side-dressed ammonium-nitrate when com was in
stage V-6. Potassium and phosphorus fertilizer for corn was surface applied prior to
planting according to soil test results. Post-emergence herbicide applications were made
in late-June or early-July. At EL in 1995, nicosulfuron (2-[[[[(4,6-dimethoxy-2-
pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3 -pyridinecarboxamide) at
0.035 kg a.i ha'l; bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) at .28 kg a.i. ha'l;
with 25% NIS was applied. At KBS in 1995, sethoxydim at .21 kg a.i. ha'1 with 2.31 L
h'1 COC was used. At EL in 1996, bromoxynil was applied at .28 kg a.i. ha'l with .25%

7

NIS. Five cm of overhead irrigation water was applied to all plots in 1996 on 20 Jul. and

19 Jul. at EL and KBS, respectively.

Plant and Soil Sampling and Nutrient Analysis

Biomass of fall seeded legumes was repeatedly sampled by taking two randomly
selected 0.25 rn'2 quadrates on each of four sample dates beginning approximately 30
days after planting. Measurement dates varied slightly between locations. Frost-seeded
red clover was sampled in early Sept, approximately 45 days after wheat harvest, and
again about two weeks later, corresponding to full flowering. Spring re-growth of both
red clover treatments was sampled prior to desiccation with a herbicide. Biomass was
dried at °6O C to a stable weight, weighed and ground to pass though a 2mm screen.
Total N content of legume tissue was determined by micro-kjeldahl digestion of 0.1 g
sample in 4 ml of 12 M H2SO4 followed by colorimetric determination of NH,“ on a
Lachat flow-injector analyzer using Lachat QuikChem Method no. 10-107-06-2-E.

Soil samples were taken during the spring and summer of both years following
the cover treatments. Measurements were repetitive with slightly different sample dates
at each location. Eight to ten soil cores, 2 cm in diameter taken to a depth of 30 cm,
were pooled for each treatment plot, dried and ground and analyzed for inorganic N.
Inorganic soil N (NO3'N + N114“) was measured in filtered 1N KCL extracts
colorimetrically on a Lachat fiow-inj ector analyzer using Lachat QuikChem Method no.
12-107-04-A. Inorganic N present in the sub-soil in spring was measured on 5 May and
8 May in 1995 at EL and KBS, respectively, and 30 May and 31 May in 1996 at EL and
KBS, respectively. Soil samples were taken to depth of 90 cm and split into 30 cm
segments, dried, ground and analyzed for inorganic N as previously described.

Corn grain yield was measured by hand harvesting 5.3 m in 1995 and 6.1 m in
1996 of the center two rows. Grain was shelled with a mechanical sheller, weighed and

sampled for dry matter and N content. Corn stover from the center two rows of each

8

subplot was harvested with a flail-type harvester, weighed and sampled for dry matter
and N content. Total N was determined as described previously for legume tissue N.
Fertilizer replacement values were determined following cover crop treatments based on

N fertilizer response equations of corn with no preceding cover crop.

Dinitrogen Fixation

Dinitrogen fixation of legumes was measured with the 15N isotope dilution
technique (McAuliffe et al., 1958) utilizing 2m2 un-confmed micro-plots located at one
end of each replication. Ammonium sulfate (10.5 atom % 15N) was applied in 1994 with
a watering can and in 1995 with a backpack sprayer. Shortly after legume germination 5
kg N ha'1 15NH4504 diluted into 2L distilled water containing D-glucose at a C:N ratio
of 20:1 was applied to the soil surface and washed in with 2 L of distilled water.
Biomass in the center of the micro-plot (border of 35 cm on each side and 25 cm in
between samples) was harvested at the last two cover crop biomass sampling dates. Top
growth was clipped, dried, and ground to pass through a 1 mm screen to analyze for total
N and 15N on a Europa Scientific CN analyzer/mass spectrometer. Percent legume N

derived from fixation was calculated as follows:

PNDFA = (l - 15N a.e. FC/ 15N a.e. NFC) x 100

where F C = N2 fixing crop and NFC = non-Nz-fixing crop (Rennie, 1984). In this
calculation atom % 15N excess for the reference crops was the mean across replications.
Non-Nz-fixing reference crops used in this study were inneffective Saranac alfalfa for
berseem and red clover, and M rugosa cv. Paraponto, for the annual medics, which is

believed to be non-nodulating unless specifically inoculated.

9

Tracer Experiment with 15N Labeled Legume Biomass

In the fall of 1995 at EL and KBS, confined micro-plots consisting of PVC
cylinders 30 cm in diameter, were pushed into the soil to a depth of 30 cm, with minimal
disturbance to the soil. Two micro-plots were centrally placed within an area 3 m by 3m
at EL and 4.6 m by 3 m at KBS located at one end of each Santiago medic and no-cover
control plot. Medic above ground biomass was removed at the time of installation. On 1
April 1996, labeled Santiago medic biomass (6.56 atom % 15N) was applied to the soil
surface in each medic micro-plot, slightly moistened with distilled water and covered
with a plastic netting to prevent removal of medic from the micro-plot. Micro-plots in
no cover treatments were treated the same way, however with no medic residue applied.

Legume biomass was labeled with 15N by applying a Hoagland fertilizer solution
containing ammonium sulfate labeled at 10 atom % 15)N to Santiago medic growing in
sand in the greenhouse. Medic biomass was harvested in a semi-mature stage by clipping
at the soil surface and dried at 60 °C to a stable weight.

Sorghum sudangrass (Sorghum bicolor L. Moench) was planted into the micro-
plots by hand on 28 May at EL and 22 May KBS. The area surrounding the micro-plots
was planted with sorghum sudangrass using a no-till grain drill at 24.6 kg ha'l. Plants
were thinned to three per micro-plot shortly after germination. No fertilizer N was
applied to sorghum sudangrass. Sorghum sudangrass in all micro-plots was harvested
three times: 52, 80, and 105 days after planting (DAP) at EL, and 57, 88, and 117 DAP
at KBS. Sorghum sudangrass biomass was dried and analyzed for total N and 15N as
previously described.

On the last harvest date surface residue was collected and dried for analysis and
the micro-plots were excavated by two depths; 0-10 cm and 10-30 cm. Sorghum
sudangrass roots and crowns in the top 30 cm were analyzed separately from the soil.
Soils were weighed, mixed and sub-sampled and then analyzed for microbial biomass N,

inorganic N and total soil N. The proportion of 15N in plant, residue and soil samples

with
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10

was determined by drying and grinding samples and analyzing them on a Europa
Tracermass Mass spectrometer. Soil inorganic N was determined by 1N KCl extraction
with analysis done on a Lachet flow-injector analyzer. Inorganic 15N in KCL extracts
was released as NI-I3 following reduction of NO3-N with Devarda's alloy and addition of
MgO. The released NH3 was trapped on acidified filter disks as NH4-N (Brooks et al.
1989). The 15NH4-N was analyzed on the Europa Scientific Tracermass after
combustion of the filter disks in the Roboprep CN analyzer. Microbial biomass N was
determined using the chloroform-fumigation incubation method (J enkinson and Powlson
1988, Paul et al. 1997). Soils were stored for 1 week prior to analysis. Soils were not
reinoculated after filmigation. Biomass N was calculated as N = Nf/ Kn where Nf =
NH4-N released during incubation and Kn = 0.57. Extracted 15Nf was determined by
diffusion methods described above. Natural abundance levels of 15N were determined
from soil samples and plant materials in the no cover micro-plot. Recovery of legume
15N by plants and soils was calculated using the equations found in Harris and Hesterman
(1990).

Experimental design for the tracer experiment was a randomized complete block
with 4 replications. In each treatment plot were two micro-plots. Data from the two
micro-plots were combined for a mean value which was used in calculation of the

treatment means and standard error.

Experimental Design and Analysis

The basic experimental design at each location was a randomized completed
block design with 4 replications. The basic design was replicated in each year at two
different locations with separate randomizations. At each location, different field sites
with similar soil types were used each year, as a result location was nested within year.
Legume biomass, tissue N, and biomass N and soil inorganic N data were combined over

year and location. Repeated observations made at various sampling dates without

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11

separate randomizations constitute a repeated measures design structure. Because of
differences in sampling dates across locations, date of sampling was nested within years
and locations. Significant interactions were investigated with simple effects tests and by
calculating the appropriate LSD. Based on the patterns of significance for main effects
and interactions, as derived in ANOVA (Table 7), trends over time were modeled using
the Mixed procedure in SAS (SAS Institute, Inc., 1989). These second-stage models
permit fitting of smooth trends treating time since conception of study as a continuous
variable.

Corn yield data were combined over years and locations prior to analysis.
Analysis of variance indicated significant year by location by cover interactions. As a
result, corn yield was analyzed separately by year and location as a split-plot with main
plots being cover treatment and subplots being applied N level. Further analysis was
conducted for years and locations separately to facilitate calculation of FRVs appropriate
to site conditions. Treatment comparisons were performed using the GLM procedure
and regressions using the REG procedure in SAS (SAS Institute, Inc., 1989).
Differences due to cover effects were determined using Fishers protected LSD.
Differences in corn yield and N uptake at O N were determined by single degree of

freedom contrasts and considered significant at P 5 0.10.

12

RESULTS AND DISCUSSION

Legume Biomass

Annual legumes accumulated greater biomass than either red clover treatment at
EL in 1994 (Table 2). Mogul medic had the greatest biomass (5.3 Mg ha’l) followed by
Berseem clover and Santiago medic (4.1 and 3.1 Mg ha'l, respectively). In 1995 at EL,
biomass levels were similar among cover crop treatments. At KBS, annual medics
produced greater biomass than fall seeded red clover in both years (Table 3). Biomass
production was similar for Berseem clover and annual medics in 1994 but Berseem
biomass was lower than medics in 1995. In 1995, frost-seeded red clover and annual
medics produced similar biomass. Other researchers have reported similar annual medic
biomass levels. When interseeded with barley, fall growth of annual medics reached 5.5
Mg ha'1 under irrigation and 2.5 Mg ha'1 under dryland conditions (Moynihan et al.,
1996). Zhu et al. (1996) reported that medics planted in the fall for hay or forage in
Minnesota produced between and 5.3 Mg ha'l, depending on experimental location.

Growth trends over time of fall-planted legumes were modeled based on four
sampling dates selected within the planting year in order to describe and predict biomass
accumulation. Legume growth differed between years and locations for the various
cover species (Table 7). For example, Santiago medic displayed a cubic growth pattern
in 1994 and quadratic in 1995 (Figure 1 and Figure 2). Annual legume species generally
reached maximum predicted biomass by mid to late-Oct. which is equivalent to 65 to 80
days after planting. Fall-seeded red clover, a short lived perennial, displayed a linear
growth pattern in all site-years except at KBS in 1995, where grth was quadratic.
F rost-seeded red clover was sampled twice in the seeding year (Figure 2). Clover was
just beginning to flower at the first sample and was at full-flower at the second sample,

which was expected to be the point of maximum biomass.

13

Most growth trends indicated a maximum biomass point, especially for the annual
legumes. Annual legumes typically began to die due to frost or ceased biomass
accumulation upon initiation of flowering and eventually set seed. In 1994 at EL, a
warm and sufficiently wet fall growing season allowed Berseem clover to flower and
Santiago medic to mature and set seed. However, no peak biomass was predicted for
Mogul medic at EL under these conditions, indicating that this species was able to utilize
a longer growing period. At KBS in 1994, precipitation was not as frequent and these
soils are more prone to drought. Under these conditions, annual legumes reached a
biomass of approximately 2 Mg ha'l, although Berseem clover had no predicted
maximum. This is much lower than biomass levels at EL in 1994, and are similar to
level in 1995, where dry and cool conditions limited growth.

In 1995, dry conditions and an early killing frost limited legume growth. Most
annual legumes reached maximum biomass around mid to late-Oct. at KBS due to cold
temperatures. Santiago medic reached maximum biomass at this time in both years
indicating a shorter life cycle than Berseem clover or Mogul medic. In addition to
temperatures and available moisture, annual legume growth appeared to be influenced by
site history. In 1994 at EL, legume biomass was between 3.1 and 5.3 Mg ha’l, whereas
it was consistently under 2.8 Mg ha'1 at other site-years. The site used for the study in
1994 at EL had been planted with alfalfa two years prior to this study and had received
regular manure applications. Both factors likely increased plant available soil N and

enhanced physical and chemical soil properties which influence plant growth.

Legume Tissue Nitrogen
Tissue N for the legumes at maximum biomass are shown in Tables 2 and 3.
Tissue N of Santiago medic was lower than for Mogul medic, Berseem and red clover in

3 of 4 site years and ranged between 23.3 and 27.2 g N kg'l. Within these same site-

Wk

14

years, tissue N for Mogul, Berseem and both treatments of red clover were not
significantly different, ranging between 30.0 and 39.3 g N kg'l.

In 1994 and 1995 at KBS, Santiago medic showed a similar cubic pattern of
tissue N concentration (Figure 4). However, at EL in 1995, Santiago tissue N
concentration demonstrated a linear pattern and in the range of 30.0 to 35.0 mg N g'l.

For the most part, annual legume tissue N decreased as the plant matured. This
would be expected in annual legumes which complete there life cycle in a relatively short
period of time. For Santiago the decline was more rapid than for other species, yet
tended to increase again at the end of the growth period. It is possible that annual medics
responded to cooler temperatures in Oct. by increasing N uptake or N2 fixation resulting
in higher tissue N. In 3 of 4 site-years, Mogul medic had trends similar to Santiago with
equivalent or higher N levels. F all-seeded red clover will not mature in the planting year
which accounts for its slow change in tissue N. Tissue N for Berseem was similar to red
clover. Berseem clover is commonly used as a multiple cut forage legume, perhaps with

an ability to utilize a longer growing season.

Biomass Nitrogen Yield and Dinitrogen Fixation

Biomass N yield for annual legumes ranged between 47 and 207 kg N ha'1
(Tables 2 and 3). Although N yield between red clover and the annual legumes was in
general not significantly different, there were several exceptions: In 1994 at EL, Mogul
medic and Berseem clover had greater N yield then either red clover treatment. Santiago
medic N yield was greater than fall-seeded red clover in 1995 at EL, and in 1994 at KBS,
Berseem clover produced greater biomass N than fall seeded red clover. Nitrogen yield
was similar between frost and fall-seeded red clover and ranged between 34 and 90 kg N
ha'l.

Results indicate that most of the biomass N produced by the legume cover crops

in the seeding year will be accumulated in the biomass by 65 days after planting (Figures

15

5 and 6). If conditions permit, as they did at EL in 1994, both Berseem clover and
Mogul medic have the ability to utilize a greater time period for growth and N
accumulation. Legume growth curves are similar to N yield curves which indicates that
biomass has a greater influence on N yield than does tissue N. However, the observed
low tissue N for Santiago had a major impact on N yield.

Dinitrogen fixation by fall planted cover crops was similar across site years and
cover crops, with the exception of Santiago in 1994 at EL. Between 40 and 65 % of
biomass N was derived from N2 fixation (Table 2 and Table 3). Santiago medic N2
fixation (15.7 %) was significantly lower in 1994 at EL than the other legumes. High
soil N levels may have reduced N2 fixation by Santiago medic at this site. In general,
there were no differences observed in % N fixed between the annual legumes and red

clover.

Spring Regrowth of Red Clover

At EL in 1995, biomass N of fall-seeded clover was twice as great as that of frost-
seeded clover (Table 4). In 1996 at KBS, biomass and biomass N were greater in fall-
seeded than frost-seeded red clover. Tissue N was equivalent between the two seeding
times in all site-years. In 1995 at KBS and in 1996 at EL there was no spring regrowth
of frost-seeded clover.

In the north-central region of the USA, frost seeded red clover has proven a
reliable and effective cover crop. However, in this study there were problems associated
with establishment and spring regrowth. In 1994, very dry conditions in May killed
clover seedlings at KBS while severe wheat lodging at EL reduced frost-seeded red
clover stands reducing both fall biomass and spring regrowth. In 1996 at EL, spring

regrowth was very sparse making a reliable biomass estimate impossible.

16

Soil Inorganic N Following Cover Crop Treatments

Data were combined over years and locations and subjected to a repeated
measures analysis over the six sampling dates. Because there was no significant location
by cover effect (Table 7), the shape of the fitted trends was not varied by location (Figure
7 and 8). In 1995, all treatments displayed a slow increase in soil N between 1 May and
20 June reaching levels of 17 to 26 mg N kg'1 at EL and 13 to 18 mg N kg'1 at KBS,
with higher soil N levels following legume treatments. In 1996 soil N levels increased
more rapidly between 1 May and 10 June than in 1995, reaching between 19 and 27 mg
N kg'l. Only in early June did soil inorganic N following red clover begin to separate in
magnitude from the other treatments.

Because there was no significant date by cover by location interaction (Table 7),
inorganic N is presented combined. over dates and locations. In 1995, soil inorganic N
following legume cover crops was greater than soil inorganic N in the no cover crop
control (Table 5). Berseem clover was associated with greater inorganic soil N than was
either Santiago medic or red clover. In 1996, red clover was associated with greater soil
inorganic N than was the no cover crop control. Cool spring conditions in 1996 may
have reduced the N mineralized from winter-killed annual legumes. Occasional warm
and wet periods may have resulted in losses due to denitrification, especially at EL where
a large portion of the field flooded for several days. There was less potential for this loss .
mechanism with red clover, which was alive during most of the spring.

Early spring soil NO3'N levels were measured in order to determine the potential
for loss of legume N through leaching. Although these data represent only one point in
time, we attempted to select a time when NO3'N is subject to movement in the soil.
Analysis of variance indicated a year by cover by depth interaction. The effect of depth
would be expected with a greater level of NO3'N to be observed in the top 30 cm of the
profile resulting from mineralization of soil organic N (Table 6). The analysis indicated

a significant year by cover interaction but not a location by cover interaction. As a result

17

data are combined over locations. A simple effects test indicated that the cover crop
treatments influenced the level of soil NO3'N in 1995 but not in 1996 (Table 6). In 1995,
soil NO3'N at 0-30 cm depth was greater following all annual cover crops then in the no
cover crop control. At 30-60 cm, NO3'N levels were again higher following the annual
legumes than following either red clover or the no cover crop control. In no case did we
find NO3'N levels above 10 mg N kg'l, which is considered the level above which
drinking water may be unsafe for some populations.

In both years, soil N03 concentration tended to decrease with sampling depth.
There were significant differences among cover crop treatments in the 0-3 0, and 30 to 60
cm depth classes, but not in the 60 to 90 class. Legume cover crop treatments did not
increase soil NO3'N levels at the 60-90 cm depth when sampled in spring, during a
period of high rainfall and increasing temperatures, when significant rates of nitrification
would be expected. Stute and Posner (1995) also found there was no increase in sub-soil
NO 3'N following red clover. Nitrogen from the winter killed annual legumes may have
been mineralized during brief warm and wet periods in the early spring. As a result,

some of this NO3'N could have been washed deeper into the soil profile.

Corn Grain and Total Biomass Yield

In two of the four site years corn grain and total biomass of no-till corn was
greater following cover crop treatments than following the control. In 1995 at EL, grain
yield and total biomass were unaffected by the annual legumes, but were reduced
following red clover when averaged across N levels (Tables 8 and 9). The EL site, prior
to this study, had a history of manure application and had been in alfalfa. As a result, the
soil may have supplied enough N to the crop to preclude any further response to either
cover crop N or applied N. In 1995, red clover was incompletely killed by herbicide,
especially at EL, and required a second herbicide application. The living clover may

have caused interruption in corn seed placement, and reduction in germination as well as

18

a reduction in soil moisture levels (Dabney et al. 1996). Other researches have reported a
reduction in available soil moisture due to over wintering cover crops and a subsequent
yield reduction. (Badaruddin and Meyer, 1989; Frye et al. 1988; Hesterman et al. 1992;
Tiffm, 1994).).

Grain yield and total biomass at KBS in 1995 were greater following Mogul
medic and Berseem clover when compared to the no cover control (Tables 8 and 9). In
1996 at EL, grain yield and total biomass were greater following all cover treatments
verses the control. There were no significant differences in grain yield or biomass at
KBS among cover crop treatments in 1996. Dry conditions coupled with a well drained
soil at KBS created moisture stress in the corn and limited yield.

There was no significant response to N fertilizer by com grain and total biomass
across cover crop treatments at EL in 1995 and a quadratic response at KBS in 1996
(data not shown) with no significant cover by N interactions. A significant cover crop by
N interaction for corn grain was observed at KBS in 1995. Corn grain following
Berseem clover and Mogul medic did not respond to N fertilizer (Figure 9), with means
of 8.21, and 8.15 Mg ha], respectively, suggesting adequate N provided by the cover
crop. Grain yield following Santiago medic and the no cover control crop displayed a
linear and quadratic response, respectively. At the highest fertilizer N rate in the control
treatment, a corn grain yield decrease was noted, perhaps due to the lower number of
plants in this treatment compared to the field average.

At EL in 1996, there were significant cover and N effects, but no interaction was
observed (Figure 10). The response of corn grain to all cover treatments followed a
quadratic trend with a tendency for yield to be lower following the no cover control and
greatest following red clover treatments. Response by total corn biomass to nitrogen at
KBS in 1995 and EL in 1996 were similar to those described for corn grain (data not

shown).

19

Fertilizer Replacement Values

Fertilizer replacement values (FRI) were calculated based on corn grain yield,
total biomass yield, N uptake by com grain and N uptake by total biomass where there
was significantly higher yield following a legume than following the no cover crop
control at O N level (Hesterman et al. 1992). A FRI based on grain yield is most
common, however, others have found the use of grain N uptake a more sensitive
indicator of corn response to fertilizer N (Hargrove, 1986; Hesterman et al., 1992;). For
Mogul medic, FRVs were calculated in two separate years and ranged between 22 and
108 kg N h'1 with greater estimates based on total biomass yield (Table 11). For
Berseem clover, FRVs were 86 and 112 kg N h'1 based on grain yield and biomass yield,
respectively in 1995 at KBS. Both red clover treatments produced significant F RVs. For
fall seeded red clover, the FRI ranged between 31 and 91 kg N h'1 in three separate site
years, with greater values generally based on total biomass yield or N uptake. One of the
comparisons attempted in this study was to compare the FRI of red clover seeded in the
spring verses in the fall, and then followed by no-till corn. Based on these results (Table
11) no conclusions can be drawn on this point. However, F RVs for both clover
treatments in this study were lower than reported by Hesterman et al. (1992) under
similar conditions (113 and 121 kg N h-1 based on grain yield and total N uptake,
respectively).

FRVs calculated for annual legume species, were comparable to those calculated
for red clover in 1995 but lower than those for red clover in 1996. These results indicate
significant positive yield effects, when measured in terms of fertilizer N, by annual
legume species on no-till corn. Jeranyama (1995) reported an FRI of 40 kg N h'1 to a
corn crop following corn interseeded with annual medic, however, Squire (1997)

reported an FRI under 10 kg N h'1 for this same interseeding system.

20

Recovery of Legume lsN

Measuring the response of corn to legumes in terms of the FRI combines rotation
effects with actual N contribution (Hesterman, 1988). The 15N method is thought to be
more precise in actually measuring N contribution, and is therefore generally lower than
FRI values (Harris and Hesterman, 1990). Total legume N uptake by the sorghum
sudangrass following Santiago medic was 8.2 kg N ha'1 at EL and 14.9 kg N ha'1 at KBS
, which is equivalent to 8.4 % and 14.3 % of the legume N applied to the soil surface,
respectively (Table 13). These N uptake values are significantly lower than the
calculated FRI for Santiago medic. Our results agree with other research which has
found FRVs to be greater than the estimated legume N uptake using l5N tracer methods
(Harris and Hesterman, 1990). There was no significant FRI for Santiago medic at KBS
in 1996, yet we measured 13.9 kg N h'1 uptake. In this case, it appears that even though
a small amount of legume N was taken up by the following crop, positive rotation effects
were limited by dry growing conditions.

Uptake of legume 15N by the crop was lower than what others have found where
over wintering cover crops were used. Ladd et al. (1983) reported uptake of N from soil
incorporated M littoralis (var. Harbinger) by a following wheat crop to be between 11
and 28 %. Harris et al. (1994) found 14 to 16 % of legume N taken up by com where red
clover had been incorporated into the soil. The lower values observed in this study may
be due in part to the localization of the legume N on the soil surface and in the upper 10
cm of soil. Others have reported lower legume lsN uptake in no-till than under
conventional tillage conditions (Wilson and Hargrove, 1986; Smith et al., 1987).
Sorghum sudangrass may have removed much of its N from below this depth. Soils at
KBS are coarser in texture and easier movement downward of N may have increased
plant access to legume N and contributed to the greater uptake of applied 15N. Another
factor which may have contributed to lower uptake levels is the difference in application

time. Annual legumes are winter killed, increasing their time of exposure to conditions

21

which cause N loss. Both denitrification N volatilization can occur from surface residues
during wet periods. Ammonia volatilization from a Lens culinaris Medik. green manure
was reported to be 5 and 14 % of biomass N (Janzen and McGinn, 1991). There was no
evidence of movement of N below 60 cm in soil depth (Table 6) and therefore no loss of
N through leaching.

Legume N absorbed by sorghum sudangrass was highest during the first 8 weeks
of crop growth and became progressively less over the course of the season (Figure 11).
In the first cutting 4.8 % and 8.4 % of the applied legume N had been taken up by the
crop at EL and KBS, respectively. Other research has shown that the majority of legume
N which mineralized in the first year is released within the first six weeks after it is
applied (Wilson and Hargrove, 1986; Smith et al., 1987).

Legume N in the soil after final harvest was found primarily in the top 10 cm
(Table 12). Recovery of legume N in the top 10 cm of soil was 47.3 % and 65.3 % of
input at EL and KBS, respectively, and about 10 % was recovered at a depth of 10-30
cm. The microbial biomass contained 10.3 °/o and 13.9 % of input at EL and KBS,
respectively. Recovery as inorganic N was less than 2 %. Surface residue consisting of
legume residue and wheat straw contained 1.7 % and 5.3 % of input at EL and KBS,
respectively.

Overall recovery of legume N in the cropping system was 69.1% and 94.1 % of
input at EL and KBS, respectively (Table 13). Loss from the system was calculated to be
30.9 % or 30.3 kg N h'1 at EL and 3.9 % or 3.8 kg N h'1 at KBS. Recovery of annual
legume N in soil was similar to what has been reported for legumes which are killed
prior to planting. Harris et el. (1994) found between 60 and 72 % the applied legume N
had remained in the soil after crop harvest. Levels at EL may have been lowered by 2
flooding events, one in mid-May and one in late-June. Conditions at EL could have
supported denitrification, leaching and ammonia volatilization at various times and could

have been viable means of N loss from the system. Nitrate levels in the subsoil in late

22

May following cover crops were no higher than in the control (Table 6). High recovery

at KBS reflected a relatively dry season and the well drained soil at that site.

CONCLUSIONS

This study sought to determine the potential of several legumes as cover crops
when established after wheat harvest, a period in the crop rotation which would
otherwise be a fallow period. The legume cover crops in this study were successfully
established and accumulated biomass N ranging from 34 to 206 kg N ha'l. Biomass N
for annual legumes was often the same or greater then for red clover in the seeding year,
however, spring regrowth by red clover accumulated between 56 and 123 kg N ha'l.
Annual legumes usually reached peak biomass within 65-80 days after planting,
indicating sufficient time for growth.

Corn grain following the cover crops was increased over a no cover crop control
in 2 of the 4 site years. Corn grain yield was greater following several annual legume
species than following red clover in 1995, however less differences were seen in 1996.
The effect of the cover crops on a following no-till corn crop was measured in terms of N
fertilizer replacement values (FRI). Even though annual legume biomass is winter killed
and remains on the soil surface, subject to conditions which promote denitrification,
ammonification, and N leaching, FRVs were comparable betvlreen annual legumes and
red clover and ranged from 12 to 112 kg N ha].

Soil inorganic N In the spring and early summer was somewhat predictive of
significant FRVs. In 1995, soil tests indicated legume N mineralization with inorganic N
greater following all legumes compared to the no cover crop control. This was also the
year with the highest FRVs, ranging from 66 to 112 kg N ha‘l. In 1996, the only cover
crop treatment with both significantly greater soil inorganic N and subsequent FRI was
red clover (Tables 5 and 11). This confirms the usefulness of the presidedress spring

nitrate test following organic N sources under no-till conditions (Meisinger et al. 1992).

23

Crop uptake of legume N measured using 15N was lower than the respective FRI
value, and lower that what other researchers have reported for legume 15N uptake.
Uptake of legume 15N was limited by dry growing conditions, especially at KBS where
96 % of the applied N was recovered and only 16 % was in the crop (Table 13). At EL,
field conditions may have promoted loss of N through denitrification and ammonification
since only 69 % of the applied N was recovered with 9.7 % in the crop.

Based on results of this study, annual and perennial legumes planted after wheat
harvest are a viable means of increasing diversity in the crop rotation while also
enhancing yield of a following crop by contributing to N needs and positive rotation

effects.

2 4
REFERENCES

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water status. Crop Sci. 29:1212-1216.

Brahim, K., and SE. Smith. 1993. Annual medic establishment and the potential for
stand persistence in southern Arizona. J. Range. Manage. 46:21-25.

Brooks, P.D., J.M. Stark, B.B. McInteer, and T. Preston. 1989. Diffusion method use to
prepare soil KCl extracts for automated N-15 analysis. Soil Sci. Soc. Am. J. 53:1707-
1711.

Crawford, E.J., A.W.H. Lake, and K.G. Boyce. 1989. Breeding annual Medicago species
for semiarid conditions in southern Australia. Advances in Agronomy. 42:399-435.

Dabney S.M., J.D. Schreiber, C.S. Rothrock, and JR Johnson. 1996. Cover crops affect
sorghum seedling growth. Agron. J. 88:961-970.

Decker, AM. A]. Clark, J.J. Meisinger, F .R Mulford, and MR McIntosh. 1994.
Legume cover crop contributions to no-tillage corn production. Agron. J. 86:126-135.

Ebelhar S.A., W.W. Frye, and RL. Blevins. 1984. Nitrogen from legume cover crops for
no-tillage corn. Agron. J. 76:51-55.

Ewing, MA. 1983. Medics return to favor. Western Australian Dep. Agr. J. Agr. 27-31.

Frye, W. W., RL. Blevins, M.S. Smith, 8.]. Corak, and J.J. Varco. 1988. Role of annual
legume cover crops in efficient use of water and nitrogen. p. 129-154. In W.L. Hargrove
(ed.) Cropping strategies for efficient use of water and nitrogen. ASA Spec. Publ. 51.
ASA, Madison, WI.

Frye, W.W., RL. Blevins, M.S. Smith, S]. Corak, and J.J. Varco. 1988. Role of annual
legume cover crops in efficient use of water and nitrogen. p. 129-154. E W.L. Hargrove
(ed) Cropping strategies for efficient use of water and nitrogen. ASA Spec. Publ. 51.
ASA, Madison, WI.

Hargrove, W.L., D.E. Kissel, and LB. F enn. 1987. Field measurements of ammonia
volatilization from surface application of ammonium salts to a calcareous soil. Agron. J.
69:473-476.

Harris, G. H. and 0B. Hesterman, 1990. tifying the nitrogen contibution from
alfalfa to soil and two succeding crops using N. Agron. J. 82:129-134.

Harris, D. and EA. Paul. 1939. Automated analysis of 15N and 1“c in biological
samples. Commun. Soil Sci. Plant Anal. 20:935-947.

Hesterman, 0.8. 1988. Exploiting forage legumes for nitrogen contributions in cropping
systems. p. 155-166. lg W.L. Hargrove (ed) Cropping strategies for efficient use of
water and nitrogen. ASA Spec. Publ. 51. ASA, Madison, WI.

Hesterman, 03., CC. Sheafl‘er, D.K. Barnes, WE. Lueschen, and J.H. Ford. 1986.
Alfalfa dry matter and nitrogen production, and fertilizer nitrogen response in legume-
corn rotations. Agon. J. 78:19-23.

25

Hesterman, O.B., T.S. Grifiin, P.T. Williams, G.H. Harris, and DR Christenson. 1992.
Forage legume-small grain intercrops: nitrogen production and responses of subsequent
corn. J. Prod. Agric. 5: 340-348.

Holderbaum, J.H., A.M. Decker, J .J . Meisinger, FR. Mulford, and LR Vough. 1990.
Fall-seeded legume cover cr0ps for no-tillage corn in the Humid East. Agron. J. 82:117-
124.

‘ Huntingtion, T.G., J .H. Grove, and W.W. Frye. 1985. Release and recovery of nitrogen
from winter annual cover crops in no-till corn production. Commun. Soil Sci. Plant Anal.
193-211.

Janzen, H.H. and SM. McGinn. 1991. Volitile loss of nitrogen during decompostion of
legume green manure. Soil Biol. Biochem. 23(3):291-297.

Jeranyama, P. 1995. Effect of planting date on dry matter yield and nitrogen
accumulation of annual medic species either clear seeded or intercropped with corn.
Master Thesis. Dept. of Crop and Soil Sciences. Michigan State Univ.

Ladd, J.N., M. Amato, RB. Jackson, and J.H.A. Butler. 1983. Utilization by wheat crops
of nitrogen from legume residues decomposing in soils in the field. Soil Biol. Biochem.
15:231-238.

Lesins, K.A., and I. Lesins. 1979. Genus Medicago (Luguminosae)-A taxogenetic study.
W.Junk, the Hauge, Netherlands.

Meisinger, J.J., V.A. Bandel, J .8. Angle, BE. O'Keefe, and CM. Reynolds. 1992.
Presidedress soil nitrate test evaluation in Maryland. Soil Sci. Soc. Am. J. 56:1527-
1532.

Moynihan J .M., SR Simmons, C.C. Sheaffer. 1996. Intercropping annual medic with
conventional height and semidwarf barley grown for grain. Agron. J. 88:823-828.

Papastylianou, I. 1987. Amount of nitrogen fixed by forage, pasture, and grain legumes
in Cyprus, estimated by the A-value and a modified difference method. Plant Soil
104:23-29.

 

Paul E.A, D. Harris, T. O'Dell, and M. King. 1997 Determination of microbial biomass
source.

Puckridge, D.W., and RJ. French. 1983. The annual legume pasture in cereal-ley
farming systems of southern Australia: a review. Agriculture, Ecosystems and
Environment, 9:229-267.

Rennie, RJ. 1984. Comparison of N balance and 15N isotope dilution to quantify N2
fixation in field-grown legumes. Agron. J. 76:785-790.

Rumbaugh, M.D., and DA. Johnson. 1986. Annual medics and related species as
reseeding legumes for northern Great Basin pastures. J. Range Manage. 39:52-58.

Scott, T.W., J. Mt. Pleasant, RF. Burt, and D. J. Otis. 1987. Contributions of ground
cover, dry matter, and nitrogen from intercrops and cover crops in a corn polyculture
system. Agron. J. 79:792-798.

26

Shrestha, A. 1996. Annual medics and berseem clover as emergency forages or green
manure for canola. Doctoral Dissertation. Dept. of Crop and Soil Sciences. Michigan
State University.

Sims, IR, and AE. Slinkard. 1991. Development and evaluation of germplasm and
cultivars of cover crops. p. 121-129. In W.L. Hargrove (ed) Cover crops for clean water.
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Soc. Ankeny, Iowa.

Smith, S.M., W.W. Frye, and J .J . Varco. 1987. Legume winter cover crops. Advances in
Soil Sciences. 7:95-139.

Stute, J.K., and Posner, J .L. 1993. Legume cover crop options for grain rotations in
Wisconsin. Agron. J. 85:1128-1132.

Tiffin, P. L. 1994. corn grain and nitrogen yield response to cover crop kill date and
subirrigation. Master Thesis. Dept. of Crop and Soil Sciences. Michigan State Univ.

Wescott, M.P., LE. Welty, M.L. Knox, and LS. Prestbye. 1995. Managing alfalfa and
berseem clover for forage and plowdown nitrogen in barley rotations. Agron. J. 87 :1 176-
1181.

Wilson, D.O. and W.L. Hargrove, 1986. Release of nitrogen from crimson clover residue
under two tillage systems. Soil Sci. Soc. Am. J. 50:1251-1254.

27

Table 1. Monthly precipitation and mean air temperature during the growing seasons of
1994-1996 at EL and KBS, MI.

 

 

 

 

Year Month EL KBS
Precip. Mean Precip. Mean
Temp Temp
mm °C mm °C
1994 May 46.2 12.7 4.0 15.8
Jun. 185.9 19.8 174.4 21.5
Jul. 121.2 20.9 160.2 22.4
Aug. 143.3 18.6 119.5 21.9
Sep. 118.9 16.7 29.6 17.9
Oct. 80.8 10.7 73.4 12.0
Nov. 120.7 5.7 106.7 6.9
1995 Apr. 69.3 5.2 76.8 6.7
May 63.5 12.6 72.7 14.8
Jun. 42.2 19.8 92.2 21.6
Jul. 100.6 21.4 82.9 24.4
Aug. 116.1 23.2 110.4 24.8
Sep. 32.3 14.6 48.4 16.1
Oct. 69.1 11.2 58.9 12.0
Nov. 78.5 -0.7 90.8 0.8
1996 Apr. 98.0 6.1 81.9 7.1
May. 71.9 12.6 70.3 14.5
Jun. 140.5 19.6 130.4 21.6
Jul. 29.5 19.7 2.56 21.3

 

28
Table 2. Legume cover crop biomass, tissue N and biomass N at maximum fall biomass

 

 

 

 

 

 

 

 

 

 

at EL, MI.
Santiago Mogul Red Berseem Red
Medic Medic Clover Clover Clover
F85
Mg ha'1
Biomass
1994 3.1c 5.3 a 1.9 d 4.1 b 1.7 d§
1995 2.2 1.8 ab 1.3 b -- 1.9 ab
8 kg"
Tissue N
1994 27.2 b 38.4 a 39.3 a 34.1 a 36.7 a
1995 32.0 a 24.8 b 26.8 ab -- 25.5 b
kg ha'1
Biomass N
1994 85.4 c 206.7 a 71.9 c 139.7 b 62.3 c
1995 67.4 a 46.6 ab 34.2 b -- 47.7 ab
%
N Fixed
1994 15.7 b 58.5 a 57.9 a 64.9 a -
1995 45.2 a 41.4 a 55.9 a 54.8 a --

 

§ Means within a row followed by the same letter are not significantly different at P5005
with Fishers Protected LSD.
5 Frost-seeded red clover.

29

Table 3. Legume cover crop biomass, tissue N and biomass N at maximum fall biomass

 

 

 

 

 

 

 

 

 

 

at KBS, MI.
Santiago Mogul Red Berseem Red
Medic Medic Clover Clover Clover
FS8
Mg ha’1
Biomass
1994 2.0 a 2.3 a 1.4 b 2.2 a§ --
1995 2.8a 2.4a 1.7b 1.6b 3.0a
g kg"
Tissue N
1994 23.3 b 30.0 a 33.0 a 33.9 a --
1995 26.1 b 31.4 a 35.0 a 31.5 a 30.3 ab
kg ha'1
Biomass N
1994 48.1 ab 70.6 ab 44.9 b 77.2 a --
1995 72.1 ab 73.8 ab 58.5 b 49.8 b 89.8 a
%
N Fixed
1995 41.4 a 50.0 a 46.4 a 38.3 a --

 

§ Means within a row followed by the same letter are not significantly different at
P_<_0.05 with Fishers Protected LSD.

5 F rost-seeded red clover.

30

Table 4. Biomass, tissue N and biomass N for spring regrowth of red clover prior
to burndown application.

 

 

Location Seeding Time Biomass§ Tissue N Biomass N
1 95 Mg ha'1 g kg'1 kg ha'1
EL Fall 3.0 a 41.3 a 123 a
Spring 1.5 a 39.0 a 56 b
KBS Fall 2.2 38.9 87
Spring -- -- --
l 96
BL Fall 2.2 34.1 76
Spring -- - --
KBS Fall 2.1 a 36.9 a 78 a
Spring 1.6 b 37.0 a 58 b

 

5 Means in a column within each site year followed by the same letter are not significatly
different at P S 0.05.

31

Table 5. Soil inorganic N following cover treatments combined over location and
sample date in 1995 and 1996.

 

 

 

 

Cover Treatment 1995§ 1996
mg kg"

Santiago medic 13.0 b 14.0 b
Mogul medic 14.0 ab 14.5 b
Red clover 13.4 b 15.8 a
Berseem clover 14.8 a 13.0 b
Red clover F S - 13.3 b
No cover 10.5 c 14.0 b

 

‘5 Means in a column followed by the same letter are not significatly different
at P _<_ 0.05.

Table 6. Soil N03 at three depths (cm) following cover treatments averaged over
two locations in MI.

 

 

 

 

 

 

Cover 1995§ 1996
Treatment
0-30 30-60 60-90 0-30 30-60 60-90
mg kg"

Santiago medic 5.2 b 3.8 b 3.0 a 3.8 a 2.1 a 1.4 a
Mogul medic 6.3 bc 6.4 c 3.7 a 4.0 a 2.1 a 1.3 a
Red clover 3.7 a 2.3 a 3.3 a 3.8 a 1.0 a 1.1a
Berseem clover 7.3 c 4.7 b 2.7 a 4.2 a 1.6 a 2.4 a
No cover 3.5 a 2.5 a 2.7 a 3.0 a 1.8 a 1.4 a

 

5 Means followed by the same letter in a column are not significantly different at
P 5 0.05.

5 Sample dates in 1995 were 5 May at EL and 8 May at KBS, and in 1996
were 30 May at EL and 31 May at KBS.

32

Table 7. Repeated measures analysis for legume biomass, tissue N, biomass N, and
soil inorganic N.

 

 

 

 

P value P value

Source df Biomass Tissue Biomass df Inorganic
N N N

Year (Y) 1 0.0007 0.0001 0.0001 1 0.0003
Location (L) [Y]§ 2 0.0001 0.0001 0.0001 2 0.0001
Block (B) 3 0.7358 0.5405 0.8012 3 0.3415
B [Y x L] 9 0.4586 0.0985 0.5173 9 0.004
Cover (C) 4 0.0001 0.0001 0.0001 5 0.0001
Y x C 4 0.0016 0.0006 0.0001 4 0.0014
L x C [Y] 6 0.3180 0.2807 0.1379 8 0.2678
Date [Y x L] 12 0.0001 0.0001 0.0001 20 0.0001
Date x C [Y x L] 35 0.0001 0.0001 0.0001 75 0.0715

 

5 Brackets indicate the source of variation is nested.

33

Table 8. Response of no-till corn grain to cover treatments averaged over applied

 

 

 

 

 

 

N levels.
1995 1996
Cover EL KBS EL KBS
Treatment
Mg ha'1
Santiago Medic 9.06 7.76 6.55 5.51
Mogul Medic 8.92 8.15 6.67 5.79
Red Clover 8.16 7.30 7.42 5.26
Berseem 9.05 8.21 - 5.29
Clover
Red Clover FS 8.19 -- 7.24 4.89
No Cover 8.84 7.55 5.59 5.49
LSD (0.10) 0.48 0.50 - ns
LSD (0.05) 0.58 0.62 0.85 ns
LSD (0.01) ns ns 1.19 ns

 

Table 9. Response of no-till corn total biomass to cover treatments averaged over

 

 

 

 

 

 

applied N levels.
1995 1996
Cover EL KBS EL KBS
Treatment
Mg ha'1
Santiago Medic 17.95 13.65 11.53 9.59
Mogul Medic 18.27 14.31 11.76 9.98
Red Clover 15.88 13.14 13.25 9.35
Berseem 18.34 14.55 -- 9.44
Clover
Red Clover FS 16.20 -- 13.12 9.03
No Cover 17.62 12.84 10.05 9.82
LSD (0.10) 1.50 1.08 1.40 ns
LSD (0.05) 1.83 1.33 1.71 ns
LSD (0.01) ns ns 2.40 ns

 

34

Table 10. Regression equations for corn grain yield (Y) as a function of applied N (x)
following cover treatments.

 

 

Year and Location Cover Treatment Equation R2
1995 KBS Santiago medic Y = 6.5 + 0.013x 0.62
Mogul medic NS Y = 8.2
Red clover NS Y = 7.3
Berseem clover NS Y = 8.2
No cover Y = 6.0 + 0.046x - 0.00019x2 0.68
1996 EL Santiago medic Y = 3.8 + 0.051x - 0.00015x2 0.79
Mogul medic Y = 3.4 + 0.060x - 0.00017x2 0.84
Red clover Y = 4.8 + 0.047x - 0.00013x2 0.92
Red clover FS Y = 3.9 + 0.064x - 0.0002x2 0.94
No cover Y = 2.7 + 0.049x - 0.00013x2 0.73

 

35
Table 11. Nitrogen fertilizer replacement values (F RV) based on corn yield and N

 

 

 

 

uptake.
Grain Yield Total Grain N Total
Biomass Biomass N
kg N ha‘1
1995 KBS
Mogul medic 85 108 .. --
Red clover 66 91 74 91
Berseem clover 86 112 -- --
1996 EL
Santiago medic 25 -- .. --
Mogul medic 22 -- 12 12
Red clover 48 57 31 35
Red clover FS 28 -- -- --
1996 KB
Red clover -- -- 37 39

Red clover F S -- -- 38 42

 

36

Table 12. Recovery of annual legume N applied to soil surface in selected soil pools
and in surface residue in 1996 at EL and KBS, MI .

 

 

 

 

Inorganic N Microbial N Total soil N
EL. %of Applied
0-10 cm 0.70 (0.03)§ 7.56 (0.24) 47.25 (5.56)
10-30 cm 0.29 (0.03) 2.76 (0.13) 10.41 (0.90)
KBS
0-10 cm 0.89 (0.06) 11.25 (0.42) 65.26 (3.26)
10-30 cm 0.49 (0.10) 2.66 (0.23) 9.60 (0.84)

 

§ Numbers in parenthesis are standard errors values.

Table 13. Recovery and loss of annual legume N applied to soil surface in 1996 at EL

 

 

and KBS, MI.
EL ‘ KBS
kg ha-1 % of kg ha'1 % of
Applied Applied
Applied 97.9 100.0 97 .9 100.0
Crop
Top 8.2 8.4 13.9 14.3
Root 1.2 1.3 1.7 1.7
Soil 56.5 57.7 73.3 74.9
Surface Residue 1.7 1.7 5.2 5.3
Total Recovey 69.7 69.1 94.1 96.1
Loss 30.3 30.9 3.8 3.9

 

37

Dry Matter Yield (Mg ha “)

88Ln 1
. .81» Ill ages. are. as ........ _aa 3

Illl gown—BEAM? .....nlnfiwm
l flame—9.2.5... ........ E
I

Till wag—5 29.2. E: ....... . E

881,.

 

 

 

meat—5m 598
Ema—8 H 332. 3 55:9. Ema on. 395.5 n39. 9.2% m: E?» we HF 85 gm.

I ...‘.‘ ‘-

A-uou

.....SE .EE: 2 55.5.5 23.3. ewe—ca .: were a: :5 :3: 757.-

38

Dry Matter Yield (Mg ha '1)

gm llll mangoes as: E. ........ are
11111 zonaaeeamr 1.1.: Em
. Ill 52. 296—. MP ........ E
was 1 1 mega. 933 Sr . ...... ... E R
, ill an. ace: :8. 882. mr ....2 . a... . ...,n Em v
g l

 

 

 

Emma Name Sean. sea. e59. 823 $23 $23
muse—En 69$
Ema—8 N. 332— 5 5582. Sea a». ram—55 «99. 9.25 5 Emu 3 Mb 3:. Ewm.

39

Tissue N (g kg-l)

 

 

 

81
R g | map—Emma 52:.” Hr ........ a
w ,. aging—mam? 1.7.1;
$1. I wan—Sonar ........ E
R. 1.11.111 anaemia—Sonar ...I... gm
8!
31
.51
um]
woL
Null
N61
51
— i _ . _ _ _ a _ _
same name name 869. .89.

maze—Fm Guam
and; w. 533 393mg 8585536: 5 ram—55 amaze m: .3.» an HE E:— Ewm.

40

Tissue N (g kg")

1 , g | museums sans E.
, lllll Sen... Eon? Er
mm 1 L l E 0.98.. MP
1 Wazoo:— n_9.2. Er
A. lll.|... E 295.. ado” moon—2— Hr
mo 1 .1
1
am. .1
45 l

 

    

 

l ....... .....w..fi%.mwtw.mv.mw.+m.
we ....,..xk.n....w, , . .2.
8|. ...
. ...?
81
not
51
_ _ _ _ H a _ _ _ _ _ a _ _ _
Ewan. Ewan. 3064—. 390—. Mg 820< EZO< NwZG<
men—Ewan 598

mam-=6 a». 382— annemg 8:855:23 m: Ems—5e Sam—8 m: 5mm we HF Ea Nam.

41

N Yield (kg ha

 

 

 

wee I. l _.
R. g I manage 32.? Hr ........ E W
‘ ,lllll Z§=_ao&emr 311.: flaw _
n, I won £95.. mp. ........ Nam _

”gin“ J Ill ”magaW—Atuadfi—wrl .r..1.1.w.IWlm l w

N8 1

5o 1

#8 l

g l

o 1
fl _ _ _ _ _ _
canny 59mm» Mammy 800—.

mus—Es” 568
3% m. 333 83— 2 manna—=82. m: Ema—Bo 69.2. 9.25 m: .3» we Hr BE mam.

42

N Yield (kg ha '1)

 

 

 

 

@813 l . .....l l l
3 3
H Ewm | muss-No 53:9 HF ........ Rum _3
1,. Till 23558:? 1.5.: Em L
_ l wanes. mr ........ _Sm _
NSIR Tannin—Sonar 1.1.15 1
3 will”. ., I ”2— 29.2. 3.3 woman.— mr .231...” Ram A
1
meal
‘8]
~81 .
3.1 L ...... 24.1.: 11 SIT
at. c. E 3
................... .... ... .
1 ...w ............... . I.
., .m. ........................................... .33
.ll 1 ........ .1. .......... ..
gl .1 ya P L 1. PL .1 I .1 L l I H I. F r... F in .IA w...r.).3..L..rw.L
_ _ _ _ L _ _ _ _ _ n _ _ _
Emma. Nam—mm. EOQH 38.. g 82¢< EZO< 82a?

mega—mam CNS
Ema—um a. 533 SS— 2 non—5.532. :— 5955 e99. 968 5 6mm 99 ab 85 gm.

..‘11 I‘VE. I‘ll.

 

hl\a.\rh

A-F urns wh-uah hCUnJr

 

43

Soil Inorganic N (mg kg“)

REM l misnoaoaamr ........ Ea
, Ullll Scenes—name 1.3.1.156
. ill wan—inns“? ........ E
81. till 5423.323 E
R Hill Goings—r 1.4.7.156

Nmi

~91

 

. _. 1.).«3 ........\L
...x.. 1; V

l .HUH..:.11. 1 rl. 1 11.1...uL-11H122 .... .....(Iw
.......... alacrt
ml ... 1,5332%. ......
wt.» . . ... t
in; l Ml. V (1.3.1 .

 

 

_ 2 _ 1 L _ _ _ L _ _ n L n L _ _ _ _
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Chapter 2

WEED SUPPRESSION BY ANNUAL LEGUIVIE COVER CROPS IN NO-
TILLAGE CORN

ABSTRACT

Among the benefits provided by cover crops is the ability to reduce the density and
biomass of annual weeds when used in no-till systems. Despite positive effects often
produced by winter annual cover crops in corn production, there is also the potential for
yield reduction due to depletion of soil moisture, N immobilization, and difficulty in
cover crop management. Currently, there is interest in annual species of Medicago
(annual medics) and other annual legumes which winter-kill for use as cover crops in
mid-westem grain cropping systems. This research was conducted to investigate the
influence of annual legume cover crops on weed populations prior to no-till corn planting
and during the early stage of corn growth. Spring annual weed density and dry weight
were often reduced following annual legumes compared to no cover control. The effect
on summer annual weed density was not as pronounced as for spring annuals, however, ‘
dry weights were reduced by 70 % in 1995 at both locations. Dry weight of perennial
weeds sampled before corn planting were almost always lower following annual legumes
compared to no cover. Perennial weed density and dry weight sampled 45 days afier
corn planting were reduced following annual medics in some cases. This research
indicates an excellent potential for annual legumes to reduce weeds density and growth in

corn grain systems.

48

49
INTRODUCTION

The use of cover crops in no-till corn production can provide a variety of
benefits, both to a following corn crop and to the long-term health of the cropping
system. Legume cover crops can replace fertilizer N (Fisk, 1997., Hesterman et al.
1992., Blevins et al. 1990), minimize soil erosion (Hargrove et al., 1984 ), maintain soil
organic matter and improve soil structure (Frye et al., 1988; Smith et al., 1987), as well
as reduce weed density and biomass. Hairy vetch (Vicia vilIosa Roth), crimson clover
(T rifolium incamatum L.) and subterranean clover (T. subterranean: L.) have been
shown to reduce weed density and dry weight of early season weeds (Y enish et al. 1996;
Teasdale et al. 1991; Johnson et al. 1993).

Most legume species which are used as cover crops in no-till corn (Zea mays L.)
production are winter annuals or short lived perennials. In northern regions of the USA,
over-wintering species are normally established in the summer or fall and accumulate
most of their biomass when they regrow in the spring. If allowed, they will mature and
set seed in summer.

Despite the positive effects often produced by winter annual cover crops in corn
production, there is also potential for corn yield reduction. Spring regrowth by legumes
can lower available water in the sub-soil creating conditions of moisture stress for corn in
years of low precipitation (Badaruddin and Meyer, 1989; Frye et al. 1988; Hesterman et
al. 1992; Tiffin, 1994). In addition, winter annuals require some form of control, either
chemical or mechanical, before or at the time of corn planting. Quick-acting herbicides
are most commonly used, however, these can result in incomplete control (Y enish et al.
1996; Worsham and White, 1987). Although herbicide options for cover crop control
have improved, variability of spring conditions can still lower their effectiveness. Field
and weather conditions can delay application as well as reduce absorbtion of herbicides

into plant tissue.

50

In contrast to winter annuals, true annual legume species will not over-winter in
northern regions of the USA or other areas with prolonged freezing temperatures. As a
result they may be able to provide the benefits of winter annuals without reducing
available soil moisture and eliminate the need for control in the spring.

Currently, there is interest in annual species of Medicago (annual medics) and
other annual legumes for use as cover crops in mid-western grain cropping systems.
Originating in North Africa and the Middle East, annual medics have adapted to a range
of environmental conditions (Ewing, 1983., Lesins and Lesins, 1979). Annual medics
were introduced for grazing purposes into Australia and New Zealand, and are now a
common component of sheep pastures. In southern Australia, annual medics are used in
ley cropping systems, where they are rotated with cereal crops (Puckn'dge and French,
1983). In these systems, medics provide high quality forage, contribute nitrogen to the
soil and non-legume pasture components and improve physical structure of the soil
(Crawford et al., 1989). Berseem clover (T rifolium alexandrinum L.) is an annual
legume used as forage plant in India and in areas with Mediterranean climates. It has the
potential to produce large amounts of biomass rapidly and can be cut several times a
year. (Bauchan and Sheaffer, 1994).

Recent investigations have indicated the potential for annual legumes to reduce
weed populations. Sheaffer and Barnes (1994) found that weed populations were
reduced where annual medics were interseeded with corn. However, in this study corn
yield was also reduced, presumabley due to competition for nutrients or moisture when
medic and corn were planted at the same time. Annual medics interswded several weeks
after corn planting did not affect corn yield, yet weed dry weight was not reduced either.
Moynihan et al. (1996) reported a 65% reduction in fall weed biomass following a grain
barley (Hordeum vulgare L.) and medic intercrop.

Winter wheat (T riticum aestivum L. ) is commonly grown in rotation with corn in

the midwest USA. The period between wheat harvest and corn planting is an ideal time

51

for establishing a cover crop. Annual medics and berseem clover planted after wheat
harvest have been shown to accumulate above ground biomass of between 2.1 and 5.3
Mg ha'1 and increase no-till corn yields (Fisk et al. 1997). This research was conducted
to investigate 1) the influence of legume cover crops established after wheat harvest on
winter annual and perennial weed populations prior to no-till corn planting, 2) the
influence of legume cover crops on summer annual and perennial weeds, and 3) to
determine the role legume residue has on summer annual and perennial weeds in this

rotation system.

MATERIALS AND METHODS

Experiments were conducted in the 1994-5 and 1995-6 growing seasons at the
Michigan State University Crop and Soil Sciences Research Farm in East Lansing (EL),
MI, and at the Kellogg Biological Station (KBS) in Hickory Corners, MI. Separate but
nearby sites were used in each year at each location. Soils were a Capac loam (fme-
loamy, mixed, mesic Aeric Ochraqualf) at EL and a Kalamazoo loam (fme-loamy,
mixed, mesic Typic Hapludalt) at KBS. The experiment consisted of five cover crop
treatments in a randomized complete block design with 4 replications at each location. .

The cropping system in this study was winter wheat / cover crop / no-till corn
rotation. The cover crops were planted after wheat harvest and either winter-killed, if
they were annual species, or were killed with a pre-plant herbicide in the spring prior to
planting no-till corn.

Cover crop treatments included two annual medic species Santiago burr medic
Wedicago polymorpha L. cv. Santiago) and Mogul barrel medic M truncatula Gaertn.
cv. Mogul), Bigbee berseem clover (T rrfolium alexandrinum L. var. Bigbee), Michigan
red clover (T nfolium pratense L.), and a no-cover crop control. Cover crops were no-till
drilled into wheat stubble (straw removed) on 8 August and 9 August in 1994 at EL and
KBS, respectively, and on 9 August and 11 August in 1995 at EL and KBS, respectively.

52

Planting was done with a John Deere Power-Till No-Till Drill in rows 20 cm apart to a
depth of 1 to 2 cm. Annual medics were seeded at a rate of 269 live seeds m2. This
translated into seeding rates of 13.4 kg ha'1 for Santiago medic and 15.7 kg ha'1 for
Mogul medic. Red and berseem clover were planted at 16.8 kg ha'1 which is the
common seeding rate for red clover in NH. Seeds were inoculated with the appropriate
Rhizobia spp. Berseem clover did not establish at EL in 1995 due to a clogged planter.
When berseem was reseeded several weeks later, it failed to produce consistent stands.

Prior to cover crop planting, each field received a pre-plant herbicide application
of glyphosate (li-(phosphonomethyl)glycine) 1.68 kg a.i. ha'l with .1% non-ionic
surfactant (NIS). In addition, sethoxydim (2-[1-(ethoxyimino)butyl]-5-[2-
(ethylthio)propyl]-3-hydroxy-2-cyclo-hexen-l-one) was applied at a rate of .32 kg a.i.
ha'l with 2.31 L h'1 COC at EL on 19 August 1994 to control volunteer wheat, large
crab grass (Digitaria sanguinalis L.), and quackgrass (Elytrigia repens (L).

Prior to corn planting in the spring of the year following cover crop planting,
each field received a burndown application of glyphosate at 1.68 kg a.i. ha'l with; 2,4-D
ester (2,4-dichlorophenoxyacetic acid, butoxyethylester) at .532 kg a.i ha'1 and .5 % non-
ionic surfactant (NIS). In 1994 at both locations, red clover was not killed by the
burndown herbicides. As a result, red clover plots were mowed by hand at EL, avoiding
the corn seedlings, followed by an application of dicamba (3,6-dichloro-2-
methoxybenzoic acid) at .56 kg a. i_ha’1 to red clover re-growth which resulted in
complete kill. Also in 1994 at EL, bentazon (3-(1-methylethyl)-(111)-2,1,3-
benzothiadiazin-4(3fi)-one2,2-dioxide) at .84 kg a.i. ha‘l with 2.31 L h'1 000 was spot-
sprayed for nutsedge (Cwerus esculentus L.) control on 3 June.

Post-emergence herbicide applications were made 45 days and 60 days after
burndown in 1995 and 1996, respectively. At EL in 1995, nicosulfuron (2-[[[[(4,6-
dimethoxy-Z-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-
pyridinecarboxamide) at 0.035 kg a.i ha'l; and bromoxynil (3,5-dibromo-4-

53

hydroxybenzonitrile) at .28 kg a.i. ha'l; with 25% MS was applied. At KBS in 1995,
sethoxydim at .21 kg a.i. ha'l with 2.31 L h'1 coc was used. At EL in 1996,
bromoxynil was applied at .28 kg a.i. ha'1 with .25% NIS.

Corn was planted using no-till equipment in mid-May of each year at 62,220
seeds ha‘l. Phosporus and potassium was surface applied prior to corn planting
according to soil test results, and nitrogen was side-dressed at four predetermined rates
when corn was in stage V-6. Complete details on fertilizer application and corn planting
can be found in Fisk et al. (1997).

Sampling for weed density and dry weight was carried out on two separate
occasions. In the first sampling, the effect of legume cover crops on spring annual and
existing perennial weed populations and growth was determined. In early May, just prior
to spring burndown herbicide application, the area within four randomly placed .25 m2
quadrates was sampled for the number of weeds by species. These samples were
removed and dried at °60 C for 72 hours and weighed by species. All samples were
further grouped by annual and perennial species and are reported as the total of four .25
m2 quadrates, or 1 m2. Chickweed (Stelleria media L.) was sampled only for dry weight
since determining the actual plant density of this species was not possible.

In the second sampling, the effect of cover crops on summer annual and perennial
weed populations and growth (weeds which germinated or otherwise initiated growth
after application of the burndown herbicide) was measured. This sampling was done as
described above, on spots adjacent to the initial sampling within the treatment plots,
approximately 45 days after burndown in 1995. In 1996, weed populations were slow to
initiate growth due to dry soil surface conditions. As a result, sampling was delayed until
60 days after burndown.

Also at this time the effect of the cover crop residue on weed populations and
growth was measured by comparing data from plots in which residue had been removed

to data from plots in which residue had not been removed. After the pre-burndown

54

sample was taken in early May, the legume residue was removed from the soil surface in
those .25 m2 quadrates and the spots were marked. Approximately forty-five days later,
weeds were sampled in these areas for density and dry weight by species and further
grouped into annuals and perennials. These results were compared to weed samples
taken at the same time in adjacent, but previously unsampled, quadrates in the same
cover treatment.

Soil temperatures were measured on selected dates in 1995 and 1996 to a 5 cm
depth using a soil thermometer. The thermometer was inserted into 5 randomly chosen
soil locations in each treatment and these values were averaged.

Data were combined over years and locations and subject to analysis of variance
using a randomized complete block model with treatments arranged as split-split-plot.
The main plot was the random effect of years, the sub-plot was location (changing each
year), and the sub-sub-plots were the five cover crop treatments. Where interactions with
year and location were significant, data were separated accordingly and re-analyzed.
There were four blocks at each location.

Weed density and dry weight data taken after burndown application were
transformed by taking the square root and log, respectively, prior to analysis of variance
to correct for heterogeneity of variance. Non-transformed data are presented with
statistical interpretation based upon transformed data. Means of each legume cover
treatment were compared to the no-cover control with a single degree of freedom F-test.
Data describing the residue effect were analyzed within cover treatment with means

compared using a T-test.

55

RESULTS AND DISCUSSION

Spring annual weed density and dry weight

There was a significant year by location by cover interaction for weed density and
dry weight. Therefore these data are presented by site-year. Spring annual weed density
was reduced following cover crop treatments in two out of four-site years (Table 1). The
greatest impact was observed at East Lansing in 1995, where weed density was reduced
following all cover crops compared to the no cover control. The dominant weeds in this
site-year included shepherdspurse, chickweed, penny cress and volunteer wheat (Table
7.). In 1996 at KBS, weed density was reduced following Santiago medic and Red
clover. In contrast, there were no observed effects of the cover treatments on weed
density at KBS in 1995 or at EL in 1996. Weed density was relatively low at these site-
years compared to those where cover crops had significantly reduced weed density.

Dry weights of winter annual weeds were lower following most cover crop
treatments in all site years (Table 1.). The greater observed impact on dry weight than on
weed density was in part due the inclusion of common chickweed (Stellaria media L.) in
dry weight analysis, but not in weed density. Chickweed accounted for 30 to 63% of dry
weights in the no cover treatments (Table 7).

Winter annual weeds germinate in the fall and reinitiate growth in the spring,
completing their life cycle by mid-summer (Stubbendieck et al. 1994) Some winter
annual species may also germinate in the spring. The reduction in weed density could
result from a negative interaction of the cover crop with weed seedlings in the fall.
Weeds would be in competition for resources and, as a result, would not develop enough
to survive the winter. In addition, weed seed germination in the fall may have been
reduced by the living cover crop as a result of reduced light (Teasdale and Mohler, 1993)
and moisture. Cover crop residue can modify the conditions under which weeds

germinate or regrow in the spring. Surface residue can reduce light interception, soil

56

temperature, increase soil moisture, release allelopathic chemicals, and present a physical
impediment to weed seedlings (F acelli et al. 1991; Teasdale, 1996; Teasdale and Mohler,
1993). In this study, soil temperature was reduced by red clover in mid-April at KBS in
1995. No other legume reduced soil temperature before corn planting (Table 9.) Weed
density and dry weight reduction resulted from factors other than soil temperature.

The growth habit of red clover differs from the other cover crops in this study in
that it reinitiates growth in the spring from crowns established the previous year. At the
time of sampling for winter annual weeds, red clover had grown to between 16 and 24
cm in height while the annual legumes had left a desiccated residue on the soil surface.
As a result, red clover may have influenced weed density and growth through
competition for light and nutrients.

Little data exist on the effect of legume cover crops on weed populations which
are present prior to crop planting. Most cover crops are still alive at this time requiring
either cultivation or chemical control, making the issue of weed presence unimportant.
However, annual legume cover crops may permit the reduction of burndown herbicide
inputs and enable a shift towards postemergence herbicide options (Teasdale, 1996). In
this case, the effect of covers on winter annual and early spring weeds is of significant

concern.

Summer annual weed density and dry weight

There was a significant year by location by cover interaction for summer annual
weed density and a year by cover interaction for weed dry weight. Summer annual
weeds germinate in the summer and complete their life cycle by fall. These weeds can
reduce crop yield as a result of competition for moisture, light, and nutrients if present at
significant levels.

In this study, cover crops had significant but inconsistent effects on summer

annual weeds. Weed density was reduced following Santiago medic compared to the no-

57

cover treatment in 1995 at EL, but showed no effect in other site-years (Table 2). Weed
density was reduced following red clover only in 1996 at EL.

Soil temperatures taken just before or after corn planting indicate that red clover
reduced temperatures during the time of summer weed germination (Table 9). The
recently killed surface residue was more effective at keeping the surface soil cool than
the annual legume residue which was winter killed. Only in one site year did red clover
have a greater effect on weeds than did annual legumes suggesting that soil temperatures
may have played a limited role in weed suppression in this study.

Similar to the effect covers had on winter annuals, the effect on summer annuals
was more pronounced for weed dry weight than density. Dry weight of summer annual
weeds was reduced following annual medics in 1995 compared to the no cover control
but was unaffected in 1996 (Table 2). Medic biomass was generally greater in 1995 than
in 1996 and may account for the differences between years (Fisk, 1997). Dominant
weeds in 1995 included lambsquarters, redroot pigweed, giant foxtail, large crabgrass,
and smooth crabgrass (Table 7). Our results for annual legumes match those of Yenish et
al. (1996) who found biomass of weeds sampled 45 days after corn planting reduced by
winter annual legume cover crops.

It has been suggested that weed biomass may be influenced less than weed
density by residue from winter annual cover crops (Teasdale 1996) because weeds will
compensate for lower density by increasing in biomass. This is not the case in this study
and may be a function of the mechanisms used by annual legumes to limit weed growth,
which at this point are unknown. However, reduced growth may have resulted from
allelopathic chemicals released by the legumes or resulting from microbial metabolic

activity on the residue (W orsham, 1991).

58

Residue effect on summer annual weeds

The effect of cover crop residue on summer weeds was tested by removing the
surface residue after the first sampling (just prior to corn planting) and re-sampling in the
same spot approximately 45 days later. These weed density and dry weights were
compared to data from adjacent sample squares where legume residue had been
undisturbed. Most weeds present would have emerged during this period since the field
had recieved a burndown herbicide just after the first sampling.

Summer annual weed density and dry weight were reduced from 27 to 60 percent
following annual medics (Table 3). The effect of red clover was not as consistent as for
the annual medics. Weed density was reduced in 1996 but not in 1995, while dry weight
was reduced in only one out of 4 site-years.

The effect of annual legumes on weed populations was greater when tested within
a cover treatment plot (residue removed or not) verses when cover treatments were
compared to the no cover control. Naturally occurring weed populations as used in this
study have high spatial heterogeneity (Cardina et al. 1997, F orcella et al. 1992) making it
more difficult to see treatment effects between cover and no-cover plots. This would
have been exacerbated by the size of the treatment plots (3m or 4.6m X 30m). Samples
with and without residue which were compared were done so within treatments, and so
would have had more similar conditions which may provide for a better comparison of

treatment effects.

Perennial weed density and dry weight

In this cropping system perennial weeds become established both in the fall
following wheat harvest, in the spring as the soil warms, and during the summer months.
Dominant perennial weeds in this study are shown in Tables 6 and 7. Samples were
taken at two different times during the course of the season. The first was in early May,

just prior to planting no-till corn corresponding to the time of a bum-down herbicide

59

application. The second was approximately 45 days afier bum-down and corresponding
to the timing of a post-emergance herbicide application.

For the first sampling date, data for weed density were combined across all site-
years since no significant cover interaction was found. Perennial weed density was not
effected by the cover treatments prior to corn planting (Table 4). This would be expected
since the most of the weeds present at this time probably established in the fall as the
cover treatments were just beginning growth. However, perennial weed dry weight was
reduced following most of the cover treatments by approximately 30 to 75 percent when
compared to the no-cover control (Table 4). Reduced growth of perennial weeds may be
a result of competition for resources in the fall and shading and reduced soil temperatures
in the spring.

The effect of legume cover crops on perennial weeds which emerge at the time of
or after corn planting was measured approximately 45 days after existing weeds were
killed with a burndown herbicide. Since a significant year by location by cover
interaction was found results are presented by site-year (Table 5). Santiago medic
reduced perennial weed density at EL both years and weed dry weight at EL in 1996.
Weed density was reduced following Mogul medic at EL in 1995 only. Previous
research has found little effect by hairy vetch residue, at naturally occurring levels, on
the density of perennial weeds such as dandelion, curly dock, and quackgrass (Mohler
and Teasdale, 1993; Curran et al., 1994). Our results indicate a good potential by annual
medics to reduce perennial weeds density during corn growth and weed dry weight prior
to corn planting.

In 1996 at KBS, perennial weed density and dry weight were greater following
red clover and than following the no-cover control. Dry soil conditions in this year may
have been ameliorated by red clover residue which can conserve surface soil moisture

and thereby enhance weed germination and growth.

Residue effect on perennial weeds

In all cases it was possible to combine data over site-years for both weed density
and dry weight (Table 6). Perennial weed density and dry weight were significantly
lower where residue was lefi on the soil surface for all legumes. As was observed for
summer annuals, the residue effect of the cover treatments was greater when measured

by removing residue within a treatment than by comparing treatments.

CONCLUSIONS

Several investigators have established that winter annual legume cover crops can
reduce weed density and biomass of summer annual weeds in corn cropping systems
(Y enish et al. 1996; Teasdale et al. 1991; Johnson et al. 1993). The effect of true annual
legume cover crops on weed density and biomass appears to be dependent on the
cropping system in which they are used. Squire (1997) found no suppression of weeds
by annual medics or berseem clover interseeded into corn. Tharp (1997) reported a
reduction of annual grass weeds when annual rye (Lolium multrflorum L.) or an annual
rye/crimson clover ( T nfolium incamarum L. ) mixture was interseeded into sweet corn,
however, crimson clover alone did not reduce grass weed densities. Moynihan et al.
(1996) reported lower fall weed biomass where annual medics were interseeded with
barley.

Our results indicate that annual legumes planted after wheat harvest can reduce
both density and dry weight of winter annual weeds prior to planting no-till corn. The
effect of the annual legumes was similar to red clover, a short lived perennial species
which over-winters in this region. Summer annual weed dry weight was reduced by
annual legumes and red clover, however, weed density was only occasionally reduced by
the legumes in this study. The suppressive effect of annual medics residue on summer
annual weed density and dry weight was consistent across all site years. Berseem clover

had no significant effect and that of red clover was mixed.

61

Perennial weed dry weight sampled in the spring prior to corn planting was
consistently reduced by both annual legumes and red clover in this study, however
density was unaffected. The annual medic varieties studied had a suppressive effect on
perennial weeds 45 to 60 days after burndown, yet this effect was not as strong as the
effect observed prior to corn planting. Residue of all legumes reduced both density and
dry weight of perennial weeds.

Although annual legumes reduced weed density and dry weight in this study, any
effect this may have had on corn grain yield was removed by the application of a post-
emergence herbicide after the final sampling. One question which remains is: Were
weed densities and dry weight reduced to the point that they would not decrease grain
yield if no further control was applied? Studies of weed-crop competition have
demonstrated that the relative time of weed emergence with respect to the crop is as or
more important than weed density in predicting the impact on corn yield (Knezevic et al.
1994, Bosnic and Swanton, 1997). When weed seeds germinate shortly after crop
emergence, there is greater impact on corn yield. The hyperbolic. crop yield model
developed by Cousens (1985) incorporates both density and relative time of emergence
to predict the effect of weeds on crop yield. Bosnic and Swanton (1997) reported that
bamyardgrass at 39 m'2 reduced corn yield by 14% when emerging at the 3-leaf corn
stage compared to 4% at the 7 leaf stage. Based on the hyperbolic model, 1.3 m-2
bamyardgrass emerging with the corn was predicted to reduce corn yield by 0.3%, up to
a maximum of 35% yield loss. In Michigan, Fausey et al. (1997) reported that corn grain
yields were reduced up to 14% by 13 m'2 giant foxtail germinating 2 days after corn
emergence. They concluded that the hyperbolic model accurately predicted yield loss at
low foxtail densities but that seasonal environmental variation affected maximum percent
crop yield loss from foxtail interference.

We cannot directly use this model to predict the effect of weeds in this study

since we do not have data on time of emergence. However, weed density in this study

62

were in the same range as those in the cited studies where yields were reduced when
germination was close to corn emergence. Other researchers have found cover crops
reduced weeds, but not enough to eliminate the need for chemical control (Y enish et al.
1996; Teasdale 1996; Curran et al., 1994; Johnson et al. 1993). Annual legumes can
reduce early season weed density and dry weight as or more effectively than red clover.
Further research is needed to determine if chemical control could be reduced or
eliminated when coupled with annual legumes. This should include effects of weed
levels following legumes on the yield of the corn crop. In addition, long term studies
using legume cover crops, including annual legumes, in no-till systems are needed to
assess the role they can play in weed suppression during the initial transition period and

as weed populations shift over time.

63

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Teasdale, John R, C. Edward Beste, and William E. Potts. 1991. Response of weeds to
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Teasdale, JR, and CL. Mohler. 1993. Light Transmittance, soil temperature, and soil
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herbicide tolerance. Masters Thesis, Michigan State Univ.

65

Tiffin, P. L. 1994. Corn grain and nitrogen yield response to cover crop kill date and
subirrigation. Masters Thesis. Michigan State Univ.

Worsham, A. Douglas. 1991. Role of cover crops in weed management and water
quality. p. 141-152. In W.L. Hargrove (ed.). Cover crops for clean water. Conference
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Worsham, A. Douglas, and Randall H. White. 1987. Legume effects on weed control in
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herbicide replacement in no-tillage corn (Zea mays). Weed Technology. 10: 815-821.

66

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Chapter 3
THE VALUE OF A PARTICIPATORY APPROACH IN SUSTAINABLE
AGRICULTURE RESEARCH
ABSTRACT

As we strive to make agriculture more sustainable our approach to research and extension
must be redirected in order to effectively support new or broadened goals. Research
designed to generate information applicable to a wide range of conditions will be less
likely to satisfy economic and ecological needs of individual farms than research which
accounts for site specific considerations. Sustainable technologies are not directly
transferable from farm to farm and require an integrative process of learning, not
commonly needed with more conventional technologies. Participatory strategies have
been advocated for conducting research and developing technologies which will lead to
more sustainable agricultural systems. In this study, we sought to find evidence that
participatory approaches to the generation and dissemination of information and
technologies around sustainable agriculture, specifically cover crops, may be more
appropriate than conventional methods. A focus group format was employed to discover
the opinions and feelings of farmers and knowledge brokers about the generation and
communication of sustainable production practices, using cover crops as an example of
such practices. Farmers using cover crops, those not using cover crops, and knowledge
brokers had similar levels of knowledge about cover crops. Much of the information
desired about cover crops by the participants was site specific in nature and fit well with
what can be best learned from participatory on-farm research. Farmers using cover crops

are learning how to integrate their farms by participating in farmer-led research and

75

76

education groups and by utilizing conventional and alternative sources of knowledge.
These farmers are aware that sustainable technologies are not directly transferable to
their farm, but instead require them to learn how to integrate the characteristics of the
technology to the ecological and socioeconomic aspects of their particular operation.
Farmers not using cover crops are using conventional sources of knowledge and are not
conducting on-farm investigations. They do not appear to have an awareness that
sustainable technologies are not directly transferable to their farm. Knowledge brokers
are valued as legitimate information sources and/or partners in learning to both groups of
farmers. Evidence was found that participatory approaches would be effective in
facilitating the generation and dissemination of sustainable agriculture technologies
including: a desire by both farmer groups for more farmer-to-farmer interaction
indicating an attraction to the participatory learning process, a desire by knowledge
brokers for greater skills in facilitating participatory methods, the fact that farmers are

currently learning to integrate their farms with participatory approaches.

77

INTRODUCTION

Consumers and producers of agricultural products have benefited from the expert-
user mode] for the generation and communication of knowledge as practiced by most
agricultural institutions in this country. The expert-user model is characterized by a
hierarchy in which information moves from the scientist down through extension services
to the users, or farmers in this case. This approach has been successful in generating and
increasing the use of technologies that farmers can adopt in essentially the same form in
which they were developed. For example hybrid seed, fertilizers, and chemical control
of pests require less adaptation to specific farm conditions in order to be used efi‘ectively.

However, many of the production issues facing farmers today grow out of the
interaction of the farm with the surrounding environment. It is necessary to develop
appropriate responses to issues such as maintenance of soil quality, loss of nutrients
through leaching and other processes, management of manure for maximum benefit and
reduced odor drifi, and ecological means of controlling weeds. These issues are all
specific to site conditions and farmers' resources. In addition to production issues there
are influences from off-farm which impact an operation such as; rising land prices,
economic pressures from concentration of production, and loss of the surrounding rural
community. Public institutions have not traditionally addressed these issues.
Nonetheless, recognition of the undesirable consequences brought about by such forces
has put pressure on public institutions to support farmers in these areas.

Solutions to these issues may not successfully be developed solely using an
expert-user approach. These issues exist over a broad set of conditions yet their
management needs to be ecologically, socially and politically sensitive. The expert-user
model requires agricultural research to be general in order to be applicable to a wide
range of farm conditions. Only in this way is technology transferable. "To be
successfully adopted, new alternative production strategies must satisfy the economic and

ecological needs of individual farmers" (Gardner, 1990). Research designed to generate

78

information applicable to a wide range of conditions will be less likely to satisfy
economic and ecological needs of individual farms than that which includes site specific
considerations. In addition to being more site-sensitive, the transfer of information is
greater when the end-user is more involved in its development (Chambers, 1983; Roling
and Van de Fliert, 1994). In order for researchers and farmers to realize the benefits of
participatory methods, multiple knowledge sources must be respected and considered
valid when decisions about development are made (Gerber, 1992). Accepting multiple
ways of knowmg has not been a strong point of the expert-user model.

Participatory strategies have been advocated for generating and communicating
information and technologies which will lead to more sustainable agricultural systems
(Rocheleau, 1994; Dlott et al. 1994; Roling and van der Fliert, 1994; Doll and Francis,
1992; Gerber, 1992; Gardner, 1990). Though early work in participatory research
methods took place in developing countries, an evolution of methods continues in both
developing and developed countries. (Rocheleau, 1994; Biggelaar, 1991). In the
developed countries advocates of integrated farming systems who desire to link the
environmental, social and economic implications of a technology to the process of its
development (Dlott et al. 1994; Hesterman and Thorbum, 1994) have brought
participatory strategies to the forefront. Participatory methods are being explored in part,
because traditional agricultural institutions have not served the needs of farmers
interested in alternative methods (Buttel and Youngberg, 1985). One reason for this is
that the structure of these institutions limits their ability to address the root issues of
sustainability. The reward system for scientists based on publications limits interest in
long-range interdisciplinary projects and on-farm research, as does the disciplinary
structure of university departments. However, it is research on agricultural systems
carried out in an interdisciplinary fashion, with at least some done on—farm, which will

result in integrated farming technologies (Buttel and Youngberg, 1985).

79

In business and industry, the importance of end-user participation and feedback is
well established (Plunkett and Rournier, 1991; Senge, 1990). It is through end-user
participation in the development process that true needs are discovered and appropriate
solutions are devised. The challenge to involve end-users may be greater in agriculture
than in other areas since there is a large number of users spread out over a vast area, each
with different site variables, including soil, climate, equipment, preferences, and goals.

Participatory methods differ from expert-user methods in the level of users'
involvement in the process of generating and disseminating knowledge. When the
farmer is involved as a decision-maker, technology is more likely to fit the farm system
than the farm system having to fit the technology. This allows for easier incorporation
into farm processes when the farmer has participated in the technology's development,
they have confidence in their ability to make it work on their farm, as well as to advise or
assist other farmers. When technology is developed by researchers alone and handed
down to farmers for adoption this is not the case.

Research conducted on working farms will lend itself to increased participation
by farmers as well as provide a realistic context in which to evaluate new technologies.
Research conducted on-farm can have an advantage over on-station research in areas
such as; agronomic and economic evaluation of production systems as they would
actually be practiced, and questions which consider the whole farm such as allocation of
labor and capital (Lockeretz, 1985). Although on-farm research has advantages, not all
important lines of investigation are best developed in this context. More controlled
conditions may be required in determining how biological processes work as well as for
long-term studies which need to be free from cropping restrictions found on-farm
(Rosmann, 1994). Employing on-farm and on-station research in a complementary
fashion will make use of their individual strengths. A research program which involves
farmers, researchers, and extension personnel will help increase the ability of all to

accept multiple ways of knowing.

80

Participatory methods of research and extension can be employed at the farm and
community level. In the simplest case, a farmer may conduct an investigation on his/her
farm with assistance from a local knowledge broker (Extension agent or crop consultant).
Together they decide what is to be investigated, who will conduct the field operations,
and what the results imply for future management decisions. Independently or together
they may decide to talk to other farmers about their work or even hold a field day to
demonstrate what they have learned. In more involved situations, a knowledge broker
would work with a group of farmers where all participants have a decision-making role. F
Periodic group meetings would provide the opportunity to exchange information, discuss

results, plan for the future, and establish kindred relationships with others of like mind.

 

 

In these meetings the knowledge broker would function more as a group facilitator and a L
co-learner than as the traditional "expe ". In both these situations, farmers have more
control over the nature of production information, and in addition, become sources of
knowledge to other farmers.

At another level, participatory approaches can be used to influence resource
allocation within institutional research arenas. At this level, a diversity of stakeholders
including researchers, knowledge brokers, farmers, and perhaps environmental advocates
and policy makers (Gardner, 1990) would have significant input towards the following
questions: What knowledge is to be pursued and what technology is to be developed?
How will the development of the technology be approached ? How will the knowledge
and technology be extended? Representatives of these stakeholder communities would
serve on decision-making boards at the local, state, and federal levels. They would
contribute to the decision-making process by emphasizing values common to the
community, thus introducing a social aspect to the pursuit of knowledge. For example,
research on meeting crop nutrient needs would consider multiple criteria, going beyond
the crop use of nutrients to include crop uptake efficiency, loss to the environment,

health implications to farmers and neighbors, evaluation of renewable nutrient sources,

81

and effects on short and long-term profitability. Community members working
alongside researchers and policy makers can effectively represent and negotiate these
multiple perspectives.

The complex issues that comprise the barriers to sustainability will require that
decision makers pursue and embrace many of the outcomes of participatory methods.
Nault (1991), from his review of the literature, indicates how participatory methods can
address the factors limiting the adoption of sustainable practices (as described by Hill,
1991) (Table l). The adoption of sustainable practices is limited by a lack of information
and the skills by farmers and others to make use of it. Participatory methods produce
site-specific information while cultivating a farmers competence with new farming
practices and research abilities. The relationships established between farmers and
scientists as they work together can create an avenue for institutional change in support
of community needs. However, the impact goes well beyond this. Such methods serve
to develop the potential and capacities of individuals involved in creating their own
future by catalyzing awareness, commitment, motivation, creativity and empowerment.
"[Participatory] research should thus be seen as an opportunity for devolving power and
establishing local capability for development..." (Biggelaar, 1991). It is our belief that in
many cases the increased participation of farmers in the generation and dissemination of
production information will increase its relevancy to farmers, its success rate on-farm,
and its support for sustainable resource use.

The case is made in the literature that sustainable agriculture technologies are
unique and as such, diverge from more conventional technologies in how they can best
be developed and disseminated (Roling and van de F liert, 1994; Nault, 1991; Dlott et al.
1994). To successfully implement sustainable technologies, farmers will need to go
through a process of adapting the technology to their conditions. Appropriate use of
sustainable technologies will vary considerably with site conditions, will require greater

understanding of basic biological processes, are most profitable when approached from a

 

82

whole system perspective including short and long term goals, and may not be directly
connected to farm income. As a result, traditional financiers are often not willing to
assist farmers in these technologies. Implementing technologies like integrated weed and
insect management and soil stewardship require an expanded knowledge base. This
adaptation process is more critical to these technologies than to more conventional
technologies such as fertilizer or herbicide use because the learning required is greater.
When farmers are involved as partners in learning, the knowledge base is expanded and
the relevancy and effectiveness of many areas of research and extension can be increased
(Dlott et al. 1994; Ashby, 1986).

In this study, we sought evidence that participatory approaches to the generation
and dissemination of sustainable agriculture information and technologies, specifically

cover crops, may be more appropriate than conventional methods.

METHODS

In this study we used a focus group format (Krueger, 1988) to discover the
opinions and feelings of farmers and knowledge brokers about the generation and
communication of sustainable production practices, using cover crops as an example of
such practices. In the focus group method, individuals who share a common attribute are
gathered for a facilitated discussion on the topic of investigation. The advantage to this
group approach is that the interaction among participants often leads to a deeper
development of ideas than does a series of one-on-one interviews or a written survey
approach.

Three distinct groups were used in this study: Group 1 were farmers currently
using cover crops in their farm operation. Group 2 were farmers not currently using
cover crops in their farm operation. Group 3 were knowledge brokers, including
Extension agents and crop consultants, who serve a variety of farmers, and are known to

have some knowledge of and experience with cover crops. Focus group sessions lasted 2

 

83

to 2.5 hours. Each session was conducted by a facilitator and a co-facilitator who
recorded what was said on a flip chart and audio tape. The facilitator guided the
discussion through four main topics: (1) assessment of the group's knowledge about
cover crops, (2) types of research and production information desired about cover crops,
(3) preferred sources of production information including, but not limited to, cover crops,
(4) participants description of current means of technology generation and transfer and
response to an alternative participatory approach (Table 2).

Farmers in Group 1 were selected from lists provided by knowledge brokers from r...-
around the state. Farmers in Group 2 were selected from lists provided by knowledge
brokers and from a Wheat 2000 (Miscellaneous, 1995) data base which provided

 

information on Michigan wheat growers and whether or not they used cover crops.

1...

Knowledge brokers in Group 3 were selected based on recommendations from extension
specialists or as a result of their involvement with cover crops in the state. All
prospective participants were sent a letter of invitation. Within 10 days of sending the
letter a follow-up phone call was made inquiring if they would be willing to participate.
Those who agreed to attend received a second phone call the day before the focus group
session to confirm their attendance.

Data were collected from each group regarding information they would like to
have about cover crops. Each group was asked to generate a list of information needs.
The list was recorded on a flip-chart. Each participant was asked to prioritize the items
on the list using a point system. Points given to each item were added and divided by the
total number of points used by the group. Data are presented as a percentage of all points
used by each group (Table 3).

84

RESULTS AND DISCUSSION

Knowledge about Cover Crops

Each group demonstrated knowledge of the potential role and benefits of cover
crops. Participants spoke about the use of cover crops for various purposes: soil
coverage to reduce erosion, nutrient contribution, management of soil organic matter,
weed suppression and soil moisture management. All participants were familiar with the
use of red clover frost-seeded into wheat, perhaps the most common cover crop option in l
grain production in Michigan. Most of the Group 1 participants were using red clover in

this way. Farmers in group 2 described some problems they had experienced with this

 

cover crop when trying it in the past: excess residue impaired planting the subsequent |_
crop; access to the field was delayed by the trapping of excess soil moisture; wheat

lodged into clover was difficult to harvest and resulted in wheat sprouting. The use of a

rye cover crop for soil coverage and moisture management in corn and soybeans was also

familiar to both farmer groups. All three groups had a strong sense of the long-term

benefits to soil productivity associated with cover crops, but some individuals in all

groups were not sure these benefits translated to economic benefits.

Farmers were asked if the use of cover crops increased or decreased risk to their
farm operation success. Roughly half of the Group 1 farmers felt there was no attendant
risk. One farmer felt they increased the stability of the operation. Another stated that
with cover crop use he was "switching risks" since every production choice, be it
fertilizer, herbicide, or tillage methods, was associated with some risk. Group 2 farmers
felt risks associated with cover crops could be avoided by substituting such practices as

fertilizer use or the maintaining of crop residues.

85

Desired Information about Cover Crops

The information most desired by farmers currently using cover crops included
specific benefits provided by each cover crop to a following crop, especially nutrient
contribution, more details on long-term soil effects (2- 5 years), and economic
information on cover crop use, which was referred to as a short-term effect (Table 3).
Similarly, farmers not using cover crops said they would be most influenced to do so by
information on short-term nutrient contributions and the long-term effects on soil quality,
putting both in relation to their influence on production costs.

Knowledge brokers were asked what information or skills they felt would help
them assist farmers in successfully utilizing cover crops. All agreed that information
demonstrating the economic benefits of cover crops would be very useful (Table 3). In
addition, knowledge of how to maximize nutrient contribution and how to establish and
manage various cover crop species was needed. Responses by knowledge brokers
reflected the needs stated by farmers and showed their awareness of factors which
farmers say influence their decisions about cover crops. Lists of prioritized information
needs can be found in Appendix 1.

Responses from the three groups were very similar, indicating both knowledge of
cover crops and agreement on how they can be used to benefit the farm system. Why
one group of farmers uses them and the other does not is not immediately evident from
the responses. Both farmer groups were aware of compelling knowledge about the
potential benefits. One farmer not using cover crops felt that to reduce erosion, the use
of no-till as well as the use of crops that leave a covering residue both remove the need
for cover crops. However, he also admitted that on soils he plows in the fall, where
erosion risk is high, he has not considered the use of cover crops. One farmer who uses
cover crops stated that, unlike himself, "Most farmers are not of the philosophical bent
that cover crops are good". This implies that for some farmers technical and economic

information may not be the major factor in deciding to use cover crops.

86

Sources of Information for Crop production and Cover Crop Use.

Both groups of farmers cited similar sources of production information including
farm magazines, extension personnel, university or industry bulletins, on-farm
demonstrations and field days, as well as talking to other farmers. These sources
provided ideas and specific information which they utilized when trying new things on
their farm. Both farmer groups felt that obtaining cover crop information from the
sources already supplying other production information would be best. For example, an
article on cover crops in a currently used magazine is more welcome than a separate
publication, seeing a cover crop demonstration at a field day with other demonstrations is
preferred to a separate cover crop demonstration. Farmers not using cover crops felt this
would enable them to get exposure to information they would not ordinarily pursue.

The relative usefulness of the cited sources varied. For example, it was felt that
extension agents know more about the dominant farming issues of their county and may
not be up on particular stewardship or conservation-type practices that are not common
to that area. Farm magazines, on the other hand, provide an array of information with
periodic articles on stewardship practices including cover crops. Most farmers felt
having someone knowledgeable with which to talk was most desirable.

Farmers who use cover crops cited specific alternative sources for
stewardship/cover crop information because it was usually not available from more
mainstream sources. If it had been available from mainstream sources, such as extension
specialists and agents, these farmers would welcome it and consider it credible. The
Michigan Agricultural Stewardship Association (MASA), a farmer-led research and
education organization, provides funding for farmers to conduct on-farm research on
alternative agricultural practices including cover crops. The results are presented at field
days and annual meetings, in newsletters and an annual research summary booklet.

MASA was cited as a good source of information, yet some questioned its reliability

87

because research presented was not always replicated and often conducted for only one
growing season. Farmers not using cover crops did not cite MASA as a source of
information. When asked if they were aware of MASA, farmers not using cover crops
recalled seeing a MASA annual research report which came as part of a Farm Bureau
newsletter. A recent Cover Crop Symposium held by University Extension at Kellogg
Biological Station was cited as a very valuable source, not so much for formal
presentation of information, but for the opportunity to interact with other farmers in
group discussion and during breaks in a facilitated learning context.

Along this same line, farmers who use cover crops were asked what they would
suggest a farmer do in beginning the use of cover crops. Most respondents pointed to the
importance of contact with someone knowledgeable (either an extension agent or

farmer), coupled with experimentation on their farm.

Generation and Transfer of Cover Crop Information

@rrgt Emergion and Trgfer of Information

All groups were asked to describe their perceptions and experiences of
information and technology generation and flow as it currently exists. Both farmer
groups said information usually flows to them from the university via the extension
service, in a one-way direction. These two groups said information from extension was
valuable and helped in making decisions for change on the farm, yet they found the agent
hard to contact. Written information sent by the agents was most accessible. Farmers
who use cover crops stated that they felt like receivers of information rather than
participants in a process of learning where their input is incorporated. One farmer stated
he is "not being served by the system" because material presented at extension functions

is already familiar to him. Another felt extension should be "more receptive to

88

innovative ideas". Farmers who don't use cover crops also expressed the feeling of
receivership and the desire for more farmer-to-farmer interaction facilitated by extension.
In sum, farmers in the focus groups experienced university representatives as
experts who provide information and not as partners in problem-solving and generation
of information. Although most found extension valuable, both farmer groups would
welcome more dialogue and interaction with knowledge brokers and other farmers. In
fact, all three groups expressed their pleasure with the focus group format used in this
study precisely because it provided a context for farmer-to-farmer contact (or broker to

broker contact) wherein their input was sought and valued.

ng'cipatog Appmach 13 Information Generation
All three groups were presented with a general model of information/technology

generation and dissemination in which farmers participate as co-leamers with knowledge
brokers or scientists. In this model, farmers have significant input regarding what is
studied, how it is researched, and how results are reviewed and interpreted and
disseminated. Knowledge brokers said they were familiar with two technologies being
developed in this manner, narrow row soybeans and Global Positioning Systems (GPS).
With GPS, Extension is working on-farm to develop the skills of farmers and knowledge
brokers. The relationship between farmers and knowledge brokers has been enhanced as
a result of their cooperative work with this new and exploratory technology. The fact
that GPS is unfamiliar to both parties affords them the experience of learning together,
while the creativity and ideas that come from both are given value.

Farmers in the two groups responded differently to the presentation of the
participatory model. Farmers who use cover crops liked the idea but not all felt they had
the time to do research and farm. Those who do take the time to research would
welcome the partnership with knowledge brokers and their resources. The full concept

of a participatory approach was difficult to communicate to both farmer groups,

89

especially the non-cover crop users. This group kept drawing a strong parallel to on-
farm demonstration where the farmer may or may not put out the study and the topic is
decided by the knowledge broker or input company. In this process the technology is
already developed and the on-fann work is simply a demonstration for area farmers.
This is a tried and true method from the diffusion-adoption approach and usually does
not create a co-learning relationship. Farmers not using cover crops felt they may not
understand the scientific aspects of research and therefore have little to contribute. They
felt demonstrations were very useful, but were not willing to take the time to carry them
out and showed little interest in having input on decisions regarding the demonstrations.
Knowledge brokers (Group 3) and cover crops users (Group 1) expressed the
desire for more resources directed toward participatory approaches. They both felt these
would complement the current learning strategies and would increase both the relevancy
and use of agricultural research results. Knowledge brokers wanted training in how to
work with farmers so that they could consciously shift field demonstrations to a more co-

leaming process.

CONCLUSIONS

Farmers in this study who are using cover crops realized that it is their
responsibility to establish environmentally sound farming systems which utilize practices
such as reduced tillage, crop rotation, cover crops, and site-specific rates for nutrients and
chemicals. Until recently, they have not found conventional sources willing or able to
provide knowledge which will support these efforts. From their on-farm work, these
farmers are aware that sustainable technologies are not directly transferable to their farm,
but instead require them to learn how to integrate the characteristics of the technology to
the ecological and socioeconomic aspects of their particular operation. These farmers are
learning how to integrate their farms by participating in farmer-led research and

education groups, which accelerates the learning process, and by utilizing conventional

 

90

and alternative sources of knowledge to carry out on-farm investigations. In each case,
knowledge brokers are valued as legitimate information sources and/or partners in
learning, depending on the orientation of the individual broker.

Farmers in this study who are not using sustainable agriculture technologies have
an appreciation for the site specific nature of many farming practices. For example, they
made a distinction between soils that are appropriate for no-tillage verses those that are
not. However, they do not appear to have an awareness that sustainable technologies are
not directly transferable to their farm and would require an integrative process beyond
that of conventional technologies. Farmers in this group were somewhat familiar with
cover crop technology and were quick to cite problems that could arise with their use.
They are using conventional sources of knowledge and are not conducting on-farm
investigations. In addition, they were not familiar with participatory approaches and did
not see an advantage to them when presented with a participatory model. However, they
did express a desire for more farmer-to-farmer interaction indicating an attraction to
participatory learning process.

It is not clear from this limited study the extent to which participatory methods
will assist in the generation and dissemination of sustainable agriculture technologies, as
suggested in the literature. Participatory approaches are relatively new, not only to
farmers but to researchers and knowledge brokers as well. Agriculture is a field that has
traditionally generated and disseminated knowledge using only the expert-user model.
Farmers are accustomed to being receivers of information in this system. It is therefore
not surprising that the communication of the participatory approach in general is still
unclear as well as under what conditions it might be useful.

As a result of our focus group responses, we predict the greater use of
participatory methods would indeed increase the relevancy of research and use of
sustainable agriculture technologies. There is evidence that participatory approaches, if

not essential, may be extremely effective in facilitating the generation and dissemination

 

91

of sustainable agriculture technologies. First, the minimal use of cover crops by farmers
in Michigan (estimated to be between 1 and 5%) indicates that conventional methods of
information transfer have not facilitated their use, even though their utility has been
demonstrated many times over. Second, both farmer groups desired more farmer-to-
farmer contact and more contact with knowledge brokers. Third, knowledge brokers
desire greater skills in participatory methods. Fourth, the growing popularity of farmer-
led research and education organizations, which in most cases have strong partnerships
with individual university scientists or extension agents, demonstrates the effectiveness

of participatory methods in developing and disseminating information.

FUTURE RESEARCH
There are several research approaches that have the potential to further elucidate
answers to the question being posed in this study; namely, is a participatory research
approach appropriate and/or essential for the development and adoption of sustainable

agriculture technologies? These approaches includes:

. Disseminating knowledge regarding a particular sustainable agriculture
technology to separate but similar groups of farmers with varying levels of end user
participation. The effectiveness of each level would be determined based on the

extent to which farmers in each group pursue the use of the technology.

. Initiating on-farm research with several groups of farmers allong for different
levels of farmer involvement in each group. Observations would be made regarding

the amount of learning about as well as increased use of the technology.

. Initiating ongoing working groups in separate communities on a common

challenge or emerging technology. These working groups would be asked to create

 

92

solutions which could be tested and further developed on-farm. Before and after
surveys and interviews would be used to determine the effectiveness of the working
group in informing and increasing the generation and adoption of sustainable

agriculture technologies.

9 3
REFERENCES

Ashby, J.A. 1986. Methodology for the participation of small farmers in the design of
on-farm trials. Agricultural Administration. 22 pp. 1-19.

Bezdicek, DP. and C. DePhelps. 1994. Innovative approaches for integrated research
and education programs. Amer.J. Alt. Agric. 9 (1,2) pp. 3-9.

Biggelaar, C. den. 1991. Farming systems development: Synthesizing indigenous and
scientific knowledge systems. Agriculture and Human Values, Winter-Spring. pp. 25-36.

Buttel, RH. and LG. Youngberg. 1985. Sustainable agricultural research and technology
transfer: Socio-Political opportunities and constraints. In T.C. Edens, C. Fridgen, and
S.L. Battenfield (eds). Sustainable Agriculture and Integrated Farming Systems, 1984
Conference proceedings. Michigan State University Press. East Lansing, MI. pp. 287-
297.

Chambers, R 1983. Rural Development: putting the last first. Harlow, England:
Longman Scientific and Technical.

Dlott, J.W., M.A. Altieri, and M.Masumoto. 1994. Exploring the theory and practice of
participatory research in US sustainable agriculture: a case study of integrated pest
management. Agriculture and Human Values, 11 2,3: 126-140.

Doll, JD. and CF. Francis. 1992. Participatory research and extension strategies for
sustainable agricultural systems. Weed Technology 6: 473-482.

Gardner, 1.0 1990. Responding to farmers needs: An evolving land grant perspective.
Amer.J. Alt. Agric. 5: 170-173.

Gerber, J.M. 1992. Farmer participation in research: A model for adaptive research and
education. Amer.J. Alt. Agric. 7: 118-121.

Hesterman, OB. and TL. Thorburn. 1994. A comprehensive approach to sustainable
agriculture: W.K. Kellogg's Integrated Farming systems initiative. Journal of Production
Agriculture. 7: 132-134.

Hill, SB. 1991. Ecological and psychological prerequisites for the establishment of
sustainable agricultural communities. In J. Martin (ed). Alternative Futures for Prairie
Agricultural Communities Edmonton Faculty of Extension, University of Alberta. pp.
197-229.

Krueger, RA. 1988. Focus Groups - A Practical Guide for Applied Research, Sage
Publications. 2111 West Hillcrest Dr. Newbury Park, CA 91320.

Lockeretz, W. 1985. US. Organic farming: What we can and cannot learn from on-farm
research. In T. C. Edens, C. Fridgen, and S. L. Battenfield (eds). Sustainable Agriculture
and Integrated Farming Systems. 1984 Conference Proceedings. Michigan State Univ.
Press. East Lansing.

Miscellaneous publication, 1995. A Partnership for Michigans' Future: Wheat 2000.
Michigan State University Extension, East Lansing, MI 48824

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Nault, J. 1991. Participatory extension strategies for the implementation of sustainable
agriculture. Masters Thesis. Dept. of Renewable Resources, McGill University,
Monaural, Quebec, Canada.

Parr, J .F., RI. Papendick, S.B. Hornick, and RE. Meyer. 1992. Soil quality: Attributes
and relationship to alternative and sustainable agriculture. Amer.J. Alt. Agric. 7 1,2: 5-
11.

Plunkett, LC, and R Roumier. 1991. Participative Management: Implementing
Empowerment, John Wiley and Sons, Inc., New York, NY.

Rocheleau, D. 1994. Participatory research and the race to save the planet: Questions,
critique, and lessons from the field. Agriculture and Human Values, 11 (2,3) pp. 4-25.

Rogers, EM. (1961, 1972, 1983) Diffusion of Innovations. Free Press. New York, NY.

Roling, N. and E. van de Fliert. 1994. Transforming extension for sustainable
agriculture: The case of integrated pest management in rice in Indonesia. Agriculture and
Human Values, 11 2,3: 96-109.

Roling, N.G. and M.A.E. Wagemakers 1997. A New Practice: Facilitating Sustainable
Agriculture. In Social Learning in Sustainable Agriculture, Roling, N.G. and M.A.E.
Wagemakers. (eds) (Forthcoming) Cambridge University Press.

Rosmann, R 1994. Farmer initiated on-farm research. Amer. J. Alt. Agric. 9 1,2: 34-37.

Senge, RM. 1990. The F iflh Discipline: The Art and Practice of The Learning
Organization. Doubleday-Currency, New York, NY.

 

95

Table 1. Comparison of outcomes of participatory research with factors limiting the
adoption of sustainable agriculture practices.

 

FACTORS LIMITING THE ADOPTION

OF
SUSTAINABLE PRACTICES

- Lack of sufficient information

- Lack of site-specific skills

° Limited institutional support

- No common vision to guide
development process

' Awareness of the non-
sustainable nature of
conventional agriculture
practices

- Individuals and communities
empowered to change

- Values related to sustainability

OUTCOMES OF PARTICIPATORY
RESEARCH

~ Site-specific information

° Competence with new farming

practices developed on site
Ability to conduct own
research

° Cooperation between farmers

and scientists creates support

- Commitment, motivation and

creativity which can provide
the groundwork for a common
vision

- Awareness

- Empowerment and confidence

° Exposure to values held by

others

 

Adapted from Nault (1991).

96

Table 2. Questions presented for discussion during the focus group interviews.

 

Knowledge assessment:

Gl.’

GZ.

G3.

- How are you using cover crops on your farm?

- What is your motivation to use cover crops?

- Do you feel cover crops have long term benefits?

What are these long term benefits?

- Would you say that the use of cover crops increases or decreases the risk

of a farm operation?

- Have you used cover crops in the past, and if so in what way?
- What other reasons are there for using cover crops?
- Do you feel cover crops have long term benefits?

What are these long term benefits?

- If you were to begin using cover crops on your farm, what contributions

or benefits would you be looking for?

- Would you say that the use of cover crops increases or decreases the risk

of a farm operation?

- What percentage of farmers in your area use cover crops and what do you

think are their main motivations for using them?

- In your opinion, why don't more farmers use cover crops?
- Do you think that most farm advisors feel knowledgeable enough about

cover crops to assist farmers in using them successfully?

Types of research results and production information desired:

G1.

G2.

G3.

- What research results or production information about cover crops would

you like to have?
Do you think most farmers who use cover crops share your feeling
on this?

- How would you like to get research results and production information?

In other words how would you like to access this information?

- Is there any difference between how you want access to cover crop

information and other production information?

- What research results or production information about cover crops would

you need in order to begin using them on your farm?
Do you think most farmers who are not using cover crops feel the
same way?

- How would you like to get research results and production information?

In other words how would you like to access this information?

- Is there any difference between how you want access to cover crop

information and other production information?

- What research results, production information or skills do you need in

order to continue assisting farmers in successfully utilizing cover crops?
Do you think this is true for most farm advisors?

~ Are there any skills you would like to have that are non-technical which

would assist you in working with farmers about cover crops?

- Do you feel that training in working with groups would be beneficial?
- How would you like to get research results and production information?

In other words how would you like to access this information?

- Is there any difference between how you want access to cover crop

information and other production information?

9 7
Table 2. (continued)

Sources of Information:

G1. - Think back to when you started using cover crops.
What was your original motivation?
How did you learn to successfully use cover crops?
Where did you get the practical information about cover crops?
- Where or from whom do you get most of your information on production
practices currently?
- Do these sources provide information on cover crops and other
stewardship or conservation practices? Which ones?
- Is this where you get most of your cover crop information?
- Is the information consistent among sources?
- If a farmer was interested in using cover crops and was not currently doing
so, how would you suggest they proceed in order to be successful?
G2. - Think back across the years that you have been farming. How did you
learn to farm the way you do?
Was there any individual who really assisted you?
- Where or from whom do you get most of your information on production
practices currently?
- How do you use this information? For example, after you read an article
what is the next step for you?
- Do these sources provide information on cover crops?
What about other stewardship or conservation practices?
- Are you familiar with Michigan Agricultural Stewardship Associations
(MASA) and the Innovative Farmers of Huron County?
Do you feel the information they put out is credible?
G3. - Is there sufficient information on cover crops available to you?
- Where do you get most of your information on cover crops?
- Is the information consistent among sources?

Current generation and transfer of information:

G1 and G2.
- How would you describe the movement of agricultural production
information between the university, agricultural extension, and the farmer?
- Do you feel like a receiver or producer of information or both?
- How could this process be more useful to you?
G3. - How would you describe the movement of agricultural production
information between the university, agricultural extension, and the farmer?
' How do you identify current or potential concerns that are important to
spend time on?
- Do you feel these are effective approaches to meeting farmers needs?
How could the process become more useful to farmers?
- In your experience, is working with farmers to facilitate cover crop use
any different than working with them on any other topic? In what ways?

Participatory approach to generation and transfer of information:
I would now like to present to you a simple model where farmers participate in

the process of generating information and extending it to others. In this model farmers
and farm

9 8
Table 2. (continued)

advisors (Extension agents, specialists, and others) work together to generate the
information they require. Each

bring different skills to the process. In this approach farmers have a major influence on
what is researched. They work with researchers to design an approach to generating the
needed information. A significant amount of research would be done on working farms.
Together farmers and researchers review the progress of the study and interpret the
results.

G1, GZ and G3.
- Do you think this would be an effective approach to providing information
about cover crops which would be useful to farmers?
- What might be some of the advantages and drawbacks of this approach?
- Have any of you had any experience with this type of on-farm research?
How do you feel about it?
Would you do it again?
G3. - Would you like the university to provide more support for you in carrying
out participatory research?
What type of support would you like?

 

1 G1 is the group of farmers using cover crops, G2 is the group not using cover crops,
and G3 is the group of knowledge brokers.

9 9
Table 3. Desired information about cover crops generated by each focus group.

 

 

 

 

Information Desired Farmers 1 Farmers not Knowledge
using cover using cover Brokers
crops crops
%
Long term effects (3-10 years) on soil 20 25 -
productivity and farm profitability
Nutrient benefits to a following crop by each 25 31 19
cover crop option
Short term costs and effect on farm income. 14 - 21
Field demonstrations of covers in cropping 11 - -
systems.
Specific cover strategies for specific 11 10 -
rotations.
System efi‘ects from a cover crop compared to 6 - -
previous crop residue.
Appropriate covers and management 6 13 -
information for use in no-till com
Methods and timing for killing covers. - - 13
Appropriate establishment methods. - 8 11
Potential problems associated with covers. 4 8 10
Brvironmental benefits associated with - - 9
covers
Sources for cover seed - - 8
Weed suppression potential and compan'bility 1 5 6
with herbicides.
Alternate uses of covers - - 3

 

1 Values are the percentage of the total points within each group given to each
information need.

APPENDIX

100

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