USING COVER CROPS IN WHEAT-CORN ROTATIONS TO PROVIDE FORAGE
WHILE IMPROVING SOIL
By
Sabra Lynn Gerdes

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
Crop and Soil Sciences ̶̶ Master of Science
2017

ABSTRACT
USING COVER CROPS IN WHEAT-CORN ROTATIONS TO PROVIDE FORAGE
WHILE IMPROVING SOIL
By
Sabra Lynn Gerdes
The time window after wheat harvest in a wheat (Triticum aestivum L.)- corn (Zea mays L.)
rotation could be used to grow cover crops (CC) to provide forage while protecting soil from
erosion. Field experiments were initiated in East Lansing, MI to determine the consequences of
partial removal of CC biomass on soil improvement and crop yield and quality. Soft red winter
wheat (‘Hopewell’ ̶̶and ̶̶‘Red ̶̶Dragon’) was planted in October of 2013 and 2014 and harvested in
July 2014 and 2015. Cover crops included: frost-seeded red clover, and summer-seeded alfalfa,
cowpea, sunn hemp, radish, oat/field pea mixture, sudangrass, sorghum x sudangrass, and
teffgrass. Half of each CC plot was mechanically harvested eight weeks after planting. Harvested
forage dry matter yield was greatest for red clover (4.3 Mg ha-1); oat-pea mix (2.5 Mg ha-1),
sudangrass/sudex (1.8 Mg ha-1) and radish (1.2 Mg ha-1) (P < 0.01) yielded less. Corn grain yield
harvested in October averaged 13.7 Mg ha-1 and did not differ across CC species or forage
harvest treatment (P > 0.05). Harvesting forage reduced total N removal (TNR) in subsequent
corn for red clover only; harvesting forage did not affect TNR after any other CC (CC x harvest
interaction, P < 0.05). In the harvested system, TNR did not differ (P > 0.05) between for any
CC, but unharvested RCL (374 kg N ha-1) had greater (P < 0.01) TNR than oat-pea mix (338 kg
N ha-1). There were no differences among treatments for soil permanganate oxidizable carbon
POXC (P > 0.05). Harvesting cover crops for forage after winter wheat harvest in Michigan can
give harvestable forage and acceptable nutritive value.

ACKNOWLEDGEMENTS

I would like to express my gratitude to Dr. Kimberly Cassida for all her guidance, time and help
throughout this project. I am very grateful to the members of my committee for their advice and
time—Dr. Christina DiFonzo, Dr. Sieglinde Snapp, and Dr. Karen Renner.
Gratitude is also expressed to the Michigan State University Agronomy Farm managers and
technicians for the use of all of their equipment and advice. Joe Paling, this project could not
have been completed without your help and expertise, thank you. Thank you to the forage lab
group at MSU for all their help on all the aspects of this project.
A very special thank you to Dr. Jennifer MacAdam for giving me support and encouraging me to
pursue a Master’s ̶̶degree ̶̶at ̶̶Michigan State University.
I would like to express my deepest gratitude to my family and especially would like to
acknowledge ̶̶my ̶̶Father ̶̶and ̶̶Mother, ̶̶Brent ̶̶and ̶̶Holly ̶̶Gerdes. ̶̶I ̶̶wouldn’t ̶̶be ̶̶where ̶̶I ̶̶am ̶̶today ̶̶
without their love, support, and inspiration. They have always encouraged me to achieve my
dreams. Little did they know that I would be following in their footsteps.

iii

TABLE OF CONTENTS

LIST OF TABLES ....................................................................................................................... vi
LIST OF FIGURES .................................................................................................................... vii
CHAPTER 1 ...................................................................................................................................1
LITERATURE REVIEW ................................................................................................................1
Crop Rotations .....................................................................................................................1
Decline of Crop Rotations ...................................................................................................2
Benefits of Crop Rotations ...................................................................................................3
Cover Crops .........................................................................................................................5
Cover Crop Groups and Niches ...........................................................................................7
Negative Impacts of Cover Crops ........................................................................................9
Cover Crops as Forage ......................................................................................................10
History of Forage Crops ....................................................................................................10
Forage Quality and Groups ...............................................................................................11
Negative Impacts of Forages .............................................................................................14
Potential Double Crops in Michigan and the Upper Midwest ..........................................15
Why Cover Crops as Forages? ..........................................................................................17
BIBLIOGRAPHY ........................................................................................................................19
CHAPTER 2 .................................................................................................................................30
USING COVER CROPS IN WHEAT-CORN ROTATIONS TO PROVIDE FORAGE WHILE
IMPROVING SOIL .......................................................................................................................30
ABSTRACT ..................................................................................................................................30
INTODUCTION ..........................................................................................................................32
MATERIALS AND METHODS ................................................................................................36
Site Description..................................................................................................................36
Experimental Design ..........................................................................................................36
Crop Management .............................................................................................................37
Measurements ....................................................................................................................38
Statistical Analysis .............................................................................................................42
RESULTS .....................................................................................................................................44
Weather ..............................................................................................................................44
Wheat Performance ...........................................................................................................44
Botanical Composition.......................................................................................................44
Ground Cover ....................................................................................................................45
Plant Canopy Height..........................................................................................................47
Harvested Forage Yield, Nutritive Value, and C, N Content.............................................48
Corn Performance .............................................................................................................48
Soil Assessment ..................................................................................................................50
DISCUSSION ...............................................................................................................................51
CONCLUSIONS ..........................................................................................................................65

iv

APPENDICES ..............................................................................................................................67
APPENDIX A Results ......................................................................................................68
APPENDIX B ANOVA Tables for Figures .....................................................................80
BIBLIOGRAPHY ........................................................................................................................89

v

LIST OF TABLES

Table 1. Variety and pure live seeding rates for cover crops grown after wheat harvest at East
Lansing, MI. in 2014 and 2015. .........................................................................................68
Table 2. Nutritive value and carbon and nitrogen concentration and ratio of forage in cover crops
harvested eight weeks after seeding following July 2014 and 2015 wheat harvest at East
Lansing, MI. .......................................................................................................................69
Table 3. ANOVA results and planned contrasts for corn grain and stover yields after cover crops
were harvested or not harvested the previous October 2014 and 2015 at East Lansing, MI.
............................................................................................................................................70
Table 4. Nitrogen concentration, carbon/nitrogen ratio, and total nitrogen removed in V-12 stage
corn ear leaves, grain and stover harvested after cover crops were harvested or not
harvested the previous October 2014 and 2015 at ̶̶East Lansing, MI ................................72
Table A1. ANOVA table for cover evaluations taken bi-weekly from red clover and annual
cover crops planted after wheat harvest approximately, (A) eight weeks after cover crop
planting (B) four weeks after cover crop harvest, (C) four weeks before corn planting (D)
four weeks after planting. Cover crops were harvested in October 2014 and 2015 and
corn was planted in May 2015 and 2016 at East Lansing, MI. ..........................................80
Table A2. ANOVA ̶̶table ̶̶for ̶̶Plant ̶̶canopy ̶̶height ̶̶taken ̶̶bi-weekly ̶̶from ̶̶red ̶̶clover ̶̶and ̶̶annual ̶̶
cover ̶̶crops ̶̶planted ̶̶after ̶̶wheat ̶̶harvest ̶̶approximately, ̶̶(A) eight weeks after planting (B)
four weeks after harvest (C) four weeks before corn planting (D) four weeks after corn
planting. ̶̶Cover ̶̶crops ̶̶were ̶̶harvested ̶̶in ̶̶October ̶̶2014 ̶̶and ̶̶2015 ̶̶and ̶̶Corn ̶̶was ̶̶planted ̶̶in ̶̶
May ̶̶2015 ̶̶and ̶̶2016 ̶̶at ̶̶East Lansing, MI. ..........................................................................83
Table A3. ANOVA table for Figure 5 forage dry matter harvested in October 2014 and 2015
from red clover and annual cover crops planted after wheat harvest in July, at East
Lansing, MI. .......................................................................................................................84
Table A4. ANOVA ̶̶table ̶̶for ̶̶Figure 6 analysis of variance for labile organic matter for November
2014 and October 2015 fall soil sampling after cover crop harvest. ̶̶Cover ̶̶crops ̶̶were ̶̶
harvested ̶̶in ̶̶October ̶̶2015 ̶̶from ̶̶red ̶̶clover ̶̶and ̶̶annual ̶̶cover ̶̶crops ̶̶planted ̶̶after ̶̶wheat ̶̶
harvest ̶̶in ̶̶July. Cover ̶̶crops ̶̶were ̶̶harvested ̶̶in ̶̶October ̶̶2014 ̶̶at ̶̶East Lansing, MI. .........85
Table A5. Carbon and nitrogen concentration in soil from the 12 cm depth sampled in November
after cover crop were harvested or not harvested in October 2014 and 2015 at ̶̶East
Lansing, MI ........................................................................................................................86

vi

LIST OF FIGURES
Figure 1. ̶̶(A) ̶̶Maximum, ̶̶minimum, ̶̶and ̶̶average ̶̶monthly ̶̶air ̶̶temperature, ̶̶(B) ̶̶cumulative ̶̶
monthly ̶̶precipitation, ̶̶and ̶̶25-year ̶̶norms ̶̶at ̶̶East ̶̶Lansing, ̶̶MI., ̶̶from ̶̶October ̶̶2013 ̶̶to ̶̶
September ̶̶2016. ̶̶Arrows indicate when soil samples were obtained. ...............................74
Figure 2. Percentage (dry matter basis) of cover ̶̶crop, ̶̶volunteer ̶̶wheat, ̶̶wheat ̶̶straw, ̶̶and ̶̶weed ̶̶
components ̶̶in ̶̶biomass ̶̶harvested ̶̶in ̶̶October ̶̶in ̶̶2014 ̶̶(A) ̶̶and ̶̶2015 ̶̶(B) ̶̶from ̶̶cover ̶̶crop ̶̶
plots ̶̶at ̶̶East ̶̶Lansing, ̶̶MI. ̶̶(‡ ̶̶RCL, frost-seeded red clover; OPmix, oat/pea mix, SUD,
sudangrass; SDX, sorghum x sudangrass; Teff, teffgrass) ................................................75
Figure 3. Cover ̶̶crop ̶̶(CC), ̶̶volunteer ̶̶wheat ̶̶(VW), ̶̶weed, ̶̶crop ̶̶residue ̶̶(RES), ̶̶and ̶̶corn ̶̶
components ̶̶of ̶̶ground ̶̶cover ̶̶when ̶̶measured: ̶̶(A) eight weeks after CC planting
following wheat harvest, (B) four weeks after Oct. CC harvest, (C) four weeks before
May corn planting the following year, and (D) four weeks after May corn planting. ̶̶
Values ̶̶are ̶̶means ̶̶from ̶̶two ̶̶site-years ̶̶(2014-2015 ̶̶and ̶̶2015-2016) ̶̶at ̶̶East Lansing, MI.
(RCL = red clover, OPmix = oat/pea mix, SUD= sudangrass, SDX = sorghum x
sudangrass, FCC = failed cover crop, NH = no CC harvest, H = CC harvested) .............76
Figure 4. Plant ̶̶canopy ̶̶height ̶̶when ̶̶measured: ̶̶(A) eight weeks after CC planting following
wheat harvest, (B) four weeks after Oct. CC harvest, (C) four weeks before May corn
planting the following year, and (D) four weeks after May corn planting. ̶̶Values ̶̶are ̶̶
means ̶̶from ̶̶two ̶̶site-years ̶̶(2014-2015 ̶̶and ̶̶2015-2016) ̶̶at ̶̶East Lansing, MI. Error bars
are SEM. (RCL = red clover, OPmix = oat/pea mix, SUD= sudangrass, SDX = sorghum
x sudangrass, FCC = failed cover crop, NH = no CC harvest, H = CC harvested) ..........77
Figure 5. Forage ̶̶dry ̶̶matter ̶̶harvested ̶̶in ̶̶October ̶̶2014 ̶̶and ̶̶2015 ̶̶from ̶̶red ̶̶clover ̶̶and ̶̶annual ̶̶
cover ̶̶crops ̶̶planted ̶̶after ̶̶wheat ̶̶harvest ̶̶in ̶̶July ̶̶at ̶̶East Lansing, MI. The error bars show
statistically different results based on SE. ̶̶(‡ ̶̶RCL, frost-seeded red clover; FCC, failed
cover crop; OPmix, oat/pea mix, SUD, sudangrass; SDX, sorghum x sudangrass; Teff,
teffgrass) ...........................................................................................................................78
Figure 6. Analysis of variance for labile organic matter for 2014 and 2015 fall soil sampling
after cover crop harvest. ̶̶Cover ̶̶crops ̶̶were ̶̶harvested ̶̶in ̶̶October ̶̶2014 ̶̶and ̶̶2015 ̶̶from ̶̶red ̶̶
clover ̶̶and ̶̶annual ̶̶cover ̶̶crops ̶̶planted ̶̶after ̶̶wheat ̶̶harvest ̶̶in ̶̶July. Cover ̶̶crops ̶̶were ̶̶
harvested ̶̶in ̶̶October ̶̶2014 ̶̶at ̶̶East Lansing, MI. The error bars show statistically different
results based on SE. (‡ ̶̶RCL, frost-seeded red clover; FCC, failed cover crop; OPmix,
oat/pea mix, SUD, sudangrass; SDX, sorghum x sudangrass; Teff, teffgrass) .................79
Figure A1. ̶̶Corn ̶̶SPAD ̶̶(Soil ̶̶Plant ̶̶Analytical ̶̶Division ̶̶value) ̶̶meter ̶̶and ̶̶PhiNPQ ̶̶readings ̶̶at V12 stage in ear leaves of corn grown after cover crops were harvested or not harvested the
previous October at ̶̶East Lansing, MI. SPAD measures active regulation of energy
towards photosynthesis and should be positively correlated with grain yield. PhiNPQ is
the measurement of active regulation of energy away from photosynthesis and should be
correlated with reduced grain yields ..................................................................................88

vii

CHAPTER 1
LITERATURE REVIEW

Crop Rotations
Crop rotations have been used for centuries. Ancient kingdoms and empires, including
the Romans, Grecians, Chinese and Egyptians, documented this agricultural practice (White,
1970; Angus et al., 2015). A three-year ̶̶crop ̶̶rotation ̶̶called ̶̶“food, ̶̶feed, ̶̶and ̶̶fallow” ̶̶was ̶̶
documented in the Middle Ages and Roman Empire. This rotation divided the farm acres into
three sections; a human food crop such as wheat, an animal feed such as barley or oats, and a
section that was not planted (fallow) (White, 1970). Later in the 18 th century, European farms
increased in size and farmers began to experiment with crop rotations, dividing the greater farm
land area into four, four-year crop rotations which consisted of turnip, barley, clover and wheat
(Evans, 1998).
Crop rotation is defined as a cropping sequence that contains fallows, forages, or specialuse crops in addition to the normally grown species crops that produce food, fiber or fuel such as
wheat and corn (Angus et al., 2015). ̶̶Though ̶̶the ̶̶terms ̶̶“crop ̶̶rotation” ̶̶or ̶̶“cropping ̶̶sequences” ̶̶
was ̶̶not ̶̶used ̶̶before ̶̶the ̶̶1960’s ̶̶and ̶̶documented ̶̶first ̶̶in ̶̶the ̶̶United ̶̶Kingdom (Selman, 1969),
many understood the benefits that came from growing unusual crops other than the normal
species grown. Theophrastus wrote in the 4th Century ̶̶that ̶̶‘wheat ̶̶exhausts ̶̶the ̶̶land ̶̶more ̶̶than ̶̶
any ̶̶other ̶̶crop’ ̶̶and ̶̶‘beans. ̶̶. ̶̶.even ̶̶seem ̶̶to ̶̶manure ̶̶it’ ̶̶(Hort, 1926). While an ancient Roman text
reads that "some crops are to be planted not so much for the immediate yield as with a view to
the following year" (Harrison et al., 1913). The increased yields that are associated with crop
rotations are now referred to as the rotation effect (Ellis et al., 1988; Pierce and Rice, 1988).

1

Decline of Crop Rotations
Before the 1940s and World War II, crop rotation was commonly used for many benefits
including controlling insect infestations, controlling weeds, and reducing soil erosion (Zentner et
al., 2002). After World War II, use of crop rotations began to decline rapidly, leading to
increasing monocultures, and cropping systems that were homogenous with little genetic and
plant diversity (Power and Follett, 1987). This decline occurred because of the introduction and
availability of inexpensive synthetic fertilizers, coupled with more effective pesticides
(Crookston et al., 1991; Bullock, 1992) that could substitute for pest suppression by the rotation.
Mechanized farming has had a huge effect on agricultural dynamics in the United States
(Bullock, 1992) as well as Europe (Leteinturier et al., 2006), allowing farmers to manage large
acreages of monoculture crops. Brazil is also moving towards more industrialized agriculture
and crop intensification patterns. This is shown by farming moving away from the typical
farming pattern of growing a single crop per year to a more intensified growing pattern of two
consecutive cash crops per year, depleting soil water and nutrients (Arvor et al., 2012).
Genetically modified organisms (GMOs), also known as genetically modified (GM)
crops, such as corn and soybeans, have also contributed to the decline of crop rotations. To a
great extent, GMOs were and are still designed to improve on the conventional crop varieties, for
various purposes. For example, in corn, VT Triple PRO® (Monsanto), P1498AM® (DuPont)
and DEKALB® GM varieties are used for pest control (DuPont, 2016; Monsanto, 2016) while
Roundup Ready® GM varieties are used to improve quality (DuPont, 2016; Monsanto, 2016) by
increasing the ease of weed control and increased yields. In the USA, Canada, Brazil, and several
other countries, GM crops like corn, soybeans, cotton, and canola are commonly used and have
replaced many of the conventional varieties (Gianessi, 2005; James, 2007; Reuter et al., 2011).

2

With the decline of crop rotation, the increase of industrialized agriculture and the use of GM
crops, synthetic fertilizer, and pesticides, negative impacts and costs began to be noticed.
Pesticide resistance has increased (Wolfenbarger and Phifer, 2000; Gianessi, 2005), leading to a
shift in plant genetics and reducing the effectiveness of pesticides for insect control.
Furthermore, the use of pesticides is associated with a decrease in the population of many
beneficial insects, such as bees (Crane and Walker, 1983), a noticeable decrease in soil health
and organic matter and an increase in soil movement or erosion (Pimentel et al., 1995).
Another negative impact of monocultures is yield drag or depression (Bullock, 1992;
Sumner et al., 1990). In the 1980s, it was documented that corn grown on land planted to corn in
the previous year or grown as a monoculture yielded up to 15% less grain than corn rotated with
other crops (Sundquist et al., 1982). Soybean yields also declined 10 to 15% when grown as a
monoculture (Bhowmik and Doll, 1982). With the realization of these potential damaging effects
and the rise of the sustainable agriculture movement, additional research occurred to test
hypothesizes as to the ̶̶role ̶̶of ̶̶crop ̶̶rotation ̶̶in ̶̶today’s ̶̶modern ̶̶farming ̶̶systems. ̶̶
Benefits of Crop Rotations
Crop rotations benefit agricultural production, and modern farmers and researchers have
recognized the need to include rotation for increased crop yields (Bhowmik and Doll, 1982;
Sundquist et al., 1982 Ellis et al., 1988; Sumner et al., 1990; Porter et al.,1997), reduced pest
damage (Bullock, 1992; Howard et al., 1998; Angus et al., 2015), reduced weeds (Liebman and
Dyck, 1993; Colbach and Debaeke, 1998), and increased organic matter leading to a richer and
healthier soil (Karlen et al., 2006; Zhang et al., 2014).
Daubeny (1845) and Lawes and Gilbert (1894) completed some of the first structured
experiments showing the value and justification of a rotation in comparison with continuous

3

cropping. Daubeny (1845) showed his results in a 10-year experiment in Rothamsted, United
Kingdom, which three-fourths of the rotating cropping systems out-yielded the continuous
cropping systems. The Lawes and Gilbert (1894) experiment showed that yields of broadleaf
crops, such as soybeans, were much greater when grown in rotation than when grown
continuously; barley yields were similar, and wheat yielded more when grown in rotation. Both
experiments showed that the productivity of the crop rotation was greater than that of the
continuous cropping system. Several other studies (Bhowmik and Doll, 1982; Sundquist et al.,
1982; Ellis et al., 1988; Sumner et al., 1990; Porter et al.,1997; Nevens and Reheul, 2001; Zhang
et al., 2014; Angus et al., 2015) also showed that rotations improved sustainability of cropping
systems over continuous planting of the same crop.
With the increased intensification of agriculture to meet the food supply demand comes a
concern for the environment (Piorr, 2003) and the impacts associated with industrialized
farming. Farmers and researchers have found that reintroducing crop rotations into agricultural
cropping systems not only increased yields, but improved soil structure and productivity. The
realization of the importance of soil, the complexity of the soil ecosystem encompassing plant,
water, nutrients, microbes, insects and mammal interactions (Bossio and Scow, 1998; Degens et
al., 2000; Girvan et al., 2003) sparked interest in sustainable agriculture (Leteinturier et al.,
2006).
Farming systems use cover crops for several reasons, some of the main reasons include
weed suppression (Teasdale,1996), reduce soil erosion (Dabney et al., 2001), increase organic
matter (Teasdale et al., 2007), and to break pest and disease cycles (Derpsch et al., 2010) and an
additional source for nutrients (Blevins et al., 1990; Honeycutt et al., 1996; Hartwig and Ammon
2002; Vyn et al., 2000; Henry et al., 2010; Schipanski and Drinkwater, 2011) to benefit the cash

4

crops. Interest and research in crop rotations, soil communities and interactions, organic matter,
tillage and chemical practices, living mulches cover crops and possible interactions between all
of them have increased in the past few decades.
Cover Crops
With the abundant, cheap, and fertile farming land that was available during ̶̶the ̶̶1800’s ̶̶
(Mitchell et al., 1991) in the United States, farmers did not have a reason to develop an
awareness or interest in preserving soil productivity through soil conservation. In the 1920s, the
U.S. Department of Agriculture recognized the problem of soil erosion, but little was done to
encourage farmers to invest in soil conservation practices (Hartwig and Ammon, 2002). This all
changed in the 1930s when the Dust Bowl hit the United States, forcing farmers and the public
alike to become concerned about soil erosion and adopt conservation practices that included
cover crops and living mulches.
A cover crop is defined as any living ground cover that is planted into or after a main
crop and then killed before the next crop is planted (Hartwig and Ammon, 2002), either by
winter kill, chemical application, or tillage practice depending on the farming system. Living
mulches are cover crops planted either before or with a main crop and maintained as a living
ground cover throughout the growing season (Pimentel et al., 1995; Hartwig and Ammon, 2002).
An example of a living mulch is red clover or alfalfa planted with wheat One of the main
rationales of growing cover crops is to have growing, living plants on fields that would otherwise
be fallow. Growing cover crops allows farmers to take better advantage of resources provide by
the soil, sun and water while improving soil health and structure (Pimentel et al., 1995). This
occurs because living plant cover protects the soil from erosion or loss (Hartwig and Ammon,
2002; Clark, 2007), scavenges nutrients that are otherwise unavailable or leached away during

5

the fallow season (Hartwig and Ammon, 2002; Clark, 2007; Henry et al., 2010), holds and cleans
water (Hartwig and Ammon, 2002), and provides nutrients to the cash crop planted after the
cover (Mitchell and Teel, 1977; Haystead and Marriot, 1978; Hargrove, 1986; Pimentel et al.,
1995; Hartwig and Ammon 2002; Vyn et al., 2000; Henry et al., 2010; Schipanski and
Drinkwater, 2011).
Cover crops have a wide variety of species diversity, adaption, uses, and benefits. Choice
of cover crop is dependent on the location of the farm and the objectives of the farmer, and
specific cover crop benefits are dependent on species choice (Snapp et al., 2005; Clark, 2007).
One cover crop will not provide all possible benefits. The benefits of cover crops include; weed
competition/suppression (Hartwig and Ammon, 2002; Clark, 2007), pest suppression and
sustaining beneficial insect populations (Lazarus and White, 1984; Bugg and Waddington, 1994;
Honeycutt et al., 1996; Hartwig and Ammon, 2002; Clark, 2007), nitrogen source and/or
scavenger (Kroontje and Kehr, 1956; Mitchell and Teel, 1977; Haystead and Marriot, 1978;
Ebelhar et al., 1984; Hargrove, 1986; Fox and Piekielek, 1988; Vyn et al., 2000), wildlife
enhancement (Clark, 2007), and grazing/forage value (Moore, 2003; Clark, 2007). Other benefits
focus primarily on soil improvement by: building soil organic matter (Dabney et al., 2001; Sainju
et al., 2001; Hartwig and Ammon, 2002), improving soil structure and reducing compaction
(Clark, 2007), reducing erosion (Pimentel et al., 1995; Kessavalou and Walters, 1999; StiversYoung and Tucker, 1999; Snapp et al., 2001; Hartwig and Ammon, 2002), recycling nutrients
(Wayland et al. 1998; Hartwig and Ammon, 2002; Weinert et al., 2002), enhancing water quality
(Danso et al., 1991; Wayland et al., 1998; Vyn et al., 1999; Dabney et al., 2001; Hartwig and
Ammon, 2002; Clark, 2007), and supporting increased activity and sustainability of beneficial
microbial communities (Hartwig and Ammon, 2002; Morrone and Snapp, 2011).

6

Cover crops are commonly divided into four groups: legumes, grasses, grains, and
brassicas (Clark, 2007; USDA NRCS, 2016). Cover crops are often also categorized by climatic
region or a niche where a cover crop is well adapted, using USDA Hardiness Zones or
photosynthetic pathway designation as cool- (C3 photosynthesis) or warm- (C4 photosynthesis)
season species (USDA NRCS, 2016).
Cover Crop Groups and Niches
In early western Europe agriculture, forage legumes slowly became more common and
noticeably improved soil fertility (Stinner et al.,1994). This led to an increase in legume
popularity not only as a feed source, but as a cover crop. Legumes used as cover crops include:
alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), white clover (Trifolium
repens L.), peas (Pisum sativum L.), cowpea (Vigna unguiculata L. Walp), sunn hemp
(Crotalaria juncea L.), and hairy vetch (Vicia villosa Roth). Legumes are desirable cover crops
because they have the potential for fixing nitrogen, a portion of which will be available in the
subsequent rotations for high-nitrogen–requiring crops such as corn (Kroontje and Kehr, 1956;
Mitchell and Teel, 1977; Haystead and Marriot, 1978; Hargrove, 1986; Ebelhar et al., 1984; Fox
and Piekielek, 1988; Hartwig and Ammon 2002; Vyn et al., 2000; Henry et al., 2010; Schipanski
and Drinkwater, 2011). Another added benefit for some legumes is the development of a deep
taproot, such as found in alfalfa (Moore, 2003; Clark, 2007), which can break up compaction
layers (Waldron and Dakessian, 1982; Disparte, 1987; Meek et al., 1990; Chen and Weil, 2011)
and scavenge for nutrients (Mitchell and Teel, 1977; Ebelhar et al., 1984; Hargrove, 1986; Vyn
et al., 2000; Chen and Weil, 2011).
Grasses and grains are used for their ability to control erosion and provide high residue
(Pimentel et al., 1995; Kessavalou and Walters, 1999; Stivers-Young and Tucker, 1999; Snapp et

7

al., 2001). Several grasses and some grains are also considered for the potential to scavenge for
nutrients (Clark, 2007), particularly nitrogen (Weinert et al., 2002; Snapp et al. 2005; Clark,
2007). This reduces loss of vital nutrients from soil and decomposing crop residues between
rotations, and once grasses and grain residues are decomposed much of the nutrients are released
back into the soil and available for uptake by the next crop. Grasses and grains used for cover
crops include: sudangrass (Sorghum bicolor L.), sorghum x sudangrass hybrid [Sorghum bicolor
x S. bicolor (Piper) Stapf.], teff grass (Eragrostis tef Zucc.), rye (Secale cereal L.), wheat
(Triticum aestivum L.), oats (Avena sativa L.), pearl millet (Pennisetum glaucum L.), barley
(Hordeum vulgare L.), and annual ryegrass (Lolium multiflorum L.).
Brassicas have been used for centuries as a food, feed, and oil source for both humans
and animals, but were rarely used as a cover crop (Gupta and Pratap, 2007). The major cover
crop benefits of the brassica group include N scavenging and weed suppression (Clark, 2007).
Some brassicas such as oilseed radish (Raphanus sativus L.), rapeseed/canola (Brassica napus
L.), and forage rape (Brassica rapa L.), have a deep tap root that can potentially break up
compaction layers (Smith and Collins, 2003; Clark, 2007). Brassicas used as cover crops include:
rapeseed/canola, forage turnip, oil seed radish and kale (Brassica napus var. pabularia (DC.)
Alef.) (Smith and Collins, 2003; Clark, 2007; Gupta and Pratap, 2007).
Cool- and warm-season terms are more broad in terms of determining a cover crop niche
(Barnes and Nelson, 2003; Clark, 2007), while USDA Hardiness Zones are more detailed
(USDA NRCS, 2016). These terms help farmers know what conditions are required for
establishment, growth, and survival as well as possible stressors and causes of cover crop death.
Cool-season cover crops using in the Upper Midwest include: alfalfa, red clover, oil seed radish,

8

cereal rye, oat and field pea. Warm-season cover crops in the Upper Midwest include: cowpea,
sudangrass, sorghum x sudangrass hybrid and teffgrass.
Cover crops can be planted in mixtures of functional groups to receive a combination of
benefits dependent on the species selected. For example, legumes are often used in mixes with
grasses or with small grains such as oats to increase nutritive value as forage (Balasko and
Nelson, 2003) as well as fixing nitrogen (Haystead and Marriot, 1978; Hargrove, 1986; Ebelhar
et al., 1984; Fox and Piekielek, 1988; Hartwig and Ammon 2002; Vyn et al., 2000; Henry et al.,
2010; Schipanski and Drinkwater, 2011). Complex mixtures that include multiple cover crop
species including grasses, grains, brassicas, and/or legumes are popularly referred to as ̶̶“cocktail ̶̶
mixtures” ̶̶(Clark, ̶̶2007).
Negative Impacts of Cover Crops
Though there are many benefits to including a cover crop in a crop rotation, there are
negatives associated with cover crops as well. Cover crops can be hard to kill and can become
weeds in subsequent crop rotations, reducing crop yields (Snapp et al., 2005; Clark, 2007) due to
the competition for water, nutrients and light (Hartwig and Ammon, 2002). Residues of cover
crops such as cereal rye can be hard to incorporate, which may delay planting of the next cash
crop and delay in nutrient release from residues (Snapp et al., 2005). Some cover crops can
reservoirs for diseases affecting the following cash crop, such as red clover being a host for
Streptomyces scabiei (scab), a common disease in potato production (Bugg and Waddington,
1994).
There are other reasons why farmers are hesitant to plant cover crops, including cover
crop seed cost and availability (Snapp et al., 2005) as well as establishment of the cover crop.
Cost of cover crop establishment can be great, with potential costs for irrigation water, planting,

9

fertilizer, pest control, and weeding (Hartwig and Ammon, 2002; Snapp et al., 2005; Clark,
2007). Weeds cannot be controlled in many of the cover crops once they become established and
sometimes the cover crop does not compete well with weeds during early establishment (Smith
and Collins, 2003).
Cover Crops as Forage
Another use for cover crops is as a forage. Many species currently being used as covers
have a long history of use as annual forage crops in livestock production systems; however, the
potential for cover crops to be harvested as forage in cash-cropping systems is an important and
relatively recent development in cover crop research. Farmers can receive the benefits of having
a cover crop as discussed above, but also receive an added benefit of feed, either for on-farm
animals or to sell (Snapp and Mutch, 2003; Snapp et al., 2005). However, there is a common
concern that some or all of the environmental and cash crop benefits of the cover crop will be
lost if it is harvested early as a forage. In addition, it is not clear if harvesting cover crops as
forage is cost-effective. Some species commonly used as both forages and cover crops in the
Upper Midwest include: alfalfa, red clover, brassicas, small grains, and field pea.
History of Forage Crops
Forage crops have a long and rich history as livestock feed. Functional groups of forage
species include various legumes, cool- and warm- season grasses, and brassicas. Grasses have
always been used as a forage, though many of the grasses used as forages today in the US were
introduced from Eurasia, the Mediterranean, Africa and Europe. The reason for this introduction
of grasses was to replace the less-productive native grasses (Buckner et al., 1979; Conant et al.,
2001; Balasko and Nelson, 2003; Barnes and Nelson, 2003; Redfearn and Nelson, 2003).

10

Many of the grassland acres were lost to cultivation and overgrazing (Seré et al., 1995;
Conant et al., 2001) and were poorly managed, and soil degradation (Oldeman, 1994), invasion
of weeds, and loss in overall quality of the lands occurred (Oldeman, 1994; Seré et al., 1995;
Conant et al., 2001). The annual forages in cropping systems, that replaced the permanent
grasslands, can potentially substitute some of the ecosystem services, such as feed for animals,
soil and plant biodiversity, and water and nutrient availability and uptake, originally provided by
the permanent grasslands that were lost (Conant et al., 2001; Balasko and Nelson, 2003; Barnes
and Nelson, 2003; Redfearn and Nelson, 2003; Sanderson et al. 2004; Brussaard et al., 2007;
Wrage et al., 2011).
Forage Quality and Groups
Each group of forages has specific characteristics of nutritive value, often referred to as
forage quality. Forage quality is defined as the potential of a forage to produce a chosen animal
response (Church, 1988; Fahey et al., 1994; Paterson et al., 1994; Collins and Fritz, 2003;
Mitchell and Nelson, 2003). An example of this response can be in optimal milk production on a
dairy farm, appropriate weight gain on steers in beef production, or wool production.
Characteristics ̶̶of ̶̶“good” ̶̶forage ̶̶quality ̶̶is ̶̶a specific nutrient concentration that is appropriate for
acceptable animal production based on animal species and class (Church, 1988; Collins and
Fritz, 2003). Not all forages provide good forage quality for all animal classes. Other quality
characteristics include palatability (i.e. easy to eat and digest), free of anti-quality factors
originating from the plant (i.e. nitrates, dust, toxic secondary compounds), and free of outside
contaminants (i.e. mold, toxic plants, soil, weeds, etc.) (Collins and Fritz, 2003).
Legumes have superior forage quality to grasses (Cherney and Cherney, 2002; McGraw
and Nelson, 2003) resulting from their high protein content (Church, 1988; Cherney and

11

Cherney, 2002; Undersander et al., 2004; Evers, 2011), high fiber digestibility (Cherney and
Cherney, 2002), high lipids (Undersander et al., 2004), and condensed tannins (for some species
of legumes) (McGraw and Nelson, 2003). Also, as discussed earlier, most legumes fix
atmospheric nitrogen (N2) which contributes to overall soil N fertility (Barnes and Nelson, 2003;
McGraw and Nelson, 2003; Evers, 2011). With this ability and excellent forage quality, legumes
are often seeded into pastures and hayfields. Legumes help meet dietary needs of many animal
classes (McGraw and Nelson, 2003; Mitchell and Nelson, 2003; Undersander et al., 2004; Evers,
2011). Some legumes used as forages include alfalfa, clovers (Trifolium spp.) and peas.
Grasses are lower in forage quality than legumes and are typically mixed with legumes in
pasture and hayfields to improve the nutritive value (McGraw and Nelson, 2003; Balasko and
Nelson, 2003). Grass species differ in palatability and physical texture, which in turn affects
animal intake and consumption. Softer leaves and fine stem of some grasses such as the
ryegrasses (Lolium spp) and bluegrasses (Poa spp), are easier to consume compared to the stiffer
leaves and thicker stems of different grass species (Paterson et al., 1994; Balasko and Nelson,
2003). Another factor is the developmental stage of growth in grasses. Depending on the growth
stage, leaves are more palatable in the vegetative stage rather than in the reproductive stage
(Paterson et al., 1994; Balasko and Nelson, 2003). Additionally, forage quality decreases in
grasses during the reproductive stages because lignin increases with maturity. Lignin can
increase rapidly from about two percent to as much as eight percent of dry weight during the
reproductive stages (Brown et al., 1968; Balasko and Nelson, 2003).
Cool-season perennial grasses provide most of the forages consumed by beef cattle and
sheep in temperate areas of the world (Balasko and Nelson, 2003). Perennial warm-season and
summer annual grasses provide forage in northern areas of the US (Barnes, 2003). However, in

12

the Midwest, warm-season grasses typically have a lower forage quality (Kephart and Buxton,
1993; Paterson et al., 1994; Balasko and Nelson, 2003) compared to cool-season grasses.
Reduced nutritive value is due to the decrease in the leaf to stem ratio (Paterson et al., 1994;
Balasko and Nelson, 2003), reduced protein concentration (Balasko and Nelson, 2003), and
greater lignin and other structural tissues in the leaves (Paterson et al., 1994; Balasko and
Nelson, 2003). An important development that improved forage quality of some warm-season
grasses was the discovery of the brown midrib trait (BMR) which reduces lignin concentration in
the plant and thus improves digestibility (Cherney et al., 1991). Commercially available BMR
varieties are available for sorghums, sudangrass, and corn.
Forage from small grain crops provides a high-quality feed (Cherney and Marten, 1982;
Church, 1988; Coblentz and Walgenbach, 2010), assists with animal growth, increases the
quality provided by animal products (i.e. milk and meat, etc.) (Church, 1988), and can be used as
an alternative feed. For example, in beef production fall forage growth from small grains
provides a source of high-quality feed (Church, 1988) and can extend the grazing season thus
reducing the need for supplemental hay during the winter months (Coblentz and Walgenbach,
2010). For other livestock producers, forage growth provided by small grains may also provide
extra forage during and after a summer drought (Coblentz and Walgenbach, 2010). Coblentz and
Walgenbach (2010) found that a variety of oat yielded more compared to wheat (Triticum
aestivum L.) cultivars and remained vegetative due to the longer colder temperatures and a longday photoperiod requirement. In a study conducted by Cherney and Marten (1982), barley
(Hordeum vulgate L.) forage nutritive value was often greater than oats, wheat, or triticale
(Triticum durum Desf. × Secale cereale L.) and wheat was the lowest yielding forage.

13

The brassica family of forages have been used for livestock feed for centuries (Smith and
Collins, 2003). Brassicas are thought to originate in Asia and have been cultivated for thousands
of years (Gupta and Pratap, 2007; Banuelos et al., 2013). In the US during the 1800s, brassicas
were used as feedstuffs, providing a high economic return in the harvesting, storing, and feeding
of the large roots (Smith and Collins, 2003; Banuelos et al., 2013). Forage brassica economic
viability hit a peak in the early 1900s, and use of brassicas then began to decline due to the high
labor cost for cultivation, harvest, and feeding (Smith and Collins, 2003). Recently brassicas
have made a return because of their value as a forage and potential as a cover crop (Clark, 2007;
Gupta and Pratap, 2007; Banuelos et al., 2013). Useful characteristics of brassicas include: high
frost tolerance – allowing them to grow and maintain biomass in colder months and lengthen the
grazing season (Smith and Collins, 2003), little decline in nutritive value with maturity (Smith
and Collins, 2003; Gupta and Pratap, 2007), and high energy content because the large storage
roots of turnips, swedes (Brassica napobrassica L.) and radish are a good source for
nonstructural carbohydrates (Smith and Collins, 2003; Gupta and Pratap, 2007). Therefore,
brassicas provide a high-quality feed for their entire growth period. Another benefit is brassicas
are easily established and grow quickly, providing suppression of weeds and a quick forage
(Wilson et al., 1992). Brassicas include turnips, swedes, forage rape (Brassica napus L.), kale,
radish (Brassica rapa L.) and ̶̶hybrids ̶̶such ̶̶as ̶̶‘Tyfon’ ̶̶which ̶̶is ̶̶a ̶̶cross ̶̶between ̶̶Chinese ̶̶cabbage ̶̶
(Brassica rapa L. subsp. pekinensis) and turnip (Rao and Horn 1995; Guo et al., 2014).
Negative Impacts of Forages
Negative impacts can be associated with forages. Grasses commonly have anti-quality
factors such as alkaloids that can cause several types of animal health risks (Collins and
Hannaway, 2003). Parturient paresis or commonly known as milk fever, is a complex metabolic

14

disorder that occurs at the onset of lactation in haylage feed or after the birth of a new born calf
(Goff, 2008). Cows fed high potassium (K) or high sodium (Na) diets can reduce the ability of
the cow to maintain Ca homeostasis (Goff and Horst 1997). Low blood calcium (Ca)
concentrations found in cow blood is a problem associated with milk fever and can cause a cow
to lose the ability to rise to her feet as Ca is necessary for nerve and muscle function (Horst et al.,
1997; Goff, 2008). Other symptoms of this disease include inappetence, tetany, inhibition of
urination and defecation, lateral recumbency, and eventual coma and death if left untreated
(Horst et al., 1997). In a study conducted by Cherney and Marten (1982) oat, barley, wheat, and
triticale were tested barley had the greatest milk fever potential, which was estimated by Ca/P
ratios. Other potential negatives of forages include persistence of forages (i.e. become weedy)
(Clark, 2007), hosts for pests/insects (Martin, 2004) and high seed cost (DeGregorio et al., 1995;
Labarta et al., 2002).
Potential Double Crops in Michigan and the Upper Midwest
Depending on location in Michigan and the Upper Midwest, the typical fallow period
from mid-summer harvest of winter wheat to planting of the subsequent crop (usually corn in
Michigan) is nine to ten months long (July through May). This includes 90 growing days in the
late summer and fall after wheat is harvested in July. The long fallow period leaves soil
susceptible to water and wind erosion, allows loss of N and C from the system, and encourages
weed proliferation (Snapp and Mutch, 2003). Farmers in Michigan and the upper Midwest have
frost seeded red clover into wheat in late March or early April for many years, providing a cover
on the soil following wheat harvest that fixes nitrogen (Vyn et al., 1999; Snapp et al., 2005).
Alternatively, a farmer could harvest wheat and then plant a cover crop to improve soil health
(Snapp et al., 2005), fix nitrogen for the next row crop in the rotation (Tanaka et al., 1997), and

15

provide a harvestable double crop of forage (Snapp and Mutch, 2003). Farmers are uncertain
which cover crops planted in or after wheat would have the greatest potential for return on
investment under Upper Midwest growing conditions, and if any of these cover crops would be
advantageous compared to red clover seeded into the growing wheat crop in early spring.
Additionally, farmers have questions concerning the harvesting of red clover or other cover crops
for forage. Would forage harvest adversely affect soil organic matter (SOM) accumulation and
future crop productivity and yield (Snapp et al., 2005)? Finally, cover crops which survive winter
including red clover, require a termination operation, thus increasing expense or delaying spring
planting. Annual legumes or other covers that do not survive Michigan winters might be able to
provide similar benefits as red clover without the added expense of termination.
In order to establish during the hot dry weather typically encountered in July and August
in Michigan, a cover crop needs to be tolerant of such conditions. To be valuable as a forage,
cover crops should have documented feeding value. Alfalfa (Medicago sativa L.) can be frost
seeded into wheat in March/April or established in July to provide high quality forage within 60
days (Barnes et al, 1988; Pfarr, 1988; Sheaffer et at., 1988; Sheaffer et al., 1989; Sheaffer et al.,
1992). The non-dormant alfalfa (non-winter-hardy variety) varieties that are used as cover crops
should winterkill under Michigan conditions. Other legume options include heat-tolerant species
such as sunn hemp (Crotalaria juncea L.) and cowpea [Vigna unguiculata (L.) Walp.]) which
have been used as forage crops as far north as Virginia (Schomberg et al., 2007) but not tested
for forage use in Michigan. Cowpea and sunn hemp can provide the benefits of a legume and can
withstand hotter temperatures usually found during Michigan summers. ‘Tropic ̶̶Sun’ ̶̶sunn ̶̶hemp ̶̶
was developed with forage potential in mind. Oat/ (Avena sativa L.) field pea (Pisum sativum L.)
mixtures are an accepted forage mixture in Michigan, providing forage throughout the growing

16

season, especially during the latter part of the growing season in fall. Warm-season grasses
include BMR varieties of sorghum (Sorghum bicolor) and sorghum x sudangrass (Sorghum
bicolor x S. bicolor (Piper) Stapf), which have superior fiber digestibility that simultaneously
makes them valuable as a forage (Cherney et al., 1991) and increases rate of residue
decomposition to active organic matter fractions in soil. Also, depending on the variety, sorghum
cover crops can have a fast growth rate and reach maximum cover in short growing periods. Teff
grass [Eragrostis tef (Zuccagni) Trotter] is another warm-season grass option for Michigan
(Roseberg et al., 2006; Miller, 2009; Young et al., 2014), reaching harvestable biomass for hay
within 60 days after planting. Oil-seed radish is a cover crop that is attracting farmer interest
across Michigan. As a forage, radish is more typically used as pasture (Monjardino et al., 2004)
rather than as hay or haylage due to its high moisture content; when grown in combination with
volunteer wheat it may be a viable option as a haylage double crop.
Why Cover Crops as Forages?
Total farm and crop acreages are decreasing, NASS (2012a) reported a long-term decline
of farms, 2.5 million farms in 1982 to 2.1 million in 2012. Farmland acres are decreasing as
shown in a five-year period, 922.1 in 2007 to 914.4 acres in 2012, which is a 0.8% decline of
farmland acres (NASS, 2012a). With this decline, corn and soybean acres are increasing, 1% and
19% respectively, and forage acres are decreasing by 9% in the 2007-2012 five-year period
(NASS, 2012a). Nationally, there is a total of 55.7 million (813,583 farms with forage acres)
acres for harvested forage, land used for all hay and all haylage, grass silage, and greenchop, in
2012 in the United States (NASS, 2012b). More specifically, of the total 55.7 million harvested
forage acres, there was 3 million harvested haylage or greenchop from alfalfa or alfalfa acres in
the United States in 2012 (NASS, 2012c). All other haylage, grass silage, and greenchop

17

consisted of 2.4 million harvested acres in the United States in 2012 (NASS, 2012d).
Additionally, there were a total of 17.5 million milk cows (NASS, 2012e) and a total of 53.6
million beef cattle in the United States in 2012 (NASS, 2012f) which is a decline from 2007,
0.1% and 0.4% respectively, (NASS, 2012a).
U.S. ̶̶Department ̶̶of ̶̶Agriculture’s ̶̶2012 ̶̶Census ̶̶of ̶̶Agriculture ̶̶reported ̶̶10.3 ̶̶million ̶̶acres ̶̶
of cover crops planted in 2012 (NASS, 2012g). SARE (2016) reported a steady increase in the
number of planted to cover crops acres from 2010-2015, and predicted a continued increase in
acreage to be planted to cover crops in the late summer or fall of 2016. The mean number of
cover crop acres planted in 2015 among 1,379 users was 298, a 25% increase in acreage over
2014. The respondents expected to increase that figure to a mean of 339 in the 2016 season, a
14% ̶̶projected ̶̶increase ̶̶in ̶̶the ̶̶average ̶̶user’s ̶̶cover ̶̶crop ̶̶acreage ̶̶in ̶̶2016. ̶̶Based ̶̶on ̶̶the ̶̶trend ̶̶line ̶̶
of ̶̶SARE’s ̶̶(2012) ̶̶survey ̶̶data, ̶̶today’s ̶̶current ̶̶cover ̶̶crop ̶̶acreage ̶̶is ̶̶projected ̶̶to be several
million acres higher than in 2012.
With forage land on the long-term decline a need for forage crops is needed to provide
feed for animals. Trends for animal production is also declining, but not as drastically as the
decline of forage acres. The increase demand for food requires a change to be made (Piorr,
2003). Cover crops could provide an additional benefit to farmers, not only as a cover crop, but
as a harvestable forage to be used for livestock production therefore possibly increasing the
economic value for cover crops and their adoption on farms. This can help improve farm
sustainability by providing a cover before and after row crops such as corn (Teasdale, 1996;
SARE, 2016). In addition, adding value to cover crops as harvested forage may help mitigate
added costs of buying cover seed and planting it (Snapp et al., 2005), thus encouraging farmers
to use cover crops after small grains, such as wheat (Tanaka et al., 1996; Angus et al.,2015).

18

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CHAPTER 2
USING COVER CROPS IN WHEAT-CORN ROTATIONS TO PROVIDE FORAGE
WHILE IMPROVING SOIL
ABSTRACT

The time window after wheat harvest in a wheat (Triticum aestivum L.)- corn (Zea mays
L.) rotation could be used to grow cover crops (CC) to provide forage while protecting soil from
erosion. However, the impact of forage harvest on soil fertility and sequential crop growth is not
well quantified. Field experiments were initiated in East Lansing, MI to determine the
consequences of partial removal of CC biomass on soil improvement and crop yield and quality.
Soft red winter wheat (‘Hopewell’ ̶̶and ̶̶‘Red ̶̶Dragon’) was planted in October of 2013 and 2014
and harvested in July 2014 and 2015. Cover crops included: frost-seeded red clover, and
summer-seeded alfalfa, cowpea, sunn hemp, radish, oat/field pea mixture, sudangrass, sorghum x
sudangrass, and teffgrass. Half of each CC plot was mechanically harvested eight weeks after
planting. Harvested forage dry matter yield was greatest for red clover (4.3 Mg ha-1); oat-pea mix
(2.5 Mg ha-1), sudangrass/sudex (1.8 Mg ha-1) and radish (1.2 Mg ha-1) (P < 0.01) yielded less.
Corn grain yield harvested in October averaged 13.7 Mg ha-1 and did not differ across CC
species or forage harvest treatment (P > 0.05). Harvesting forage reduced total N removal (TNR)
in subsequent corn for red clover only; harvesting forage did not affect TNR after any other CC
(CC x harvest interaction, P < 0.05). In the harvested system, TNR did not differ (P > 0.05)
between red clover (297 kg ha-1) and oat-pea mix (284 kg ha-1), but unharvested RCL (374 kg ha1

) had greater (P < 0.01) TNR than oat-pea mix (338 kg ha-1). There were no differences among

treatments for soil permanganate oxidizable carbon POXC (P > 0.05). Harvesting cover crops for

30

forage after winter wheat harvest in Michigan can give harvestable forage and acceptable
nutritive value.

31

INTRODUCTION

Total farm and crop acreages are decreasing, NASS (2012a) reported a long-term decline
of farms, 2.5 million farms in 1982 to 2.1 million in 2012. Farmland acres are decreasing as
shown in a five-year period, 922.1 in 2007 to 914.4 million acres in 2012, which is a 0.8%
decline of farmland acres (NASS, 2012a). With this decline, forage acres are in a decreasing by
9% in the 2007-2012 five-year period (NASS, 2012a). Nationally, there is a total of 55.7 million
acres for harvested forage, land used for all hay and all haylage, grass silage, and greenchop, in
2012 in the United States (NASS, 2012b). Additionally, there were a total of 17.5 million milk
cows (NASS, 2012e) and a total of 53.6 million beef cattle in the United States in 2012 (NASS,
2012f) which is a decline from 2007, 0.1% and 0.4% respectively, (NASS, 2012a).
With forage land on the long-term decline, forage crops are still needed to provide feed
for animals. Even though cattle numbers are declining, it is not as drastic as the decline of forage
acres. The increased demand for food requires a change to be made (Piorr, 2003). Cover crops
(CC) could provide an additional benefit to farmers, not only as a CC, but as a harvestable forage
to be used for livestock production therefore possibly increasing the economic value for CC and
their adoption on farms. U.S. ̶̶Department ̶̶of ̶̶Agriculture’s ̶̶2012 ̶̶Census ̶̶of ̶̶Agriculture ̶̶reported ̶̶
10.3 million acres of CC planted in 2012 (NASS, 2012g). SARE (2016) reported a steady
increase in the number of planted to CC acres from 2010-2015, and predicted a continued
increase in acreage. Using CC can help improve farm sustainability by providing a cover before
and after row crops such as corn (Teasdale, 1996; SARE, 2016). Adding CC to crop rotations
takes advantage of resources provided by the soil, sun and water (Andraski and Bundy 2005;
Wortman et al. 2012) while improving soil health and structure (Pimentel et al., 1995; Andraski

32

and Bundy 2005; Clark, 2007) thus benefiting by protecting against soil erosion or loss (Hartwig
and Ammon, 2002; Andraski and Bundy 2005), scavenging of nutrients that would otherwise be
unavailable or leached (Ranells and Wagger, 1997; Clark, 2007), holding and cleaning water
(Hartwig and Ammon, 2002), and providing nitrogen to the cash crop planted subsequently
(Decker et at., 1994; Pimentel et al., 1995; Andraski and Bundy, 2005). Additionally, adding
value to CC as harvested forage may help mitigate added costs of buying cover seed and planting
it (Snapp et al., 2005), thus encouraging farmers to use CC after small grains, such as wheat
(Tanaka et al., 1996; Angus et al.2015), though there is little to no information on the effects of
harvesting CC as forage on CC benefits.
The typical fallow period from mid-summer harvest of winter wheat to planting of the
subsequent crop (usually corn in Michigan) is nine to ten months long (July through May). This
includes 90 growing days in the late summer and fall after wheat is harvested in July. The long
fallow period leaves soil susceptible to water and wind erosion, allows loss of N and C from the
system, and encourages weed proliferation (Snapp and Mutch, 2003). Farmers in Michigan and
the upper Midwest have frost-seeded red clover into wheat in late March or early April for many
years, providing a cover on the soil following wheat harvest that fixes nitrogen (Vyn et al., 1999;
Snapp et al., 2005). Alternatively, a farmer could harvest wheat and then plant a cover crop to
improve soil health (Snapp et al., 2005), fix nitrogen for the next row crop in the rotation
(Tanaka et al., 1997), and provide a harvestable double crop of forage (Snapp and Mutch, 2003).
Farmers are uncertain which cover crops planted in or after wheat would have the greatest
potential for return on investment under Upper Midwest growing conditions, and if any of these
cover crops would be advantageous compared to red clover seeded into the growing wheat crop
in early spring. Additionally, farmers have questions concerning the harvesting of red clover or

33

other cover crops for forage. Would forage harvest adversely affect soil organic matter (SOM)
accumulation and future crop productivity and yield (Snapp et al., 2005)? Finally, cover crops
which survive winter including red clover, require a termination operation, thus increasing
expense or delaying spring planting. Annual legumes or other covers that do not survive
Michigan winters might be able to provide similar benefits as red clover without the added
expense of termination.
Choice of CC or forage species is dependent on the location and the specific benefits
desired by the producer. A single species will not provide all possible benefits, so species should
be chosen with specific goals in mind. Our selection criteria for potential forage double-cropping
with wheat in Michigan were the ability to establish during hot, dry weather in July and August,
acceptable forage nutritive value at harvest, maintenance of winter ground cover, natural winterkill to avoid the cost of spring termination, and maintenance or improvement of subsequent corn
grain yield and quality. Red clover (Trifolium pratense L.) served as the positive control
treatment. Non-dormant alfalfa (Medicago sativa L.) can provide high quality forage within 60
days after a late summer planting and should winterkill (Barnes et al, 1988; Pfarr, 1988; Sheaffer
et at., 1988; Sheaffer et al., 1989; Sheaffer et al., 1992). Heat-tolerant legumes like sunn hemp
(Crotalaria juncea L.) and cowpea [Vigna unguiculata (L.) Walp.] have been used as forage
crops as far north as Virginia (Schomberg et al., 2007), but not tested for forage use in Michigan.
Oat/field pea (Avena sativa L./Pisum sativum L.) mixtures are an accepted annual forage crop in
Michigan (Johnson et al., 1998). Brown-midrib cultivars of the warm-season grasses sorghum
(Sorghum bicolor L.) and sorghum x sudangrass [S. bicolor x S. bicolor (Piper) Stapf] hybrids,
popularly called sudex, accumulate biomass quickly in summer and have superior fiber
digestibility, compared to other warm-season grasses, that simultaneously makes them valuable

34

as a forage (Cherney et al., 1991) and increases rate of residue decomposition to active organic
matter fractions in soil. Warm-season teffgrass [Eragrostis tef (Zuccagni) Trotter] reaches
harvestable biomass within 60 d after planting in Michigan (Roseberg et al., 2006; Miller, 2009;
Young et al., 2014). Finally, oilseed radish is attracting interest as a CC across Michigan. As
forage, radish is typically used as pasture (Monjardino et al., 2004) rather than as hay or haylage
due to its high moisture content, but it may be a viable haylage crop if grown in combination
with a small grain.
With the increasing CC acres and decreasing forge acres, the potential for CC to be
double cropped is a viable option and could close the growing gap between available forage and
animals. CC diversity can be applicable to different farming types to meet the various needs of
farmers and CCs double-cropped as a forage can provide feed for various animal types. CC, with
growing application and acres, will grow shorter time periods of the growing season allowing
farmers to gain CC benefits, double-cropping benefits and still allow cash crops to grow without
impediment. Given the interesting potential opportunity to use CC as a double-crop, a forage, our
objectives were: 1) determine whether harvesting CC planted after wheat could provide useful
forage yields and nutritive value, (2) determine whether specific CC species change labile soil
organic matter, soil C, or soil N, and (3) determine how partial removal of CC biomass affects
corn grain and stover yield and quality.

35

MATERIALS AND METHODS

Site Description
This research was conducted at the Michigan State University Agronomy Farm, East
Lansing, Michigan (42o42’N, ̶̶84o28’W, ̶̶elevation ̶̶262 ̶̶m) on two adjacent fields. Soil taxonomy
and initial fertility characteristics for rotation sequences initiated in 2013 and 2014 were: 2013,
Capac silt loam (fine-loamy, mixed, active, mesic Aquic Glossudalfs), pH 7.3, 110 g kg-1 P, and
1100 g kg-1 K, 30 g kg-1 soil organic matter (SOM); 2014, Brookston silt loam (fine-loamy,
mixed, superactive, mesic Typic Argiaquolls), pH 7.0, 300 g kg-1 P, and 2080 g kg-1 K, 35 g kg−1
SOM. Monthly total precipitation, minimum, average, and maximum monthly air temperature,
soil temperature and moisture (10 cm depth), and growing degree days (GDD, 5°C base for
alfalfa/CC and 10°C base for corn) data were obtained from a weather station located within 1
km of the research site (MAWN, 2016). Twenty-five-year weather norms were obtained from
the National Oceanic and Atmospheric Administration (NOAA, 2016).
Experimental Design
The cropping system was a no-till rotation consisting of winter wheat-cover crop-corn.
The rotation sequence was initiated in 2013 and again in 2014 for a total of two independent siteyear sequences (first-year and second-year). Fields used for first-year and second-year were
immediately adjacent to each other. The experimental design was a randomized compete block
(RCBD) with four replications and a split plot treatment arrangement. The main plots were ten
CC treatments: fallow, red clover frost-seeded (RCL), and alfalfa, cowpea, oat/pea mix (OPmix),
oilseed radish (Radish), sunn hemp, sudangrass (SUD), sudex (SDX), and teffgrass (Teff) seeded

36

no-till following wheat harvest. The subplots were two CC harvest treatments (NH—not
harvested, or H— harvested). Plots measured 3 x 7 m for first-yearand 3 x 8 m for second-year.
Crop Management
Soft red winter wheat was planted at 168 kg ha-1 on 29 October 2013 (cultivar
‘Hopewell’) ̶̶and ̶̶20 September 2014 ̶̶(cultivar ̶̶‘Red ̶̶Dragon’) ̶̶to ̶̶begin ̶̶the ̶̶rotation ̶̶in each year.
Wheat was harvested 21 July 2014 and 23 July 2015 using plot combines (SPC40 and SPC20 in
2014 and 2015, respectively, Almaco Co., Nevada, Iowa). No CC were planted on the negative
control fallow plots. To allow assessment of volunteer wheat as ̶̶a ̶̶“cover ̶̶crop,” volunteer wheat
was not controlled in untreated volunteer wheat (UTVW) fallow subplots, but was removed from
fallow subplots through application of glyphosate at 5 kg a.i. ha-1 plus 4 kg ha-1 ammonium
sulfate on 13 September 2015 and 20 August 2015. The red clover was frost-seeded into wheat
using a hand-pulled drop spreader on 28 March 2014 and 18 March 2015. All other CC
treatments were seeded into wheat stubble at a row spacing of 19 cm on 4 August 2014 and 27
July 2015 using a no-till drill (Great Plains Manufacturing, Inc., Salina, KS). The CC seeding
rates and varieties are given in Table 1. The H treatment was harvested approximately 60 days
after planting using a flail-type forage plot harvester (Carter MFG CO., Inc. Brookston, IN) at a
stubble height of 10 cm. Post-harvest regrowth in the harvested cover crop treatments was left in
place over the winter; the entire biomass remained overwinter in the NH treatments. Two weeks
prior to corn planting, weeds and overwintering CC were terminated with an application of 5 kg
a.i. ha-1 glyphosate plus 4 kg ha-1 ammonium sulfate. Corn (Dekalb ‘DKC44-13RIB,’ glyphosate
resistant) was no-tilled into each plot at a row spacing of 75 cm (four corn rows per subplot) on 1
May 2015 and 9 May 2016. Corn plots were sprayed twice with glyphosate at a rate of 5 kg a.i.
ha-1 plus 4 kg ha-1 ammonium sulfate during the early growing season to control weeds. All corn

37

plots were fertilized according to fall soil test results (see soil measurements) and nutrient
recommendations for crops in Michigan (Warncke et al., 2009). Wheat plots were fertilized with
101 kg ha-1 of N. Corn was fertilized with a 100 kg ha-1 of K at the time of corn planting and a
recommend (MRTN 2016) 84 kg ha-1 of N (UAN 28%), was knifed in at the V4 corn stage on all
plots for each year.
Measurements
Wheat and corn grain yields were measured using weigh functions on the respective plot
combines. Grain samples were taken at harvest for each plot by placing grain in a cloth bag and
then were tested for grain moisture content. Grain moisture content from subsamples was
determined using a grain analysis scanner (Model No. GAC 2100, Dicky-John, Co., Auburn,
Illinois), and grain yield was corrected to standard moisture levels of 13.5%. At CC harvest,
subsamples were obtained for nutritive value and botanical composition analyses. The CC
harvest consisted of recording a fresh weight from each harvested plot using a flail type harvester
(Carter MFG CO., Inc. Brookston, IN) which harvested 10 cm above ground. Subsamples of
harvested herbage were collected from the fresh weight sample at random with approximately 46 hand samples, per plot, placed in paper bags and were dried in a forced air dryer for 3 days at
60 C, and used to calculate moisture at harvest and correct forage yield to a DM basis. Botanical
composition samples were taken directly after CC harvest from 60 cm of remaining row along
the harvested strip, selected so each sample was representative of the whole plot. Nutritive value
samples were then ground sequentially in Wiley (Thomas Scientific, Swedesboro, NJ) and UDY
(UDY Corporation, Fort Collins, Co.) mills with 4- and 1-mm screens.
Forage quality samples were analyzed for crude protein (CP), neutral detergent fiber
(NDF), and acid detergent fiber (ADF). The percent of nitrogen (N) and total carbon (C) was

38

determined by dry combustion, using a Costech-elemental combustion system (Model No.
Costech ECS 4010 and Zero Blank Autosampler, Costech Analytical Technologies Inc.,
Valencia, CA). The CP was calculated by multiplying percent of N by 6.25 (Conklin-Brittain et
al., 1999).
Percentages of NDF and ADF were determined sequentially using the procedures of
Goering and Van Soest (1970); however, sodium sulfite was not used in the NDF analysis per
the recommendation of Van Soest and Robertson (1980). An ANKOM Fiber analyzer (Model
No. 200, Ankom Technology, Fairport, NY) and F57 25-micron porosity Fiber Filter Bags
(Ankom Technology, Fairport, NY) were used to conduct NDF and ADF analysis.
A visual estimate of ground cover components, which included volunteer wheat, bare
ground, weeds, and CC, was taken biweekly starting on 10 September 2014 and 11 August 2015
after CC planting. The percent of each ground cover component was determined by the same
observer using visual estimation in three 1.2-m2 quadrats per plot, and averaged. Visual ratings
were obtained by dividing the quadrat into four sections, each equaling 25% of the area. When
the quadrat was placed on the plots, a visual estimation of the components in each section was
taken at 5% increments starting at zero and added together to equal 100%. Spring ground cover
was also visually estimated biweekly beginning 13 April 2015 and 18 April 2016 and ending
approximately 4 weeks after corn planting. A corn category was added to the cover components
after corn was planted. Plant canopy height, for both CC and corn, was measured using a meter
stick at the same time as cover measurements. Canopy height was recorded from three plants and
averaged per 1.2-m2 quadrat. Corn population and height was taken in May 2015 and June 2016
by measuring three meters of the two middle rows of each plot. To further analyze the ground
cover, CC and volunteer wheat mix (planted CC + volunteer wheat), live cover (planted CC +

39

volunteer wheat + weeds) and total cover (crop + volunteer wheat + weeds + residue/straw)
groups were created and analyzed.
Three corn ear leaf samples were randomly taken at the V12 stage during 27 July 2015
and 8 August 2016 from each plot. SPAD meter readings were taken using PhotosynQ (Venturit,
Inc., East Lansing, MI) meters in 22 July 2015 and 3 August 2016 to determine light
interception, plant stress, and potential corn yield. On 9 October 2015 and 7 October 2016, 60
cm of the yield rows of corn for each plot was hand-harvested for grain. On 12-13 October 2015
and 11 October 2016, stover was harvested from the same yield rows. Corn ear samples were
placed in cloth bags, dried in a forced air oven for 24 h at 60 C, and shelled in a corn sheller
(John Deere, Co., Moline, IL). Corn stover biomass was measured by cutting stalks from two
row-feet of the center two rows at ~45cm above the base, and recording fresh weight and number
of stalks. Corn stalks were then chopped in a yard-scale wood chipper and subsampled.
Subsamples were dried in a forced air oven at 60 C for 3 days to determine DM percentage and
allow calculation of dry stover biomass. The remaining corn in plots was mechanically harvested
using a Massey Ferguson Combine (AGCO Co., Duluth, GA) with HarvestMaster (Juniper
Systems and HarvestMaster, Logan, UT) software which provided yield and moisture content.
The hand-sampled grain yields were added to machine-harvested yields to give total grain yield
per plot.
All corn grain and stover samples were subsampled for N analysis and ground in Wiley
(Thomas Scientific, Swedesboro, NJ) and UDY (UDY Corporation, Fort Collins, Co.) mills with
4- and 1 mm screens, respectively. Corn ear leaf samples were subsampled for N analysis and
ground in a twenty-centimeter lab mill (Christy Turner Ltd., Suffolk, England). Nitrogen content
of corn grain, stover, and ear leaf was determined by using the Costech-elemental combustion

40

system (Model No. Costech ECS 4010, Costech Analytical Technologies Inc., Valencia, CA)
and methods as previously described.
Soil samples were taken from each plot on 15 Nov. 2014 for the first-year plots; 30 Oct.
2015 for the second-year plots (15-cm depth, 10 to 12 cores composited per plot per sampling
date). The soil samples were crumbled by hand, and air dried for a week. A 100-g subsample was
analyzed for pH (2:1 water: soil) (Crowther, 1925), Mehlich III available K2O, available P
(Mehlich III corrected to report as Bray) (Bray and Kurtz, 1945), Mehlich III cation exchange
capacity (Mehlich, 1984), and soil organic matter (SOM) by the loss on ignition method
(Walkley and Black, 1934) at a commercial soil analysis laboratory (A and L Great Lakes
Laboratories, Fort Wayne, IN). Soil concentration of C and N was determined on the soil
samples obtained from each plot after CC harvest on 15 Nov. 2014 and 30 Oct. 2015. A 5-g
subsample was oven dried at 60 C for 24 h, and placed in glass vials with stainless steel
hexagonal tumblers (Mavco Industries, Inc. Science Hill, Kentucky), 3.8-cm height, 1.2-cm
diameter, 30.6 g, and ground using a SampleTek Model 200 Vial Rotator roller mill (Mavco
Industries, Inc., Science Hill, Kentucky). The soil samples (15-20 mg) were weighed on a
Sartorius Cubis Ultra microbalance (Sartorius AG, Göttingen, Germany) and soil C and N
concentrations were determined using a Costech-elemental combustion system (Model No.
Costech ECS 4010, Costech Analytical Technologies Inc., Valencia, CA).
Procedure for determining permanganate oxidizable carbon (POXC) was conducted on
2014 and 2015 fall soil samples, after CC harvest. All POXC analyses were based on Weil et al.
(2003) but modified slightly as described by Culman et al. (2012). Briefly, 2.5 g of air-dried soil
were weighed into polypropylene 50-mL screw-top centrifuge tubes. To each tube, 18 mL of
deionized water and 2 mL of 0.2 M KMnO4 stock solution were added and tubes were shaken

41

for exactly 2 min (240 rpm), allowed to settle for exactly 10 min. After 10 min, 0.5 mL of the
supernatant were transferred into a second 50-mL centrifuge tube and mixed with 49.5 mL of
deionized ̶̶water. ̶̶An ̶̶aliquot ̶̶(200 ̶̶μL) ̶̶of ̶̶each ̶̶sample ̶̶was ̶̶loaded ̶̶into ̶̶a ̶̶96-well plate containing
a set of internal standards, including a blank of deionized water, four standard stock solutions
(0.00005, 0.0001, 0.00015, and 0.0002 mol L-1 KMnO4), a soil standard and a solution standard.
All standards and soil samples were replicated on a separate 96-well plate. Sample absorbance
was read with a SpectraMax M5 spectrophotometer at 550 nm. Permanganate oxidizable C was
determined following Weil et al. (2003) equation:
POXC [mg kg-1 soil] = [0.02 mol L-1 ̶̶ (a+b+Abs)]x
(9000 mg C mol-1 )(0.02 L solution Wt-1)
Where
0.02 mol L-1 is the concentration of the initial KMnO4 solution,
a is the intercept and b is the slope of the standard curve,
Abs is the absorbance of the unknown soil sample,
9000 mg is the amount of C oxidized by 1 mol of MnO4 changing from Mn7+ to Mn4+,
0.02 L is the volume of KMnO4 solution reacted, and
Wt is the mass of soil (kg) used in the reaction
Statistical Analysis
Data was analyzed using PROC MIXED in SAS Version 9.4 (SAS, Inc, Cary, NC). Fixed
variables were CC and harvest treatments, and random variables were site-years (SY) and
blocks. Means for CC and CC x harvest interactions were compared using single degree of
freedom contrasts, with group contrasts constructed for legumes (LEG: RCL and OPmix), SUD
and SDX (SUD/SDX), warm-season grasses (WSG: SUD, SDX, and Teff), and failed CC (FCC:

42

alfalfa, cowpea, and sunnhemp). Fallow treatment was compared to the RCL-NH, all other not
harvested treatments, and all harvested treatments. Unless otherwise stated, a trend was declared
at P<0.10, and significance was declared at P<0.05.

43

RESULTS

Weather
Mean air temperatures were cooler than normal from Jan. to Apr. in 2014 and 2015 while
wheat crops were growing in the first phase of rotation for each site-year (Figure 1a). It was also
unusually cool during July 2014 immediately before CC were planted. During the CC growth
period from Aug. to Sept. in both site-years, precipitation was near or greater than normal
(Figure 1b), and mean air temperature was near the 25-year average. During the corn rotation
phases in 2015 and 2016, precipitation was slightly below normal in June and July 2015, and
greatly below normal in June and July 2016. Mean air temperature was near normal throughout
the corn growth period in both site years. While CC were growing between 1 August to 31
November, there were 1126 GDD in 2014 and 1407 GDD in 2015 (MAWN, 2016). For the corn
rotation, there were 2705 GDD between 1 May and 31 October in 2014 and 2909 for the same
period in 2015 (MAWN, 2016). The 20-year GDD averages (1995-2015) were 1233 GDD for
the CC period and 2642 GDD for corn (MAWN, 2016).
Wheat Performance
Wheat grain yield averaged 4.09 and 6.21 Mg ha-1 in 2014 and 2015, respectively. Frostseeded red clover did not affect wheat grain yield (P > 0.05) in either site-year.
Botanical Composition
Because some CC treatments failed to establish successfully, botanical composition of
harvested CC (Figure 2a, 2b) is presented separately for each site-year to document our criteria
for setting contrast comparisons among treatments. Successful CC were defined as achieving at
least 20% of biomass DM in harvested plots. Red clover (RCL), oat/pea mix (OPmix),

44

sudangrass (SUD), and sudex (SDX) were successful in achieving over 20% of biomass in both
site-years. However, alfalfa, cowpea and sunn hemp failed to reach 20% of biomass in the firstyear (Figure 2a) and alfalfa, cowpea, sunn hemp, radish, and teffgrass failed to reach it in the
second-year (Figure 2b). Because alfalfa, cowpea, and sun hemp treatments failed in both siteyears, they were grouped into a single contrast designated as failed CC (FCC) and presented as
such for all subsequent discussions. The FCC treatment consisted primarily of volunteer wheat,
which was present to some degree in most plots.
Botanical composition of harvested forage is presented in Figure 2. Botanical
composition of harvested forage from RCL plots did not differ from OPmix for any component
(P > 0.10). Botanical composition did not differ between SUD and SDX for any component (P >
0.10). Harvested biomass contained a greater (P < 0.01) proportion of CC for RCL (85%) than
SUD/SDX (57%), FCC group (8%), or radish (31%). The LEG group contained a greater (P <
0.01) proportion of harvested CC biomass (79%) than the WSG group (45%). Harvested biomass
of RCL (2%) contained less (P < 0.01) volunteer wheat than SUD/SDX (28%), FCC group
(63%) or radish (43%). Harvested biomass percentage of the weed component did not differ
among treatments (P > 0.10). The proportion of wheat straw in harvested biomass did not exceed
4% for any treatment.
Ground Cover
Ground cover percentages for botanical components at four key points in the rotation
sequence are presented in Figure 3. Because the harvest treatment had not yet been applied, there
were no harvest or CC x harvest effects 8 wk after CC planting (P > 0.05, Figure 3A). Across
treatments, planted CC covered more ground (P < 0.01) for RCL (97%) than OPmix (49%),
SUD/SDX (48%), Radish (51%) or the FCC group (21%). In contrast, volunteer wheat covered

45

less ground (P < 0.02) in RCL treatments (2%) than OPmix (41%), SUD/SDX (40%), Radish
(34%) or the FCC group (63%). CC covered more ground (P < 0.01) in the legume group (73%)
than for the WSG group (39%), while volunteer wheat cover (21%) was less (P < 0.05) for
legume then WSG (63%). Volunteer wheat covered less ground (P < 0.01) in the fallow
treatment (6%) than in all other treatments (49%). Weed cover was less (P < 0.01) for RCL (1%)
than the FCC group (6%). The sum of CC and VW was greater (P < 0.05) for RCL (98%) than
SUD/SDX (88%), Radish (86%) and the FCC (92%) treatments. Live cover and total cover did
not differ among treatments (P > 0.05)
Four weeks following CC harvest (Figure 3B), a CC x harvest interaction existed (P <
0.05) for all ground cover components except straw and live cover. The interaction (P < 0.02)
indicated that ground cover of summed CC and VW was greater (P < 0.02) for RCL-NH (97%)
than Radish-NH, Radish-H (74% and 55%, respectively) and FCC-NH, FCC-H (66% and 58%,
respectively) treatments. Live cover did not differ among treatments (P > 0.05). Harvesting CC
reduced residue cover across all treatments (P < 0.01).
Overwintering of CC and soil cover was assessed two weeks before corn planting (Figure
3C). There were CC x harvest interactions for CC, volunteer wheat, residue, and summed live
plant components of ground cover (P < 0.01), but not for weeds or total ground cover of live
plants plus residues (P > 0.10). The only CC that survived the winter was RCL regardless of
harvest treatment and a few alfalfa plants in the FCC-H group. Volunteer wheat survived the
winter on all CC treatments except RCL. Harvesting RCL the previous fall increased spring CC
and live ground cover (P < 0.01) compared to not harvesting. Harvesting forage increased spring
volunteer wheat cover for OPmix, teff, FCC group, and SUD/SDX plots (P < 0.05). Weed cover
was less (P < 0.01) for RCL (10%) than for OPmix (18%), SUD/SDX (16%), Radish (16%) or

46

the FCC group (16%). Weed cover was greater (P < 0.05) in the fallow treatment (27%) than in
all NH (14%), harvested (16%) and RCL-NH (10%) treatments.
The only CC that survived to one month after corn planting (Figure 3D) was RCL (mean
26% ground cover) and a few alfalfa plants in the FCC group (< 1% ground cover). There were
no CC x harvest interactions for any ground cover component at this time point (P > 0.05).
Ground cover of the surviving CC was not affected by harvest (P >0.05). Across harvest
treatments, live and total cover was greater while residue cover was less (P < 0.05) for RCL than
OPmix, SUD/SDX, Radish or the FCC group. Residue cover was greater (P < 0.05) for fallow
(45%) than for RCL-NH (38%), but less (P < 0.05) than all NH (53%) treatments.
Plant Canopy Height
Plant canopy height, is presented in Figure 4. Eight weeks after CC planting, SUD had
the tallest plant canopy averaging 501 mm and was different from SDX at 389 mm (P < 0.01).
Plant canopy height was taller (P < 0.01) for RCL (491 mm) than for radish (227 mm) and FCC
(406 mm) treatments. Plant canopy height was lower (P < 0.02) for fallow compared with all CC
plots that were not harvested CC (368 mm), all harvested CC (366 mm) and RCL-NH (490 mm)
treatments. Four weeks after CC harvest, a CC x harvest interaction existed (P < 0.01). The
treatment x harvest interaction (P < 0.01) indicated harvesting forages reduced plant canopy
height in regrowth, but there were no differences between any CC (P > 0.10) in the harvested
system. In the no harvested system, OPmix regrowth (573 mm) was taller than RCL (396 mm)
and SUD (459 mm) was taller (P < 0.01) than SDX (385 mm). Corn plant canopy height, taken
as part of the visual pre- and post- corn planting corn evaluations, did not differ among
treatments (P > 0.10).

47

Harvested Forage Yield, Nutritive Value, and C, N Content
Forage dry matter yield, presented in Figure 5, was greatest (P < 0.01) for RCL (4.3 Mg
ha-1) than OPmix (2.5 Mg ha-1), SUD/SDX (1.8 Mg ha-1), Radish (1.2 Mg ha-1) and the FCC (1.4
Mg ha-1) treatments. The SUD and SDX yield was not significantly different (P < 0.10). Forage
dry matter yield was greater (P < 0.01) for the legume group (3.4 Mg ha-1) than the WSG group
(1.6 Mg ha-1). Average harvested yield over all CC treatments was 2.0 Mg ha-1.
Nutritive composition of harvested CC is presented in Table 2. The CC species differed
(P < 0.01) in moisture concentration at harvest. The RCL treatment (754 g kg-1) had a greater (P
< 0.01) moisture concentration than the FCC (631 g kg-1) group. Moisture concentration at
harvest was greatest for the Legume group (763 g kg-1) than the WSG group (687 g kg-1).
Concentrations of NDF were least (P < 0.02) for RCL (586 g kg-1) than for SUD/SDX (675 g kg1

) and the FCC (645 g kg-1) treatments. Concentrations of ADF and ash did not differ among any

treatments (P > 0.10). Concentration of CP was greater (P < 0.04) for RCL (144 g kg-1) than
OPmix (107 g kg-1), SUD/SDX (85 g kg-1), Radish (108 g kg-1), and the FCC (100 g kg-1)
treatments. The legume group had a greater (P < 0.01) concentration of CP (126 g kg-1) than the
WSG group (92 g kg-1). The C:N ratio was lowest (P < 0.06) for RCL (19); SUD/SDX was 33,
radish 32, and FCC 22. Nitrogen (N) concentrations mirrored the CP results presented in Table 2.
Corn Performance
Corn grain and stover yields are presented in Table 3. Corn grain yield averaged 12.7 Mg
ha-1 and were not affected by harvesting CC as forage (P > 0.05). Corn stover biomass averaged
13. 6 Mg/ha-1 and was not affected by CC or harvest treatments (P > 0.10). Results for N
concentration of corn ear leaf are presented in Table 4. Corn ear leaf N concentration were

48

affected by CC harvest (P < 0.06), but contrasts found no differences between treatments (P >
0.10).
Results for N concentration and C:N ratio of corn grain and stover are presented in Table
4. Corn grain N concentration was greatest (P < 0.04) for RCL (18 g kg-1) than OPmix (15 g kg1

), SUD/SDX (16 g kg-1), Radish (15 g kg-1), and the FCC (15 g kg-1) treatments. Legume and

WSG corn grain N concentration did not differ (P > 0.10). Corn grain N concentration was less
(P < 0.05) for the fallow (13 g kg-1) treatment than for all not harvested (16 g kg-1) and harvested
(15 g kg-1) CC and RCL-NH (20 g kg-1). Corn stover N concentration was greatest (P < 0.01) for
RCL (11 g kg-1) than OPmix (8 g kg-1), SUD/SDX (9 g kg-1), Radish (9 g kg-1), and the FCC (10
g kg-1) treatments. Corn stover N concentration was less (P < 0.05) for the fallow (9 g kg-1)
treatment than for RCL-NH (11 g kg-1). Corn stover C:N ratio was less (P < 0.01) for RCL (43)
than OPmix (54), SUD/SDX (53), Radish (48), and the FCC (49) treatments. The fallow
treatment did not differ from any other treatments (P > 0.10).
Total N removed (TNR) in corn grain and stover results are presented in Table 4. The
treatment x harvest interaction (P < 0.01) indicated that harvesting forage reduced total N
removal in the subsequent corn for RCL but not for OPmix, SUD/SDX, radish and the FCC
treatments. In the harvested system, TNR did not differ (P > 0.05) between RCL (297 kg N/ha-1)
and OPmix (284 kg N/ha-1), but unharvested RCL (374 kg N/ha-1) had greater (P < 0.01) TNR
than OPmix (338 kg N/ha-1), but not greater (P > 0.10) than SUD/SDX (349 kg N/ha-1) and the
FCC (349 kg N/ha-1) treatments.
Photosynthetic data collected using the PhotosynQ system did not reveal useful data,
possibly because of the beta-testing status of the instrument. Data are included in Appendix B.

49

Soil Assessment
There were no main effect or interactions for POXC (Figure 6, P > 0.05) or for
concentration of soil C, soil N concentration, and soil C:N ratio (Table 5, P > 0.05). There was a
trend (P < 0.10) for an interaction in POXC between Radish and RCL, whereby harvesting
forage increased POXC under Radish but decreased it under RCL.

50

DISCUSSION

In 2013 to 2014 winter months, the air temperature was much colder than usual, resulting
in winter kill and yield reduction of wheat in 2014. Though air temperature and precipitation
followed the 25-year norms, growing degree days (GDD) were low in the summer of 2014. The
first-year had 1126 GDD versus the following year, which had 1407 GDD (MAWN 2016). The
first-year GDD days were 107 GDD lower than the 20-year norms, whereas the second-year
GDD had 174 more than the norm. This 281 GDD difference could help explain why alfalfa and
especially the warm season CCs ̶̶cowpea, ̶̶sunn ̶̶hemp, ̶̶and ̶̶teff, ̶̶didn’t ̶̶perform ̶̶as ̶̶well ̶̶as ̶̶expected ̶̶
the first-year. Fick (1984) reported that 720 GDD were required, in a perennial cropping system,
for alfalfa (average of nine cultivars) to reach first flower at the first cutting in Ithaca, NY. ̶̶‘Hi ̶̶
Nitro’ ̶̶alfalfa ̶̶has ̶̶been ̶̶tested ̶̶and ̶̶shown ̶̶to ̶̶give ̶̶high ̶̶quality ̶̶feed ̶̶and ̶̶useful ̶̶yields ̶̶in ̶̶60 ̶̶days ̶̶
(Pfarr, 1988; Sheaffer et at., 1988; Sheaffer et al., 1989; Sheaffer et al., 1992). However, we
found ̶̶that ̶̶the ̶̶‘Hi ̶̶Nitro’ ̶̶alfalfa ̶̶did ̶̶not ̶̶establish well when planted after wheat harvest, even
when there was sufficient GDD. Additionally, sunn hemp, cowpea, and teff did not establish well
in one of two years. Possible reasons for this occurrence, despite adequate GDD, could be
attributed to volunteer wheat competition, especially in the second site-year, or perhaps the lack
of ideal growing conditions, such as high competition from volunteer wheat, for the alfalfa.
Additionally, we looked at precipitation to see if moisture was adequate for cover crop
establishment 28 d and 14 d before and 14 and 28 d after cover crop planting. We found that
precipitation during these critical time periods was less in the second-year than in the first year of
this study. Precipitation averaged >1 mm and 10 mm 28 d and 14 d before cover crop planting,
respectively, and averaged 30 mm at both 14 and 28 d after cover crop planting (MAWN 2016).
While the second-year precipitation 28 d and 14 d before cover crop planting was higher than the

51

first-year, averaging at 2 mm and 31 mm respectively while 14 d and 28 d after cover crop
planting averaged 68 mm and 34 mm respectively (MAWN 2016). Adequate precipitation and
soil moisture is needed for plant establishment (Veihmeyer and Hendrickson, 1950; Stanhill,
1957; Denmead and Shaw, 1962; Lipiec et al., 2013) In our study the low GDD in the first-year
combined with the low precipitation before and after cover crop planting, potentially leading to a
lower soil moisture content, could have contributed to poor cover crop establishment.
The first-year corn had adequate precipitation and temperatures (2705 GDD). Corn
requires about 2700 GDD to reach full maturity (Neild and Newman, 1987), depending on the
hybrid, while our hybrid only needed 2350 GDD (Monsanto 2016). Both site-years had sufficient
GDD and were above the 20-year GDD norm. The second-year of corn had adequate
temperatures and 2909 GDD, but precipitation was much lower than the 25-year norm, putting
the site in moderate drought conditions (US Drought Monitor, 2016) and leading to lower overall
corn yields. The recommended 84 kg ha-1 of N placed on corn at the V4 stage, was decided
because this was the minimum amount to still have adequate corn growth and reach a desired
corn yield while also hoping to see cover crop differences on corn grain and stover yield.
Volunteer wheat presented an unanticipated challenge to the experiment, especially in the
second-year where greater wheat yields and delayed harvest due to slow grain drying led to
considerable shattering of overripe wheat at harvest. Applying glyphosate before CC planting did
not control volunteer wheat because it germinated after CC were planted. Volunteer wheat
competed with the CC and appeared to limit their growth (Figure 2b). While part of CC success
is defined by the ability to suppress weeds (Lal et al., 1991; Reeves, 1994; Smeda et al., 1996;
Dabney et al., 2001), wheat can itself be used as a CC (Tyler et al., 1987; Holderbaum et al.,
1990; Worsham 1991; Stivers-Young and Tucker, 1999) and makes excellent forage

52

(Christiansen et al., 1998; Redmon et al., 1995; Pinchak et al., 1996; Ralphs et al., 1997; Epplin
et al. 2000; Giunta et al., 2017). Therefore, in this study we simply consider the volunteer wheat
to be an additional, unplanned CC grown in mixtures with the planned CC.
Ground cover evaluations were used to determine canopy closure and CC treatment
establishment. Most CC treatments reached 80% canopy closure by the time of harvest eight
weeks after CC planting; frost-seeded red clover had greater than 95% ground cover at this time
(Figure 3A). Creamer et. al (1997) reported 30% canopy closure for thirteen different covers
(mainly legumes) by four weeks after planting and 100% by 16 weeks after planting. In our
study, volunteer wheat, weeds, and CC all contributed to canopy closure, but the proportion of
weed species was relatively low. Plots designated as pure volunteer wheat due to CC failure had
canopy closures of 30% eight weeks after CC planting and 60% four weeks after CC harvest
(Figures 3A and 3B).
Results provide insight on the ability of different CC to establish after wheat harvest in
Michigan and compete with volunteer wheat. Frost-seeded red clover was very competitive with
volunteer wheat because of earlier establishment and a longer growth period compared to the
other cover crops seeded after wheat harvest (Figure 3). Mutch et al. (2003) and Blaser et al.
(2006) reported few weeds in frost-seeded red clover. Teffgrass was not competitive with
volunteer wheat in our production system, contradicting research by Aberra (1992), where
teffgrass was competitive when nonselective herbicides were applied before sowing. However,
the Aberra (1992) study was in a conventional tillage system with different ploughing methods
while our study was a no-till system. Volunteer wheat seed would have been buried below the
germination zone and then teffgrass seeded shallow after tillage. Habtegebrial et al. (2007) and

53

Tulema et al. (2008) reported that teffgrass yield was suppressed in reduced tillage systems if
weeds were not controlled by herbicide or handweeding.
Suppression of weeds by wheat, alfalfa, oats, sudangrass and red clover CC was reported
in New York by vegetable growers (Stivers-Young and Tucker, 1999), and sorghum-sudangrass
and oats CC suppressed weeds at a vegetable research station in Arizona (Burgos and Talbert,
1996). In a North Carolina study, sudangrass and sorghum-sudangrass not only suppressed
weeds, but produced more biomass than most of the eight CC studied (Creamer and Baldwin,
2000). In our study, sudangrass, sorghum-sudangrass and oat/pea mix treatments as well as the
unplanned ̶̶volunteer ̶̶wheat ̶̶“cover ̶̶crop” ̶̶suppressed weeds. Additionally, wheat straw residues
could have potentially contributed to weed suppression (Putnam and DeFrank, 1983; Barnes and
Putnam, 1983; Shilling et al.,1985; Akemo et al., 2000), though this is not always the case
(Teasdale and Daughtry, 1993; Akemo et al, 2000). In our study, we saw an increase in weeds
after cover crop harvest which could be due to the opening of the plant canopy (Ballaré and
Casal, 2000)
Oilseed radish competed successfully with weeds until forage harvest in October, but
radish was not competitive with weeds in late October through November because there was
little no regrowth from crowns after forage harvest. In our study, the weed cover in oilseed radish
averaged 10% and fall weed cover consisted of 11%, which was not a significant change.
Stivers-Young (1998) found that oilseed radish was most competitive with weed populations in
the fall when planted in early spring due to early canopy development and closure. StiversYoung (1998) study also showed that spring planted oil seed radish reduced weeds by 40% in the
fall compared to other brassicas, kale and turnip, which reduced weeds by 55-65%. In this study,
they disked the soil first before seeding CC, thus allowing for quicker radish establishment and

54

canopy development and the spring planting allowed for a longer growth period, differing from
our study. In other field experiments (Lawley et al., 2011) had almost complete weed
suppression observed in all 4 site-years in early spring following forage radish, however
suppression began to decline by mid-spring, although weed cover was still lower than that in the
no cover control. Similarly, in another study, Lawley et al. (2012) found that oilseed radish is
most competitive in the fall, when planted and fertilized in late summer. Similarly to the StiversYoung (1998), Lawley et al., (2011) and Lawley et al. (2012) experiments, we found that oilseed
radish, along with volunteer wheat, could suppress weeds sufficiently in the fall before CC
harvest but less suppression was observed as the growing season continued into late fall and after
CC harvest. The discrepancy between our results and the literature, could be that our study is a
no-till cropping system and the radish seeds may not have had optimal conditions for quick
growth and establishment (i.e. cooler, darker under the residue, lower soil-seed contact). We
found volunteer radish in both site-years of corn plots. This could be related to the lack of
optimal growing conditions, high residues, and that radish has a hard seed coat which protects it
from germinating in poor conditions. Overall, oilseed radish did not compete as well as other
annual CC in our study.
In our research, alfalfa (non-winter-hardy variety), cowpea, and sunn hemp failed to
establish enough biomass to be useful as a CC in this system. Several factors may have
contributed to this failure, including the unexpectedly cool temperatures, potentially low soil
moisture and low GDD in late summer, lack of starter fertilizer at CC planting, large amounts of
wheat residue that may have interfered with CC seed placement at planting, and competition
from volunteer wheat. We chose not to apply starter fertilizer to CC because we felt farmers
would be unlikely to pay to fertilize CC and because we wanted to encourage the N fixation

55

benefit from our legume covers. However, small amounts of fertilizer can be beneficial to
improving CC establishment and growth (Lawley et al., 2012).
We chose to leave wheat straw residue in the field because it could potentially increase
SOM, water holding potential, and decrease soil erosion (Mannering and Meyer, 1963; Unger,
1975; Crutchfield et al., 1986); however, large amounts of residue can also decrease successful
seed planting and germination (Day, 1968; Crutchfield et al., 1986; Hicks et al., 1989). In our
study, CC established successfully on the edges of the plot where straw residues and competition
from volunteer wheat was lower--this was noticeable in all treatments except for red clover.
Farmers will often remove straw from the field for uses such as roughage in feed, compost, or
bedding (Ashfield, 1978; Rynk et al. 1992; Wang et al., 2004). If the straw was removed, it could
potentially solve the problem of CC establishment in high residue situations while also providing
additional value from the system. Another possible solution is to minimal till or strip-till to create
a more suitable seedbed for the CC.
Some degree of volunteer wheat establishment is inevitable after a commercial wheat
harvest due to shatter of grain during harvest. Because wheat can be used as a CC (Mannering
and Meyer, 1963; Unger, 1975; Crutchfield et al., 1986; Decker et al., 1994), this is not
necessarily a negative when a CC is desired. However, the seeding rate of such volunteer plants
is not controlled by the farmer and therefore may prove to be too competitive when a deliberately
seeded CC is also being planted. In our study, an unusually high rate of shatter occurred during
harvest because of plot combine design and weather that delayed harvest of the grain.
Overwintering planted CC in our study consisted of red clover and alfalfa. Additionally,
there was also overwintering of volunteer wheat (Figure 3). Volunteer wheat survival ranged
from 1% volunteer wheat cover in the red clover plots to about 40% in SUD/SDX. The positive

56

side of volunteer wheat was weed suppression. Most treatments with volunteer wheat kept weed
cover below 16%. The CC control weeds through competition, increasing water holding capacity
and aeration (Creamer et al. 1996; Conklin et al., 2002). Weed suppression can reduce herbicide
use resulting in lower production costs; however, the overwintering of red clover, alfalfa, and
volunteer wheat as well as the presence of spring weeds still requires herbicide applications to
remove living plants and prevent undue competition with corn (Van Heemst, 1985; Hall et al.,
1992; Murphy et al., 1996; Liu et al., 2009; Otto et al., 2009; Tursen et al. 2016). One month
after corn was planted, red clover and alfalfa were still the only CC to survive, with few weeds or
volunteer wheat. Most plots had 90% of greater of the soil surface covered by the combination of
surviving CC, weeds, volunteer wheat, corn, and straw/residue. In a crop management
experiment with simulated rainfall applications in southwestern Brazil, Panachuki et al. (2011)
reported higher runoff and soil loss under no-till system without residue, significantly less runoff
under a no-till system with 2 tons/ ha-1 of surface soybean residue, and no runoff or soil loss
under a no-till system with 4 ton/ha-1 of surface soybean residue. Water infiltration rates were
likewise higher in no-till system with surface residue (Tisdall and Oades, 1982). The high degree
of soil cover and residue in our study can potentially help reduce soil erosion, increase water
infiltration and soil nutrients and recycling (Laflen and Colvin, 1981; Aulakh et al., 1991;
Zibilske et al., 2002; Roldán et al., 2003; Govaerts et al., 2006; Bertol et al., 2007).
The CC with the largest accumulation of biomass was red clover (Figure 5) which agrees
with Decker et al. (1994) who found that clover was the highest yielding of hairy vetch (Vicia
villosa Roth.), winter pea and winter wheat. Red clover is planted 5 months earlier than the other
CCs, as an undersown CC, which provides a unique advantage for this CC system (add
something along this line). In addition, oat/pea mix, sudangrass, and sorghum-sudangrass

57

produced enough yield to potentially cover the cost of harvest (Figure 5). Akemo et al. (2000a)
in Ohio found that a pea/rye mix yielded > 4 Mg ha-1 of biomass which shows that peas can be
high yielding when grown with a cereal. Akemo et al. (2000b) also found that pea-rye yields
were greatest when soil moisture was between 80-100 mm of moisture. In the Akemo et al.
(2000) study, cold and wet weather prevailed in 1996 and 1997 from April through June, which
could have contributed to the greater yields of the pea/oat mix during the first site-year because
of possible soil moisture retention with high residues and adequate precipitation. Both site-years
of our study showed adequate moisture for pea establishment, but as discussed previously several
other factors could have effected pea establishment and growth (i.e. volunteer wheat
competition, high residues, etc.). Andraski and Bundy (2005) had a similar study, looking at oats,
rye and triticale, and found that CC dry matter yielded 1.16 ± 0.86 Mg ha-1, which is equal or
lower to what we found in our experiment.
Sudex and sorghum are reported to have very high forage dry matter yields in some cases
> 8 Mg ha-1 (Finney et al., 1988; Creamer and Baldwin, 2000). However, the Creamer and
Baldwin (2000) study was conducted in the southern region of the US and therefore had more
favorable growing conditions for these warm season grasses, when compared to the northern
region’s ̶̶cooler ̶̶and ̶̶wetter ̶̶growing ̶̶conditions, ̶̶particularly ̶̶in ̶̶Michigan. Due to unfavorable
growing conditions and the excessive competition with volunteer wheat in our study, harvested
forage yields were very low for teff, radish and VW (Figure 5), and farmers might not profit
from harvesting low-yielding CC as double crops in Michigan due to seed, labor, and machinery
costs (Teasdale, 1996). As a rule of thumb, forage harvests yielding less than about 1 Mg ha -1
may not produce enough value to cover the mechanical and labor cost of harvest in Michigan
(Cassida, personal communication).

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In addition to yield, nutritive value of harvested forage is important. Red clover had the
highest CP content with oat/pea mix and radish being the next highest CP content, averaging 144
g kg-1, 107 g kg-1 and 108 g kg-1 respectively (Table 2). This was an expected result since
typically legumes have a greater CP content than grasses (Balde et al., 1993; Dewhurst et al.,
2003), however, we would expect a 30-200g kg-1 greater CP concentration in the legumes than
what our study showed. Typical CP concentration range for most legumes are 130 g kg-1 to 300 g
kg-1 (Buxton et al., 1985; McGraw and Marten, 1986). The CP content for the grasses in this
study were consistent with the literature (Robinson, 1969; Cherney et al., 1991; Pedersen and
Toy, 1997; Ghanbari-Bonjar and Lee 2002; McCrown et al., 2012). Cassida et al. (2000)
reported that alfalfa and red clover had high CP content during summer growth averaging 215 g
kg-1 and 192 g kg-1, respectively in a perennial forage cutting system. Average CP was lower in
this study then what Cassida et al. (2000) found, which can be explained by the different
management and cropping systems as well as the presence of volunteer wheat in all treatments
(Table 2). The harvested volunteer wheat in the plots potentially reduced CP in forages because
no additional N fertilized was added. This lack of fertilizer combined with the higher plant
densities, the volunteer wheat was most likely unable to find adequate amounts N (about 100 kg
N ha-1) for wheat growth and higher N content (Evans, 1983; Valenti and Wicks, 1992; Delogu
et al., 1998; Staggenborg et al., 2003). One indicator of the volunteer wheat N deficiency we
noticed in our study was the tops to middle of the volunteer wheat leaves were yellow (Evans,
1983; Valenti and Wicks, 1992; Stone et al., 1996; Staggenborg et al., 2003). Roseberg et al.,
(2006) reported that teffgrass CP was responsive to N fertilizer and water with CP content
ranging from 119 to 166 g kg-1, while McCrown et al., (2012) reported teffgrass CP content
between 89 to 100 g kg-1. The CP content of teffgrass in our study agreed more with the

59

McCrown et al., (2012) study which is surprising since there was so much volunteer wheat in our
teffgrass plots and the McCrown et al. (2012) study had mostly pure stands of teffgrass.
Cell wall content is measured by NDF and ADF and is considered a negative nutritive
value component (Collins and Fritz, 2003). The NDF content was greatest for SUD/SDX and the
FCC group, 675 g kg-1 and 645 g kg-1 respectively, while the legumes, red clover and the oat/pea
mix, 586 g kg-1 and 628 g kg-1 respectively, had the lowest NDF content. Legumes, RCL and the
OPmix, and the warm season grasses group, which included sudangrass, sudex and teffgrass,
were significantly different from each other which was an expected result, since legumes have
typically a lower NDF content than grasses (Balde et al., 1993; Dewhurst et al., 2003), depending
on the growth stages of the grasses (Paterson et al., 1994; Balasko and Nelson, 2003). The reason
for such high NDF content in all treatments in our study could be the volunteer wheat and straw
contamination in all the plots. Wheat straw is almost pure cell wall with high NDF content and
therefore increases the NDF of a forage mix containing straw (Leng, 1990; Poore et al., 1991;
Moore et al., 1999).
Chapko et al. (1991) conducted a study with 4 different treatments consisting of oat, oatpea, barley, and barley-pea. Looking at forage yield and forage quality of these treatments and
found that the addition of pea to oat decreased NDF content by 7.1 percentage units and
increased CP by 4.4 percentage units. Chapko et al. (1991) compared the oat-pea mix with all
other treatments and found that the oat-pea mix had superior forage quality, though it was lower
yielding compared to the other treatments. In the Chapko et al. (1991) study the forage quality of
their oat/pea mix, CP, ADF and NDF values, were similar to our study, with very little
difference. There was no difference in the ADF content for any treatments in the study, which
could be explained by volunteer wheat contamination in all treatments (how did the average

60

ADF compare to recommended values for different livestock systems? Add some more context
here). We did not examine digestibility of the harvested forage, which is another potential area of
research for forages grown in this type of management (Yun et al., 1999).
Covers with the greatest moisture concentration at harvest were OPmix and RCL, 772 g
kg-1 and 754 g kg-1 respectively and would therefore require the most wilting before ensiling,
while the FCC group contained the least moisture at 631 g kg-1. Recommended moisture for
ensiling alfalfa and similar forage crops is 65-70% moisture (Jones et al., 2004), which compared
to the 77% moisture content in RCL and 75% in OPmix treatments would require at least a 5-7%
moisture decrease. Small grains, such as wheat and oats require a moisture content of 60-70%
before ensiling (Jones et al., 2004), showing that the FCC group was in the range for direct
chopping or baling, and the oats in the OPmix needed to dry about another 5% before ensiling.
The other grass treatments in our study were in the recommended range for ensiling grasses,
between 60-70% (Jones et al., 2004).
Corn grain or stover yields were not affected by a preceding CC (Table 3), therefore CC
can potentially be used as a double crop in Michigan, though competition from a biannual CC
such as red clover could potentially reduce corn yields if not managed (Kasper et al., 1990;
Drury et al., 1999; Zemenchik et al., 2000). Andraski and Bundy (2005) found that corn yields
were not affected by CC treatment if it was winterkilled. Dyke and Liebman (1995) also found
that corn yields did not change in a study with red clover and oat residues incorporated into the
soil before corn planting. Griffin et al. (2000) conducted a study in Maine looking at biomass and
N accumulation of alfalfa, winter rye (Secale cereale L.), and hairy vetch (Vicia villosa Roth
subsp. Villosa) plus rye. They found that the legumes accumulated more N than the rye cover
grown alone, though biomass was similar for all covers. Both legumes accumulated more N than

61

rye grown alone, although total biomass was similar. Several researchers have shown greater
corn N uptake and/or yield following a clover CC compared with no cover (Torbert and Reeves,
1991; Dapaah and Vyn, 1998; Vyn et al., 2000; Gentry et al., 2013). In the Griffin et al. (2000)
study, sweet corn yields were affected by CC red clover, oats, and N fertilizer rates. Similarly,
the unharvested RCL treatment in our study had the greatest corn grain N concentration among
all treatment combinations, but corn grain N concentration was reduced by 25% when RCL was
harvested (20 to 15 g kg-1, for unharvested and harvested, respectively) (Table 4). Harvesting
RCL also reduced ear leaf N by 17% compared to unharvested RCL (23 vs. 19 g kg-1). These
reductions in ear leaf and corn grain N concentrations were not reflected in corn grain yields.
The difference in the corn yields found in the Griffin et al (2000) study compared to the no
difference in corn yields in our study could be due to the different crop (sweet corn versus field
corn) and management of plots. We fertilized all our corn plots at the minimum required N for
corn growth based on the MRTN (2016) rates for Michigan.
Total N removed by our corn crop showed a CC x harvest interaction. The harvesting of
forage led to greatest reduction of corn crop TNR for the RCL, and had a lesser effect on OPmix,
SUD/SDX, and radish treatments. The RCL and OP in the harvested system did not differ by
TNR by corn, but RCL in the unharvested system had a greater TNR, though there was still no
significant effect on corn yield. This finding potentially shows a quantifiable N removal rate of
corn grown after CCs, especially for the RCL and OPmix treatments. This could help farmers
better understand the benefits and negatives of harvesting a CC for forage and where to adjust for
fertilizer rates, if needed. However, more research is needed to look at TNR of harvesting CC
and its effect on corn.

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Corn ear leaf N concentration was reduced for all harvested treatments except for radish,
where forage harvest increased ear leaf N to 22 g kg-1 in corn the following year compared to 20
g kg-1 for ear leaf N when radish was not unharvested (Table 4). The same treatment pattern
occurred for N content of corn grain after a radish CC (16 vs. 13 g kg-1 in the harvested vs not
harvested plots, respectively). This could potentially be explained by Smith and Collins (2003)
study, which found that broadleaf and brassica crops residues degrade quickly and therefore do
not impede corn establishment and growth if weed competition is reduced or removed. A study
by Jani et al. (2016) conducted in the Southeastern USA found that pea, clover and vetch roots
decompose and release N rapidly and that termination by disking or roller-crimping does not
affect these processes. Additional studies showed similar results of legumes CC shoots
decompose and release N rapidly following termination, because of their low C:N ratio and
percent lignin which favors fast rates of decomposition and N release (Buchanan and King,
1993; Sainju et al., 2005). Conversely, legume cover-crop roots have higher C:N ratios, elevated
lignin content, and are often protected from microbial decomposition within the soil (Buchanan
and King, 1993; Puget and Drinkwater, 2001; Schmidt et al., 2011; Dungait et al., 2012), all of
which lead to slower rates of legume root decomposition and N release relative to shoots.
Although legume cover-crop root decomposition and N release is relatively slow, roots can
account for about 30% of total legume biomass (Sainju et al., 2005).
As discussed above, most harvested treatments saw a reduction in corn grain N, however,
RCL and OPmix had the greatest decrease in corn grain N content. Rajcan and Tollenaar (1999)
compared two corn hybrids and found that a higher N uptake during grain filling was related to a
higher dry matter accumulation. This differs from some of the CC treatments in our study, when
compared to stover biomass at harvest, oat/pea mix, sudex and FCC treatments had a higher corn

63

grain N content with a lower corn stover biomass. Many of the studies are based on N uptake
compared to other corn hybrids (Rajcan and Tollenaar, 1999) or C and N in the soil (Elliott,
1986; Utomo et al., 1990; Drinkwater et al, 1998; Dabney et al., 2001; Wilhelm et al., 2007) not
the direct effects of CC on corn tissue, which makes evaluation difficult and leaves this an area
open for more research for better comparisons.
Soil organic matter (SOM) did not respond to CC treatments. This is not surprising since
it typically takes multiple years to detect changes in SOM (Sainju et al. 2002). Total C and N
tests showed that overall, total soil N and C was similar among CC treatments (Table 5). This
could be due to sampling error and/or change in bulk density over time (Logsdon et al., 2008).
However, POXC results have shown to be good indicators of changes in a short period (Culman
et al., 2012; Culman et al., 2013). There was a similar trend for POXC in red clover, oat/pea mix
and the warm season grasses (Figure 6). These treatments had a lower POXC value for the
harvested treatments compared to the not harvested treatments. Teffgrass was the only warm
season grass that was the opposite, having a lower POXC value for the no harvest treatment.
Culman et al. (2013) saw a significant difference in POXC values comparing three management
systems including conventional till, an integrated system including CCs such as red clover, and
compost. However, POXC in Culman et al. (2013) was measured over time both short-term and
long-term, in comparison to our study which only looked at one point in a period. In the Culman
et al. (2013) short-term study, POXC values were significantly lower for the conventional
fertilizer management systems versus compost and cover crop alternative management. In three
studies previously conducted in Michigan, red clover interseeded with wheat found increased
soil C and N mineralization (Mutch and Martin 1998; Sanchez et al., 2001; Snapp et al., 2003),
which is another potential area for further research.

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CONCLUSIONS

Seeding CCs after winter wheat harvest in Michigan and then harvesting the CC for
forage eight weeks later can provide harvestable forage. Red clover, oat/pea mix and sudangrass
could be potential forage crops for double-cropping with acceptable nutritive value for some
classes of livestock, such as dry cows and heifers, and they yielded the most forage and were
best at competing with the weeds and volunteer wheat in Michigan. Sunn hemp, cowpea,
teffgrass, and alfalfa did not establish following wheat harvest in our research and were not
successful as cover crops or as forage crops. Seeding rates were a recommended seeding rate for
cover crop establishment, however the high volunteer wheat and straw could have prevented
cover crops to be no-till drilled in successfully. The removal of straw, which can provide on farm
use such as bedding and as a roughage feed, and potentially a minimal or strip till could help
with cover crop establishment. Therefore, allowing the cover crops to better compete with weeds
and volunteer wheat and potentially increasing forage yield and quality, though more research of
the effect on weed and volunteer wheat competition with these cover crops will need to be
researched. Volunteer wheat can function as a CC and was accounted for in cover evaluations
including canopy closure and height. Volunteer wheat was not the desired CC in this specific
study and could have caused differences, or lack of differences, in quality and nutritional value
in the desired CCs. There were no negative consequences of partial removal of CC biomass for
forage on corn grain or stover yield. If a grower does not get red clover frost-seeded or does not
want a perennial cover crop to terminate in the spring, an alternative cover crop is an oat/pea
mixture following wheat harvest which will winter kill and still provide N and adequate forage
yields. However, harvesting CCs such as frost-seeded red clover, oat/pea mix and volunteer

65

wheat following wheat harvest in a Michigan wheat-corn rotation could potentially decrease
available N during corn uptake, effecting corn quality and lower CP in corn grain. Measures of
soil quality including SOM and POXC did not differ among CC treatments during this study,
though more research should be done to quantify SOM and POXC for a longer term. Soil
nutrient, C and N concentrations and C:N showed no differences because our study was not long
enough to detect changes and should be done in a longer term study to see more accurate
changes.

66

APPENDICES

67

APPENDIX A

Results

TABLES
Table 1. Variety and pure live seeding rates for cover crops grown after wheat harvest at East
Lansing, MI. in 2014 and 2015.
Cover ̶̶crop

Cover ̶̶Crop ̶̶
Variety

Seeding ̶̶Rate ̶̶
(kg ̶̶ha-1)

red ̶̶clover

variety ̶̶not ̶̶stated

14.6

$4.27

$62.34

alfalfa

 ̶̶‘Hi ̶̶Nitro’

17.9

$9.68

$173.27

cowpea

variety ̶̶not ̶̶stated

56.0

$2.28

$127.68

sunn ̶̶hemp

‘Tillage ̶̶Sunn’

22.4

$4.07

$91.17

oil ̶̶seed ̶̶radish

20.2

$6.01

$121.40

oats ̶̶

‘CSS ̶̶Tillage ̶̶
Radish’
‘Jerry’

33.6

$0.91

$30.01

field ̶̶pea

‘LC64040’

44.8

$1.32

$59.14

BMR ̶̶sudangrass

‘Piper’

22.4

$1.98

$44.35

BMR ̶̶sudex

‘GW ̶̶300 ̶̶BMR’

33.6

$1.98

$66.53

teffgrass

Seed ̶̶cost ̶̶
(per ̶̶kg)

Cost ̶̶
kg/ha-1

2014-’Reprieve’ ̶̶ ̶̶ ̶̶
11.2
$6.42
$71.90
2015-’Dessie’
Seeding rates were recommendations found on the Midwest cover crop council (MCCC)
website: http://mccc.msu.edu/ and seed cost were obtained from the individual seed companies
where seed was obtained from and costs at that specific point in time (seed costs may differ).

68

Table 2. Nutritive value and carbon and nitrogen concentration and ratio of forage in cover crops
harvested eight weeks after seeding following July 2014 and 2015 wheat harvest at East Lansing,
MI.

NDF†

RCL‡
OPmix
SUD
SUX
Teff
Radish
FCC

586
628
682
668
634
638
645

SE

1.6

ADF

CP

Ash

Harvest
moisture

1.2

0.7

0.8

1.6

C: N
C
N
Ratio
---------------------------------- g kg-1 -------------------------------------374
144
91
754
448
23
19
363
107
90
772
440
17
26
375
89
92
717
441
14
30
380
81
111
689
445
13
36
366
107
97
655
439
17
27
376
108
108
691
432
14
32
382
100
93
635
438
16
22
0.5

0.1

2.1

--------------------------------------- P < ----------------------------------------Model
Cover crop

0.01

NS§

0.07

NS

0.04

0.01

0.07

NS

Contrasts
RCL vs. FCC
0.02 NS
0.01
NS
0.01
0.04
0.01
0.06
RCL vs. OPmix NS
NS
0.04
NS
NS
0.01
NS
NS
RCL vs. Radish NS
NS
0.01
NS
NS
0.01
0.01
0.05
RCL vs.
SUD/SDX
0.01 NS
0.01
NS
NS
0.07
0.01
0.02
SUD vs. SDX
NS
NS
NS
NS
NS
0.04
NS
NS
LEG vs. WSG
0.01 NS
0.01
NS
0.02
⸷NS
0.02
0.04
† ̶̶NDF, neutral detergent fiber; ADF, acid detergent fiber; CP, crude protein; FCC, failed cover
crop; LEG, legume group: RCL and OPmix; OPmix, oat/pea mix; N, nitrogen; RCL, frostseeded red clover; SUD, sudangrass; SDX, sorghum x sudangrass; Teff, teffgrass; WSG, warmseason grass group: SUD, SDX, teffgrass.
‡ ̶̶All values are dry matter basis except harvest moisture.
§ NS, not significant (P >0.10).

69

Table 3. ANOVA results and planned contrasts for corn grain and stover yields after cover crops
were harvested or not harvested the previous October 2014 and 2015 at East Lansing, MI.
Treatment
Fallow
RCL‡
RCL
OPmix
OPmix
SUD
SUD
SDX
SDX
Teff
Teff
Radish
Radish
FCC
FCC

Harvest Treatment
fallow
NH†
H
NH
H
NH
H
NH
H
NH
H
NH
H
NH
H

SE

Grain, Mg/ha-1
14
12
11
13
13
13
13
12
13
13
13
13
13
13
13

Stover, Mg/ha-1
13
13
13
15
14
14
13
14
14
14
15
13
13
14
13

0.7

0.5

------------------------ P < -------------------------Model
Cover crop (CC)

NS§

NS

Harvest (harv)

NS

NS

CC t*harv
Contrasts
RCL vs. FCC
RCL vs. OPMix
RCL vs. Radish
RCL vs. SUD/SDX
SUD vs. SDX
LEG vs. WSG
Interaction Contrasts
RCL vs FCC for harv
RCL vs. OPmix for harv
RCL vs. Radish for harv
RCL vs. SUD/SDX for harv
SUD vs. SDX for harv
LEG vs. WSG for harv

NS

NS

NS
NS
NS
NS
NS
NS

NS
NS
NS
NS
NS
NS

NS
NS
NS
NS
NS
NS

NS
NS
NS
NS
NS
NS

70

Table 3. (cont’d)
Fallow vs. all not harvested CC
NS
NS
Fallow vs. all harvested CC
NS
NS
Fallow vs. RCL-NH
0.06
NS
† ̶̶NH, ̶̶Not ̶̶Harvested; FCC, failed cover crop; H, Harvested; LEG, legume group: RCL and
OPmix; OPmix, oat/pea mix; N, nitrogen; RCL, frost-seeded red clover; SUD, sudangrass; SDX,
sorghum x sudangrass; Teff, teffgrass; WSG, warm-season grass group: SUD, SDX, teffgrass.
‡ ̶̶All values are dry matter basis except harvest moisture.
§ NS, not significant (P >0.10).

71

Table 4. Nitrogen concentration, carbon/nitrogen ratio, and total nitrogen removed in V-12 stage
corn ear leaves, grain and stover harvested after cover crops were harvested or not harvested the
previous October 2014 and 2015 at ̶̶East Lansing, MI.

Treatment
Fallow
RCL‡
RCL
OPmix
OPmix
SUD
SUD
SDX
SDX
Teff
Teff
Radish
Radish
FCC
FCC
SE
Model
Cover Crop (CC)
Harvest (harv)
CC*harv
Contrasts
RCL vs. FCC
RCL vs. OPMix
RCL vs Radish
RCL vs. SUD/SDX
SUD vs. SDX
LEG vs. WSG
Interaction Contrasts
RCL vs FCC for harv
RCL vs. OPmix for harv
RCL vs. Radish for harv

Harvested
fallow
NH†
H
NH
H
NH
H
NH
H
NH
H
NH
H
NH
H

Corn
Ear
Leaf
N, g
kg-1
19
23
19
18
18
19
18
20
19
20
19
20
22
19
19

Corn Grain
N, g
kg-1
C:N
13
29
20
23
15
27
16
27
13
30
17
25
15
27
14
28
15
28
16
26
14
28
13
30
16
26
16
28
15
28

Corn Stover
N, g
kg-1
C:N.
9
49
11
42
10
44
8
52
8
55
9
50
9
52
8
56
8
55
9
50
9
51
9
48
9
47
10
49
9
50

Total N
removed,
kg/ha-1

308
374
297
338
284
343
366
293
304
339
327
291
335
349
316

0.6
0.1
1.0
0.1
3.9
21.3
--------------------------- P < ------------------------NS§
0.06
NS

0.10
NS
NS

NS
NS
NS

0.08
NS
NS

NS
NS
NS

NS
0.01
0.03

NS
NS
NS
NS
NS
NS

0.03
0.02
0.04
0.03
NS
NS

NS
NS
NS
NS
NS
NS

0.01
0.01
0.01
0.01
NS
0.04

0.01
0.01
0.01
0.01
NS
0.08

NS
NS
NS
NS
NS
NS

NS
NS
NS

NS
NS
0.02

NS
NS
NS

NS
NS
NS

NS
NS
NS

0.01
0.01
0.01

72

Table 4. (cont’d)
RCL vs. SUD/SDX for
harv
NS
0.10
NS
NS
NS
0.01
SUD vs. SDX for harv
NS
NS
NS
NS
NS
0.07
LEG vs. WSG for harv
NS
NS
NS
NS
NS
0.02
Fallow vs. all not
harvested CC
NS
0.5
NS
NS
NS
NS
Fallow vs. all harvested
CC
0.07
0.05
NS
NS
NS
NS
Fallow vs. RCL-NH
NS
0.01
NS
0.05
NS
0.01
† ̶̶NH, ̶̶Not ̶̶Harvested; ̶̶FCC, failed cover crop; H, Harvested; LEG, legume group: RCL and
OPmix; OPmix, oat/pea mix; N, nitrogen; RCL, frost-seeded red clover; SUD, sudangrass; SDX,
sorghum x sudangrass; Teff, teffgrass; WSG, warm-season grass group: SUD, SDX, Teff.
‡ ̶̶All values are dry matter basis except harvest moisture.
§ NS, not significant (P >0.10).

73

FIGURES

A

B

Figure 1. (A) Maximum, minimum, and average monthly air temperature, (B) cumulative
monthly precipitation, and 25-year norms at East Lansing, MI., from October 2013 to
September 2016. Arrows indicate when soil samples were obtained.

74

Forage Components, %

100

A

80
60
40
20
0

Forage Components, %

100

B

80
60
40

20
0

Cover Crop

Peas

Volunteer Wheat

Straw

Weeds

Figure 2. Percentage (dry matter basis) of cover ̶̶crop, ̶̶volunteer ̶̶wheat, ̶̶wheat ̶̶straw, ̶̶and ̶̶weed ̶̶
components ̶̶in ̶̶biomass ̶̶harvested ̶̶in ̶̶October ̶̶in ̶̶2014 ̶̶(A) ̶̶and ̶̶2015 ̶̶(B) ̶̶from ̶̶cover ̶̶crop ̶̶plots ̶̶in ̶̶
East ̶̶Lansing, ̶̶MI. ̶̶(‡ ̶̶RCL, frost-seeded red clover; OPmix, oat/pea mix, SUD, sudangrass; SDX,
sorghum x sudangrass; Teff, teffgrass)

75

Figure 3. ̶̶Cover ̶̶crop ̶̶(CC), ̶̶volunteer ̶̶wheat ̶̶(VW), ̶̶weed, ̶̶crop ̶̶residue ̶̶(RES), ̶̶and ̶̶corn ̶̶
components ̶̶of ̶̶ground ̶̶cover ̶̶when ̶̶measured: ̶̶(A) eight weeks after CC planting following wheat
harvest, (B) four weeks after Oct. CC harvest, (C) four weeks before May corn planting the
following year, and (D) four weeks after May corn planting. ̶̶Values ̶̶are ̶̶means ̶̶from ̶̶two ̶̶siteyears ̶̶(2014-2015 ̶̶and ̶̶2015-2016) ̶̶at ̶̶East Lansing, MI. (RCL = red clover, OPmix = oat/pea mix,
SUD= sudangrass, SDX = sorghum x sudangrass, FCC = failed cover crop, NH = no CC harvest,
H = CC harvested)

76

Figure 4. ̶̶Plant ̶̶canopy ̶̶height ̶̶when ̶̶measured: ̶̶(A) eight weeks after CC planting following
wheat harvest, (B) four weeks after Oct. CC harvest, (C) four weeks before May corn planting
the following year, and (D) four weeks after May corn planting. ̶̶Values ̶̶are ̶̶means ̶̶from ̶̶two ̶̶siteyears ̶̶(2014-2015 ̶̶and ̶̶2015-2016) ̶̶at ̶̶East Lansing, MI. Error bars are SEM. (RCL = red clover,
OPmix = oat/pea mix, SUD= sudangrass, SDX = sorghum x sudangrass, FCC = failed cover
crop, NH = no CC harvest, H = CC harvested)

77

5.0
4.5

Harvested Dry Matter, Mg -1

4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0

Treatment
Figure 5. ̶̶Forage ̶̶dry ̶̶matter ̶̶harvested ̶̶in ̶̶October ̶̶2014 ̶̶and ̶̶2015 ̶̶from ̶̶red ̶̶clover ̶̶and ̶̶annual ̶̶
cover ̶̶crops ̶̶planted ̶̶after ̶̶wheat ̶̶harvest ̶̶in ̶̶July, ̶̶at ̶̶East Lansing, MI. ̶̶The error bars show
statistically different results based on SE. (‡ ̶̶RCL, frost-seeded red clover; FCC, failed cover
crop; OPmix, oat/pea mix, SUD, sudangrass; SDX, sorghum x sudangrass; Teff, teffgrass)

78

900

POXC, mg C kg-1

800

Harvested (H)

Not Harvested (NH)

700
600
500
400
300
200
100
0

Treatment
Figure 6. Analysis of variance for labile organic matter for 2014 and 2015 fall soil sampling
after cover crop harvest. ̶̶Cover ̶̶crops ̶̶were ̶̶harvested ̶̶in ̶̶October ̶̶2014 ̶̶and ̶̶2015 ̶̶from ̶̶red ̶̶clover ̶̶
and ̶̶annual ̶̶cover ̶̶crops ̶̶planted ̶̶after ̶̶wheat ̶̶harvest ̶̶in ̶̶July. Cover ̶̶crops ̶̶were ̶̶harvested ̶̶in ̶̶
October ̶̶2014 ̶̶at ̶̶East Lansing, MI. ̶̶The error bars show statistically different results based on SE.
(‡ ̶̶RCL, frost-seeded red clover; FCC, failed cover crop; OPmix, oat/pea mix, SUD, sudangrass;
SDX, sorghum x sudangrass; Teff, teffgrass)

79

APPENDIX B

ANOVA Tables for Figures

Table A1.  ̶̶ANOVA table for cover evaluations taken bi-weekly from red clover and annual
cover crops planted after wheat harvest approximately, (A) eight weeks after cover crop planting
(B) four weeks after cover crop harvest, (C) four weeks before corn planting (D) four weeks after
planting. Cover crops were harvested in October 2014 and 2015 and corn was planted in May
2015 and 2016 at East Lansing, MI.
------------------------------------------------------P < --------------------------------------------------Four weeks after cover crop harvest
Eight weeks after cover crop planting
Response
Variable
Model
Cover
crop
(CC)
Harvest
(harv)
CC
*Harv
SE
Contrasts

Volunteer
Wheat

Cover
Crop

Weed

Bare
Ground

Straw

Voluntee
r Wheat

Cover
Crop

Weed

Bare
Ground

Straw

0.01

0.01

NS§

NS

NS

0.01

0.01

0.01

NS

NS

NS

NS

NS

NS

NS

NS

0.01

0.01

0.07

0.01

NS

NS

NS

NS

NS

0.01

0.01

0.01

NS

NS

4.04

1.03

1.99

1.81

3.94

3.52

0.41

2.61

1.65

4.02

0.01

0.03

NS

0.05

0.01

0.01

0.01

NS

0.03

0.01

NS

NS

NS

0.01

0.01

0.01

NS

NS

0.01

NS

NS

0.08

0.01

0.01

0.01

NS

NS

0.01

NS

NS

NS

0.01

0.01

0.01

NS

0.05

NS

NS

NS

NS

NS

NS

0.04

NS

NS

0.01

0.01

NS

NS

0.01

0.01

0.04

NS

0.06

NS

NS

NS

NS

0.01

0.01

NS

NS

0.06

NS

NS

NS

NS

NS

0.03

NS

NS

NS

RCL† vs.
FCC
0.01
RCL vs.
OPMix
0.01
RCL vs.
Radish
0.02
RCL vs.
SUD/SD
X
0.01
SUD vs.
SDX
NS
LEG vs.
WSG
0.01
Interaction Contrasts
RCL vs
FCC for
harv
NS
RCL vs.
OPmix
for harv
NS

80

Table A1. (cont’d) ̶̶
RCL vs.
SUD/SD
X
SUD vs.
SDX for
harv

NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

LEG vs.
WSG for
harv

NS

NS

NS

NS

Fallow
vs. all
not harv
CC

0.01

0.01

NS

0.01

0.01

NS

0.01

Fallow
vs. all
harv CC
Fallow
vs. RCLNH†

0.05

NS
0.01

NS

NS

NS

NS

0.01

NS

NS

NS

0.01

0.01

NS

NS

NS

NS

0.01

0.01

0.03

NS

0.01

0.01

NS

NS

NS

0.01

NS

NS

NS

NS

0.01

0.01

0.01

0.03

0.01

NS

0.01

0.01

------------------------------------------------------P < --------------------------------------------------Post-Corn Planting
Pre-Corn Planting
Response
Variable
Model

Volunteer
Wheat

Cover
Crop

Weed

Bare
Ground

Straw

Corn

Cover
Crop

Weed

Bare
Ground

Straw

0.01

0.01

0.10

NS§

0.08

NS

0.01

NS

NS

0.03

0.01

0.01

0.01

0.01

0.01

0.01

NS

0.01

NS

0.01

CC *Harv

0.01

0.01

NS

NS

0.01

NS

NS

NS

NS

NS

SE
Contrasts
RCL† vs.
FCC
RCL vs.
OPMix
RCL vs.
Radish

4.04

1.03

1.99

1.81

3.94

3.52

0.41

2.61

1.65

4.02

0.01

0.01

0.01

0.01

0.10

NS

0.01

0.04

0.05

0.01

0.01

0.01

0.01

0.07

0.01

NS

0.01

0.03

NS

0.01

0.01

0.01

0.01

0.06

0.01

NS

0.01

NS

0.01

0.01

Cover crop
(CC)
Harvest
(harv)

81

Table A1. (cont’d) ̶̶
RCL vs.
SUD/SDX
0.01
SUD vs.
SDX
NS
LEG vs.
WSG
0.01
Interaction Contrasts
RCL vs
FCC for
harv
0.05
RCL vs.
OPmix for
harv
0.01
RCL vs.
Radish for
harv
NS
RCL vs.
SUD/SDX
for harv
0.05
SUD vs.
SDX for
harv
NS
LEG vs.
WSG for
harv
NS
Fallow vs.
all not harv
CC

Fallow vs.
all harv CC
Fallow vs.
RCL-NH†

0.01

0.01

0.01

0.01

NS

0.01

0.05

0.01

0.01

NS

NS

NS

NS

NS

NS

NS

NS

NS

0.01

NS

0.01

NS

NS

0.01

NS

0.05

0.01

0.01

NS

NS

0.01

NS

0.03

NS

NS

NS

0.01

NS

0.04

0.03

NS

NS

NS

NS

NS

0.01

NS

NS

0.01

NS

NS

NS

NS

NS

0.01

0.10

0.08

0.01

NS

0.08

NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

NS

0.01

NS

NS

0.01

NS

NS

NS

NS

NS

0.01

0.01

0.02

0.01

NS

0.03

0.09

0.04

NS

0.03

NS

0.01

0.01

NS

0.01

NS

0.08

NS

NS

0.07

0.02

0.01

0.01

0.01

NS

NS

0.01

0.01

NS

NS

† ̶̶NH, ̶̶Not ̶̶Harvested; ̶̶FCC, failed cover crop; H, Harvested; LEG, legume group: RCL and
OPmix; OPmix, oat/pea mix; N, nitrogen; RCL, frost-seeded red clover; SUD, sudangrass; SDX,
sorghum x sudangrass; Teff, teffgrass; WSG, warm-season grass group: SUD, SDX, Teff.
§ NS, not significant (P >0.10).

82

Table A2.  ̶̶ANOVA ̶̶table ̶̶for ̶̶Plant ̶̶canopy ̶̶height ̶̶taken ̶̶bi-weekly ̶̶from ̶̶red ̶̶clover ̶̶and ̶̶annual ̶̶
cover ̶̶crops ̶̶planted ̶̶after ̶̶wheat ̶̶harvest ̶̶approximately, ̶̶(A) eight weeks after planting (B) four
weeks after harvest (C) four weeks before corn planting (D) four weeks after corn planting. ̶̶
Cover ̶̶crops ̶̶were ̶̶harvested ̶̶in ̶̶October ̶̶2014 ̶̶and ̶̶2015 ̶̶and ̶̶Corn ̶̶was ̶̶planted ̶̶in ̶̶May ̶̶2015 ̶̶and ̶̶
2016 ̶̶at ̶̶East Lansing, MI. ̶̶
-----------------------------------P < ----------------------------------

Model
Cover crop (CC)
Harvest (harv)
CC*Harv
Contrasts
RCL† vs. FCC
RCL vs. OPMix
RCL vs. Radish
RCL vs. SUD/SDX
SUD vs. SDX
LEG vs WSG
Interaction Contrasts
RCL vs FCC for harvest
RCL vs. OPmix for harv

Eight weeks
after cover
crop planting

Four weeks
after cover
crop harvest

Pre-Corn
Planting

Post-Corn
Planting

0.01
NS
NS

0.01
0.01
0.01

NS§
NS
NS

NS
NS
NS

0.01
NS
0.01
0.09
0.01
0.01

0.03
0.01
0.02
NS
NS
0.04

NS
NS
NS
NS
NS
NS

NS
NS
NS
NS
NS
NS

NS

0.01
0.01

NS

NS

NS

NS

NS

NS

NS
0.01

RCL vs. Radish for harv

NS

RCL vs. SUD/SDX for harv
SUD vs. SDX for harv

NS
NS

NS
0.01

NS
NS

NS
NS

LEG vs. WSG for harv

NS

0.01

NS

NS

Fallow vs. all not harv CC

0.01

0.01

NS

NS

Fallow vs. all harv CC
Fallow vs. RCL-NH†

0.02
0.01

0.02
0.01

NS
NS

NS
NS

† ̶̶NH, ̶̶Not ̶̶Harvested; ̶̶FCC, failed cover crop; H, Harvested; LEG, legume group: RCL and
OPmix; OPmix, oat/pea mix; N, nitrogen; RCL, frost-seeded red clover; SUD, sudangrass; SDX,
sorghum x sudangrass; Teff, teffgrass; WSG, warm-season grass group: SUD, SDX, Teff.
§ NS, not significant (P >0.10).

83

Table A3. ANOVA ̶̶table ̶̶for ̶̶Figure ̶̶5 ̶̶forage ̶̶dry ̶̶matter ̶̶harvested ̶̶in ̶̶October ̶̶2014 ̶̶and ̶̶2015 ̶̶
from ̶̶red ̶̶clover ̶̶and ̶̶annual ̶̶cover ̶̶crops ̶̶planted ̶̶after ̶̶wheat ̶̶harvest ̶̶in ̶̶July, ̶̶at ̶̶East Lansing, MI.
Model
---- P < ---0.02

Cover crop
Contrasts
RCL‡ vs. FCC†
0.01
RCL vs. OPMix
0.01
RCL vs. Radish
0.01
RCL vs. SUD/SDX
0.01
SUD vs. SDX
NS§
LEG vs. WSG
0.01
† ̶̶FCC, failed cover crop; LEG, legume group: RCL and OPmix; OPmix, oat/pea mix; N,
nitrogen; RCL, frost-seeded red clover; SUD, sudangrass; SDX, sorghum x sudangrass; Teff,
teffgrass; WSG, warm-season grass group: SUD, SDX, Teff.
‡ ̶̶All values are dry matter basis except harvest moisture.
§ NS, not significant (P >0.10).

84

Table A4. ANOVA ̶̶table ̶̶for ̶̶Figure 6 analysis of variance for labile organic matter for November
2014 and October 2015 fall soil sampling after cover crop harvest. ̶̶Cover ̶̶crops ̶̶were ̶̶harvested ̶̶in ̶̶
October ̶̶2015 ̶̶from ̶̶red ̶̶clover ̶̶and ̶̶annual ̶̶cover ̶̶crops ̶̶planted ̶̶after ̶̶wheat ̶̶harvest ̶̶in ̶̶July. Cover ̶̶
crops ̶̶were ̶̶harvested ̶̶in ̶̶October ̶̶2014 ̶̶at ̶̶East Lansing, MI. ̶̶
Model
------P < -------NS§
NS
NS

Cover Crop (CC)
Harvest (harv)
CC*harv
Contrasts
RCL‡ vs. FCC†
NS
RCL vs. OPMix
NS
RCL vs. Radish
NS
RCL vs. SUD/SDX
NS
SUD vs. SDX
NS
LEG vs WSG
NS
Interaction Contrasts
RCL vs FCC for harv
NS
RCL vs. OPmix for harv
NS
RCL vs. Radish for harv
0.09
RCL vs. SUD/SDX for harv
NS
SUD vs. SDX for harv
NS
LEG vs. WSG for harv
NS
Fallow vs. all not harv CC
NS
Fallow vs. all harv CC
NS
Fallow vs. RCL-NH
NS
† ̶̶NH, ̶̶Not ̶̶Harvested; ̶̶FCC, failed cover crop; H, Harvested; LEG, legume group: RCL and
OPmix; OPmix, oat/pea mix; N, nitrogen; RCL, frost-seeded red clover; SUD, sudangrass; SDX,
sorghum x sudangrass; Teff, teffgrass; WSG, warm-season grass group: SUD, SDX, Teff.
‡ ̶̶All values are dry matter basis except harvest moisture.
§ NS, not significant (P >0.10).

85

Table A5. Carbon and nitrogen concentration in soil from the 12 cm depth sampled in November
after cover crop were harvested or not harvested in October 2014 and 2015 at ̶̶East Lansing, MI.
Treatment

Harvested

C ̶̶g ̶̶kg-1

N ̶̶g ̶̶kg-1

Fallow
RCL‡

Fallow
NH†

20.1
19.4

2.3
2.1

RCL
OPmix
OPmix
SUD
SUD
SDX
SDX
Teff
Teff
Radish
Radish
FCC
FCC

H
NH
H
NH
H
NH
H
NH
H
NH
H
NH
H

19.9
19.8
20.4
18.2
20.8
18.5
20.7
19.6
21.1
18.2
18.5
20.5
19.4
0.2

1.8
2
2
2
2
2
2
2
2
1.8
1.8
2
2
1.5

SE
 ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶̶--------------- ̶̶P ̶̶< ̶̶-------------------Model
Cover ̶̶crop ̶̶(CC)
NS§
NS
Harvest ̶̶(harv)
CC ̶̶*harv
Contrasts
RCL ̶̶vs. ̶̶FCC
RCL ̶̶vs. ̶̶OPMix
RCL ̶̶vs. ̶̶Radish
RCL ̶̶vs. ̶̶SUD/SDX
SUD ̶̶vs. ̶̶SDX
LEG ̶̶vs ̶̶WSG
Interaction ̶̶Contrasts
RCL ̶̶vs ̶̶FCC ̶̶for ̶̶harv
RCL ̶̶vs. ̶̶OPmix ̶̶for ̶̶harv
RCL ̶̶vs. ̶̶Radish ̶̶for ̶̶harv
RCL ̶̶vs. ̶̶SUD/SDX ̶̶for ̶̶harv

NS
NS

NS
NS

NS
NS
NS
NS
NS
NS

NS
NS
NS
NS
NS
NS

NS
0.08
NS
NS

NS
NS
NS
NS

SUD ̶̶vs. ̶̶SDX ̶̶for ̶̶harv

NS

NS

86

Table A5. (cont’d)
LEG ̶̶vs. ̶̶WSG ̶̶for ̶̶harv
NS
NS
Fallow vs. all not harv CC
NS
NS
Fallow vs. all harv CC
NS
NS
Fallow vs. RCL-NH
NS
NS
† ̶̶NH, ̶̶Not ̶̶Harvested; ̶̶FCC, failed cover crop; H, Harvested; LEG, legume group: RCL and
OPmix; OPmix, oat/pea mix; N, nitrogen; RCL, frost-seeded red clover; SUD, sudangrass; SDX,
sorghum x sudangrass; Teff, teffgrass; WSG, warm-season grass group: SUD, SDX, Teff.
‡ ̶̶All values are dry matter basis except harvest moisture.
§ NS, not significant (P >0.10).

87

Figure A1. ̶̶Corn ̶̶SPAD ̶̶(Soil ̶̶Plant ̶̶Analytical ̶̶Division ̶̶value) ̶̶meter ̶̶and ̶̶PhiNPQ ̶̶readings ̶̶at V12 stage in ear leaves of corn grown after cover crops were harvested or not harvested the
previous October at ̶̶East Lansing, MI. SPAD measures active regulation of energy towards
photosynthesis and should be positively correlated with grain yield. PhiNPQ is the measurement
of active regulation of energy away from photosynthesis and should be correlated with reduced
grain yields

88

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