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This is to certify that the
thesis entitled

EVALUATION OF GLYPHOSATE-RESISTANT ALFALFA
ESTABLISHMENT IN A FORAGE PRODUCTION SYSTEM

presented by

Sarah Ann McCordick

has been accepted towards fulfillment
of the requirements for the

MS. degree in Crop and Soil Sciences

 

 

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EVALUATION OF GLYPHOSATE-RESISTANT ALFALF A ESTABLISHMENT
IN A FORAGE PRODUCTION SYSTEM

By

Sarah Ann McCordick

A THESIS

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

MASTER OF SCIENCE
Department of Crop and Soil Sciences

2006

ABSTRACT

EVALUATION OF GLYPHOSATE-RESISTANT ALF ALFA ESTABLISHMENT
IN A F ORAGE PRODUCTION SYSTEM

By
Sarah Ann McCordick

Field studies were conducted in 2004 and 2005 to determine the effect of
establishment method and weed control method on forage production, forage quality and
alfalfa stand establishment. Weed control with glyphosate was more consistent than with
imazamox or imazamox + clethodim. In 2004, total seasonal forage yield was the highest
where no herbicide was applied in the oat companion seeded system. In 2005, seeding
method or weed control method did not affect total seasonal forage production. Alfalfa
established by clear seeding methods with glyphosate yielded the highest alfalfa dry
matter in both years. Alfalfa established with an oat companion crop had a lower weed
biomass than the clear seeded system where no herbicide was applied in both years. The
greatest differences in forage quality were observed at the first harvest in both
establishment years. Forage quality was lower where an oat companion crop was used in
establishment compared to clear seeded alfalfa when herbicides were not applied.

Field studies were conducted in 2005 to determine the effect of seeding rate on
glyphosate-resistant alfalfa establishment, yield, forage quality and weed control. Alfalfa
yields increased with increasing seeding rates. Glyphosate applications increased alfalfa
yields at the 4.5 kg ha”1 and 9.0 kg ha‘1 seeding rates, but not at the 17.9 kg ha'1 rate.
Multiple applications of glyphosate did not increase alfalfa or total forage yield compared
to a single application. Glyphosate applications increased forage quality at the first

harvest at all seeding rates. Alfalfa density was not affected by weed control method.

ACKNOWLEDGMENTS

Many people have contributed significantly to my research and experience at
Michigan State University, and without them none of this would be possible. I would
like to especially thank Dr. Jim Kells for his guidance, support and patience throughout
the last two years. I would also like to thank Dr. Richard Leep and Dr. Christina Difonzo
for their input, time and willingness to be a part of my research project.

Thank you to Andy Chomas and Tim Dietz for their hard work and fun working
environment in the field. Appreciation is also extended to my fellow graduate students:
Kathrin Schirmacher, Dana Harder, Scott Bollman, Mark Bemards, Brad Fronning, Erin
Hill and Terry Schulz, who provided friendship, laughter and help that will never be
forgotten. I would also like to thank my summer interns Amber Black and Crystal Schulz
for helping me sort through hundreds of forage samples. Thank you to Tom Galecka for
spraying, Brian Graff for making room in the dryers, Christy Sprague and Dr. Penner for
kind words of encouragement and Gary Powell for his unique outlook on life.

A special thank you to my husband Russel, for the endless support, patience and
sacrifice he made to allow me to pursue my dream. I would also like to thank my parents
Van and Pat for teaching me to love the land and to be proud of my agricultural
upbringing. Thank you to my brother Joal for always keeping me in check, while giving
me a new perspective on every situation. Finally I would like to thank Jesus my Lord and

Savior for giving me the direction and the ability to finish this chapter of my life.

iii

TABLE OF CONTENTS

LIST OF TABLES ............................................................................................ vi
LIST OF FIGURES ........................................................................................... x
CHAPTER 1
ESTABLISHMENT SYSTEMS FOR GLYPHOSATE-RESISTANT
ALFALFA.
ABSTRACT ................................................................................................. 1
INTRODUCTION ....................................................................................... 2
MATERIAL AND METHODS .................................................................. 8
RESULTS AND DISCUSSION ............................................................... 12
Alfalfa Injury ................................................................................ 12
Weed Control ............................................................................... 13
Weed Control: Year after Establishment ..................................... 14
Yield Components: Establishment Year ..................................... 15
Yield Components: Year after Establishment ............................. l8
Alfalfa Stem Weight .................................................................... 18
Stand Density ............................................................................... 19
Summary ...................................................................................... 19
REFERENCES .......................................................................................... 22
CHAPTER 2

F ORAGE QUALITY AND ECONOMICS OF GLYPHOSATE-
RESISTANT ALFALFA AS IN FLUENCED BY ESTABLISHMENT

SYSTEMS.
ABSTRACT ............................................................................................. 36
DITRODUCTION .................................................................................... 37
MATERIAL AND METHODS ............................................................... 42
Forage Quality Analysis .............................................................. 44
Milk Yield .................................................................................... 44
Economic analysis ........................................................................ 44
Statistical analysis ........................................................................ 45
RESULTS AND DISCUSSION .............................................................. 46
Forage Quality .............................................................................. 46
Forage Quality: Year after Establishment ................................... 52
Economic Analysis ...................................................................... 52
Summary ...................................................................................... 54
REFERENCES ......................................................................................... 56

iv

CHAPTER 3
EFFECT OF SEEDING RATE ON GLYPHOSATE-RESISTANT

ALFALFA ESTABLISHMENT.
ABSTRACT ............................................................................................. 68
INTRODUCTION .................................................................................... 69
MATERIAL AND METHODS ............................................................... 72
Forage Quality Analysis .............................................................. 74
Economic Analysis ...................................................................... 75
Statistical Analysis ....................................................................... 76
RESULTS AND DISCUSSION .............................................................. 77
Alfalfa Injury ................................................................................ 77
Weed Control ............................................................................... 77
Yield Components ........................................................................ 77
Alfalfa Stem Weight .................................................................... 80
Forage Quality .............................................................................. 81
Alfalfa Stand Density ................................................................... 84
Economic Analysis ...................................................................... 84
Summary ...................................................................................... 86
REFERENCES ......................................................................................... 88
APPENDIX I .................................................................................................. 101
APPENDIX 11 ................................................................................................. 105
APPENDIX III ............................................................................................... 1 13

LIST OF TABLES

CHAPTER 1
ESTABLISHMENT SYSTEMS FOR GLYPHOSATE-RESISTANT
ALFALF A.

Table 1.1 Harvest dates for glyphosate-resistant alfalfa in 2004 and 2005. ................... 25

Table 1.2 Alfalfa injury as determined by visual evaluation 7, 14, 21 and 28 days
after treatment (DAT) from glyphosate and imazamox (clear seeding) and glyphosate
and imazamox + clethodim (companion seeding) in 2004 and 2005 ............................... 26

Table 1.3 Monthly precipitation recorded at the Michigan State University Department
of Horticulture Teaching and Research Center, East Lansing, MI. ................................. 27

Table 1.4 Control of annual weeds 14 days after treatment established by clear
and companion seeding methods in 2004 and 2005 ......................................................... 28

Table 1.5 Control of annual weeds at harvest 1 established by clear seeding and
companion seeding methods in 2004 and 2005 ................................................................ 29

Table 1.6 Weed yields in 2005 in four harvests and seasonal totals for alfalfa established
by clear and companion seeded methods in the spring of 2004 ...................................... 30

Table 1.7 Weed yields in the 2004 and 2005 establishment year in three harvests
and seasonal totals for alfalfa established by clear and companion seeded methods. ..... 31

Table 1.8 Alfalfa weight per stern for the 2004 and 2005 establishment year, in
alfalfa established under clear seeding and companion seeding methods. Years are
reported separately for harvest 1 and 2 and combined for harvest 3 ................................ 32

Table 1.9 Alfalfa plant densities in the spring and fall of the 2004 and 2005
establishment years and the year after establishment for the 2004 establishment study. 33

CHAPTER 2
F ORAGE QUALITY AND ECONOMICS OF GLYPHOSATE-RESISTANT
ALFALFA AS IN FLUENCED BY ESTABLISHMENT SYSTEMS.

Table 2.1 Mean stage by count (MSC), crude protein (CP), neutral detergent fiber

(NDF). Acid detergent fiber (ADF) and relative feed value (RFV) for harvest 1 in the
2004 and 2005 establishment year ................................................................................... 59

vi

Table 2.2 Milk production estimated based on kg of milk produced per Mg of forage,
total forage yield and milk per hectare at harvest 1 in the 2004 and 2005
establishment year. ............................................................................................................. 60

Table 2.3 Mean stage by count (MSC), crude protein (CP), neutral detergent fiber
(NDF). Acid detergent fiber (ADF) and relative feed value (RF V) for harvest 2 in the
2004 and 2005 establishment year ................................................................................... 61

Table 2.4 Milk production estimated based on kg of milk produced per Mg of forage,
total forage yield and milk per hectare at harvest 2 in the 2004 and 2005
establishment year. ............................................................................................................. 62

Table 2.5 Mean stage by count (MSC), crude protein (CP), neutral detergent fiber
(NDF). Acid detergent fiber (ADF) and relative feed value (RFV) for harvest 3 in the
2004 and 2005 establishment year ................................................................................... 63

Table 2.6 Milk production estimated based on kg of milk produced per Mg of forage,
total forage yield and milk per hectare at harvest 3 in the 2004 and 2005

establishment year. ............................................................................................................. 64
Table 2.7 Seasonal total forage yield and milk per hectare in the 2004 and

2005 establishment years. .................................................................................................. 65
Table 2.8 Economic comparisons of establishment systems and weed control programs
for 2004 and 2005 glyphosate resistant alfalfa establishment. ........................................ 66
Table 2.9 Economic comparisons of establishment systems and weed control programs
for 2004 and 2005 glyphosate resistant alfalfa establishment. ......................................... 67
CHAPTER 3

EFFECT OF SEEDING RATE ON GLYPHOSATE-RESISTANT ALFALFA
ESTABLISHMENT.

Table 3.1 Weed yields at each of the four harvest and seasonal totals, established by
low, medium and high seeding rates in 2005 ................................................................... 90

Table 3.2 Alfalfa weight per stem at each of the four harvests, established by high,
medium and low seeding rates in 2005 ............................................................................. 91

Table 3.3 Alfalfa maturity (MSC), crude protein (CP), neutral detergent fiber (NDF),
acid detergent fiber (ADF) and relative feed value (RF V) at harvest 1, established by
low, medium and high seeding rates in 2005 .................................................................... 92

vii

Table 3.4 Alfalfa maturity (MSC), crude protein (CP), neutral detergent fiber (NDF),
acid detergent fiber (ADF) and relative feed value (RF V) at harvest 2, established by
low, medium and high seeding rates in 2005 .................................................................... 93

Table 3.5 Alfalfa maturity (MSC), crude protein (CP), neutral detergent fiber (NDF),
acid detergent fiber (ADF) and relative feed value (RFV) at harvest 3, established by
low, medium and high seeding rates in 2005 .................................................................... 94

Table 3.6 Alfalfa maturity (MSC), crude protein (CP), neutral detergent fiber (NDF),
acid detergent fiber (ADF) and relative feed value (RFV) at harvest 4, established by

low, medium and high seeding rates in 2005 .................................................................... 95
Table 3.7 Economic comparisons of seeding rates and weed control programs in

2005 glyphosate resistant alfalfa establishment ................................................................ 96
Table 3.8 Economic comparisons of seeding rates and weed control programs in

2005 glyphosate resistant alfalfa establishment ................................................................ 97
APPENDIX I

Table AI.1 Forage dry matter yields in 2005 for alfalfa established by clear and
companion seeded methods in the spring of 2004 .......................................................... 102
Table AI.2 Alfalfa dry matter yields in 2005 for alfalfa established by clear and
companion seeded methods in the spring of 2004 .......................................................... 103
Table AI.3 Alfalfa weight per stem in 2005 for four harvests established by clear and
companion seeded methods in the spring of 2004 .......................................................... 104
APPENDIX II

Table AII.1 Second year alfalfa maturity data, reported as mean stage by count for the
four harvests in the year after establishment by established by clear seeding and
companion seeding methods in the spring of 2004 ......................................................... 106

Table AII.2 Percentages of crude protein (CP), neutral detergent fiber (NDF), acid
detergent fiber (ADF) in four harvests the year after establishment, established by clear
seeding and companion seeding methods in the spring of 2004 .................................... 107

Table AH.3 Second year milk per hectare estimates at each of the four harvests and

seasonal totals, established by clear seeding and companion seeding methods in the
spring of 2004 .................................................................................................................. 108

viii

Table AII.4 Milk production based on kg of milk per Mg of forage at each of the four
harvests in 2005, established by clear seeding and companion seeding methods in the
spring of 2004 .................................................................................................................. 109

Table AII.5 Second year relative feed values of the four harvests in 2005, established by
clear seeding and companion seeding methods in the spring of 2004 ........................... 110

Table AII.6 Economic comparisons of establishment systems and weed control programs

for 2004 and 2005 glyphosate resistant alfalfa establishment ....................................... 111
Table AH.7 Economic comparisons of establishment systems and weed control programs
for 2004 and 2005 glyphosate resistant alfalfa establishment ....................................... 112
APPENDIX 111

Table AIII.1 Economic comparisons of seeding rates and weed control programs in 2005
glyphosate-resistant alfalfa establishment ....................................................................... 114

Table AIII.2 Economic comparisons of seeding rates and weed control programs in 2005
glyphosate-resistant alfalfa establishment ....................................................................... 115

ix

LIST OF FIGURES

CHAPTER 1
ESTABLISHMENT SYSTEMS FOR GLYPHOSATE-RESISTANT
ALF ALFA.

Figure 1.1 Dry matter yield by forage components at harvest one and two in 2004

and 2005. Bars with the same letter are not different at or=0.05. Capital letters

denote differences in total forage matter yield; lower case letters denote differences

in alfalfa yield ................................................................................................................... 34

Figure 1.2 Dry matter yield by forage components at harvest three and seasonal totals

in 2004 and 2005. Bars with the same letter are not different at o:=0.05. Capital letters
denote differences in total forage matter yield; lower case letters denote differences

in alfalfa yield ................................................................................................................... 35

CHAPTER 3
EFFECT OF SEEDIN G RATE ON GLYPHOSATE-RESISTANT ALF ALF A
ESTABLISHMENT.

Figure 3.1 Dry matter yield by forage components at harvest one, two, three and four.
Bars with the same letter are not different at 0:005. Capital letters denote differences

in total forage dry matter yield; lower case letters denote differences in alfalfa yields
........................................................................................................................................... 98

Figure 3.2 Seasonal dry matter yield by forage components in 2005. Bars with the
same letter are not different at a=0.05. Capital letters denote differences in total forage
dry matter yield; lower case letters denote differences in alfalfa yields ......................... 99

Figure 3.3 Alfalfa stand density in the spring of 2005, established by low, medium and
high seeding rates. Capital letters denote differences in alfalfa crown densities at
a=0.05 ........................................ . .............................................................................. 100

 

Figure 3.4 Alfalfa stand density in the fall of 2005, established by low, medium and
high seeding rates. Capital letters denote differences in alfalfa crown densities at
a=0.05 ............................................................................................................................. 100

CHAPTER 1
ESTABLISHMENT SYSTEMS FOR GLYPHOSATE-RESISTANT ALFALFA
Abstract: Glyphosate-resistant alfalfa offers new weed control options for alfalfa
establishment. Field studies were conducted in 2004 and 2005 in to determine the effect
of establishment method and weed control method on forage production and alfalfa stand
establishment. Seeding methods included clear seeding and companion seeding with
oats. Herbicide treatments included glyphosate, imazamox or imazamox + clethodim,
and no herbicide. Glyphosate injury was minimal, short-lived and no longer evident at
the first harvest in 2004. No glyphosate injury was observed in 2005. Weed control with
glyphosate was more consistent than imazamox or imazamox + clethodim. In 2004, total
seasonal forage yield was the highest where no herbicide was applied in the oat
companion crop and was reduced where a herbicide was applied in both establishment
systems. In 2005, seeding method or weed control method did not affect total seasonal
forage production. Alfalfa established by clear seeding methods with glyphosate yielded
the highest alfalfa dry matter in both years. Imazamox injury reduced first harvest alfalfa
yield in the clear seeded system in both years. When no herbicide was applied, alfalfa
yield was higher in the clear seeded system. The oat companion crop suppressed alfalfa
yield significantly in both years. Alfalfa established with an oat companion crop had a
lower weed biomass than the clear seeded system where no herbicide was applied in both
years. Weed biomass was reduced in the year following establishment where a herbicide
was applied in the 2004 establishment year. However, there were no significant
differences in alfalfa yield, forage quality and alfalfa stand density observed in the year

afier establishment.

INTRODUCTION

Glyphosate-resistant crops have become a significant part of cropping systems in
North America. In 2005, glyphosate-resistant crops occupied approximately 85% of the
soybean (Glycine max L.), 60% of the cotton (Gossypium hirsutum L.), and 17% of the
corn (Zea mays L.) hectares across the United States. Alfalfa (Medicago sativa L.) is the
most recent crop to have glyphosate-resistant technology introduced. Alfalfa is the third
most economically important crop produced in the United States, occupying 8.9 million
ha with an estimated 64 million Mg produced in 2005 (Anonymous, 2005). In Michigan
there are approximately 450,000 ha of alfalfa produced annually, valued at 57 million
dollars (Anonymous, 2004).

Alfalfa is considered to be the “queen of forages” and the premier livestock
forage. High quality alfalfa is demanded extensively in the dairy production sector, and
to a lesser extent in beef, horse and sheep production systems (Barnes et al., 1995). A
large portion of alfalfa is also exported either as dry hay or condensed alfalfa by-products
with United States exports valued at 90 million dollars in 2004 (Anonymous, 2005).
Alfalfa is the foundation of many crop rotations due to the potential for high biomass
production, high nutritional quality and biological nitrogen fixation (Entz, et al., 2002).
Alfalfa can increase subsequent crop productivity by improving soil water holding
capacity, increasing soil organic matter, adding nitrogen residues while reducing some
soil pathogens (Barnes et al., 1995).

Glyphosate-resistant alfalfa was developed similar to the other glyphosate-
resistant crops by incorporating the genetic resistance to glyphosate into the alfalfa plants

through a single bacterial gene (CP4) insertion that modifies 5-enolpyruvylshikimate-3-

phosphate synthase (EPSP) (Van Deynze et al., 2004). Commercially available varieties
of glyphosate resistant alfalfa demonstrate excellent cr0p safety at all stages of alfalfa
growth and preliminary research shows no negative effects on forage yield or other
important agronomic traits (McCaslin et al., 2000). Glyphosate-resistant alfalfa offers a
new tool in weed control for establishing alfalfa.

Traditionally, weed control in alfalfa establishment has been a challenge for
forage producers. Weed competition can reduce alfalfa yield (Moyer, 1985; Wilson,
1981), lower forage quality and impact stand densities (Becker et al., 1998). Weeds may
also reduce palatability (Marten and Andersen, 1975) and increase drying time (Doll,
1984). Alfalfa establishment methods often impact the choice of weed control in seedling
alfalfa stands. In the past, companion crops were used almost exclusively to establish
alfalfa, effectively controlling weeds through cultural control methods (Simmons et al.,
1995). Recent success in the herbicidal control of weeds in alfalfa has increased the
practice of clear seeding alfalfa establishment (Becker et al., 1988). An alternative alfalfa
establishment method (not commonly practiced) utilizes the techniques in both
companion and clear seeded alfalfa systems, resulting in a mulch system (Curran et al.,
1993)

Establishing alfalfa with a companion crop has been used to provide quick
ground cover and reduce weed competition (Lanini et al., 1991) and soil erosion (Moyer
et al., 1995), while giving shelter to seedling alfalfa from insect pests and adverse
growing conditions (Simmons et al., 1992). Small grains are the most widely used
companion crops, providing grain and straw or extra forage in the establishment year

(Chapko et al., 1991). Oats (Avena sativa L.) is a common companion crop as it is the

least competitive cereal with alfalfa (Peters, 1961). Lanini et a1. (1991) found that
seeding oats at a reduced rate optimized alfalfa yields while reducing weed biomass.
Companion crop harvest management is critical in alfalfa establishment, as initial and
subsequent alfalfa yields and stand densities may be reduced (Simmons et al., 1995).
Companion crops should be harvested between the late boot and early heading stage to
provide good quality forage (Chapko et al., 1991) and to reduce competition in seedling
alfalfa (Curran et al., 1993).

Companion crops increase total dry matter yield in the establishment year (Kust,
1968; Lanini et al., 1991; Simmons et al., 1995) and suppress weed biomass (Peters,
1961; Simmons et al., 1995). Hoy et a1. (2002) found that establishment methods for
alfalfa that included oat as a companion crop suppressed weed growth more than
herbicide treatments. However, companion crops compete with alfalfa for nutrients, light
and moisture, reducing alfalfa yield and decreasing plant density in the establishment
year (Moyer et al., 1995; Simmons et al., 1995; Lanini et al., 1991; Sheaffer et al., 1988).

Clear seeding alfalfa establishment systems require the use of herbicides to obtain
productive stands (Sheaffer et al., 1988). Herbicides reduce weed densities and allow
better stands of pure alfalfa to be established (Schmid and Behrens, 1972). Alfalfa yields
during the establishment year are usually greater for clear seeding than for companion
crop establishment systems (Schmid and Behrens, 1972; Genest and Steppler, 1973;
Sheaffer et al., 1988). Curran et a1. (1993) however, estimated clear seeded alfalfa
establishment increased soil erosion ten fold because of prolonged soil exposure.

Imazamox is a selective postemergence herbicide that is applied to seedling

alfalfa, controlling a broad spectrum of grassy and broadleaf weeds. Imazamox is most

effective when it is applied to 3-5 cm weeds and when alfalfa has reached the two
trifoliate leaf stage (Sprague et al., 2005). Canevari et a1. (2003) concluded that
imazamox should be applied at the smallest weed size allowable as 95-100% weed
control can be achieved in alfalfa, but overall weed control is significantly lower when
applications are delayed. Peterson and Duncan (2002) and Miller and Alford (2002)
observed no injury from imazamox in conventional alfalfa and glyphosate-resistant
varieties. Orloff et al. (2003) observed up to 20% alfalfa grth reduction when
imazamox was applied to glyphosate-resistant alfalfa in California in 2002. Johnson et
a1. (2001) and Wait and Johnson (2002) observed less then 5% growth reduction and
quick plant recovery from imazamox applications. Canevari et a1. (2003) speculated that
imazamox injury in alfalfa was closely related to plant stress at the time of application.

A less common alfalfa establishment system includes the combination of a
companion crop with a herbicide application. Small grain crops are planted to protect
alfalfa and decrease soil erosion and are then killed at 5-10 cm by using a selective grass
control herbicide, allowing alfalfa growth to proceed with minimal competition from the
companion crop (Stute and Posner, 1993). Curran et a1. (1993) found that chemical
control of an oat companion crop provided greater establishment year alfalfa yields than
typical companion cropping systems and greater protection from soil erosion than clear
seeding. Hoy et a1. (2002) found that an oat residue mulch establishment system did not
suppress weeds as well as an oat companion crop or where herbicides where applied in a
clear seeded system.

Studies show that alfalfa yields and forage quality the year afier establishment

were unaffected by method of establishment (Schmid and Behrens, 1972; Hoy et al.,

2002; Curran et al., 1993; Brink and Marten, 1986), and forage produced during the year
following establishment was nearly weed free (Brink and Marten, 1986; Curran et al.,
1993). Alfalfa densities in the fall of the establishment year were higher for clear seeded
and oat mulch systems compared to oat companion seeded but was not different the year
after establishment (Becker et al., 1998; Hoy et al., 2002; Scheaffer, 1988). Previous
research suggests that alfalfa establishment method choice should reflect the specific
forage needs, weed control and soil erosion potential in the establishment year (Hoy et
al., 2002; Becker et al., 1998; Sheaffer et al., 1988; Curran etal., 1993).

Glyphosate is a broad-spectrum non-residual herbicide that effectively controls
most annual and perennial weed species found in forage production (Gianessi et al.,
2002). Glyphosate-resistant alfalfa is insensitive to glyphosate at all stages of growth,
increasing the application window compared to other herbicides currently available (Van
Deynze et al., 2004). Orloff et al. (2003) found that weed control with glyphosate was
95% or greater on all weeds species in glyphosate-resistant alfalfa at three locations
across California in 2003. They also concluded that a 1.68 kg ac ha’l rate of glyphosate
resulted in more rapid weed kill, but was generally not needed, as the 0.84 kg ae ha"1 was
sufficient. Miller et al. (2002) found that glyphosate did not injure or reduce glyphosate-
resistant alfalfa stands. Weed control was greater with glyphosate than conventional
herbicide standards, and weed control with glyphosate was influenced by application
timing but not rate. Doll (2003) concluded that glyphosate-resistant alfalfa has excellent
glyphosate resistance and allows for complete and flexible weed management
applications for all weeds. Orloff et al. (2003) found that the best time to apply

glyphosate was at the 3 to 4 trifoliate stage. Early applications (unifoliate to 2 trifoliate)

allowed late germination of weeds, requiring a second application prior to the first
harvest. Later applications (6 to 9 trifoliate) allowed greater weed competition at early
alfalfa growth stages.

Glyphosate resistant alfalfa represents a significant new technology for weed
management in Michigan alfalfa production. The objectives of this study were (1) to
determine the effect of weed control with glyphosate on glyphosate resistant alfalfa
establishment, forage production and stand persistence, (2) to determine the effect of
establishment method on glyphosate resistant alfalfa establishment and (3) to study the
interaction between establishment method and weed control system in glyphosate

resistant alfalfa.

MATERIALS AND METHODS

Field experiments were established in the spring of 2004 and 2005 at the
Michigan State University Agronomy Farm in East Lansing on adjacent sites. The soil
type was Capac loam (fine-loamy, mixed mesic, Aerie Ochraqualt). Seedbed preparation
included a glyphosate application at 0.84 kg ae ha'1 followed by a fall moldboard plow in
2003 and a spring moldboard plow in 2005. Each site was field cultivated twice then
leveled with a cultipacker prior to planting. Plots were fertilized as needed based on
annual soil test recommendations from the Michigan State University laboratory1 by
applying P205, K20 and boron using a Gandy 1.52m drop spreaderz.

Experimental design was a split-plot with four replications. Main plot treatments
were seeding methods (companion seeding with oats and clear seeded) and sub plot
treatments were herbicide treatments. Oats were seeded first (east to west) at 38 kg ha'1
using a 3910 John Deere seed drill3. Alfalfa was seeded second (north to south) using a 5
row Carter Nursery seeder4 at a seeding rate of 20 kg ha]. Glyphosate resistant alfalfa
seed from Forage Genetics5 was used. Oats and alfalfa were seeded on April 28, 2004
and April 18, 2005.

A single plot was 2.7 m x 7.6 m, consisting of three 0.9 m passes from the nursery
seeder. The center pass was used to apply the herbicide treatments, collect visual
evaluations, dry matter yield and forage quality analysis. The right (west) pass was used

for destructive plant measurements and included plant densities, alfalfa weight per stem,

 

' Michigan State University Soil Lab, East Lansing, MI 48824.
2 Candy Coroporation, Inc., Owatonna, MN 55060.

3 John Deere Co., Moline, IL 61265.

‘ Carter Manufacturing Co. Inc., Brookston, IN 47923.

5 Forage Genetics, West Salem, WI 54669.

botanical composition and alfalfa maturity. The left (east) pass was not used for data
collection in 2004 or 2005.

Initial herbicide treatments were applied in the establishment year when weeds
reached 5 cm and alfalfa had 3 trifoliates. No herbicide applications were made the year
after establishment. Initial herbicide applications were made on June 9 in 2004 and May
26 in 2005. Herbicide treatments included an untreated, glyphosate (0.84 kg ae ha'l),
imazamox (52.5 g ai ha'l) + crop oil concentrate (1% v/v) in the clear seeded system and
imazamox (52.5 g ai ha'l) + clethodim (140 g ai ha'l) + crop oil concentrate (1% v/v) in
the oat companion seeded system. All treatments in both seeding systems received
ammonium sulfate at 2% w/w (19 kg ha'l). Subsequent glyphosate applications at the
initial rate of 0.84 kg ae ha'1 were applied 7-10 days following each harvest to glyphosate
treatments. Subsequent herbicide applications were made on July 13, August 19 and
October 28 in 2004 and July 7, August 5 and September 5 in 2005. All herbicide
applications were made using a C02 backpack sprayer with TeeJet6 8003 flat fan nozzles,
delivering 187 L ha'1 at 270 kPa. Cyfluthrin and lambda-cyhalothrin were applied at
standard rates, as needed, to control potato leaflropper (Empoascafabae).

Alfalfa injury and weed control were determined by visual evaluations using the
rating scale 0 (no injury) to 100 (completely killed). Alfalfa injury was recorded 7, 14,
21 and 28 days after treatment (DAT) in 2004 and 2005. Predominant broadleaf and
grass weed species were rated 14, 21 and 28 DAT in 2004 and 2005.

Plots were harvested three times (Table 1.1) in the establishment year and four
times (Table 1.1) in the second year. First harvest was taken in 2004 and 2005 when 750

growing degree-days were accumulated (base temperature 5 C). Subsequent harvests

 

‘5 TeeJet Spraying Systems Co., Wheaton, IL 60188.

were taken when alfalfa reached bud to one—tenth bloom stage. However, the third
harvest of the 2004 establishment year study was delayed until after October 15 to ensure
the winter survival of the alfalfa stand. Forage dry matter was determined by harvesting
a 0.9 X 7.6 m strip from each plot. Plots were harvested using a Carter flail harvester7 at
a cutting height of approximately 9.0 cm from the soil surface. The fi'esh weight of a
500 g bulk sample from the harvest area was recorded then dried at 60 C for 72 hours and
reweighed for dry matter determination. An additional 500 g sample was collected from
the yield strip of each plot, dried at 60 C for 72 hours and shipped to Dairy One Forage
Lab8 for forage quality analysis.

Alfalfa and weed dry matter yields were determined by two random subsamples
taken at each harvest. A 0.093 m2 sampling square was randomly placed between two
rows of alfalfa near the north end of the plot and the area was harvested and labeled as
the first subsample; this procedure was then repeated near the south end of the plot and
was labeled as the second subsample. Garden shears were used to cut the two 0.093 m2
subsamples approximately 9.0 cm from the soil surface from each plot. All plant biomass
was harvested from the 0.093 m2 subsamples, hand separated based on species, and then
counted. Separated species samples were then dried at 60 C for 72 hours and dry weights
were recorded. The weight of each species was then used to calculate the percentage of
total weed and alfalfa biomass from each of the plots.

Alfalfa weight per stem was determined by dividing the dry matter weight of the

alfalfa subsample by the number of recorded stems. Alfalfa maturity was determined

 

7 Carter Manufacturing Co. Inc., Brookston, IN 47923.
8 Dairy One Forage Lab, 730 Warren Rd, Ithaca, NY 14850.

10

using the mean stage by count method as described by F ick and Mueller (1989). The first
of the 0.093 m2 hand separated subsamples were used to determine alfalfa maturity.

Stand persistence was determined by plant counts that were taken 7-10 days
following the first and final harvest each year. A round-nosed shovel was used to remove
alfalfa crowns from two randomly selected 0.093 In2 areas in each plot. All taproots
within the sampling area were counted and recorded.

Data were subjected to ANOVA using the PROC MIXED procedures of SAS
8.029 to determine the analysis of variance. Normality of the residuals and homogeneity
of the variances were evaluated. Data were combined over years where significant
interactions did not exist; year was considered to be a fixed factor. Means were separated

using Fischer’s Protected Least Significance Difference at an alpha level of 0.05.

 

9 SAS Institute Inc., 100 SAS campus drive, Cary, NC 27513.

11

RESULTS AND DISCUSSION
Alfalfa Injury

In 2004, alfalfa injury was the highest in the imazamox treatment in the clear
seeded system (Table 1.2). Alfalfa injury was the greatest l4 DAT, with 12.5% injury
observed. Glyphosate injury in the clear seeded system was only visible 14 and 21 DAT
and did not exceed 4%. In the oat companion seeded system there were no differences
between imazamox + clethodim and glyphosate injury. At the first harvest (28 DAT), the
only treatment where injury was still evident was with imazamox in the clear seeded
system, but injury was minimal.

In 2005, the only injury observed was in the imazamox and imazamox +
clethodim treatments, where injury was observed at all evaluation dates in both
establishment systems (Table 1.2). At the first harvest (28 DAT), injury from the
imazamox and imazamox + clethodim was still evident at 8.8% and 9.5%, respectively.

The injury observed from glyphosate in 2004 was likely the result of plant stress
from excessive moisture and cool growing conditions at the time of application (Table
1.3). Glyphosate injury in 2004 did not exceed 6% across any of the evaluation dates or
establishment systems and was no longer evident at the first harvest. Orloff et al. (2003)
also concluded that glyphosate injury on glyphosate resistant alfalfa was zero to slight
with injury symptoms insignificant, short lived and no longer present at the first harvest.
In 2005, growing conditions were more consistent and plants were less stressed, resulting

in no observed glyphosate injury.

12

Weed Control

Weed control at 14 DAT was not significantly different between establishment
methods or herbicide treatments in 2004, with each herbicide providing at least 93%
control of each weed species (Table 1.4). In 2005, glyphosate provided a broader
spectrum of weed control than imazamox and imazmox + clethodim combinations.
Glyphosate controlled redroot pigweed greater than imazamox or imazamox + clethodim.
Pennsylvania smartweed and white cockle control was incomplete, with no significant
differences between imazamox and glyphosate in the clear seeded system, however
glyphosate increased control compared to imazamox + clethodim in the companion
seeded system. Giant foxtail control was similar among herbicide treatments in 2005.

At the first harvest in 2004, giant foxtail control was higher with imazamox than
glyphosate in the clear seeded system (Table 1.5). This is most likely the result of the
residual activity of imazamox resulting in control of later emerging grasses. Taylor-
Lovell et al. (2002) noted that the use of imazamox in legume crops provided residual
weed control afier application. In 2005, there were no differences in giant foxtail control
between herbicide treatments between establishment systems. Redroot pigweed control
was reduced in the absence of the oat companion crop with both imazamox and
glyphosate in 2005. Initial weed suppression provided by the oat companion crop
probably reduced redroot pigweed growth, allowing better control in the oat companion
crop when herbicides were applied compared to the clear seeded system. Pennsylvania
smartweed control was less with imazamox in the clear seeded system compared to the
other herbicide treatments in 2004. In 2005, glyphosate was less effective than imazamox

and imamazox + clethodim for control of Pennsylvania smartweed between establishment

13

systems. White cockle control was higher with glyphosate than imazamox in the clear
seeded system in both 2004 and 2005. Imazamox + clethodim was less effective for
control of white cockle in 2005 compared to glyphosate in the companion seeded system.
Weed Control: Year after Establishment

Weed control in the establishment year affected weed yields in the year after
establishment in the 2004 study. At harvest 1 and harvest 2, weed biomass was
numerically highest in each establishment system where no herbicide was applied in 2004
(Table 1.6). Significantly higher weed yields were observed at harvest 1 in the
companion seeded system where no herbicide or imazamox + clethodim was applied. At
harvest 2 weed yields were highest where no herbicide was applied in the oat companion
seeded system. At harvest 3 and 4 there were no differences in weed yields among weed
control treatments or establishment systems. Seasonal weed biomass was greatest in the
companion seeded system where no herbicide was applied in the establishment year.
Similar results were reported by Moyer (1985) and Moyer et a1. (1995). In contrast,
Lanini et al. (1991) found weed yields in the second year of production was reduced by
the inclusion of an oat companion crop during alfalfa establishment. Production practices
between this study and those of Moyer (1985) and Moyer et al. (1995) in Canada are
similar and reflect dryland alfalfa production systems in the Midwest. The observations
made by Lanini et al. (1991) were under irrigated alfalfa production in California.
Differences in weed, alfalfa and oat companion crop growth under these irrigated

conditions may explain the contrasting results.

14

Yield Components: Establishment Year

Harvest 1
In 2004 and 2005 the highest total forage yield at harvest 1 was in the untreated

companion seeded treatments, due to the contribution fiom the cat companion crop
(Figure 1.1). Similar results were reported by Schmid and Behrens (1972) and Peters
(1961). Herbicide treated plots had the lowest total forage yield. The highest weed yield
was in the untreated, clear seeded system (Table 1.7). Similar results have been reported
by Peters (1961) and Simmons et al. (1995).

In 2004, the highest alfalfa yield was in the glyphosate treatments in the clear
seeded system while in 2005, alfalfa yield was highest in the glyphosate treatment, and
similar between the clear and oat companion establishment systems. In 2005, alfalfa
yield was lower where imazamox was applied in each establishment system, compared to
glyphosate. Alfalfa stunting observed at the first harvest where imazamox and imazamox
+ clethodim was applied in each establishment system probably resulted in lower alfalfa
yields. Competition from oats reduced alfalfa yield in 2004. Competition from weeds
and oats lowered alfalfa yield in the untreated plots in 2005.

Harvest 2

Total forage and alfalfa yield was reduced at harvest 2 from the oat companion
crop in both years (Figure 1.1). Similar results were reported by Lanini et al. (1991).
Alfalfa yield was the greatest wherever a herbicide was applied. No differences in alfalfa
yield or total forage yield were observed where either glyphosate or imazamox was

applied in each establishment system. Weed yields tended to be higher where imazamox

15

had been applied in both establishment systems, but were not significantly higher than
glyphosate (Table 1.7).

In 2004, total forage yield was the greatest in the untreated clear seeded system
due to the weed component. However, in 2005 forage yield was reduced in the untreated
clear seeded system at harvest 2 (Figure 1.1). High weed yields observed at harvest 1 in
2005, probably resulted in alfalfa suppression at harvest 2 (Table 1.7). Conversely, in
2004 highest weed yields were not observed until harvest 2. In 2005, total forage yield
was the greatest wherever a herbicide had been applied. No differences in total forage
yield or alfalfa yield were observed between glyphosate and imazamox in either
establishment system. Alfalfa yield was lower where no herbicide was applied in both
establishment systems each year. Weed yield was the highest in the untreated plots
within each establishment system in both years (Table 1.7). Significantly higher weed
yields were observed in the clear seeding system in both years.

Harvest 3

Total alfalfa yield was reduced at the final harvest in both years in the untreated
companion seeded system from the initial oat competition (Figure 1.2). In 2004, alfalfa
yield was similar among herbicide treatments in the companion seeded system. There
were no differences in alfalfa yield between the untreated and herbicide treatments in the
clear seeded system. Total forage yields were very similar to alfalfa yields since weed
yields at the final harvest were lower than in previous harvests.

In 2005, alfalfa yield was greatest where a herbicide was applied, with no
differences between glyphosate and imazamox observed. Total alfalfa yields were

similar between the untreated plots in both establishment systems. Total weed yield was

16

higher where a herbicide was not applied in the clear seeded system (Table 1.7). There
were no differences in total forage yield among any of the treatments at the final harvest.
Hoy et al. (2002) also found similar forage dry matter yields at the frnal harvest in the
establishment year compared to earlier harvests.

Seasonal

In both 2004 and 2005, alfalfa yields were greatest in the clear seeded glyphosate
treatment (Figure 1.2). Total weed yield was the greatest in the untreated clear seeded
system (Table 1.7). Alfalfa yield was reduced in the untreated oat companion seeded
system due to the competition from oats. Reduced alfalfa yield was anticipated when a
companion crop was used (Peters, 1961; Scheaffer et al., 1988; Lanini et al., 1991).

In 2004, total forage yield was similar where a herbicide was applied. Total
forage yield was the greatest in the untreated oat companion seeded system due to the
contribution of the oats to the total forage yield. Alfalfa yields were the highest where
glyphosate was applied in the clear seeded system. In the oat companion seeded system
no differences in alfalfa yield were observed between imazamox + clethodim and
glyphosate treatments. Total weed yield was the highest in the untreated clear seeded
system (Table 1.7).

Total seasonal forage yield was similar among all treatments in 2005. Hall et al.
(1995) and Becker et al. (1998) also found that differences in alfalfa and weed yields did
not affect total seasonal forage. Alfalfa yield was the greatest where glyphosate was
applied in both establishment systems. Reduced alfalfa yields at harvest 1 where
imazamox and imazamox + clethodim were applied resulted in lower seasonal alfalfa

yields in 2005. Alfalfa yield was reduced where a herbicide was not applied, with the

17

greatest reduction observed where an oat companion crop was used in establishment.
The highest seasonal weed yields occurred where no herbicide was applied but were
greater in the clear seeded system, since the oat companion crop reduced weed yield
when a herbicide was absent (Table 1.7). Previous research from Peters (1961) and
Scheaffer et al. (1988) reported similar results.
Yield Components: Year after Establishment

There were no differences in total forage yield or alfalfa yield at any of the four
harvests in the year after establishment (Appendix 1). These results are similar to
research conducted by Schmid and Behrens (1972), Hoy et al. (2002), Curran et al.
( 1993), and Brink and Marten (1986). This suggests that establishment method or weed
control method in the establishment year does not impact second year total forage or
alfalfa production.
Alfalfa Stem Weight

Alfalfa stem weight was reduced significantly in the companion seeded system at
harvest 1 in 2004, regardless of weed control method (Table 1.8). In 2005, alfalfa stem
weight was reduced where no herbicide was applied in each establishment system. The
greatest reduction was observed in the untreated companion seeded system, due to
competition with oats. Glyphosate increased alfalfa stem weight over imazamox +
clethodim in the companion seeded system, most likely because it controlled the oats
more rapidly than imazamox, thus reducing competition faster. Doll (2003) observed that
an oat companion crop was 18 cm shorter when killed with glyphosate than clethodim at

the first harvest. Doll (2003) commented that alfalfa growth would benefit with

18

glyphosate-resistant alfalfa as interference from an oat companion crop would be
removed faster with glyphosate than conventional herbicides.

At harvest 2 in both 2004 and 2005, alfalfa stern weight was reduced where no
herbicide had been applied in each establishment system (Table 1.8). Greater stem
weights with glyphosate were observed in 2004 in each establishment system. In 2005,
no differences in stem weight were observed between glyphosate and imazamox in the
clear seeded system. In the cat companion seeded system, slightly higher stem weights
were observed where imazamox + clethodim was applied compared to glyphosate. There
were no differences in alfalfa stem weight at harvest 3.

Stand Density

The oat companion crop reduced alfalfa stand density in the spring of the 2004
and 2005 establishment year where no herbicide was applied (Table 1.9).
Simmons et al. (1995), Lanini et a1. (1991), and Hoy et al. (2002) all observed negative
effects of oat companion crops on alfalfa stand density in the establishment year. Highest
alfalfa stand densities in the spring were observed in the cat companion seeded system
where imazamox + clethodim were applied in both years. There were no differences in
alfalfa stand density in the fall of the establishment year. Weed control system or
establishment method in the establishment year did not impact alfalfa stand density in the
year after establishment in the 2004 study (Table 1.9). Similar results have been reported
by Becker et al. (1998), Hoy et al. (2002), and Scheaffer, (1988).
Summary

Glyphosate injury to glyphosate-resistant alfalfa was minimal, indicating

excellent crop tolerance with this new technology. Alfalfa injury has been a concern in

19

the past with conventional alfalfa herbicide programs. Imazamox injury observed in
these studies reconfirms the potential grth reduction with conventional herbicides,
especially when injury was still visible at the first harvest. Weed control with glyphosate
was more complete across growing conditions and weed species compared to imazamox
and imazamox + clethodim treatments in both establishment systems.

Glyphosate-resistant alfalfa established by clear seeding methods yielded the
highest alfalfa dry matter in the establishment year in both studies. This suggests that
establishing glyphosate-resistant alfalfa under a clear seeded system may maximize
alfalfa production with glyphosate-resistant alfalfa. Increased crop safety at the first
harvest with glyphosate contributed to higher alfalfa yields compared to imazamox at the
first harvest in the clear seeded system in 2004 and both establishment systems in 2005.
Although no differences between glyphosate and imazamox were observed within
establishment systems at the second and third harvests, seasonal alfalfa yields were
reflective of the first harvest. This suggests that seasonal alfalfa yields are impacted by
weed control systems and specific herbicides at the first harvest, which is a critical
seasonal alfalfa production factor. Glyphosate maximized alfalfa production at the first
harvest, by providing compete weed control and increased crop safety compared to
imazamox.

Higher total forage yields observed in an untreated oat companion crop in 2004
indicates that when environmental conditions are less then favorable for establishing
alfalfa, forage yield may be increased with a companion crop. However, this type of
system may not coincide with production goals of certain producers who require pure

alfalfa at the first harvest. Furthermore, seasonal alfalfa yields were reduced where

20

alfalfa was established with a companion in crop both years. Alfalfa yield was increased
in a clear seeded system when no herbicides were applied compared to an oat companion
seeded system. However, alfalfa established with an oat companion crop tended to
reduce weed yields in comparison to the clear seeded system. The effective broad
spectrum weed control observed with glyphosate indicates that a companion crop is
probably not necessary in suppressing weeds with glyphosate-resistant alfalfa. The
addition of an oat companion crop may be beneficial with glyphosate-resistant alfalfa if
high soil erosion potential exists, but those conditions were not studied in this research.
These results indicate that choice of establishment method should consider forage needs
not only at the first harvest but total forage production during the establishment year.

The reduction of weed biomass in the second year of production between
establishment systems indicates a benefit beyond the establishment year for herbicide
use. However, no significant differences in total forage yield, alfalfa yield or alfalfa
stand density were observed in the second production year. Thus establishment method
and weed control method should reflect growers forage needs during the establishment
year. Further research is needed to evaluate the long-term impacts of glyphosate-resistant

alfalfa establishment with glyphosate.

21

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Barnes, R.F., D.A. Miller, and OJ. Nelson. 1995. Forages: An introduction to grassland
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Becker, R.L., C.C. Sheaffer, D.W. Miller, and DR. Swanson. 1998. Forage quality and
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Brink, GE, and GO Marten. 1986. Barley vs. oat companion crops: 11. Influence on
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Canevari, W.M., S.B. Orloff, R.N., Vargas, and K]. Hembree. 2003. Raptor, a new
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Chapko, L.B., M.A. Brinkman, and K.A. Albrecht. 1991. Oat, oat-pea, barley, and
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4:486-491.

Curran, B.S., K.D. Kephart, and E.K. Twidwell. 1993. Oat companion crop
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Doll, J .D. 1984. Effects of common dandelion on alfalfa drying time and yield. Proc.
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22

Hall, M.H., W.S. Curran, E.L. Werner, and LE. Marshall. 1995. Evaluation of weed
control practices during spring and summer alfalfa establishment. J. Prod. Agric. 8:360-
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Hoy, M.D., K.J. Moore, R.J. George, and EC. Brummer. 2002. Alfalfa yield and quality
as influenced by establishment method. Agron. J. 94:65-71.

Johnson, D.H., P. Ogg, D. Colbert, G. Goddard, and M. Britva. 2001. Imazamox plus
tank mix partners for weed control in alfalfa. Proc. North Cent. Weed Sci. Soc.56:172.

Kust, C. 1968. Herbicides or oat companion crops for alfalfa establishment and forage
yields. Agron. J. 52:627-630.

Lanini, W.T., S.B. Orloff, R.N. Vargas, J .P. Orr, V.L. Marble, and R.G. Stephen. 1991.
Oat companion crop seeding rate effect on alfalfa establishment, yield, and weed control.
Agron. J. 83:330-333.

Marten, GO, and RN. Andersen. 1975. Forage nutritive value and palatability of 12
common annual weeds. Crop Sci. 15:821-827.

McCaslin, M., S. Fitzpatrick, and S. Temple. 2000. Roundy Ready Alfalfa: progress
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McCaslin, M. 2002. An update on the development of Roundup Ready Alfalfa. Proc.
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Miller, SD, and CM. Alford. 2002. Weed control and glyphosate tolerant alfalfa
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Moyer, J .R. 1985. Effect of weed control and a companion crop on alfalfa and sainfoin
establishment, yields and nutrient composition. Can. J. Plant Sci. 65:107-116.

Moyer, J.R., D.E. Cole, D.C. Maurice, and AL. Darweny. 1995. Companion crop,
herbicide and weed effects on establishment and yields of alfalfa-bromegrass mixture.
Can. J. Plant Sci. 75:121-127.

Orloff, S.B., R.N. Vargas, W.M. Canevari, and K.J. Hembree. 2003. The fit for roundup
ready alfalfa: initial field results in California. Proc. CA Weed Sci. Soc. 55:112-116.

Peters, RA. 1961. Legume establishment as related to the presence or absence of an oat
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23

Simmons, S.R., C.C. Sheaffer, D.C. Rasmusson, D.D. Stuthman, and SE. Nickel. 1995.
Alfalfa establishment with barley and oat companion crops differing in stature. Agron. J.
87:268-272.

Simmons, S.R., N.P. Martin, C.C. Sheaffer, D.D. Stuthman, E.L. Schiefelbein, and T.
Haugen. 1992. Companion crop forage establishment: producer practices and
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Schmid, A.R., and R. Behrens. 1972. Herbicides vs oat companion crops for alfalfa
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Sheaffer, C.C., D.K. Barnes, and GO Marten. 1988. Companion crop vs. solo seeding:
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Sprague, C.L. J .J . Kells and, K. Schinnacher. 2005. Weed control guide for field crops.
Extension Bull. E-434. East Lansing, MI: Cooperative Extension Service, Michigan State
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Stute, J .K., and J .L. Posner. 1993. Legume cover crop options for grain rotations in
Wisconsin. Agron. J. 85:1128-1132.

Taylor-Lovell, S., L.M. Wax, and G. Bollero. 2002. Preemergence flumioxazin and
pendimethalin and postemergence herbicide systems for soybean. Weed Technol. 16:502-
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Van Deynze, A., D.H. Putnam, S. Orloff, T. Lanini, M. Canevari, K. Hembree, S.
Mueller, and L. Teuber. 2004. Roundup ready alfalfa: an emerging technology.
Extension Bull. 8153. Oakland, CA: University of California, Agriculture and Natural
Resources, Communication Services. p.1-12.

Wait, J. and Johnson, W.G. 2002. Curly dock control in alfalfa. Proc. North Cent. Weed
Sci. Soc. 59:23.

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Weed Sci. 29:615-618.

24

Table 1.1 Harvest dates for glyphosate-resistant alfalfa in 2004 and 2005.

 

 

 

 

2004 Establishment 2005 Establishment
Year 2004 2005 2005
Harvest
One July 6 May 31 June 30
Two August 12 June 30 July 28
Three October 21 July 28 August 31
Four August 31

 

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35

CHAPTER 2

F ORAGE QUALITY AND ECONOMICS OF GLYPHOSATE-RESISTANT
ALF ALF A AS INFLUENCED BY ESTABLISHMENT SYSTEMS.

Abstract: Field studies were conducted in 2004 and 2005 to determine the effect of
establishment method and weed control method on forage quality and the economics of
using glyphosate—resistant alfalfa in the establishment year. Seeding methods included
clear seeding and companion seeding with oats. Herbicide treatments included
glyphosate, imazamox or imazamox + clethodim, and no herbicide. The greatest
differences in forage quality were observed at the first harvest in both establishment
years. In 2004, forage quality at the first harvest was reduced where an oat companion
crop was used in establishment, regardless of weed control method. Forage quality was
similar between imazamox and glyphosate at the first harvest in both establishment
systems. In 2005, forage quality was lower where no herbicide was applied in both
establishment systems. Forage quality was lower where an oat companion crop was used
in establishment compared to clear seeded alfalfa when herbicides were not applied.
Glyphosate used for weed control resulted in more mature and higher yielding alfalfa at
the first harvest, compared to imazamox in both establishment systems in 2005. At the
final harvest of the establishment year, forage quality was similar where a herbicide had
been applied. The use of herbicides to establish alfalfa resulted in forage of the highest
quality and value at the first harvest, however gross margins were not increased after
production costs were considered. Gross margins were similar within establishment
systems where either glyphosate or imazamox was applied. There were no differences in

forage quality observed the year afier establishment.

36

INTRODUCTION

Alfalfa (Medicago sativa L.) the most recent crop to have glyphosate-resistant
technology commercialized, now offers new weed control options for alfalfa
establishment. Development of glyphosate-resistant alfalfa was similar to other
glyphosate resistant crops by incorporating the genetic resistance to glyphosate into the
alfalfa plants through a single bacterial gene (CP4) insertion that modifies 5-
enolpyruvylshikimate-3-phosphate synthase (ESPS) (Van Deynze et al., 2004).
Preliminary research comparing glyphosate-resistant alfalfa technology to conventional
alfalfa weed control programs has indicated forage quality can be enhanced with this new
alfalfa technology (McCaslin et al., 2002).

Alfalfa quality is a major concern for livestock producers but quantifying quality
is often a difficult task as forage quality encompasses many factors. Temme et al. (1979)
expressed the goal of good forage quality in terms of animal consumption, nutritional
value, digestibility and finally animal grth or milk production. Near infrared
spectroscopy (NIRS) has become a common choice of lab testing procedures to
determine forage quality rapidly and inexpensively (Coors et al., 1986). Producers are
then able to select forages based on quality estimates.

The most important forage quality indicators traditionally have been crude protein
(CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF) (Barnes et al., 1995).
In general higher CP values and lower NDF and ADF indicate good forage quality (Hall
et al., 2000). CP is composed of true proteins and non-protein nitrogen and is measured
by determining the nitrogen content and multiplying by 6.25 (Barnes et al., 1995). NDF

and ADF are used to estimate the digestibility of a forage. NDF represents the total fiber

37

content, including cellulose, hemicellulose, lignin and cutin, and is closely related to feed
intake (Robinson, 1999). ADF is NDF without the hemicellulose and represents the
indigestible fraction of forages (Robinson, 1999).

Forage quality indicators are ofien combined in equations to make direct forage
quality comparisons easier. Relative feed value (RFV) is extensively used in the
Midwest to separate forages based on quality. RFV uses NDF to calculate dry matter
intake (DMI) and ADF is used to estimate digestible dry matter (DDM) of the forage.
DMI and DDM are then used to calculate RFV. RFV is used to separate forages based on
energy content and potential animal utilization (Kuehn et al., 1999). However, a
challenge to producers has been to maximize forage quality and yield, which are
inversely related (Sanderson, 1992). A model (MILK 2000) was developed to combine
forage yield and quality into a single term, using the concept of milk produced per
hectare of forage. The model allows for changes in yield, forage quality, and production
costs, thus quantifying the value of high forage quality (Undersander et al., 1993).

Establishment systems, weed control methods, and harvest timings are the most
influential management factors that affect forage quality (Hoy et al. 2002). Weeds can
alter the composition of the forage, increase drying time (Doll, 1984), and reduce
palatability (Canevari, 2003). Frequently, weeds are similar in chemical composition and
quality with alfalfa (Doll, 1986); however, as weeds mature their nutritive quality rapidly
declines, ofien not coinciding with alfalfa harvests (Canevari, 2003). Temme et a1.
(1979), found that lower quality weeds were primarily responsible for decreasing the

quality of alfalfa, since they are nutritionally inferior to alfalfa.

38

Forage establishment management is critical in achieving high quality and
productive alfalfa stands (Curran et al., 1993). It is recommended that companion crops
should be harvested between the late boot and early heading to provide good quality
forage (Chapko et al., 1991). Brink and Marten (1986) found that the value of forage
declines rapidly as oats mature past the five-leaf stage. A survey of producers indicated
that harvesting oat companion crops for maximum forage quality was the most difficult
task in alfalfa companion establishment management (Simmons et al., 1993).

Success in chemical control of weeds in alfalfa has increased the practice of clear
seeding alfalfa establishment. Becker et al. (1998) concluded that the highest quality and
value alfalfa was established under a clear seeded system with a herbicide application
prior to the first harvest, and the lowest forage quality was established with an oat
companion or a clear seeded system and no herbicide application. Forage quality did not
change in a clear seeded establishment system in the presence or absence of herbicide
treatments (Sheaffer et al., 1988; Marten and Andersen, 1975; and Zaman et. a1, 2002).

Hoy et al. (2002) found that alfalfa seeded with an oat companion crop, or clear
seeded without herbicide treatments, produced the lowest forage quality when compared
to clear seeded and oat mulch establishment systems that included a herbicide treatment.
Becker et al. (1998) concluded that oat and weed regrowth at the second harvest in
untreated oat companion and clear seeded systems lowered the forage quality compared
to treatments that included a herbicide treatment.

Alfalfa maturity is influential on the quality of forage harvested (Hall et al. 2000),
as there is an inverse relationship of advancing alfalfa maturity and the decline of forage

quality (Hintz and Albrecht, 1991 and Sulc et al., 1997). Decreases in stem quality as

39

alfalfa matures have been largely associated with the reduction in forage quality
(Albrecht et al., 1987). Temperature has also been indicated as a factor in decreasing
forage quality as alfalfa maturity advances (Griffin et al., 1994). Kalu and Pick (1983)
developed a classification system for evaluating the morphological stage of alfalfa
development, commonly referred to as mean stage by count. In this classification, alfalfa
is divided into categories based on maturity, and forage quality estimates are then made
from the number of stems recorded at each maturity stage.

Economical benefits of herbicide applications in alfalfa establishment have been
questioned in the past. Smith et a1. (1997) and Zaman et al. (2003) concluded that
herbicide applications during forage establishment did not affect forage yield and quality
enough to increase profits over costs associated with herbicide application. Hall et al.
(1995) recommended that no herbicides or oat companion crop should be used when
establishing alfalfa, as the costs associated were not justified. Brothers et al. (1994)
concluded that establishment without herbicides is economical in a clear seeded system
when weed pressure is low. Becker et al. (1998) and Sheaffer et al. (1988) observed an
increase in forage quality where herbicides were applied in establishing alfalfa, however
they concluded the increase in net return with high forage quality was not greater then
higher forage yield that included weeds. In contrast, Canevari et al. (2003) concluded
that under California alfalfa production conditions managing weeds using herbicides is
cost effective, extending the life of the stand and providing high quality forage.

Glyphosate-resistant alfalfa represents a significant new technology for weed
management in Michigan alfalfa production. Evaluating glyphosate-resistant alfalfa

quality and gross margins in the establishment year needs to be understood, to fully

40

integrate this new technology. The objectives of this study were (1) to determine the
effect of weed control with glyphosate on glyphosate-resistant alfalfa forage quality and

(2) to determine economics of using glyphosate-resistant alfalfa in the establishment year.

41

MATERIALS AND METHODS

Experiments were conducted at the Michigan State University Agronomy Farm
on adjacent sites in 2004 and 2005. The soil type was Capac loam (fine-loamy, mixed
mesic, Aerie Ochraqualf). Fields received a glyphosate application at 0.84 kg ae ha‘1
followed by a fall moldboard plow in 2003 and a spring moldboard plow in 2005. Prior
to planting each site was field cultivated twice and leveled using a cultipacker. Cats and
alfalfa were seeded on April 28, 2004 and April 18, 2005. A 3910 John Deere seed drilll
was used to seed oats (east to west) at 38 kg ha’I and a 5 row carter nursery seeder2 was
used to seed alfalfa (north to south) at a seeding rate of 20 kg ha". Glyphosate resistant
alfalfa seed from Forage Genetics3 was used. Fertilizer was applied as needed based on
annual soil test recommendations from the Michigan State University laboratory4 by
applying P205, K20 and boron, using a Gandy 1.52m drop Spreaders.

Herbicide applications were made in the establishment year when alfalfa had 3
trifoliates and weeds reached 5 cm. No herbicide applications were made the year afier
establishment. Initial herbicide applications were made on June 9 in 2004 and May 26 in
2005. Herbicide treatments included an untreated, glyphosate (0.84 kg ae ha"),
imazamox (52.5 g ai ha'l) + crop oil concentrate (1% v/v) in the clear seeded system and
imazamox (52.5 g ai ha") + clethodim (140 g ai ha'l) + crop oil concentrate (1% v/v) in
the oat companion seeded system. All treatments in both seeding systems received

ammonium sulfate at 2% w/w. Following each harvest (7-10 days) a subsequent

 

' John Deere Co., Moline, IL 61265.

2 Carter Manufacturing Co. Inc., Brookston, IN 47923.

3 Forage Genetics, West Salem, WI 54669

4 Michigan State University Soil Lab, East Lansing, MI 48824.
5 Gandy Coroporation, Inc., Owatonna, MN 55060.

42

glyphosate application at the initial rate of 0.84 kg ae ha'l was applied to glyphosate
treatments. Subsequent herbicide applications were made on July 13, August 19 and
October 28 in 2004 and July 7, August 5 and September 5 in 2005. All herbicides were
applied using a C02 backpack sprayer calibrated to deliver 187 L ha’l at 270 kPa using
TeeJet6 8003 flat fan nozzles. Cyfluthrin and lambda-cyhalothrin were applied as
needed, to control potato leafliopper (Empoascafabae).

Experimental design was a split-plot with four replications. Main plot treatments
were seeding methods (companion seeding with oats and clear seeded) and sub plot
treatments were herbicide treatments. A plot consisted of three 0.9 m passes from the
nursery seeder and was 2.7 m x 7.6 m. Plots were harvested three times (Table 1.1) in the
establishment year and four times (Table 1.1) in the second year. In 2004 and 2005 the
first harvest was taken when 750 growing degree-days had been accumulated (base
temperature 5 C). Subsequent harvests were taken when alfalfa reached bud to one-tenth
bloom stage. In the 2004 establishment year study the third harvest was delayed until
after October 15 to ensure the winter survival of the alfalfa stand.

Forage dry matter was determined by harvesting a 0.9 X 7.6 m strip from each
plot using a Carter flail harvester7 at a cutting height of approximately 9.0 cm from the
soil surface. The weight of a fresh 500g bulk sample was recorded, dried at 60 C for 72
hours and reweighed to determine dry matter. An additional 500 g sample was collected
from the yield strip of each plot, dried at 60 C for 72 hours and shipped to Dairy One

Forage Lab8 for forage quality analysis.

 

6 TeeJet Spraying Systems Co., Wheaton, IL 60188
7 Carter Manufacturing Co. Inc., Brookston, IN 47923
8 Dairy One Forage Lab, 730 Warren Rd, Ithaca, NY 14850.

43

Forage Quality Analysis

Forage quality was determined by Dairy One Forage Lab, using near infrared
reflectance spectroscopy. Crude protein (CP) was determined by measuring N content
using Kjeldahl techniques (1981) and then multiplying N percentages by 6.25. Neutral
detergent fiber (NDF) and acid detergent fiber (ADF) were determined using the
ANKOM A200 filter bag technique according to procedures by Van Soest et al. (1991).
In vitro neutral detergent fiber digestibity (NDFD) was determined according to Chemey
et al. (1997), using the Daisy II ZOO/22° in vitro incubator and the ANKOM ZOO/220 fiber
analyzer. Ash content was determined by combustion at 500 C for 4 hours.
Milk Yield

Potential milk yields were estimated from the spreadsheet Milk 2000, developed
by Undersander et al. (1993) and modified by Schwab and Shaver (2001). Milk per Mg
of forage, a forage quality index, was calculated from NDF, NDFD, ADF, CP, and ash
concentrations. Milk yield per hectare was calculated as milk per Mg of alfalfa forage x
dry matter yield.
Economic Analysis

Economic comparisons among weed control methods and establishment systems
were conducted to determine the gross margin above the technology fees and weed
control costs. The value of glyphosate-resistant alfalfa was assumed to be $71 Mg based
on the 2005 average Wisconsin hay market prices and were adjusted based on relative
feed value (RFV). Herbicide costs averaged over three pesticide distributors were used;
glyphosate, imazamox and clethodim at typical application rates were assumed to cost

$20.05, $37.18 and $21.52 ha'l, respectively. Herbicide application costs were assumed

44

to be $15 ha'l, based on the average of several Michigan custom applicators. Oats were
assumed to cost $20 ha"l based on the 38 kg ha'1 seeding rate. A $112.50 ha'ltechnology
fee based on the alfalfa seeding rate of 20 kg ha”1 was added to the cost of glyphosate-
resistant alfalfa programs. This technology fee is based on the 2005 technology fee that
is added to the commercial seed cost in Michigan. The following equation was used to
quantify the gross margin of glyphosate-resistant alfalfa:
Gross Revenue = (dry matter yield)(market price based on RFV)
Gross Margin = Gross Revenue — (weed control costs + seeding costs)
Statistical Analysis

Data were subjected to ANOVA using the PROC MIXED procedures of SAS
8.029 to determine the analysis of variance. Normality of the residuals and homogeneity
of the variances were evaluated. Data were combined over years where significant
interactions did not exist; year was considered to be a fixed factor. Means were separated

using Fischer’s Protected Least Significance Difference at an alpha level of 0.05.

 

9 SAS Institute Inc., 100 SAS campus drive, Cary, NC 27513.

45

RESULTS AND DISCUSSION
Forage Quality
Harvest 1

Alfalfa maturity was often delayed where an oat companion crop was used in
establishment (Table 2.1). Curran et a1. (1993) also observed competition between an oat
companion crop and alfalfa suppressed alfalfa maturity at the first harvest. Alfalfa was
the most advanced physiologically where glyphosate was applied in the clear seeded
system.

In 2005, alfalfa maturity was delayed where no herbicide was applied in both
establishment systems (Table 2.1). The high weed pressure in the clear seeded system in
2005 likely suppressed alfalfa and delayed maturity at the first harvest more in 2005 than
2004. Alfalfa maturity was delayed the most where an oat companion crop was not
controlled. Imazamox injury delayed alfalfa maturity compared with glyphosate in both
establishment systems in 2005. A glyphosate application in both establishment systems
reduced weed and oat competition allowing alfalfa to mature more rapidly at the first
harvest.

Crude protein (CP) was lower with an oat companion crop, and was the lowest
where the oat companion crop was not controlled in both years (Table 2.1). Oats have
been noted to lower forage quality (Becker et al., 1998; Hoy et al., 2002; Zaman et al.,
2002 and Temme et al., 1979). CP was also reduced in the clear seeded system where a
herbicide was not applied but to a lesser extent than the uncontrolled oat companion crop.
Similar results were reported by Zaman et a1. (2002), Hoy et a1. (2002), and Temme et a1.

(1979). There was no difference in CF in 2004 where imazamox or glyphosate was

46

applied in either establishment system. The highest relative feed values (RFV) were
observed where a herbicide was applied in the clear seeded system. Oats reduced RFV in
the companion seeded system regardless of weed control methods.

In 2005, CP was significantly lower where glyphosate was applied compared to
imazamox in both establishment systems (Table 2.1). Glyphosate treated alfalfa was
more mature than imazamox at the first harvest. Imazamox injury delayed alfalfa
maturity, thus increasing forage quality at the first harvest. The highest forage quality as
measured by RFV, was where imazamox and imazmox + clethodim had been applied.
Alfalfa harvest management would be different under commercial production, as the
glyphosate treatments would have been harvested at an earlier maturity and imazamox
treatments would have been delayed, to maximize forage quality and yield.

Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were higher where
an oat companion crop was used in 2004 (Table 2.1). Similar results have been observed
by Zaman et al. (2002), Temme et a1. (1979), and Hoy et al. (2002). Weeds increased
NDF and ADF in the clear seeded system. There were no differences in NDF or ADF
where a herbicide was applied in either establishment system. NDF was the highest in
2005 where oats were not controlled with a herbicide. The delayed maturity from
imazamox and imazamox + clethodim in both establishment systems, resulted in a lower
NDF and ADF and ultimately a higher forage quality compared to glyphosate treated
alfalfa which was more physiologically advanced.

Milk production per Mg of forage was the lowest where an oat companion crop
was used in establishment, regardless of weed control method in 2004 (Table 2.2). In the

clear seeded system Milk per Mg of forage was slightly lower than where herbicides had

47

been applied, but not significantly lower. Previous research has shown that alfalfa
established under a clear seeded system, where no herbicide was applied, had higher
forage quality than companion seeded alfalfa, regardless of weed control method (Brink
and Marten, 1986; Sheaffer et al., 1988 and Temme et al., 1979). In 2005, milk
production per Mg of forage was reduced where a herbicide was not applied in either
establishment system. Milk per Mg of forage was higher where imazamox and imazmox
+ clethodim had been applied in both establishment systems in 2005. This is a reflection
of the alfalfa maturity being lower where imazamox was applied, thus increasing forage
quality, as previously discussed with RFV. Alfalfa maturity has been noted in previous
research as being one of the most influential factors on forage quality (Hall et al., 2000).
In the companion seeding establishment system milk per hectare was the highest
where a herbicide was not applied in both years (Table 2.2). In 2004, milk per hectare
was not significantly different where glyphosate or imazamox was applied in either
establishment system. Milk per hectare was the lowest where imazamox and imazamox
+ clethodim had been applied in both establishment systems in 2005. Lower dry matter
yields fi'om imzamox injury accounted for the lower milk production per hectare.
The milk per hectare calculation was developed to encompass both forage quality
and forage dry matter yield to reflect the overall nutritive and production value of a
forage. However, it appears that the Milk per hectare is very sensitive to yield and may
not sufficiently account for the quality of the forage. All forage quality indicators (CP,
NDF, ADF and RFV) show a much lower forage quality of the oat companion crop, but

the milk production per hectare is significantly higher because of the high oat yield.

48

Therefore, we must consider all forage quality indicators and not rely solely on milk
models to predict forage quality and yield.
Harvest 2

Alfalfa maturity was suppressed at harvest two from the uncontrolled oat
companion crop during establishment in 2004 (Table 2.3). In the clear seeded system,
alfalfa maturity was delayed where a herbicide was not applied and was the most
advanced where glyphosate had been applied. In 2005, alfalfa maturity was suppressed
where a herbicide was not applied in both establishment systems. Similar observations
were made by Curran et a1. (1993). Hoy et a1. (2002) reported that alfalfa maturity was
delayed at one of two locations at the second harvest where an oat companion crop was
used to establish alfalfa and herbicides were not applied. There was no difference in
alfalfa maturity where imazamox or glyphosate had been applied in either establishment
system.

In the companion seeded system CP was the highest where glyphosate was
applied in 2004 (Table 2.3). There were no differences in CF among weed control
methods in the clear seeded system. ADF, NDF and RFV (Table 2.3) were not
significantly different among weed control methods or between establishment systems at
harvest 2 in 2004.

CP was increased and NDF and ADF were reduced in the oat companion
establishment system where a herbicide was not applied in 2005 (Table 2.3). Hoy et al.
(2002) reported similar results for alfalfa harvested after an oat companion crop had been
used for establishment. Alfalfa maturity was lower at harvest 2 because of the

competition from the oat companion crop during establishment, thus increasing forage

49

quality at harvest two. CP and NDF were similar among all other weed control methods
and establishment systems. ADF was reduced slightly at harvest two where herbicides
were not applied in the clear seeded system. This is mostly likely from the weed
suppression during establishment delaying alfalfa maturity at harvest two. RFV was
increased in the oat companion establishment system where a herbicide was not applied
due to the delayed alfalfa maturity (Table 2.3). In contrast, Becker et al. ( 1998) found
forage quality was lowered at the second harvest where herbicides were not applied prior
to the first harvest. Becker et al. (1998) indicated that an oat companion crop and giant
foxtail was not adequately controlled by forage harvest at the first harvest, resulting in
lower quality at harvest 2. In 2005, there was very little oat and weed re-growth observed
at harvest 2, as the highest weed yields were seen at the first harvest, and much lower
weed yields were observed at the second harvest (Table 1.7). This difference in weed
and oat-regrth probably explains the contrasting forage quality results. There were no
significant differences in RFV among any of the herbicide treatments at harvest two,
regardless of establishment method. Hoy et al. (2002) observed no differences in forage
quality at the second harvest where a herbicide was applied during establishment.

There were no differences in milk per Mg of forage at harvest two in 2004 (Table
2.4). Milk per Mg of forage was increased where a herbicide was not applied in the oat
companion seeded system in 2005 and was similar between herbicide treatments within
establishment systems. Uncontrolled oats reduced milk per hectare at harvest two in
2004 (Table 2.4). Higher weed yields at harvest two in 2004 increased milk per hectare
production where no herbicide was applied in the clear seeded system (Table 1.7). There

were no differences in milk per hectare where a herbicide was applied within

50

establishment systems in both years. Milk per hectare was reduced where no herbicide
was applied in both clear seeded and oat companion crop establishment systems in 2005.
This is a result of the lower dry matter yields at harvest two, from oat and weed
suppression observed at harvest one.

Harvest 3

There were no differences in alfalfa maturity at harvest 3 in 2004 and 2005 (Table
2.5). In 2004, forage quality was increased where a herbicide was not applied in the clear
seeded and companion seeded establishment systems. The CP was higher, ADF and
NDF were lower and RFV were higher compared to where herbicides had been applied.
In 2005, there were no differences in CP, NDF, ADF or RFV at the final harvest.

Milk per Mg of forage was increased as a result of the higher protein and lower
fiber where no herbicide had been applied in the oat companion and clear seeded systems
in 2004 (Table 2.6). Milk per hectare was reduced at the final harvest in 2004 were no
herbicide was applied in the oat companion seeded system. The lower milk per hectare is
a reflection of the low dry matter yield, which was still reduced from the oat companion
crop during establishment. There were no differences in milk per Mg of forage or milk
per hectare in 2005.

Seasonal Milk Yields

Milk per hectare was increased where a herbicide was not applied in both
establishment systems in 2004 (Table 2.7). Milk per hectare was the highest in the oat
companion seeded system, as the uncontrolled oats in the first harvest contributed to total
forage yield. There were no differences in milk per hectare between herbicides or

establishment methods in 2004. In 2005, there were no differences in milk per hectare

51

among weed control methods or between establishment systems, as there were no
differences in seasonal dry matter forage yield between any of the treatments.
Forage Quality: Year after Establishment

There were no differences in CP, NDF, ADF, RFV, milk per Mg of forage or milk
per hectare in the year after establishment in alfalfa established in 2004 (Appendix 11).
Similar results have been reported by Hoy et a1. (2002), Curran et al. (1993) and Brink
and Marten (1986). Thus forage establishment choice and weed control methods should
reflect the forage quality needs in the establishment year.
Economic Analysis

Gross revenue trends were similar to total forage yield results in both 2004 and
2005 (Tables 2.8, 2.7). In 2004, the highest gross revenues occurred where no herbicides
were applied in both establishment systems. Gross revenue was the highest in the oat
companion seeded system where no herbicide was applied. Although the oats reduced
forage quality at the first harvest, yields were much greater thus increasing gross revenue.
In 2005, there were no differences in gross revenue between establishment methods or
among weed control methods, which is similar to the observed seasonal forage yields.

Gross margins were calculated based on several variable establishment costs and
assumptions. Assuming the entire technology fee would be allocated in the establishment
year in 2004, the highest gross margins were observed where no herbicides were applied
in each establishment system (Table 2.8). Gross margins were higher in the clear seeded
system when herbicides were applied, as the additional seed and weed control costs
associated with the companion seeded system resulted in lower gross margins. In 2005,

there were no significant differences in gross margins between establishment systems or

52

among weed control methods. However, these gross margins calculations were made
under several assumptions that should be taken into consideration when drawing
conclusions from this research. First, it was assumed that a value would be placed on the
oat forage at the first harvest, and the value would be lowered according to RFV. This
assumption would not be valid if alfalfa hay was targeted at a specialty market and
increased premiums for weed free alfalfa hay were received. In this case both forages
produced where no herbicides were applied would not be highly marketable, especially at
the first harvest when weed and oat biomass was the highest. Second, gross margins
were calculated assuming that the livestock fed the forage would consume the entire
forage. It is possible that livestock may eat around the lower quality weeds and oats, thus
changing the actual economic value of weed and oat free hay that received herbicide
applications.

Allocating glyphosate-resistant technology fees to the life of four year alfalfa
stand was also considered and gross margins were calculated accordingly (Table 2.9).
Trends in gross margins remained the same as the previous calculations when technology
fees were based on the establishment year. An increase in gross margins in the
glyphosate treatments were observed under these assumptions. Gross margins where
glyphoste was applied was similar to imazamox or imazamox + clethodim in 2004. No
differences were seen between the establishment systems and among weed control
methods in 2005. However, under this scenario it is assumed that glyphosate-resistant
alfalfa technology would have equal value in each year of the stand, which has not been

confirmed.

53

Further assumptions including generic glyphosate (Appendix II, Table A2.6) or
generic glyphsoate + allocating technology fee over the life of the alfalfa stand
(Appendix II, Table A2.8) did not change the gross margins significantly from what was
discussed previously in either year. In each scenario, costs are lowered but not enough to
increase gross margins over establishments systems where no herbicides were applied.

Previous research has indicated that using herbicides produces superior alfalfa
quality in the establishment year (Temme et al., 1979), but costs associated my not be
justified. Smith et al. (1997) and Zaman et al. (2002) concluded that herbicide
applications during forage establishment did not affect forage yield and quality enough to
provide economic benefit. Hall et al. (1995) recommended that cat companion crops and
herbicides not be used in establishing alfalfa, as the dry matter yield and net economic
return do not justify the cost. Further research conducted by Brothers et al. (1994)
suggested that alfalfa establishment in a clear seeded system can be successful without
herbicide applications if weed pressure is low. The observations from this study indicate
that the same conclusions can be made with glyphosate-resistant alfalfa technology that
were made with conventional alfalfa varieties. However, studying the long term impacts
of this technology in the establishment year over the life of an alfalfa stand should be
considered in any conclusions regarding the value of this technology.

Summary

Impacts of establishment systems and weed control methods on forage quality
appear to be the greatest at the first harvest, as distinct differences were observed in both
years. Forage quality was reduced at the first harvest when an oat companion crop did

not receive a herbicide application. Even when herbicides were applied in 2004, an oat

54

companion establishment system still reduced forage quality over that of the clear seeded
system. High weed yields at the first harvest in 2005 also reduced forage quality.
Reductions in forage quality from an oat companion crop appear to be higher than a clear
seeded establishment system when herbicides were not applied. Establishment with oats
discounted forage quality significantly, and thus must be considered when choosing
establishment systems.

Alfalfa maturity was reduced when competition was high or herbicide injury
existed. The effects of alfalfa maturity on forage quality appear to substantially influence
forage quality. At the final harvest, forage quality was similar where herbicides had been
applied, indicating that there were no differences between glyphosate and imazamox.
Although herbicides tended to increase forage quality and value at the first harvest, gross
margins were not equally increased by the use of herbicides in either establishment
system. However, forage quality should not be compared independently of forage yield,
as the goal of forage production is to maximize both. Clear seeded systems offer higher
forage quality at the first harvest but forage yield may be sacrificed when alfalfa
establishment is less then ideal. Economics revealed that herbicides may not increase
gross margins under the assumptions of these analyses, but may exist under different
scenarios. In the year after establishment no differences in forage quality was observed.
Thus the choice of establishment system and weed control methods must reflect the

markets and forage needs of a particular production system in the establishment year.

55

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67

CHAPTER 3

EFFECT OF SEEDING RATE ON GLYPHOSATE-RESISTANT ALFALFA
ESTABLISHMENT

Abstract: Recommendations for alfalfa seeding rates are based on conventional varieties.
The introduction of glyphosate resistant alfalfa offers a new weed management system
for alfalfa establishment. Determining optimum seeding rates will provide forage
producers with the information to maximize yield, quality, and profitability with this new
technology. Field experiments were conducted in 2005 to determine the effect of seeding
rate on glyphosate resistant alfalfa establishment, yield, forage quality and weed control.
Seeding rates of 4.5, 9.0, and 17.9 kg ha'1 were evaluated. Weed control methods
included no herbicide, glyphosate applied once before the first harvest, and glyphosate
applied once before the first harvest and then 7-10 days following each harvest. No
injury was observed from glyphosate. The greatest differences in alfalfa forage and weed
yields were observed at the first and second harvests. There were no differences in
forage, alfalfa or weed yields among seeding rates and weed control methods at the third
and fourth harvests. Alfalfa yield increased with increasing seeding rate. Glyphosate
applications increased alfalfa yield at the 9.0 and 4.5 kg ha'lseeding rates. At the 17.9 kg
ha’1 seeding rate, weed control did not affect alfalfa yield. Multiple glyphosate
applications reduced weed yields at the 4.5 kg ha'1 seeding rate compared to the 9.0 and
17.9 kg ha'1 seeding rates. Glyphosate applications increased forage quality at the first
harvest at all seeding rates. Alfalfa stand density in the fall of the establishment year was
not affected by weed control method, regardless of weed control method. This data
suggests that seeding rates established for conventional alfalfa should not be modified for

glyphosate-resistant alfalfa.

68

INTRODUCTION

The introduction of glyphosate-resistant alfalfa into commercial production offers
additional weed control strategies for alfalfa stand establishment. Glyphosate is a broad-
spectrum non-residual herbicide that effectively controls most annual and perennial weed
species found in forage production (Gianessi et al., 2002). Glyphosate-resistant alfalfa
varieties have demonstrated excellent crop safety at all stages of alfalfa growth and
preliminary research shows no negative effects on forage yield or other important
agronomic traits (McCaslin et al., 2002).

Establishment and weed control methods are two of the most important
management factors that affect forage yield and quality during the establishment year
(Hoy et al. 2002). Alfalfa quality is a major concern for livestock producers but
quantifying quality is often a difficult task as forage quality encompasses many factors.
Temme et al. (1979) expressed the goal of good forage quality in terms of animal
consumption, nutritional value, digestibility and finally animal growth or milk
production. Forage quality indicators are often combined in equations to make direct
forage quality comparisons easier. Relative feed value (RFV) is extensively used in the
Midwest to separate forages based on quality. RFV uses NDF to calculate dry matter
intake (DMI) and ADF is used to estimate digestible dry matter (DDM) of the forage.
DMI and DDM are then used to calculate RFV (Kuehn et al., 1999).

Weed competition can suppress alfalfa yield (Moyer, 1985; Wilson, 1981) and
impact stand densities (Becker et. al., 1998). Weeds also alter the composition of the
forage, increasing drying time (Doll, 1984) and reducing palatability of alfalfa (Canevari

et al. 2003). Temme et al. (1979) found that lower quality weeds were primarily

69

responsible for decreasing the quality of alfalfa, since they are chemically inferior to
alfalfa. Frequently, weeds compare in quality with alfalfa; however, as weeds mature
their nutritive quality rapidly declines, ofien not coinciding with alfalfa harvests (Doll,
1986)

Alfalfa seeding rates have been studied extensively over the last 35 years,
producing mixed results (Hall et al., 2003). Traditionally it was thought that high seeding
rates ensured good stand establishment when environmental conditions were less than
ideal, increasing stem density and resisting weed invasion (Shewmaker et al., 2001).
However, alfalfa seeding rate recommendations range from 4 to 40 kg ha", depending on
location and climate (Kephart et al., 1992).

If no herbicide is applied, a higher seeding rate will reduce weed biomass and
increase forage quality at the first harvest (Hansen and Krueger 1973; Wakefield and
Skaland 1965; Moline and Robison, 1971). Hansen and Krueger (1973) found that as
alfalfa seeding rates were increased from 4.5 kg ha”] to 17 .9 kg ha], dry matter yield also
increased. However, there was no change in forage quality where herbicides were
applied. In the year after establishment, there were no differences in dry matter
production between a 9.0 kg ha'1 seeding rate and 17.9 kg ha".

Nelson et a1. (1996) and Hall (1993) concluded that there is no relationship
between seeding rate and yield after the establishment year. Hall et al. (2003) found that
increasing seeding rates past 17 kg ha'1 provided no long term benefit to alfalfa stand
establishment as stands thinned themselves out after 6 months. Bolger and Meyer (1983)
found that there were no differences in alfalfa yields from stands established at 9 kg ha'1

to 22.4 kg ha".

70

Glyphosate-resistant alfalfa represents a significant new technology for weed
management in Michigan alfalfa production. Recommendations for alfalfa seeding rates
are based on conventional varieties. Determining optimum seeding rates will provide
forage producers with the information to maximize yield, quality and profitability with
this new technology. The objectives of this study were (1) to determine the effect of
weed control with glyphosate on glyphosate-resistant alfalfa establishment, forage
production, forage quality, and stand persistence at varying seeding rates, (2) to
determine the effect of seeding rate on glyphosate-resistant alfalfa establishment and (3)

to determine the economics of using glyphosate resistant alfalfa in the establishment year.

71

MATERIALS AND METHODS

Field experiments were conducted in 2005 at the Michigan State University
Agronomy farm in East Lansing on a Capac loam soil (fine-loamy, mixed mesic, Aeric
Ochraqualf). Seedbed preparation included a glyphosate application at 0.84 kg ae ha'l
followed by a spring moldboard plow. The site was field cultivated twice and then
leveled using one pass from a cultipacker prior to planting. No fertilizer was applied to
the site prior to seeding because soil tests indicated no need for fertilizer.

The experimental design was a two-factor factorial in a randomized complete
block design with four replications. The first factor was alfalfa-seeding rates (4.5 kg ha",
9.0 kg ha'1 and 17.9 kg ha'l) and the second factor was herbicide treatments. Alfalfa was
seeded using a 5 row Carter Nursery Seederl on April 18, 2005. Glyphosate-resistant
alfalfa seed from Forage Genetics2 was used. One plot was 2.7 m x 7.6 m, consisting of
three 0.9 m passes from the nursery seeder. The center pass was used to apply the
herbicide treatments, and to collect visual evaluations, dry matter yield, and forage
quality analysis. The pass to the left of the center pass was used for destructive plant
measurements and included plant densities, alfalfa weight per stem, botanical
composition and alfalfa mattuity. The pass to the right of the center was maintained for
data collection in future years.

Herbicide treatments included an untreated, glyphosate (0.84 kg ae ha'l) applied
once before the first harvest, and glyphosate (0.84 kg ae ha'l) applied once before the first
harvest and then 7-10 days following each harvest. All treatments received ammonium

sulfate at 2% w/w during each herbicide application. Initial herbicide treatments were

 

' Carter Manufacturing Co., Inc., Brookston, IN 47923
2 Forage Genetics, West Salem, WI 54669

72

applied on May 26, 2005 when weeds reached 5 cm and alfalfa reached 3rd trifoliate.
Subsequent herbicide treatments were applied July 7, August 8, September 13 and
October 27, 2005. All herbicide applications were made using a C02 backpack sprayer
with TeeJet3 8003 flat fan nozzles, delivering 187 L ha“l at 270 kPa. Lambda-cyhalothrin
was applied as needed to control potato leafhopper.

Alfalfa injury and weed control were determined by visual evaluations using the
rating scale 0 (no injury) to 100 (completely killed). Alfalfa injury was recorded 7, 14,
21, 28 and 35 DAT. Control of predominant broadleaf and grass weed species were
evaluated 14, 21, 28 and 35 DAT in 2005.

Plots were harvested on June 29, August 1, September 6, and October 20 in 2005.
The first harvest was taken when 750 growing degree-days had been accumulated (base
temperature 5 C). Subsequent harvests were taken when alfalfa reached bud to one-tenth
bloom stage. Forage dry matter was determined by harvesting a 0.9 X 7.6 m strip from
each plot. Plots were harvested using a Carter flail harvester4 at a cutting height of
approximately 9.0 cm from the soil surface. The fresh weight of a 500g sample from the
strip was recorded, dried at 60 C for 72 hours, and then reweighed for dry matter
determination. An additional 500 g sample was collected from the yield strip of each
plot, dried at 60 C for 72 hours, and then shipped to Dairy One Forage Lab5 for forage
quality analysis.

Alfalfa and weed dry matter yields were determined using two random
subsamples taken at each harvest. A 0.093 m2 sampling square was randomly placed

between two rows of alfalfa near the north end of the plot and the area was harvested and

 

3 TeeJet Spraying Systems Co., Wheaton, IL 60188
‘ Carter Manufacturing Co., Inc., Brookston, IN 47923
5 Dairy One Forage Lab, Ithaca, NY 14850

73

labeled as the first subsample. This procedure was then repeated near the south end of
the plot and was labeled as the second subsample. Garden shears were used to cut the two
0.093 m2 subsamples approximately 9.0 cm from the soil surface. All plant biomass was
harvested from the 0.093 m2 subsamples and hand separated based on species, and then
counted. Separated species samples were then dried at 60 C for 72 hours and weights
were recorded on a dry matter basis. The species weights were then used to calculate the
total weed and alfalfa biomass from each of the plots.

Alfalfa weight per stem was determined by dividing the dry matter weight of the
alfalfa subsample by the number of recorded stems. Alfalfa maturity was determined
using the mean stage by count method as described by Kalu and F ick (1983). The first of
the 0.093 m2 hand separated subsamples were used to determine the alfalfa maturity.

Stand persistence was determined by plant counts that were taken following the
first and final harvest each year. Plant counts were taken 7-10 days following the first and
final harvest each year. A round nosed shovel was used to remove alfalfa crowns from
two randomly selected 0.093 m2 areas in each plot. All taproots within the sampling area
were counted and recorded.

Forage Quality Analysis

Forage quality was determined by near infrared reflectance spectroscopy. Crude
protein (CP) was determined by measuring N content using Kjeldahl techniques (1981)
and then multiplying N percentages by 6.25. Neutral detergent fiber (NDF) and acid
detergent fiber (ADF) were determined using the ANKOM A200 filter bag technique
according to procedures by Van Soest et al. (1991). In vitro neutral detergent fiber

digestibity (NDFD) was determined according to Chemey et al. (1997) using the Daisy II

74

ZOO/22° in vitro incubator and the ANKOM ZOO/220 fiber analyzer. Ash content was
determined by combustion at 500 C for 4h.
Economic Analysis

Economic comparisons among weed control methods and seeding rates were
conducted to determine the gross margin above the technology fees, seeding costs and
weed control costs. The value of glyphosate-resistant alfalfa was assumed to be $71 Mg
based on the 2005 average Wisconsin hay market prices and were adjusted based on
relative feed value (RFV). Herbicide and application costs were averaged over three
pesticide distributors; glyphosate at a typical application rate was assumed to cost $20
ha'1 and application costs were assumed to be $15 ha'l. Prices of glyphosate-resistant
alfalfa seed were averaged over three seed dealers and 4.5 kg ha", 9.0 kg ha'1 and 17 .9 kg
ha'1 seeding rates were assumed to cost $45 ha'l, $90 ha'1 and $180 ha", respectively. A
technology fee based on alfalfa seeding rates was added to each of the seeding costs. The
technology fees for the 4.5 kg ha", 9.0 kg ha'1 and 17.9 kg ha’1 seeding rates were
assumed to be $25 ha'l, $50 ha'l, and $100 ha", respectively. This technology fee is
based on 2005 technology fee that is added to the commercial seed cost in Michigan. The
following equation was used to quantify the gross margin estimates:
Gross Revenue = (dry matter yield)(market price based on RFV)

Gross Margin = Gross Revenue — (weed control cost + seeding costs + technology fee)

75

Statistical Analysis
Data were subjected to ANOVA using the PROC GLM procedures of SAS 8.026

to determine the analysis of variance. Means were separated using Fischer’s Protected

Least Significance Difference at an alpha level of 0.05

 

6 SAS Institute Inc., 100 SAS campus drive, Cary, NC 27513

76

RESULTS AND DISCUSSION
Alfalfa Injury

There was no visual alfalfa injury observed from glyphosate at any of the
evaluation dates at any of the seeding rates in 2005 (data not shown).
Weed Control

Weed control was nearly complete with each glyphosate application. There were
no differences in visual weed control ratings for any of the evaluated species between
seeding rates at each evaluation date (data not shown).

Yield Components
Harvest 1

Total forage yield was increased significantly within each of the seeding rates
when herbicides were not applied as result of the high weed yields (Figure 3.1). Total
forage yield was the highest at the high (17.9 kg ha'l) seeding rate where glyphosate was
not applied. Total forage yield was similar between the medium (9.0 kg ha") and low
(4.5 kg ha!) seeding rates within weed control methods. Total forage yield and alfalfa
yield was significantly higher at the high seeding rate compared to the low seeding rate,
within a weed control method.

Alfalfa yield was reduced where glyphosate was not applied at the medium and
low seeding rates. At the high seeding rate, alfalfa more effectively competed with
weeds, as alfalfa yield was not reduced to the extent of the lower seeding rates when
glyphosate was not applied. Alfalfa yield was similar at the low and medium seeding
rates where glyphosate was applied. However, alfalfa yield was lower at the low and

medium seeding rates compared to the high seeding rate when glyphosate was applied.

77

Weed yields were similar within weed control methods, regardless of seeding rate
(Table 3.1). Weed yield at the first harvest did not appear to be impacted by seeding
rates, as similar weed yields were observed at each seeding rate. Weeds often reduced
alfalfa yield, however the relative reduction in alfalfa yield in the presence of weeds
appears to be lower at the high seeding rate. Similar observations have been made by
Wakefield and Skaland (1965), Moline and Robison (1971) and Hansen and Krueger
(1973).

Harvest 2

Total forage yield was similar among seeding rates within each weed control
method (Figure 3.1). Alfalfa yields were lower in the untreated plots compared to plots
treated with glyphosate at each seeding rate. Weed competition prior to the first harvest
significantly reduced alfalfa yields, where glyphosate was not applied, regardless of
seeding rate. Alfalfa yields were higher at the high seeding rate than the low seeding rate
within each weed control system. Where glyphosate was not applied, alfalfa yields were
higher with the medium and high seeding rates, compared to the low seeding rate.
Multiple applications of glyphosate did not increase alfalfa yield at any seeding rate
compared to a single application of glyphosate.

Total weed yield was the highest at the low seeding rate where glyphosate was not
applied and reduced alfalfa yield as a result (Table 3.1). Multiple glyphosate applications
reduced weed yields at the low seeding rate compared to a single application, however
total forage yield or alfalfa yield did not increase significantly from a second glyphosate

application. Weed yields were similar at the medium and high seeding rates, regardless

78

of weed control method. Multiple glyphosate applications did not reduce weed yields at
the medium and high seeding rates.
Harvest 3 and Harvest 4

There were no differences in total forage yield or alfalfa yield at harvest 3 or
harvest 4 (Figure 3.1). The highest weed yields at harvest 3 and 4 were observed at the
low seeding rate where glyphosate was not applied (Table 3.1). However, at harvest 3
weed yields were not significantly higher than the other seeding rates. At harvest 4, weed
yields were significantly higher where glyphosate was not applied at the low seeding rate.
Weed control method appears to have affected weed yields much more at the lower
seeding rate as alfalfa was less able to tolerate weed competition throughout the entire
growing season.
Seasonal

Total seasonal forage yield was similar among weed control systems within each
seeding rate (Figure 3.2). Although total forage yield was increased at harvest 1 from
high weed yields at each seeding rate, alfalfa growth was reduced at the subsequent
harvests resulting in no differences in total seasonal forage yield within each seeding rate.
Higher total forage and alfalfa yields were observed at the high seeding rate compared to
the low seeding rate.

Alfalfa yield responded positively to increased seeding rates during establishment,
with higher alfalfa yields observed at higher seeding rates (Figure 3.2). These
observations have also been made by Kruegar (1973), Volenec et a1. (1987), and Hall et

al. (2003). A glyphosate application increased alfalfa yields at the low and medium

79

seeding rates. Multiple applications of glyphosate did not improve alfalfa yields at any of
the seeding rates.

Seasonal weed yields were the highest at each seeding rate where glyphosate was
not applied (Table 3.1). Seasonal weed yields were reduced more at a high seeding rate
compared to the low seeding rate, when glyphosate was not applied. Alfalfa seeded at
higher seeding rates appears to reduce weed yields more than lower seeding rates.
Multiple applications of glyphosate reduced weed yields but did not significantly reduce
weed yields compared to a single glyphosate application.

Alfalfa Stem Weight

Alfalfa stem weight was increased at the low seeding rate where glyphosate was
applied at the first two harvests (Table 3.2). The reduced competition between alfalfa
and weeds can explain the increase in stem weight. Alfalfa plants at reduced seeding
rates appear to compensate for lower populations by increasing individual plant growth.
Volenec et al. (1987), Bolgerand and Meyer (1983), and Rumbaugh (1963) observed that
alfalfa plant density is positively associated with total dry matter yield but negatively
associated with dry matter yield per plant.

Alfalfa stem weights were similar among seeding rates where glyphosate was not
applied at harvest 1. Alfalfa stem weights were very different between the high and low
seeding rates where glyphosate was applied. Lower alfalfa stem weights were previously
observed in alfalfa stands using high seeding rates (Krueger and Hansen, 1974; Volenec
et al., 1987).

At harvest 2, alfalfa stem weights were reduced at the low seeding rate, where no

herbicide had been applied compared to multiple glyphosate treatments. At the medium

80

and high seeding rate, no differences were observed in alfalfa stern weights among weed
control methods. At harvest 3, differences in alfalfa stem weights were not consistent at
each seeding rate or weed control method. At harvest 4 there were no differences in
alfalfa stem weight among seeding rates or weed control methods.

Forage Quality

Harvest 1

At harvest 1, alfalfa maturity was not significantly different among any of the
weed control methods or seeding rates (Table 3.3). Crude protein (CP) was the lowest at
each seeding rate where glyphosate was not applied and was similar among seeding rates.
High weed biomass observed at each seeding rate where glyphosate was not applied most
likely lowered CP (Table 3.1). Temme et a1. (1979) found that weeds were primarily
responsible for decreasing the quality of alfalfa, when herbicides were not applied. A
glyphosate application increased CP at each seeding rate. Becker et al. (1998) and Hoy et
al. (2003) reported forage quality was increased in the first harvest where a herbicide had
been used in establishment.

NDF was higher where no herbicide was applied at the medium and low seeding
rates. At the high seeding rate, NDF was similar among all weed control methods.
Similar results were seen by Hansen and Krueger ( 1973), Wakefield and Skaland (1965)
and Robison (1971). There were no differences in ADF among weed control methods
within seeding rates at the first harvest. ADF tended to increase at a high seeding rate but
was not significant.

RFV was the highest where glyphosate had been applied at the medium and low

seeding rates. At the high seeding rate there were no differences in RFV among weed

81

control methods. RF V values at the high seeding rate among weed control methods were
similar to RFV values observed where no glyphosate applications were made at the low
and medium seeding rates. Higher alfalfa yields at the first harvest in all weed control
methods at the high seeding rate most likely resulted in the similar forage qualities
observed. Hansen and Krueger (1973) and Moline and Robison (1971) reported the same
observations.

Harvest 2

Reduced competition at the low seeding rate where glyphosate was applied
resulted in increased alfalfa maturity compared to the medium and high seeding rates
(Table 3.4). Higher competition between alfalfa plants or alfalfa and weeds prior to the
first harvest likely delayed alfalfa maturity. A delay in alfalfa maturity was observed
where no herbicide was applied at low and medium seeding rates and at all high seeding
rate treatments. Maturity observations at harvest 2 are reflected in most of the forage
quality data, as alfalfa maturity influenced the forage quality estimates.

CP was similar among weed control methods at the low and medium seeding
rates. CP was increased at the high seeding rate where no herbicide was applied. NDF
and ADF were similar among weed control methods within the low and medium seeding
rates. NDF and ADF were higher where a single application of glyphosate was made at
the high seeding rate.

At the high seeding rate, the highest forage quality as measured by RFV was
observed where no herbicide was applied. Lower ADF and NDF concentrations probably
resulted in the higher RFV. At the low seeding rate the RFV was much higher where

glyphosate had been applied for a second time compared to a single glyphosate

82

application. A reduction in weed biomass at this harvest appears to have resulted in a
higher RFV (Table 3.1).
Harvest 3

Alfalfa maturity was similar among weed control methods at the medium and
high seeding rates (Table 3.5). Alfalfa maturity was delayed at the low seeding rate
where no herbicide was applied compared to where glyphosate was applied multiple
times. It appears that weed competition has a greater effect on alfalfa establishment at
lower seeding rates, as seen by the delay in alfalfa maturity that was still evident at the
third harvest.

Forage quality results at harvest 3 were inconsistent and very few distinct
differences were observed between treatments. This is probably related to yield data
which indicated no significant differences in total forage yield or total alfalfa yield at
harvest 3 (Figure 3.1). Furthermore, weed yields were low and no differences were
observed among weed control methods at any of the seeding rates, thus weeds most likely
had no effect on forage quality (Table 3.1).

At the low seeding rate, CP was similar among all weed control methods. At the
medium and high seeding rates CP was higher where no glyphosate application had been
made compared to a single glyphosate application. NDF and ADF were higher where a
single application of glyphosate was made at the high seeding rate. Furthermore, a lower
RFV value was observed in this treatment, which is a reflection of high NDF and ADF.
This treatment did not have advanced alfalfa maturity, increased forage or alfalfa yield or

weed yield differences. Thus differences must be accounted for by variations in sampling.

83

Harvest 4

Alfalfa maturity, CP, NDF, ADF and RFV were similar among all weed control
methods at each seeding rate at the final harvest (Table 3.6).
Alfalfa Stand Density

Higher alfalfa stand densities were observed at the high seeding rate in the spring
and fall, regardless of weed control method (Figures 3.3, 3.4). Alfalfa stand densities in
the spring and fall were similar among weed control methods within all seeding rates.
Alfalfa crown mortality over the growing season was greater at the high seeding rate than
at the lower seeding rates. Hall (1993) and Nelson et al. (2001) reported the same trends
as they observed that higher populations experienced higher mortality rates, but
differences in plant densities still existed between high and low seeding rates. It appears
that at the low seeding rate, competition among alfalfa crowns was reduced as the
mortality rate over the season was less than the higher seeding rates. It would be
interesting to monitor the crown densities in the year after establishment to observe
effects of seeding rate on crown densities afier establishment, especially at the lower
seeding rates.
Economic Analysis

Gross revenues tended to increase with increasing seeding rates (Table 3.7). The
highest gross revenue was observed at the high seeding rate where no herbicides were
applied. Gross revenues were significantly different between the high and low seeding
rates when no herbicide was applied. There were no differences in gross revenue among

weed control methods within each seeding rate.

84

Gross margins were the highest at each seeding rate where no herbicide was
applied and was generally similar among seeding rates. One application of glyphosate
generated slightly higher gross margins than multiple applications of glyphosate,
regardless of seeding rate, although the difference was not significant. Costs were less at
a medium seeding compared to a high seeding rate and yields were increased over a low
seeding rate, resulting in higher gross margin. Allocating the technology fee over the life
of the alfalfa stand did not substantially change the relative differences in gross margins
among the treatment comparisons. At the high seeding rate in particular gross margin
was higher where glyphosate was not used in the establishment year.

Gross margin calculations were made under several assumptions that should be
taken into consideration when drawing conclusions from this research. First, alfalfa hay
prices were based on average hay prices but did not take into consideration increased
premiums for weed free alfalfa hay. In this case, forages produced where no herbicides
were applied would not be highly marketable, especially at the first harvest when weed
biomass was the highest. Second, gross margins were calculated assuming that the
livestock fed the forage would consume the entire forage. It is possible that livestock may
eat around the lower quality weeds, thus not giving a true economic picture of the value
of weed free hay that received herbicide applications.

Further cost scenarios, such as applying generic glyphosate, did not change the
gross margins significantly from what was discussed previously (Appendix 3, Table
A3.1). However, using generic glyphosate plus allocating technology fees over the life of
the alfalfa stand, resulted in no significant difference in gross margins between weed

control methods and seeding rates (Appendix 3, Table A3.2). This low cost scenario

85

indicates that economic benefits of glyphosate applications at standard seeding rates
might exist in the establishment year. However, this scenario assumes that using
glyphosate resistant alfalfa technology will benefit alfalfa stands beyond the
establishment year, which has not been confirmed.

Economic conclusions are difficult to draw at this point since only one year of
data has been collected. In order to draw the most accurate economic conclusions, the
seeding rates and weed control methods should be established again in a separate study.
Additionally, studies should be monitored in the years after establishment to determine
the longer term impacts of seeding rates and weed control methods in the establishment
year.

Summary

Alfalfa yields tended to increase with increasing seeding rates. A glyphosate
application increased alfalfa yield at the medium and low seeding rate compared to
treatments where no herbicides were applied. However, at the high seeding rate, there
were no increases in yield from weed removal.

Multiple applications of glyphosate were not necessary at the medium and high
seeding rates. However, at the low seeding rate a second glyphosate application reduced
weed yield, increasing RFV, but not alfalfa yield. The first-year benefits of multiple
glyphosate applications at low seeding rates in the establishment year do not justify the
added costs. It would be interesting to monitor the effects of multiple glyphosate
applications in the establishment year over the life of the alfalfa stand established at low

seeding rates.

86

A glyphosate application increased forage quality at the first harvest, within all
seeding rates. A lesser influence on forage quality was observed at the high seeding rate.
There appeared to be no correlation between seeding rates and forage quality where
glyphosate was applied. Forage quality was similar among seeding rates and weed
control methods at the final harvest of the season.

Weed control method did not affect alfalfa density, regardless of seeding rate.
Economic analysis revealed that at recommended seeding rates an application of
glyphosate did not significantly improve gross margins over treatments where no
herbicide was applied. One application of glyphosate at all seeding rates generated
higher gross margins than multiple applications of glyphosate.

Current data suggests that seeding rates established for conventional alfalfa
should not be modified for glyphosate-resistant alfalfa. Recommended seeding rates
reflect a threshold where a productive alfalfa stand can be established under ideal or less
then ideal growing conditions. The 2005 establishment year included exceptional
growing conditions for establishing alfalfa. Rainfall was timely and temperatures were
high, resulting in very successful stand establishment. Perhaps results would be different
under less then ideal establishment conditions, as lower seeding rates may result in
unacceptable alfalfa and forage production. It would be interesting to look at the effects
of seeding rates and weed control methods under a less than ideal establishment
environment. Second year production data is needed to evaluate the impact of seeding
rates and weed control methods on alfalfa yield, weed densities and stand persistence

after the establishment year.

87

REFERENCES

Becker, R.L., C.C. Sheaffer, D.W. Miller, and DR. Swanson. 1998. Forage quality and
economic implications of systems to manage giant foxtail and oat during alfalfa
establishment. J. Prod. Agric. 112300-308.

Bolger, TR, and D.W. Meyer. 1983. Influence of plant density on alfalfa yield and
quality. P. 37-41. Proc. Am. Forage and Grassl. Council, Eau Claire, WI. 23-26 J an.1983.
Am. Forage and Grassl. Counc., Georgetown, TX.

Chemey, D.J.R., M.J. Traxler, and J .B. Roberston. 1997. Use of Ankom fiber
determination systems to determine digestibility. Proc NIRS Forage and Feed Testing
Consortium Ann. Conf. Madison, WI. P.19-20.

Doll, J .D. 1984. Effects of common dandelion on alfalfa drying time and yield. Proc.
North Cent. Weed Control Conf. Vol. 39:113-114.

Doll, J .D. 1986. Do weeds affect forage quality? Proc. National Alfalfa Symposium.
P.161-170.

Hall, M.H., C.J. Nelson, J .H. Coutts, and RC. Stout. 2004. Effect of seeding rate on
alfalfa stand longevity. Agron. J. 96:717-722.

Hansen, L.H., and CR. Krueger. 1973. Effect of establishment method, variety, and
seeding rate on production and quality of alfalfa under dryland and irrigation. Agron. J.
65:755-759.

Hoy, M.D., K.J. Moore, R.J. George, and EC. Brummer. 2002. Alfalfa yield and quality
as influenced by establishment method. Agron. J. 94:65-71.

Kalu, B.A., and G.W. F ick. 1983. Morphological stage of development as a predictor of
alfalfa herbage quality. Crop Sci. 23:1167-1172.

Kephart, K.D., E.K. Twidwell, R. Bortnem, and A. Boe. 1992. Alfalfa yield component
responses to seeding rate several years after establishment. Agron. J. 84:827-831.

Keuhn, C.S., H.G. Jung, J .G. Linn, and NP. Martin. 1999. Characteristics of alfalfa hay
quality grades based on relative feed value index. J. Prod. Agric. 12:681-684.

McCaslin, M. 2002. An update on the development of roundup ready alfalfa. Proc.
California Alfalfa Symposium.2002:207.

Moline, W.J., and LR. Robinson. 1971. Effects of herbicides and seeding rates on
production of alfalfa. Agron. J. 63:614-616.

88

Moyer, J .R. 1985. Effect of weed control and a companion crop on alfalfa and sainfoin
establishment, yields and nutrient composition. Can. J. Plant Sci. 65: 107-1 16.

Nelson, C.J., M.H. Hall, and J .H. Coutts. 1996. Seeding rate, plant density, and
persistence of alfalfa. P.231-235. Proc. Am. Forage and Grassl. Counc., Vancouver, BC,
Canada. 13-15 June . Am. Forage and Grass]. Counc., Georgetown, TX..

Nelson, C.J., M.H. Hall, R.L. Kallenbach, and J .H. Coutts. 2001. Effects of seeding
rateson plant thinning and crown development of alfalfa. P. 1 80-184. Proc. Am. Forage
and Grassl. Counc. Springdale, AR. 22-25. Apr.2001. Am. Forage and Grassl. Counc.,
Georgetown, TX.

Rumbaugh, MD. 1963. Effects of population density on some components of yield of
alfalfa. Crop Sci. 3:423-424.

Shewmaker , G.E., M. H. Hopwood, and KL. Roemer. 2002. Implications of seeding
rates and seed coating with improved alfalfa varieties. Proc. Western Alfalfa and Forage
Conference.p.1 1-14.

Temme, D.G., Harvey, R.S., F awcett, RS. and Young, A.W. 1979. Effects of annual
weed control on alfalfa forage quality. Agron. J. 71 :51-54.

Van Deynze, A., D.H. Putnam, S. Orloff, T. Lanini, M. Canevari, K. Hembree, S.
Mueller, and L. Teuber. 2004. Roundup ready alfalfa: an emerging technology.
Extension Bull. 8153. Oakland, CA: University of California, Agriculture and Natural
Resources, Communication Services. pp1-12.

Van Soest, P.J., J .B. Roberston and, B.A. Lewis. 1991. Methods for dietary fiber,
neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J.
Dairy Sci. 74:3585-3597.

Volenec, J .J ., J .H. Chemey, and K.D. Johnson. 1987. Yield components, plant
morphology, and forage quality of alfalfa as influenced by plant population. Crop Sci.
27:321-326.

Wakefield, RC, and N. Skaland. 1965. Effectsof seeding rate and chemical weed
control on establishment and subsequent growth of alfalfa (Medicago sativa L.) and
birdsfoot trefoil (Lotus comiculatus L.). Agron. J. 67:547-550.

Wilson, R.G. 1981. Weed control is established dryland alfalfa (Medicago sativa).
Weed Sci. 29:615-618.

89

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106

 

 

 

 

02 02 02 02 02 02 02 02 02 02 02 02 .00.0. 000
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107

 

 

 

 

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108

 

 

 

 

02 02 02 02 000.00 :00
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109

 

 

02 02 02 02 000.00 000
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N00 3: :0 0m 0 0205000 00
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0 000g: 0. 00.03000 N 000%: _ 003.003 0000000300000—

 

.voom .00 m0t0~0 05 00 0005000 w0m0000 020000000 000
w0m0000 000—0 03 0000200000 .moom 5 0000300 000.0 05 .00 0020> 000.0 0050—00 00000 00000m 22 030B

110

.00000 0000005000 000 005.000 002000 00000 000000000 0
00000 0000000000000 05 00 00000000 00 00003 00.0 0300000000 :5 000 0000 000000 003 00000005w 00000w 005 00000000. 0
.0mo.ou0V 00mg 0000000000 0.0000000 00 w00000000 000000.000 0050005000 000 000 000200 00505 0000— 00000 05 00 00300000 00002 0

 

 

 

 

111

02 00 02 00 000.00 .000
00.000 0 8.20 om.m: om o0.m~ 00.0mm 0 00.000 0000055w
00.02. 0 flown o om 3.3. 3.30 0 RN00 0800000000
00.000. 0 omdmn o om o 00.0“: 0 2.1000 00005000 00

”00005 020000000
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omdmn 0 0.0.000 o o omdm 3.000. 0 0.0.000 0800000000
00.0.00 0 0.0.50 o o o 00.000 0 0.0.50 000000000 00
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0.000 m
moom 0oo~ 0000 00000 00000 moom 0oo~ 00502
0&002 00000 32000000. 000m 0000000 000 2r. 00005.00 00000 00000000000005

 

0000000030000 0.000.000 000000000
0000055w moon 000 0oo~ 00.0 00000w000 0000000 0003 000 000000000 0000000030000 .00 0000000000000 00000000m 0.0040. 030.0.

.00000 0000002000 000 000000.000 002000 0000 000000020 0
00000 0000000 0000 0 0 00>0 00000020 00 00003 000 0300002000 000 0000 002000 003 0000020bm 000000w 0020 0000090 0
.Amoduav 0mg 000000000 0.002000 00 w00000000 000000000 0000000000030 000 000 0000000 00003 000000 00000 05 02 0030200 00002 a

 

02 K 02 E 00.00 .00.0
00.000 00 00.000 00.00 00 00.00 00.000 0 00.000 20000000
3.000 0 00.000 0 00 0.0.00 00.000 0 00.000 008000000
00.00 0 0.0.000 0 00 0 00.0: 0 00.00 0220020 0:

M00000m 0000000000

 

 

 

was: 00 00.80 2.0m 0 000mm 00.0mm 0 00.000 000002030
00.0mm 0 5.000 0 o 3.3 00.000. 0 0.0.000 0800000000
00.000. 0 0050 o o 0 00.000 0 0080 000000002 00
”00000m 000.0

702 m
moom 000m 0000 00000 00000 moon 0oo~ 002002
003002 00000 $200288 000m 0000000 000 30 000200 00000 00000202000000

 

000002020000 0000020 000000000
000002003 meow 000 0oom 000 00000w000 0000000 0003 000 000000000 0000020200000 00 000000000000 00000000m 0.00400 0300.

112

APPENDIX III

113

. .0000 000002000 000 00032000 0000000 00000 000000000 0

.0000 0000020200000 00.0 00 00000000 00 02003 000 300002000 200 000 0000 002000 003 000002003 000000w 005 00.00.0010 0
God 0 qu 000000000 0.0020000 00 w00000000 000000000 3000000030 000 000 000200 0 02003 000000 00000 000 .3 0030200 000020
00003002 00000 00 00000 0000020000» 00 000002000 03000 ”0000002030

60003002 2000 0030200 + 00003002 00000 00 000000 00000203» 00 0000002000 00000000 ”0000002030

 

 

 

114

 

 

000 000 . 000.00 00.0
0 00.3.0 000 000 000 00 0000 00.00: 0200000000
00 00.000 000 000 000 00 00 00.00: 3000000000
0 00.0000 000 0 000 0 0 00.0000 00000020 00
0.0:. 00. 0.0.0 0000
000 00.000 000 00 00 00 000 00.00: 0200200000
000 00.000 000 00 00 00 000 00.00: 0008000000
00 00.0000 000 0 00 0 0000 00.00: 0005020 8
9.2 00 0.00 8.0002
0000 00.000 00 00 00 00 80 00.0000 020800000
020 00.000 0: 00 0.0 00 0 00.0000 00800000
000 00.000 00 0 00 0 00 00.0000 0003000 8
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00w0000 00000 0000. 00000000000. 000.0 0000.3 00000 0000 M00000m
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000000000 0000020bw moom 00 00000w000 0000000 0003 000 00000 w000000 00 0000000000000 0000000000 0.000400 0300.

.0000 000002000 000 00032000 002000 00000 00000020 9
00000 02020 0000 0 0 00 002 020 00>0 00000020 02 00003 $200208 200 000 0000 002000 003 00002003 000000w 0020 0000000< 0
God 0 am; 000000000 0.002000 00 w00000000 000000.20 0000000090 000 000 000200 0 00223 0002 00000 020 02 0030200 0000020
.000>002 00000 00 0000 000002003 00 000002000 2w000 ”00000020000
60003002 2000 w0030200 + 00302 0000 00 02000 00000203w 00 0000002000 2002000 ”0000002030

 

 

 

 

02 000 “000.00 00.0
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0.2. 00. 0.00 0000
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0000020220000 0.20.20 000000000
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115

   

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