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0 f ._( Michigan state
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This is to certify that the
thesis entitled

CELERY (AP/UM GRA VEOLENS L.) AND WEED RESPONSE TO
COVER CROPS AND NUTRIENT MANAGEMENT ON MUCK SOIL

presented by
Kevin Charles

has been accepted towards fulﬁllment
of the requirements for the

Master degree in Horticulture

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2/05 chlRCMnhdd-p.“

CELERY (AP! UM GRA VEOLENS L.) AND WEED RESPONSE TO COVER CROPS
AND NUTRIENT MANAGEMENT ON MUCK SOIL

By

Kevin Charles

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

MASTER OF SCIENCE
Department of Horticulture

2005

ABSTRACT

CELERY (APIUM GRA VEOLENS L.) AND WEED RESPONSE TO COVER CROPS
AND NUTRIENT MANAGEMENT ON MU CK SOIL

By

Kevin Charles
Michigan ranks second in the nation for celery production. Most of Michigan celery is
produced under intensive systems with limited crop rotation. Many celery growers are
increasingly interested in sustainable practices, such as the use of cover crops, to reduce
external inputs, suppress weeds, enhance soil quality, and immove yield and quality.
This study was undertaken to as$ess the potential to integrate cover crops into intensive
celery production systems. Speciﬁc goals were to measure celery growth and yield under
different cover crops, evaluate the effects of the cover crops on soil fertility, measure the
weed suppressiveness of the cover crops, and determine if the cover crops can enable
growers to reduce fertilizer inputs. Our results indicated that cover crops could ﬁt into
celery cropping systems, especially for early planted crop that is usually harvested
between July and August. Oilseed radish and mustard species showed the greatest
beneﬁt, both at the research station and at a grower’s farm compared with rye or hairy
vetch. Celery growth and yield was enhanced by oilseed radish. Hairy vetch (a legume)
failed to improve nitrogen concentration in the soil primarily because of low nodulation'
under muck soil. On the other hand, oilseed radish recycled large amount of potassium
and nitrogen. All cover crops studied suppressed weed early in the season with oilseed
radish providing the greatest effect. Combining oilseed radish with different fertilizer
rates showed that growers can potentially reduce their fertilizer inputs by up to 50%

without any yield reduction.

DEDICATION

HTP DE NASUT USIR, INPU

De snu prt khru, ta, henket, Kha tau, kha henktu, kha kau, Kha apedu, kha seshu, kha
menkhtu, Kha kht, nbt, nfrt, wabt, Ankh NTR em N Ka n Imaky Tehuti, Imaky Queen
Tiye, Imaky Queen Nefertari, Imaky Ahmose I, Imaky Queen Nefertiti, Imaky
Akhenaten, Imaky Ramses II, Imaky Thutmose IH, Imaky Senusret III, Imaky
Amenemhet III, Imaky Aha, Imaky Imhotep, Imaky Tehuti, Imaky MerNeith, Imaky
Hatshepsut, Imaky Queen Tetisheri, Imaky Taharqa, Imaky Piankhi, Imaky Charles
Harris, Imaky Joshua Harris, Imaky Mable Wallace, Imaky Andrew Charles, Imaky
Nelly Charles, Imaky Queen Sheba, Imaky Menilik AI, Imaky Menilik II, Imaky Rt. Hon.
Prince Emmanuel Charles Edwards the 7“, Imaky Marcus Garvey, Imaky HIM Haile
Selassie I, Imaky HIM Menilik II, Imaky Malcohn X, Imaky John Henrik Clarke, Imaky
Dr. Cheikh Anta-Diop, Imaky Eida Harris, Imaky Anselm Charles, Imaky Louise
Dowling, Imaky Gustavo Dowling, Imaky Clarke Theus Charles, Imaky Kebra-Seyoun

Charles

iii

AKNOWLEDGEMENTS

I would like to express my revered appreciation to Dr. Mathieu Ngouajio, my major
professor, for his scientiﬁc mastery, his superb support, and for his kilter kindness.
Expressions of genuine gratitude must be extended to Dr. Darryl Warncke and Dr.
Kenneth Poff for their select expertise, their leadership, and their participation as oo-
advisory committee members. I especially thank Dr. Marquita Chamblee, Dr. Yevonne
Smith, Dr. Eunice Foster, and Dr. William Gordon for their excellent recruitment and
retention efforts. I am also grateful to Dr. Sieglinde Snapp, and Dr. Dale Mutch for their
mentoring during those sweltering summer internships in which their innovative thoughts
inﬂuenced me. Acknowledgements of special thanks to my lab-mates, Mohan and Erin,
in Dr. Ngouajio laboratory for assistance. I duly recognize the contribution of Ron
Gnagey, Eding Brother’s Farm, Mr. and Mrs Theodore, Dieudonne Baributsa, Marcia
LaCorbiniere-Jn Baptiste, Mr. Jon Dahl, Mr. Xuewen Huang, and countless others who
have contributed to the success of this study. Finally, I thank Herodotus and Count C.F.
Volney. Indeed, their wisely written accounts are colossal contributions to humanity only
to be equaled and surpassed in magnitude by the illustrious Dr. Cheikh Anta Diop and

Dr. Yosef A.A. Ben-Jochannan.

iv

PREFACE

This thesis is written as a manuscript in the style required for publication in
Agg'cultureLEcosvstem and Egonment; J ourn_al of Plant Nutrition and Soil Science;

and Weed Science.

TABLE OF CONTENTS

LIST OF TABLES ............................................................................. VIII

LIST OF FIGURES ............................................................................... IX

Chapter 1. Literature review ..................................................................... 1
Introduction.................... .................................................................................. 1
Sustainability ................................................................................. 2
Cover crop and soil fertility ................................................................ 4
Cover crop and weeds ....................................................................... 7
Oilseed radish, cereal rye, and hairy vetch ............................................. 10
Monitoring soil NO; N pool .............................................................. 12
Total % soluble solids ..................................................................... 12
Michigan celery production ............................................................... l3
Hypothesis ................................................................................... 15
Objectives ................................................................................... 15
References cited ............................................................................. 17

Chapter 2. Celery Mpium graveolens L.) growth responses to various cover crops

and soil fertility levels ............................................................................ .24
Abstract ...................................................................................... 24
Introduction ................................................................................. 25
Materials and Methods ..................................................................... 27

Experimental site .................................................................. 27
Laingsburg experiment ............................................................ 27
Hamilton experiment ............................................................. 29
Data collection ..................................................................... 30
Statistical analysis ................................................................. 31
Results ........................................................................................ 32
Cover crop biomass production ................................................. 32
Celery biomass production ...................................................... 32
Crop grth rate (CGR) and Relative growth rate (RGR) .................. 34
Celery stalk lengths ............................................................... 36
Celery yield ........................................................................ 37
Celery total soluble solids ........................................................ 38
Discussion ................................................................................... 38
Acknowledgements ........................................................................ 41
References cited ............................................................................ 42

vi

Chapter 3. The effects of cover crops and fertilization on soil properties and celery

(Apium graveolens L.) on Houghton muck soil ................................................ 66
Abstract ...................................................................................... 66
Introduction ................................................................................. 67
Materials and Methods ..................................................................... 69

Experimental site .................................................................. 69
Laingsburg study ................................................................... 70
Nitrogen leaching assessment ........................................... 72

Hamilton study ..................................................................... 72

Data collection ..................................................................... 73
Statistical analysis ................................................................. 74
Results ........................................................................................ 74
Climate .............................................................................. 74

Cover crop biomass production ............................................ ‘ ..... 75

Soil mineral concentration ....................................................... 76

Soil microbial respiration and microbial biomass C ........................... 77

IER NO3' N accumulation ........................................................ 78

Tissue NO; N concentration ...................................................... 79

Celery yield ........................................................................ 79
Discussion ................................................................................... 81
Acknowledgements ........................................................................ 83
References cited ............................................................................ 84

Chapter 4. Integration of cover crops and fertilizer rates for weed management in

celery (Apium graveolens L.) .................................................................... 107
Abstract ..................................................................................... 107
Introduction ................................................................................ 109
Materials and Methods ................................................................... 112

Experimental site ................................................................ 112
Data collection ................................................................... 113
Statistical analysis ............................................................... 114
Results and Discussion ................................................................... 115
Climate ............................................................................ 1 15
Cover crop biomass production ................................................ 115
Effects of cover crop and fertilizer on weed density and species
composition ....................................................................... 115
Effects of cover cr0p and fertilizer on weed dry biomass .................. 118
Effects of cover crop and fertilizer on celery yield .......................... 119
Acknowledgements ....................................................................... 123
References cited ........................................................................... 124

vii

LIST OF TABLES

Table 2.1: Cover crop seeding rate and dry biomass production in 2003 and 2004 at
Laingsburg and Hamilton ........................................................................ 45

Table 2.2: Effects of cover crop and fertilizer rate on celery total dry weight at different
dates on Houghton muck soil in Laingsburg and Hamilton during 2003 and g
2004 .................................................................................................. 46

Table 2.3: Coefﬁcient estimates for the logistic equation y = [a + (l + (x + x0)”) ] ﬁtted
with celery total dry weight data for Laingsburg and Hamilton during 2003 and
2004 ................................................................................................... 47

Table 2.4: Effects of cover crop and fertilizer rate on celery crop growth rate (CGR) in
Laingsburg and Hamilton in 2003 and 2004 .................................................... 48

Table 2.5: Coefficient estimates for the logistic equation y = [a -=- (1 + (x + xo)")] ﬁtted
with celery crop growth rate (CGR) data for Laingsburg and Hamilton in 2003 and
2004. . .' ................................................................................................ 49

Table 2.6: Effects of cover crop and fertilizer rate on celery relative growth rate (RGR) in
Laingsburg and Hamilton in 2003 and
2004 .................................................................................................... 50

Table 2.7: Coefﬁcient estimates for the polynOmial equation y = y0 + ax + bx2 ﬁtted with

celery relative growth rate data for Laingsburg and Hamilton in 2003 and
2004 .................................................................................................... 51

Table 2.8: Effects of cover crop and fertilizer rate on celery stalk length at different dates
in Houghton muck soil in Laingsburg and Hamilton during 2003 and
2004 .................................................................................................... 52

Table 2.9: Coefﬁcient estimates for the logistic equation y = [a + (1 + (x + x0)”)] ﬁtted
with celery stalk length data of Laingsburg and Hamilton in 2003 and
2004 .................................................................................................... 53

viii

Table 2.10: Effects of cover crop and fertilizer rate on total and marketable celery yield
(weight and stalk number) m Laingsburg during 2003 and
2004 ................................................................................................... 54

Table 2.11: Effects of cover crop on total and marketable celery yield (weight and stalk

number) in Hamilton during 2003 and
2004 .................................................................................................... 55

Table 2.12: Effects of cover crop and fertilizer rate on total soluble solids on Houghton
muck soil in Laingsburg and Hamilton during 2003 and
2004 .................................................................................................... 56

Table 3.1.: Cover crop seeding rate and total (above and below ground) dry biomass
production in 2003 and 2004 at Laingsburg and Hamilton .................................... 88

Table 3.2.: Effects of cover crop and fertilizer on soil mineral nutrient composition in
Laingsburg during 2003 and 2004 ................................................................ 89

Table 3.3.: Effects of cover crop on soil mineral nutrient composition in Hamilton during
2004 .................................................................................................... 90

Table 3.4.: Effects of cover crop and fertilizer on soil microbial activity in Laingsburg
and Hamilton during 2004 .......................................................................... 91

Table 3.5.: NO3' N accumulation by Ion exchange resin (IER) in Laingsburg during
2003 .................................................................................................... 92

Table 3.6.: Effects of cover crop and fertilizer on celery N03' N concentration in
Laingsburg and Hamilton during 2003 and 2004 ................................................ 93

Table 3.7.: Effects of cover crop and fertilizer on marketable celery yield in Laingsburg
and Hamilton during 2003 and 2004 ............................................................... 94

Table 4.1.: Effects of cover crop and fertilizer rate on total weed density at different dates
in Houghton muck soil during Summer 2003 and 20048 ..................................... 128

ix

Table 4.2: Effects of cover crop and fertilizer rate on weed species,r compositionjn
Houghton muck soil during celery growing season 2003‘ ................................... 129

Table 4.3: Effects of cover crop and fertilizer rate on weed species composition in
Houghton muck soil during celery growing season 2004a ................................... 130

Table 4.4: Effects of cover crop and fertilizer rate on number of weed species in
Houghton muck soil during Summer 2003 and 2004 a ....................................... 131

Table 4.5: Effects of cover crop and fertilizer rate on weed dry biomass at different dates
in Houghton muck soil during Summer 2003 and 2004 ...................................... 132

LIST OF FIGURES

Figure 2.1: Growing degree days (GDD base 10 °C) during celery growth in 2003 and
2004 at Laingsburg and Hamilton. Celery transplanted on 23 May 2003 and 28 June 2004
in Laingsburg and on 13 May 2003 and 10 May 2004 in Hamilton. DAT is days after
transplanting .......................................................................................... 57

Figure 2.2: The relationship between celery dry matter accumulation and growing degree
days (GDD base 10 °C) under different cover crop: oilseed radish (a), cereal rye (b), and
hairy vetch (c) and fertilization treatments during 2003-04. Observed data were ﬁtted to a
3 parameter equation. Regression coefﬁcients are indicated in Table 2.3
......................................................................................................... 58

Figure 2.3: The relationship between celery dry matter accumulation and growing degree
days (GDD base 10 °C) as effected by cover crop treatments. Observed data were ﬁtted to
a 3 parameter equation. Regression coefﬁcients are indicated in Table 2.3
......................................................................................................... 59

Figure 2.4: Crop growth rate versus growing degree days under cover crop: oilseed radish
(a), cereal rye (b), and hairy vetch (c) and fertilizer treatments. Observed (symbol)
predicted (lines) of celery dry plant at Laingsburg. Observed data were ﬁtted to a 3
parameter equation. Regression coefﬁcients are indicated in Table

2.5 ...................................................................................................... 60

Figure 2.5: Crop growth rate versus growing degree days under cover crop: 2003 (a) and
2004 (b) for Hamilton. Observed (symbol) predicted (lines) of celery dry plant. Predicted
values for 2003 (a) regression were not ﬁtted to logistic equation. Observed data were
ﬁtted to a 3 parameter model equation. Regression coefficients are indicated in Table 2.5.
.......................................................................................................... 61

Figure 2.6: Mean predicted relative growth as a function of the cumulative growing
degree (GDD) after celery transplanting under cover crop: oilseed radish (a), cereal rye
(b), and hairy vetch (c) and fertilizer treatments in 2003 and 2004 at Laingsburg.
Regression coefficients are indicated in Table

2.7 ...................................................................................................... 62

xi

Figure 2.7: Mean predicted relative growth as a function of the cumulative growing
degree (GDD) after celery transplanting in 2003 and 2004 at Hamilton. Regression
coefﬁcients are indicated in Table

2.7 ....................................................................................................... 63

Figure 2.8: Day after transplanting (DAT) predicted function and observed means of
celery under cover crop: oilseed radish (a), cereal rye (b), and hairy vetch (c) and
fertilizer treatments at Laingsburg, MI (2003 and 2004). Regression coefficients are
indicated in Table

Figure 2.9: Day after transplanting (DAT) predicted function and observed means of
celery under cover crop treatments at Hamilton, MI (2003 and 2004). Regression
coefﬁcients are indicated in Table

Figure 3.1: Daily maximum (A) and minimum (B) temperature of Laingsburg during
celery growth season in 2003 and 2004. Data recorded in Bath weather
station .................................................................................................. 95

Figure 3.2: Daily maximum (A) and minimum (B) temperature of Hamilton during celery
growth season in 2003 and 2004. Data recorded in Hudsonville weather
station .................................................................................................. 96

Figure 3.3: Total monthly rainfall at Laingsburg and Hamilton during celery growth
seasonin 2003 and 2004. Data recorded in Bath and Hudsonville weather stations. The
long term means are from 2001-2003 in Laingsburg and Hamilton .......................... 97

Figure 3.4: Cover crop (total) biomass yield in 2003 and 2004 growing seasons. In
Hamilton, mustards were not seeded in 2003 nor was hairy vetch in 2004 .................. 98

Figure 3.5: Laingsburg microbial respiration (A) and microbial biomass C (B) during
celery growing season in 2004 ..................................................................... 99

Figure 3.6: Hamilton microbial respiration (A) and microbial biomass C (B) during
celery growing season in 2004 .................................................................... 100

xii

Figure 3.7: Celery total yield before trimming stalks as inﬂuenced by cover crop and
fertilization in 2003 (A) and 2004 (B) at Laingsburg. Means separation by the least
squares means test, P < 0.05 ..................................................................... 101

Figure 3.8: Celery total yield before trimming stalks as inﬂuenced by cover crop in 2003
(A) and 2004 (B) at Hamilton. Means separation by the least squares means test, P <
0.05 .................................................................................................. 102

Figure 3. 9: Celery marketable yield after trimming stalks as inﬂuenced by cover crop and
fertilization in 2003 (A) and 2004 (B) at Laingsburg. Means separation by the least
squares means test, P < 0. 05 ...................................................................... 103

Figure 3.10: Celery marketable yield afrer trimming stalks as inﬂuenced by cover crop
and fertilization in 2003 (A) and 2004 (B) at Hamilton. Means separation by the least
squares means test, P < 0.05 ...................................................................... 104

Figure 3.11: Number of marketable celery stalks as inﬂuenced by cover crops and
fertilization in 2003 (A) and 2004 (B) at Laingsburg. Means separation by the least
squares means test, P < 0.05 .............................................................. ‘ ........ 105

Figure 3.12: Number of marketable celery stalks as inﬂuenced by cover crops and
fertilization in 2003 (A) and 2004 (B) at Hamilton. Means separation by the least squares
means test, P < 0.05 ................................................................................ 106

Figure 4.1: Total monthly precipitation. Data recorded in Bath weather station near
located at about 10 km from the experimental site. Long term mean rainfall available
were from 2001-2003 .............................................................................. 133

Figure 4.2: Daily maximum (A) and minimum (B) temperature at different days after
transplanting (DAT) during celery growth in 2003 and 2004. Celery transplanted on 23
May 2003 and 28 June 2004 in Laingsburg and. Data recorded in Bath weather station
located at about 10 km from the

experimental site ................................................................................... 134

Figure 4.3: Biomass production (kg ' ha'l) by the cover crops prior to incorporation and
transplanting of celery in 2003 and 2004. Vertical bars represent standard errors of the
means. Biomass of oilseed radish was measured in October of the year preceding the
growing season (before they were killed by frost). Cereal rye and hairy vetch biomass
was estimated in May prior to land preparation ................................................ 135

xiii

Figure 4.4: Major weed species and contribution to total weed density in 2003 (A) and
2004 (B). Other includes all species contributing less than 10 % to total weed
density ............................................................................................... 136

Figure 4.5: Total before trimming celery yield as inﬂuenced by cover crop and
fertilization in 2003 and 2004. Fertilizer rates are Low (90 kg ' ha'l N), Half (90, 45, and
225 kg - ha" N, P205, K20), and

Full (180, 90, and 450 kg ha" N, P205, K20) ................................................... 137

Figure 4.6: Marketable after trimming celery yield as inﬂuenced b cover crop and
fertilization in 2003 and 2004. Fertilizer rates are Low (90 kg ' ha' N), Half (90, 45, and
225 kg - ha" N, P205, K20), and

Full (180, 90, and 450 kg ha”1 N, P205, K20) .................................................. 138

Figure 4.7: Number of marketable celery stalks as inﬂuenced by cover crops and
fertilization in 2003 and 2004 .................................................................... 139

xiv

 

Chapter 1. Literature Review
Introduction

In 2004, the USDA reported 1.95 million acres of fresh vegetables were
harvested at an estimated total market value of US$ 9.82 billion (USDA, 2005). In the
state of Michigan, 65 thousand acres of fresh vegetables were harvested, adding US$ 18.8
million to the state’s economy. Unfortunately, crop specialization, intensive use of farm
land, and reliance on external inputs has resulted in environmental stress leading to a
decline in agroecosystems productivity. Moreover historically, the mainstream approach
of commercial agricultural practices has often caused speciﬁc ecological disturbances
(Shi, 2004). Some of the documented effects of conventional cropping systems are ﬁeld
resistance (N gouaj io and McGiffen, 2002), poor soil fertility, and increased potential for
water pollution (Hallberg, 1989). As a result, over the past several decades there has been
activism against conventional farming usage of synthetic inputs and more urging to
develop alternate management strategies (Kelly, 1990; Phatak, 1992).

Substantial efforts are currently directed to the restoration of soil health and
improvement of agroecosystems efﬁciency. Globally, there is a collective advocacy on
the part of science to develop and promote the use of agricultural sustainable methods
(Shi, 2004). Considering the known beneﬁts, rehabilitating soil organic matter (SOM) has
become the key to soil fertility and productivity (Allison, 1973). In view of this fact,
adoption of sustainability as a means to use renewable inputs (Sainju and Singh, 1997)
and researching the optimum amounts of fertilizer for vegetable production has gained
favor (Hochmuth, 2003). In this study, we focus on several cover crops to help improve

growth and development of celery in Michigan. In addition, the study evaluated the

overall cover crop performance in achieving speciﬁc management goals i.e., weed control

and enhancement of soil mineral composition.

Sustainability

Opinions vary considerably in the deﬁnition of sustainable agriculture (Phatak,
2003). Today, management strategies that uses less external inputs (Liebman and Davis,
2000) and relies on a comprehensive cropping systems’ approach (USDA, 1980) has
gained broad acceptance. Consequently, reliance on conventional cultural practices is
declining considerably with scientiﬁc advances. This inverse correlation results ﬁ'om
present attempts to remedy the consequences of production, albeit harmful, farming
practices levied upon agroecosystem. The intensity in which the natural environment has
been modiﬁed to attain past productive capacity has directly resulted in degradation of
the natural resources, notably land and water that sustain these very systems (Oberle,
1994). Today, new advances are being developed as the search for alternative solutions
continues to shift toward reuse of the environment and on-fann resources (Sanchez et al.,
2001). Greater adoption of low-extemal-input (LEI) management systems has been
proposed ways that can ameliorate environmental problems associated with conventional
farming systems (Liebman and Davis, 2000). Current research activities include viable
resource management of on farm recyclable sources to facilitate a LEI farming system.
Although LEI systems occupy only a small portion of the agricultural landscape in most
regions, they are becoming increasingly prominent as regulatory, and biological pressures
on conventional farming systems intensify (Liebman and Davis, 2000). The overall

awareness caused by the development of LEI systems has revived sustainability efforts.

No longer is “sustainability” a catch term, its meaning is being applied in scientiﬁc
research as solutions are developed to answer the effects of past farming practices. The
term has also become a synonym for sound and acceptable economic, social, and
ecological development of society (Francis, 2004; Lewandowski et al., 1999). Today,
cropping systems that efﬁciently recycles on ﬁeld resource by managing crop residues
has become a key component in sustainability efforts (Ruffo and Bollero, 2003). Soil
organic matter (SOM) is considered a major component in agriculture systems (Sikora et
al., 1996), because SOM inﬂuences many of the physical, chemical and biological
properties in soil. Some of the properties are soil structure, inﬁltration water holding
capacity, nutrient dynamics, and biological activity. Due to this importance, SOM
becomes a precious on farm commodity therefore, sustaining its health and productive
quality is crucial. Thus, soil-conserving efforts using sustainability principles and
practices can preserve agroecosystems conditions for long-term farm productivity.
Sustainability can be accomplished by a variety of approaches using cropping sequences
and cash crop diversiﬁcation practices. Crop rotation requires rotating crops over
successive growing seasons (Locke et al., 2002). Studies have shown marked
improvement in cropping systems using well-timed crop rotation designs. For instance,
Odihiambo and Bomke (2001), demonstrated cover crop planted in late August provides
an N source during early spring growth. This fact results ﬁom the accumulation of soil
available N, which would be leached or washed with erosion during the fallow period.
Because of recycling, this N accumulation is essentially used as a nutrient source for
plant growth in the following year. By retaining N, farmers can potentially limit the

amount of inorganic fertilizer used the subsequent year and prevent the environmental

 

 

consequences of nitrate leaching. Equally important, crop rotation schemes using cover
crop must be viewed as a viable environmental and economical option to farmers (Stute
Posner, 1995). Therefore, soil-improving methods using crop rotations can play a role
and provide beneﬁts to cropping systems. For instance, crop rotation using alternative -
crops such as cover crops during the off-season improves soil quality and preserves
agroecosystems productivity. In a study conducted to determine soil productivity,
Wortmann et al. (2000), reported signiﬁcant performance by maize and bean crops due to
N ﬁxation and green manure biomass production. Moreover, cover crops when planted
after harvest produce biomass prior to winter (Teasdale, 1996) and can offer value added
to subsequent crop yields. This biomass establishment and function is vital to cropping
system sustainability focus of improving soil quality, soil health and sustaining
agroecosystems’ productivity. To conclude, agroecosystems’ management strategies
recycling N within its boundaries can potentially reduce inorganic N inputs and is a

viable approach to achieving sustainability (Sanchez et al., 2001).

Cover Crop and Soil Fertility

In the last century, the application of N fertilizer to grow crops received
tremendous growth. This in part was due to dramatic declines in the cost of nitrogen
resulting from great improvements in technology for manufacturing (Aldrich, 1980).
Because of the apparent exhaustible supply and relative low cost of nitrogen fertilizer,
farmers used less nitrogen capturing crops (Aldrich, 1980). Today, nitrate contamination
of surface and groundwater is a major environmental concern (Peng and Tabatabai,

2000), because excess soil N03' N can accumulate from residual fertilizer N during

 

winter fallow period (Jackson et al., 1993). Presently, one of the major sources of
contamination is the liberal application of inorganic fertilizers used in intensive crop
production systems (Roth and Fox, 1990). Therefore, reducing nitrate leaching can
prevent ground water NO3’N accumulation (Strebel et al., 1989) and lessen
environmental impact. The contamination (problems that result from N mineralization can
lead to detrimental consequences. Hence, the need for alternative ﬁeld management
practices, i.e., cover cropping has accelerated. Management practices which minimize
N03' N concentrations include: modifying cropping systems by integrating cover crops
and growing a winter cover crop to assimilate NO3' N into organic plant N (Stevenson,
1999). If synchronized with crop demand, using cover crops and supplemental inorganic
N applications can reduce the liberal use of fertilizers and lessen the associated
environmental consequences (N yiraneza, 2003).

Cover crops are vegetation that is grown in the off-season for soil beneﬁts and
have been long considered a vital practice in sustainable cropping systems. Cover crops
have been used for hundreds of years (Bloodworth and Johnson, 1995). Early on
Xenophon (434-355 BC.) the Greek historian, may have noticed herbage beneﬁts having
suggested turning up the grass may serve as manure (Thomas and Frye, 1984). Today, the
use of cover crOps is widely recognized and has been reported for known beneﬁts. For
instance, beneﬁts of cover crops include increased soil fertility (Griffen et al., 2000;
Ranells and Wagger, 1996), weed suppression, (Kenerley and Bruck, 1983; Pinkerton et
al., 2000; Utkhede and Hogue, 1999) and improved management of soil borne diseases
(Czarnota et al., 2001; Herrero et al., 2001; Liebman and Davis, 2000; Ohno et al., 2000,

Ohno and Doolan, 2001). Because of the countless contributions, cover crops can play a

 

pivotal role in achieving environment sustainability by the reuse of natural resources.
Sustainable practices that include both a soil and crop management focus can have a
profound inﬂuence on agroecosystem efﬁcacy. Mention must be made to the soil
improving ability of cover crops. Cover crops have been used for many years because of
beneﬁts to soil fertility and structure (Teasdale et al., 1993). Utilization of cover crop is
dependant upon determined goals as a way to develop strategies in achieving agricultural
aims. Generally, the production objectives are to maintain quality yields in view of
environmental factors, i.e. resource regimes.

To achieve agricultural aims, cover crops can play a crucial role in N management
schemes (Kowalenko, 1987). Previous studies conducted with the integration of cover
crops into vegetable production systems rendered favorable results (Teasdale, 1996). For
instance, legume cover crops have demonstrated an N contribution to the growth of
principal crops by ﬁxing atmospheric N. Symbiotic biological ﬁxation from the
intimately formed relationship between soil microbes and legumes can provide
meaningful amounts of N (Dabney et al., 2001). Consequently, cover crops can
potentially increase production yields. Abdul-Bald et al. (1996), found signiﬁcantly
higher tomato yields and enhanced early fruiting in plant mulch. In addition, Ngouajio
and Mennan (2004) reported high yields in rye and sorghum sudangrass system and
concluded cucumber yields may be potentially improved using cover crops. Clearly,
using legume cover crops in crop management systems offers the opportunity to enhance
yields (Boquet et al., 2004). On the other hand, non-legume cover crops have been
associated with reducing N leaching by removing residual available N (Isse et al., 1999)

and have been advocated to reduce nutrient loss (N junie et al., 2004). The ability of

cover cr0ps to improve soils by trapping soil residual N left from by previous crops is
well documented (Singogo et al., 1996). Logsdon et al. (2002) found signiﬁcant NO3' N
reduction in cat and rye cover crops during their ﬁeld studies. Furthermore, Shipley et al.
(1992) study concluded that cover crops reduced the risk of leaching because of uptake of
soil N03'N. These cover crop ﬁmctions of N provisions and reducing nitrate leaching
from agricultural soils can replace some intensively applied inorganic N (Burket et al.,
1997). Therefore, cover crops can be useful in cycling nutrients as a crop management
strategy to preserve nutrient loss and offer N credits as well. It is abundantly clear that
establishing cover crops in crop rotations to manage nutrients can enhance both

agroecosystems productivity and sustainability.

Cover Crop and Weeds

Due to today’s market economy, more and more growers are specializing on one
or two major crops, thereby reducing their rotations systems to a strict minimum. The
monoculture specialization has contributed to the resurrection of ﬁeld problems i.e.,
resistant weeds, and pathogen populations, which have become difﬁcult to control. The
continuous cropping method makes weed management challenging (Derksen et al., 2002)
and causes considerable frnancial losses (Swanton et al., 1993). In addition, weed
response to other agronomic practices has resulted in community composition shifts
(Derksen et al., 2002). Consequently, conventional control measure tendencies were to
rely on agrochemicals to ameliorate the problem. As a result, the use of synthetic
pesticides has lead to the reduction in biodiversity, creating a less productive

agroecosystem (N gouajio and McGiffen, 2002) and threatens farm proﬁtability (Liebman

and Davis, 2000). The environmental risks associated with agrochemical exposure,
include shifts in weed dynamics and other pests towards pesticide-resistant species
(Benbrook, 1996). Therefore, much attention has been given to strategies that improve
weed management and are among the top research priorities (Liebman and Davis, 2000).
One approach is to introduce crop rotation systems to disrupt and prevent the
regeneration of weed species (Liebman and Davis, 2000). Furthermore, there is
signiﬁcant empirical evidence that two or more crops within a rotation can reduce weeds
(Teasdale et al., 2004). Moreover, crop rotations offer different vegetative growth habits
and thereby alter weed life cycles (Liebman and Cyck, 1993). Many studies have
reported cover crops’ inﬂuence in weed suppression when incorporated into a crop
rotation system (Johnson et al., 1993; Teasdale et al., 1991; Yenish et al., 1996). Crop
patterns including non-host crops are effective ways of managing weeds, and diseases
while improving soil health. Therefore, cover crops have shown good potential,
remedying some of the problems created by short-term 0r lack of crop rotations
(Kenerley and Bruck, 1983; Pinkerton et al., 2000; Utkhede and Hogue, 1999). Weed
suppression is another beneﬁt attributed to cover crops. Several studies have reported the
positive effect of cover crops on weed suppression. Generally, the relative location of
cover crop residue to soil surfaces alters growth conditions of weeds (Teasdale and
Mohler, 1993). The principle goal of using cover crops for weed control is replacing an
unmanageable weed population with a manageable cover crop (Teasdale, 1996). The
presence of winter vegetation provides a protective cover during winter while preventing
weed emergence at a critical time. The objective of using a winter annual cover crop for

weed management is the production of sufficient residue to create an unfavorable

environment for weed germination and establishment (Teasdale, 1996). The correlation
between reduced weed density and cover crop biomass is a function of residue levels.
This is indirectly due to the substantial biomass production by cover crops changes
environmental conditions. Both provide signiﬁcant soil cover and alter weed seed
germination because of the proximity to weed seed bank site. Cover crop residue
inﬂuences weed populations in no-tillage cropping systems because of the proximity of
residue to the site of seed germination at the surface of soils (Teasdale and Mohler, 1993)
and modify the growing conditions under which weeds germinate or emerge (Fisk et al.,
2002). The presence of ground covers provided by cover crops becomes a physical
barrier impeding weed growth because of plant architecture and morphology (Ponce et
al., 1996). Seavers and Wright (1999) reported a strong suppressive ability of cover
crops on weeds in their study. Weed infestation can be reduced over time by cover crops
(N gouajio et al., 2003). For these reasons, crop rotation is recognized as an important tool
for weed management because some crops in the rotations suppress weeds by competing
for resources (Liebman and Dyck, 1993). This has the double advantage of reducing
herbicide inputs and monoculture practices that have otherwise created insurmountable
challenges.

The beneﬁts of crop rotations are well understood by most growers. For instance,
fall-seeded winter cover crops are the most commonly used practice by celery growers in
Michigan. The winter hardy cover crops, which survive the frost, are incorporated into
soil prior to the spring growing season. The cover crop is usually killed late in the spring

by cultivation or by herbicide application, followed by crop planting (Mutch and Martin,

1998). The idea that with timely management, the spring cultivated cover crop will

supply nitrogen and suppress weed growth.

Oilseed Radish, Cereal Rye and Hairy Vetch

Understanding cover crop inﬂuences on cropping systems is important. As
Michigan farmers seek sustainable agroecosystems innovations, integrating cover crops
and crop rotation practices are gaining wide acceptance in the state of Michigan.
Primarily, cover crops are used during the fall period to reduce soil erosion (Ranells and
Wagger, 1996) and prevent nutrient leaching when the bare ground is vulnerable (Shipely
et al., 1992). Because of the amount of time vegetation is present during the winter
period, cover crop offer the opportunity to reduce nitrate leaching (Stock et al., 2004).
The fallow period of most cropping systems is short (Jackson et al., 1993) therefore
limiting nitrate leaching can be achieved with efﬁcient and quickly established cover
crops (Meisinger et al., 1991). Notwithstanding, improving cropping systems using
cover crops has been a general convention in Michigan (N gouaj io and Mutch, 2004).
Speciﬁcally, Michigan celery growers are becoming increasingly interested in adopting
cover crops into their intensive production designs. Farmer adoption facilitates the need
to ensure competitive production yields and maintain a sustainable agroecosystem. To
achieve these goals, Michigan celery growers are integrating cover crops into existing
ﬁeld operations to maximize cover crop beneﬁts. Thus, cover crops have become a viable
option for sustainable agriculture purposes because farmers realize the contributions to
soil fertility, improved crop performance (Smith et al., 1987) and weed suppression

(Teasdale and Daughtry, 1993) cover crops provide. The use of cover crops to absorb

10

soil nutrients is also an important component in production yield objectives. Nutrients
that would otherwise be loss to the agriculture systems are recycled on site with cover
crop. Sainju et al. (1998) reported rye demonstrated recycling efﬁciency of soil

NO3’N. Non-legume cover crops have been associated with reducing N leaching loss
(Isse et al., 1999). Two winter hardy cover crops, hairy vetch (Vicia villosa Roth), rye
grass (Secale cereale L.) are well adapted to relatively cool environment; along with
oilseed radish (Raphanus sativus [L.] var oleiferusMetzg [Stokes]). They are annual
cover crops used in ﬁeld management practices during the frost fallow season. Due to N
ﬁxation, hairy vetch a legume can have an important role in increasing N concentration at
spring planting (Odhiarnbo and Bomke, 2001). On the other hand, cereal rye grass
produces fall biomass while sequestering a moderate amount of soil available N
(Meisinger et al., 1991). As a biculture, both hairy vetch and rye grass can be used
simultaneously in cropping systems for nutrient beneﬁts (Wagger et al., 1998). In
consecutives years, Ranells and Wagger (1996), reported signiﬁcant amounts of N
content in hairy vetch and rye grass biculture of 82 and 200 kg ha". Also, Jackson et al.
(1993) reported reduced soil moisture, indicator of decline in N03' N leaching tendencies.
Similarly, oilseed radish was found to sequester residual soil NO3' N following wheat

. harvests (Vyn et al., 2000).

Several researchers found that hairy vetch residue suppressed some weed species
(Hoffman et al., 1993; Teasdale, 1993) due to biomass production. Similarly, rye cover
crop suppressed certain broad-leaved and grass weeds (Shilling et al., 1986). Ngouajio
and Mutch (2004), found that oilseed radish planted in the fall can provide weed

suppression.

11

Monitoring Soil NO3' N Pool

Nitrogen is considered the most limiting nutrient in agriculture productivity
(Woodmansee et al., 1978). Agricultural crops take up N in two forms, primarily from
soil organic matter, inorganic N from fertilizer, manure, and N ﬁxation by legumes
(Nyiraneza, 2003). Soil NO3' N leaching threatens groundwater quality and is a major
issue to agroecosystems ﬁmction and structure (Strebel et al., 1989). Therefore, a
nutrient management strategy monitoring N transformation can provide soil N03' N. One
method of monitoring trace metals is by using ion exchange resin (IER). IER are resin
within a membrane with a strongly basic anion exchanger or counter ions. IER can be
used in ionic form for sorption and exchange of low molecular weight anions i.e., sample
ions. Using IER can be a useful tool in measuring the concentration of NOg'N found in
soil and can be used to quantify N mineralization rates. Dodd et al. (2000) reported a
correlation between increased soil water and N03' N leaching using resin bags when
assessing N mineralization. In these studies, results suggest the presence of nitrate on
IER reﬂects its ability to absorb ions in the soil. IER can be effective in attracting
nutrients transported by mass ﬂow that potentially leaches through the soil (Chen et al.,
2003). There are ecological consequences, due to nitrogen enrichment practices of the
last century. Thus IER can provide management systems with a tool to monitor soil

nitrate dynamics and better manage the rates of inorganic fertilizers.

Total Soluble Solids

Fruit quality is determined by a few sensory attributes i.e., color, size, shape,

ﬂavor, and ﬁrmness. Visually, the term ‘quality’ suggests a degree of excellence (Abbott,

12

1999), but when measured do not account for the hidden and equally important
nutritional value (Shewfelt, 1999). Plant sap contains self-nourishing nutrients, which
determines overall plant health. These soluble elements found in plants are mobile
nutrients used by plants as a source of nutrition. To assess the nutritional qualities,
instrumentation is often required (Abbott, 1999) and is currently being used to evaluate
internal fruit quality (V alero et al., 2004). Measuring plant tissue can provide valuable
information for crop management. For instance, a good sap or Brix level of 12 or higher
offers greater disease resistance, higher yields, longer shelf lives, and improved taste

(N arendranath and Power, 2005). A low Brix value indicates sub-standard fruit quality.
Measuring plant tissue can provide information of how to modify cropping management

techniques to ensure greater disease resistance, higher yields and better quality crops.

Michigan celery production

There are approximately 1,550 vegetable farms on 65,964 ha of farmland in
Michigan (MDA, 2003). Michigan vegetable growers produced 882,410 tons of fresh
and processed vegetables in 2003 (MDA, 2004). Dual purpose vegetable acreages are
used for both fresh market and processing. The value of production totaled $227 million.
Nationally, Michigan ranked second after California in fresh celery (Apium graveolens
L.) production (6.2 % of total national production). In 2004, c. 890 ha of celery was
harvested at a value of $18.8 million. Celery comes from a biennial, herbaceous plant of
the Apiaceae (formerly Umbelliferae) family, and is believed to have originated from the
Mediterranean basin. The ﬁrst production of celery in the United States is thought to
have occurred mainly in Florida. Today, Celery is being grown in California, Michigan,

Florida, Texas, Ohio, New York, and Pennsylvania. Its seed was brought to Kalamazoo,

l3

Michigan, in the 1850s from Scotland, and it became a commercial crop there. Currently,
the majority of celery production in Michigan is concentrated on the southwest side of the
state along Lake Michigan in Newaygo, Oceana, Muskegon, Ottawa, Kent, Allegan, and
Van Buren counties. Celery transplants are produced in controlled environments for 12
weeks at 18 to 21 °C. In Michigan, celery is mainly grown on muck soil. Organic muck
soils are ideal for celery production due to its water holding capacity. Once transplanted,
most common celery varieties require 12 weeks to mature and grow best at a daily
optimum temperature of c. 18° C. Most Michigan celery growers plant from 80 - 104,000
plants per hectares. Michigan farmers face major problems that threaten ﬁeld production
and can potentially limit annual yields. The continued use of synthetic inputs coupled
with limited crop rotations, have reduced sustainability of celery production. In addition,
weeds interfere with ﬁeld operations, competing for useful resources i.e., space, nutrients,
moisture, light and space required in celery production (Hausbeck, 2002). Each year,
diseases can cause signiﬁcant losses to crop production (Summer et al., 1986). Fusarium
yellows of celery is a detrimental disease that can severely destroy the crop. Bacterial
blights are diseases affecting celery in Michigan causing annual leaf and petiole
destruction. Early blight is common and destructive (Kucharek and Berger, 2000). Also,
leathoppers (Macrosteles quadrilineatus) and nematodes are both pests that negatively
affect celery growth and quality in Michigan. Realizing this fact, Michigan celery
growers are increasingly seeking sustainable practices that will offer solutions to
aforementioned problems and still maintain competitive productivity. The use of cover
crops is among the options currently being evaluated for celery production by Michigan

farmers.

14

Objectives

The overall objective of this study is to provide celery production alternatives to
Michigan growers interested in sustainable farming practices. Establishing cover crops
after harvest of early transplanted celery can provide beneﬁts to the production system.
Therefore, winter cover crops will be selected to suitably ﬁt the crucial time interval
before and after periods of main crop production. The fall fallow season is critical to the
program’s sustainability efforts and will receive paramount emphasis. Results will be
shared with growers to develop sustainable systems and enhance their existing ﬁeld
operations.
To achieve this objective; we will (i) evaluate the potential to integrate cover crops into
celery production system; (ii) measure the effect of cover crops at providing non-
chemical weed suppression, and their impacts on weed species composition of weed
populations; (iii) determine if cover crops can reduce the use of fertilizer inputs in celery
production;(iv) study the effects of cover crop and fertilizer rates on celery quality,
growth, and yield; (v) measure the ability of cover crops to reduce nitrate leaching in

celery production systems.

Rationales are:
1. Early transplanted celery is harvested in Mid July. This allows a signiﬁcant window
at which to introduce cover crops into ﬁeld operations prior to the frost and winter

season. Assuming celery is grown the next year.

15

Evaluating weed population response to cover crops will provide relative
information to ﬁeld composition trends of resource competitors during growing
season.

Reducing the use of external inputs while maintaining competitive celery yield
production will provide a model system for sustainable farming practices.
Determine if the interaction between both factors improves the overall celery
production system.

Assessing tissue and IER resin extractions will provide information about nutrient

(N O3'N) mobility in the presence of cover crops.

16

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33:1,010-1,016.

Stute, J .K. and J .L. Posner. 1995. Legume cover crops as a nitrogen source for corn in an
oat—com rotation. J. Prod. Agric. 8:385-390. .

Summer D.R., E.D. Threadgill, D.A. Smittle, S.C. Phatak, and A.W. Johnson. 1986.
Conservation tillage and vegetable diseases. Plant Disease 70:906-911.

Swanton, C.J., K.N. Harker, and R.L. Anderson. 1993. Crop losses due to weeds in
Canada. Weed Technol. 7:537-542.

Teasdale J .R 1993. Interaction of light, soil moisture, and temperature with weed
suppression by hairy vetch residue. Weed Science 41:46-51.

Teasdale, J .R. 1996. Contributions of cover crops to weed management in sustainable
agricultural systems. J. Prod. Agric. 9:475-479.

Teasdale, J .R., C.E. Beste, and WE. Potts. 1991. Response of weeds to tillage and cover
crop residue. Weed Sci. 39:195—199. '

Teasdale, J .R. and CL. Mohler. 1993. Light transmittance, soil temperature, and soil
moisture under residue of hairy vetch and rye. Agron. J. 85:673-680.

Teasdale, J .R., R.W. Magnum, J. Radhakrishnan, and M.A. Cavigelli. 2004. Weed seed
bank dynamics in three organic farming crop rotations. Agron. J. 96:1,429-1,435.

Teasdale, J .R., and CS. Daughtry. 1993. Weed Suppression by live and desiccated hairy
vetch (Vicia villosa). Weed Sci. 41 :207-212.

Utkhede, RS. and E.J. Hogue. 1999. Inﬂuence of ground cover on the development of
phytophthora crown and root rot of apple trees. Can. J. Plant Pathol. 21 :106-109.

USDA (United States Department of Agriculture). 2005. National Agriculture Statistic
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USDA (UnitedStates Department of Agriculture). 1980. Report and recommendations on
organic farming. Washington, DC.

Vyn, T.J., J .G. Faber, K.J. Janovicek, and E.G. Beauchamp. 2000. Cover crop effects on
nitrogen availability to corn following wheat. Agron. J. 92:915-924. '

22

Valero, C., M. Ruiz-Altisent, R. Cubeddu, A. Pifferi, P. Taroni, A. Tonicelli, G.
Valentini, D. Johnson, and C. Dover. 2004. Selection models for the internal

quality of fruit, based on time domain laser reﬂectance spectroscopy. Biosys. Eng.
88:313-323. '

Wagger, M.G., M.L. Cabrera, and N.N. Ranells. 1998. Nitrogen and carbon cycling in
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no-tillage corn (Zea mays ). Weed Technol. 10:815—821.

23

Chapter 2: Celery (Apium graveolens L.) growth responses to various cover crops

and soil fertility levels.

ABTRACT

Our objective was to determine the combined effects of different annual cover
crops and fertilizer rates on celery (Apium graveolens L.) growth, quality, and yield.
Field experiments were conducted from 2002 to 2004 on Houghton muck soil in
Laingsburg and Hamilton, MI. Oilseed radish consistently produced higher biomass at
both sites during the ﬁrst year at 719 (Laingsburg) and 585 g m'2 (Hamilton) compared to
all other treatments. Celery dry matter (DM) accumulation, crop. growth rate (CGR),
relative growth rate (RGR), and marketable yields were usually low in the bare ground
system. The use of cover crops improved celery growth and yield under the low and half
rate of fertilizer. Oilseed radish showed the highest beneﬁts. Celery grth and yield
was highly affected by heat accumulation (growing degree days), which may also have
effected decomposition of cover crops. Faster growth and high yield were observed
under warm conditions. These results suggest that growers can use cover crops as a part

of crop rotation system to improve celery grth and yield.

24

INTRODUCTION

Vegetable production is an important part of the agricultural industries in most of
the United States (Hochmuth, 2003). In 2004, c. 0.79 million hectares of fresh market
vegetables were harvested with an estimated value of $9.82 billion (USDA 2005). Celery
is one of the major vegetables produced for fresh market or processing. In 2004 c.

11,048 hectares were harvested with a corresponding value of $283.9 million.
Nationally, Michigan ranks second after California in celery [Apium graveolens L. var.
rapaceum (Mill.) Gaud.-Beaup] production (6.6 % of total national production in 2004)
with c. 890 hectares of celery harvested, and a value of $18.8 million to Michigan’s
economy (USDA 2005).

The development of specialized farming operations has resulted in dependence on
synthetic fertilizer for vegetable production (Singogo et al., 1996). Until recently, the use
of high-input synthetic systems was a widely used method to maximize yield and product
quality (Abdul-Baki et al., 1996). Recently, many farmers and scientists have recognized
a need to develop alternative production systems that can preserve productivity and
maintain proﬁtability (Wells et al., 2000). Consequently, there has been a resurging
emphasis on sustainability (Petersen et al., 2005).

The renewed interest in sustainability includes the use of cover crops in vegetable
production as a viable option to rebuild soil organic matter content (Sherman, 1992). Soil
organic matter is important to maintaining soil fertility levels (Allison, 197 3). The
agricultural practice of cover cropping has been used in this context to improve soil
organic matter accumulation (Wagger et al., 1998) that in turn, can maintain and increase

soil nitrogen (N) content. Ditsch and Alley, (1991) demonstrated in their study that N

25

can be conserved in agriculture systems by cover cropping. Additionally, Kuo et al.
(1997a) observed large amounts of available N in the systems using leguminous cover
crops. During spring, N ﬂom the decomposing plant material is released over a longer
time span than most inorganic N sources (Burket et al., 1997) and can reduce the amount
of inorganic fertilizer used in intensive vegetable cropping systems. Short and long term
release of available nitrogen varies with cover crop species and may affect crop growth at
different stages (Kuo et al. 1997a). Studies documenting the additional N provided by
cover crops resulted in differential vegetable crop yields (Stivers and Sherman, 1991;
Stirzaker and White, 1995). Kuo et al. (1996, 1997a, 1997b) Showed that the type of
cover crop (leguminous versus non-leguminous species) and total biomass were the
major divers for changes in soil N levels (and availability), soil organic matter levels, and
crop yield. Loecke et al. (2004) showed that soil organic amendment affect crop growth
and yield. In their study corn treated with composted swine manure produced 10% more
grain and 12 to 15% more dry matter than corn treated with ﬂesh manure. The
differences in the two systems were detected with growth analysis during the season, with
for example greater values of crop growth rate (CGR) found in the composted manure
system (Loecke et al. 2004). Thus, soil organic amendments including the use of cover
crops can potentially enhance sustainable growth and development of vegetable crops.
Celery requires about 12 weeks to reach maturity under Michigan growing
conditions. Harvest of early-planted celery is usually completed by late July. Therefore,
allowing for the establishment of cover crops between July and October prior to ﬁrst
ﬂost. Yield increases have been documented in systems using cover crops. Growth

analysis is a useful tool for illustrating the relationship between plant growth and

26

environmental ﬂux (Hunt, 1982). Growth analysis could provide a better understanding
of changes during the growing season that are responsible for the differential yields (Hunt
1982). To our knowledge, no study has focused on the effect of cover crops and fertilizer
regimes on vegetable growth and development on muck soils in general, and on celery in
particular. Because of the high organic matter content of muck soil and the high soil
fertility requirements of celery, integration of cover crops and fertilization regimes may
have signiﬁcant effects on celery growth, development, and yield. Investigation of such '
analysis would lead to a better understanding of how cover crop and fertilization improve
celery production in Michigan. For this reason, the main objectives of this study were (1)
to compare and evaluate winter annual cover crops in an intensive celery production
system; (2) study the effects of cover crops and different fertilizer rates on celery growth,

yield, and stalk quality.

2. MATERIALS AND METHODS
2.1. Experimental site

Studies were conducted ﬂom 2002 to 2004 at the Michigan State University Muck
Soils Research Farm in Laingsburg, MI and at a commercial celery farm in Hamilton,
M1. The soil at both sites was a Houghton muck with 80 % organic matter and pH of 6.2-
6.9. Heat accumulation (degree days) was very different between growing seasons (Fig.
1)
2.2. Laingsburg Experiment

The site was fallow in the year preceding the start of the study. The experimental

design was a randomized complete block design with four replications. The treatments

27

consisted of a combination of different cover crops and fertilizer rates. Cover crop
treatments were oilseed radish (cv. diakon) (Raphanus sativus (L.) var. oleiferus Metzg
(Stokes), cereal rye (cv. VNS) (Secale cereale L.), hairy vetch (cv. common) (Vicia
Villosa Roth), and a bare ground. The fertilizer rates were: full rate (180, 90, and 450 kg
ha" N, P205, K20), half rate (90, 45, and 225 kg ha“1 N, P205, K20), and low rate (90 kg
ha'1 N). The full rate was the recommended rate for commercial celery production.
Cover crop treatments were applied to large plots (10.7 m long by 12.9 m wide). Using
large plots for the cover crops allowed minimal residue movement among experimental
units during land preparation. Each cover crop plot was further divided into smaller plots
‘ (10.7 m long by 4.1 m wide) to accommodate the different fertilizer rates. A total of 9
treatments (combination of cover crop and fertilizer rate) were used. This included: the
bare ground control plus each of the 3 fertilizer rates, and the three cover crop species
(cereal rye, hairy vetch, and oilseed radish) plus the Half and Low fertilizer rates.
Combining cover crops and high fertilizer rate treatments was not practically economical
and was therefore excluded ﬂom this study. Therefore, the experiment was not a
factorial. All of the P, K and 25% of N was applied as top dressing; with equal amounts
of remaining N applied in 3 side dressings at 23, 43, and 64 days after transplanting
(DAT) in 2003 and 2004. Individual experimental units contained four rows of celery at
0.15 m- in-row spacing and 0.79 m between row spacing, corresponding to 83,000 plants
ha ".

The cover crops were established in late summer of the year preceding each growing

season (26 August 2002 and 25 August 2003). The seed was broadcast and incorporated

28

by discing. Seeding rates were 28 kg ha" for oilseed radish, 112 kg ha" for cereal rye,
and 39 kg ha'1 for hairy vetch.

Top dressed fertilizers were broadcast on 20 May 2003 and 28 June 2004 and
incorporated by discing. Celery was transplanted on 23 May 2003 and 28 June 2004.
Subsequent N side dressings occurred on 13 June, 3 July, 25 July 2003 and 21 July, 10
August, and 31 August 2004. Cover crop total biomass was determined by harvesting
plants in a 50- by 50-cm quadrat placed randomly in each plot. Because oilseed radish
winter kills, its biomass was sampled prior to the October ﬂost in 2002 and 2003. Cereal
rye and hairy vetch over-wintered, and continued growth through spring, and were then
killed with glyphosate [N — (phosphonomethyl)- glycine)] prior to celery transplanting.
Hairy vetch and rye biomass samples were sampled on 8 May 2003 and 6 May 2004.
Dry biomass of cover crop was determined after oven drying at 60 °C until constant

weight.

2. 3. Hamilton Experiment

The experiment was arranged in a complete block design with three replications.
Plots were12.2 m by 18.3 m and consisted of 18 double row beds (total of 36 rows). The
cover crop treatments and seeding rates were identical to the Laingsburg site described
above, with the additional cover crops: yellow mustard (cv. tilney) (Sinapis alba L. Syn
Brassica hirta Moenah) 22 kg ha" and oriental mustard (cv. forge) [Brassicajuncea (L.)
Cosson] 13 kg ha" seeding rates in the 2004 season. Planting dates of cover crops were 9
August 2002 and 30 August 2003. Celery was transplanted on raised double row beds

system on the 13 May 2003 and 10 May 2004. In row spacing was 0.15 m, spacing

29

between the two rows on the same bed was 0.31 m, and spacing between consecutive

beds (center to center) was 1.01 m. Final plant density was 130,000 plants ha‘.

2.4. Data Collection

At Laingsburg, celery plants were sampled at 23, 43, and 64 DAT in both 2003 and
2004. At Hamilton, celery plants were sampled at 32, 44, and 64 DAT in 2003 and on
31, 52, and 72 DAT in 2004. During plant sampling, 5 whole celery plants were
randomly collected ﬂom each plot. Druing all dates, ﬂesh and dry weights and stalk
lengths were measured. Celery dry weight was determined after oven drying at 60 °C
until constant weight. At Laingsburg, one of the two middle rows of each plot was used
for destructive sampling and the other for ﬁnal crop yield estimation. During Laingsburg
harvest, 20 plants were collected on 12 August 2003 and 20 September 2004. During
Hamilton harvest, 10 plants were collected on 29 September 2003 and 20 plants on 6
August 2004. At harvest, plants were separated into marketable and non-marketable
stalks, according to market standards. Generally, marketable plants are qualiﬁed as well
developed, well-formed plants with stalk lengths of c. 0.36 m (USDA, 1959). Stalk
weight was measured before and aﬁer trimming for each yield category. At both sites
during harvest, a random sample of 5 petiole segments was collected ﬂom each plot for
total soluble solids measurement. Total soluble solids content was measured using a
digital reﬂactometer (Palette PR-3 2, ATAGO C0., LTD.32-10 Honcho, Itabashi-ku,

Tokyo). Growth analysis was performed using above and below ground plant materials.

30

2. 5. Statistical Analysis
Analysis of variance (AN OVA) was conducted on all data using the PROC GLM of
SAS (SAS institute, Inc., 1999). The least signiﬁcance differences were deﬁned at a =
0.05 level (LSDO_05) for all data sets. Means of crop growth rate (CGR) and relative
growth rate (RGR) of celery were calculated using the following equations (N gouaj io et
al., 2001).
Mean CGR=(W2- W1)/(ATGA) [l]
MeanRGR=(an2—ln W1)/AT [2]
GA is ground area, W1 is dry weight at a given sampling date, W2 is dry weight at the next
consecutive sampling date, AT is the number of days between the two consecutive
samplings, and In is the natural logarithm. Celery data on dry matter (DM) per plant,
CGR, RGR, and stalk length were ﬁtted to nonlinear regression model using Sigmaplot
(2005).
The observed DM per plant, CGR, and stalk length data were ﬁtted to the following 3-

parameter logistic equation.
a

where y represents biomass accumulation (or CGR, or stalk length), x0 is the degree day

y:

(base 10 °C) at maximal value, x is degree day at each sampling date, a is the maximal
value of y, and b describes any deviation ﬂom logistic growth.

The RGR data were ﬁtted to the following polynomial quadratic equation.

y=y0+ax+bx2 [3]

31

All growth analysis regressions were conducted using growing degree days instead of
days after celery transplanting (Russelle et al. 1984).

3. RESULTS

3.]. Cover crop biomass production

There were signiﬁcant differences in cover crop biomass (total) production during
each year at both sites (Table 2.1). In Laingsburg, oilseed radish consistently produced
the greatest biomass in both years with 719 and: 480 g m‘2 for 2003 and 2004,
respectively. Biomass of cereal rye was 284 g m’2 in 2003 and 270 g m‘2 in 2004. Hairy
vetch produced the lowest biomass with 181 g m'2 in 2003 and 114 g m‘2 in 2004. In
Hamilton, the highest DM biomass yield was signiﬁcantly greater in oilseed radish in
2003 and in cereal rye treatment in 2004. Cereal rye stand was excellent in 2004,
resulting in the greatest biomass (1599 g ml). Biomass in the oilseed radish, yellow
mustard and oriental mustard was similar and ranged ﬂom 691 to 822 g m".

Generally, cereal rye biomass was lower than expected in Laingsburg and Hamilton
in 2003 due to poor germination in the fall and destruction by herbivores during winter.
Observations suggest difficulties for rye establishment under high organic matter soil
conditions. Irrigation after sowing may help improve seed germination and seedling

establishment.

3.2. Celery biomass production
At Laingsburg, the DM accumulation of all treatments was consistently smaller in

2003 than in 2004 (Table 2.2, Fig. 2.2). The high biomass production in 2004 was

32

probably due to the late transplanting of celery when warmer air temperatures were
conducive for rapid growth (Fig. 2.1).

In 2003, all treatments containing oilseed radish enhanced early celery growth. At 23
DAT, biomass (1.0 g plant") in the oilseed radish-half fertilizer rate was similar to that in
the control-full rate (0.8 g plant“). All treatments with cover crops improved celery
growth compare to the bare-ground system (Fig. 2.2).

In 2004, no treatment effect was observed (Table 2.2). This may be attributed to two
factors: (1) The long delays between land preparation (cover crop kill) and celery
transplanting, and (2) nutrient loss resulting ﬂom unusually high rainfall. In 2004, the
experimental site in Laingsburg received 233.7 mm of rainfall during May in comparison
to 97.5 mm in 2003. This delayed celery transplanting at the Laingsburg site to June 28
in 2004 while transplanting was conducted on May 10, 2004 in Hamilton.

At Hamilton, hairy vetch, oilseed radish, and cereal rye did not improve celery
growth over the bare soil system (control) in 2003 (Table 2.2, Fig. 2.3). However, in
2004 celery growth in plots previously occupied by cereal rye showed signiﬁcant growth
reduction, especially in early stages. At 31 DAT, celery biomass was only 1.7 g plant"1 in
the cereal rye plot and varied ﬂom 2.7 to 4.3 g plant " in other treatments. This
corresponds to the season when cereal rye produced the greatest biomass, suggesting
potential nutrient immobilization or allelopathic interference.

Non-linear regression analysis between celery biomass and growing degree days
(GDD) showed excellent ﬁt for all locations and years (Table 2.3, Fig. 2.2 and 2.3).
Regression coefficients of determination (r2) were 0.99 for all treatments (Table 2.3). The

maximum value of celery biomass (a) was extremely high, especially for the Laingsburg

33

site, indicating that sampling ceased while celery was still at the exponential growth
stage. Allowing more time for growth and additional samplings would have resulted in

quality and yield loss.

3. 2. Crop Growth Rate (CGR) and Relative Growth Rate (RGR)

Crop growth rate (CGR) over the entire sampling period is presented in Table 2.4 and
Fig. 2.4 for Laingsburg. In 2003 and 2004, mean CGR consistently increased during each
growth period. In 2004, the mean CGR were higher than 2003 at each sampling date. In
all years, there were no statistical differences in plant dry weight gain among the
treatments during the ﬁnal time period. In 2003, the mean CGR varied considerably
throughout the growing season but were signiﬁcant only for the ﬁrst evaluation
conducted at 23 DAT. The weight gain was the highest in the oilseed radish treatment
that received half fertilizer rate (0.2 g m2 d") and was statistically greater than the control
treatment with either low or half fertilizer rate. Throughout the season, celery growth in
control plots with low fertilizer rate had the slowest CGR (Fig. 2.4). In 2004, similar
mean CGR trends persisted early on, but weight gain at all growth stages was not
statistically different. As previously mentioned, CGR were higher at each growth stage in
2004 than 2003.At the ﬁnal sampling date, celery previously grown in the cereal rye plus
half fertilizer plots offered the highest plant weight gain in both years (Fig. 2.4).

In 2003, at Hamilton, there were no signiﬁcant differences in celery weight gain
throughout the season (Table 2.4). However, the CGR was generally greater with hairy
vetch treatments at early growth stages. In 2004, the weight gain during the ﬁrst and

second CGR, were less than those observed in 2003 because of the warmer temperatures

34

following celery transplanting in 2003 (Fig. 2.1). Unlike 2003, the weight gain in 2004
increased consistently with time in all treatments. This was likely due to low temperature
at later growth stages of celery growth in 2003 (Fig. 2.1).

In 2003, at Laingsburg, mean RGR of plants consistently increased during the second
sampling interval (21 July — 10 August), but generally decreased in the ﬁnal sampling
interval (31 August — 20 September) (Table 2.6; Fig. 2.5). Moreover, in 2003, there were
generally no RGR differences among the cover crop and fertilizer treatments at the ﬁnal
sampling interval (31 August - 20 September). In 2004, the mean RGR of plants in all
treatments were higher than those in 2003during the ﬁrst sampling (0-21 July) interval.
At either low or half rate of fertilizer, RGR for plants ﬂom the oilseed radish cover crop
were signiﬁcantly greater than values for plant ﬂom the bare ground with similar
fertilizer rate for evaluation conducted at 23 DAT. RGR values of all treatments were
comparable during the remainder of the season. In 2004, RGR trends were similar to
2003.

In Hamilton during 2003, there were no signiﬁcant differences in mean RGR of
plants among treatments during all sampling intervals (Table 2.6 and Fig. 2.6). The “mean
RGR declined as time progressed. The mean RGR values of celery in 2004 were
generally greater than those in 2003 after the ﬁrst sampling. In 2004, the initial dry
weight increase was higher in the oilseed radish treatment during the ﬁrst (10 June)
sampling interval. Cereal rye treatment provided signiﬁcantly higher plant dry weight
increase in the second (1 July) sampling interval. There were no statistical differences in

mean RGR among all treatments during the third (21 July) sampling intervals. Smooth

35

curves were ﬁtted Fig. 2.5 and 2.6 with celery relative growth rate and growing degree

relationship for Laingsburg and Hamilton.

3. 3. Celery Stalk Lengths

As expected, celery stalk length increased throughout the sampling period at both
locations and years (Table 2.8, Fig. 2.8 and 2.9). In Laingsburg, celery stalks in 2004
were longer under all treatment and fertilizer rate combinations than in 2003. This was
likely due to warmer temperatures in 2004. Stalk length among treatments was similar at
23 DAT. However, at 43 and 64 DAT, celery stalks were generally shorter under the
system with low fertilizer rate. Under those systems, addition of oilseed radish or cereal
rye improved stalk length in 2003, but did not have any positive effect in 2004. In all
cases, combining cover crop with half rate of the fertilizer seemed to improve celery
plant length. However, the differences were generally not signiﬁcant when compared
with the bare ground system containing the full or the half rate of fertilizer.

In Hamilton, celery stalk length was not affected by the cover crop treatments in 2003
(Table 2.8 and Fig. 2.9). In 2004 however, stalks were shortest in the cereal rye plots
throughout the sampling period. At 31 DAT, celery stalk length was 14.7 cm in the cereal
rye plot and 18.7 cm in the control plot. Early in the season, plants were taller in the
oilseed radish treatments. During the ﬁnal sampling date, celery stalk lengths grown in
oriental and yellow mustard plots were the longest (70.3 cm each) and signiﬁcantly

greater than those grown under the cereal rye treatment (65.3 cm).

36

3.4. Celery yield

Generally, yield differences observed at both locations are attributed to original plant
densities. In Laingsburg, celery yield was affected by the different treatments in both
2003 and 2004. (Table 2.10). This was observed for total and marketable yield, of the
trimmed and untrirnmed stalks, as well as for the number of marketable stalks. -

In 2003, yields of the bare ground and hairy vetch treatments with low fertilizer rate
had the lowest values in all categories. This observation indicates the importance of
adequate soil fertility in celery production. For instance, total marketable plant weight
before stalk trimming was 38.0 ton ha" (in the control plus low fertilizer treatment) and
37.4 ton ha‘1 (in the hairy vetch plus low fertilizer treatment), compared to 45.4 to 70.5
ton ha" in other treatments. The combination of oilseed radish and half rate of fertilizer
signiﬁcantly increased yield. Moreover, yields in the oilseed radish plus half rate was
greater or equal to yield of the control-full fertilizer rate. Similar results were observed
with the number of marketable stalks. The highest numbers of marketable stalks were
recorded in the oilseed radish (66,000 plants ha") that received the half rate of fertilizer.

In 2004, low yields were observed in the bare ground plots receiving the low fertilizer
rate. In those plots, yields were increased with increasing fertilizer rates. Also, all cover
crop species improved celery yield under the low fertilizer rate program, with oilseed
radish showing the greatest effects. In 2004 however, there was no beneﬁt of the cover
crops for half rate of fertilizer.

In Hamilton, celery yield was not affected by the cover crop treatments in 2003
(Table 2.11). The yields observed in 2004 were all greater than yield in 2003. In 2004,

there was a greater variation in total yields among the treatments. Celery yield was

37

reduced in the cereal rye as cover crop system. Total yield before stalk trimming was
169.0 ton ha" in the control and 159.4 ton ha’1 in the cereal rye plots. The yield penalty
associated with cereal rye was observed in both trimmed and untrimmed marketable
stalks. Higher yields were observed in the oilseed radish and yellow mustard treatments

but weren’t different ﬂom yields in the control plot.

3.5. Celery total soluble solids
There were no statistical differences in %—dissolved solids of celery sap grown under
the various treatments (Table 2.12). In Laingsburg, the means ranged ﬂom 2.35 to 3.58

and ﬂom 3.21 to 3.57 in 2004. Similar observations were made for Hamilton experiment.

4. DISCUSSION

The aim: of this work was to study the potential of cover crop inclusion into a celery
production system. Additionally, we wanted to determine how the cover crops may help
reduce fertilizer rates while maintaining acceptable celery growth and yield. Results
indicate the cover crops tested can ﬁt well into celery cropping systems especially for
crops harvested early in the season (July — August). Under those conditions, the cover
crops could produce signiﬁcant biomass before being killed by ﬂost (oilseed radish), or
by herbicide or cultivation the following season (cereal rye, hairy vetch). While oilseed
radish and hairy vetch biomass was stable across location and year, cereal rye biomass
productions seemed to vary with growing conditions. In Hamilton for example, cereal rye
biomass in 2004 was over 4 fold greater than in 2003. The main difference between the

years was more rainfall directly following rye planting in 2003. Apparently, adequate soil

38

moisture during germination and subsequent seedling establishment may be critical for
cereal rye on Houghton muck soil.

Low fertilizer rate (90 kg ha'1 N) produced the lowest dry matter accumulation and
ﬁnal stalk yield, especially in the systems without cover crop. With half rate (90, 45, and
225 kg ha“1 N, P205, K20), and full (180, 90, and 450 kg ha'1 N, P205, K20) rates of
fertilizer, celery growth and yield were enhanced. This result stresses the importance of
not only N but also P and K in celery production. Unlike cereal rye and oilseed radish,
hairy vetch cover crop did not increase celery yield under the low fertilizer rate systems.
Not only was hairy vetch biomass production low but its roots showed very few nodules.
Hairy vetch seed used in this study was not inoculated with rhizobium, which may
explain the low nodulation on the root system. However, the same seed showed high
. nodule formation when grown on a sandy soil (data not shown). Future studies should
test the effect of soil type on rhizobium association with hairy vetch roots.

Cereal rye enhanced celery growth and yield. However, high residue production may
be detrimental to celery. When large cereal rye biomass was produced (Hamilton 2004),
this resulted in stunting, yellowing, and low celery yield. Those growth inhibitory
conditions may be attributed to either nutrient immobilization or allelochemical
interactions. Cereal rye is known to produce allelochemicals that interfere with normal
growth of several species (Barnes and Putnam, 1983; Barnes et al., 1987). Therefore,
when using cereal rye as a cover crop, sufficient time should be allowed for residue
decomposition prior to planting.

Oilseed radish increased celery growth and yield both under the low and half rates of

fertilizer. By producing large amounts of biomass, oilseed radish probably improved

39

microbial activity and created an environment more conducive to celery growth. Oilseed
radish has been shown to produce glucosinolates, secondary metabolites that suppress
weeds, nematodes, and some soil borne plant pathogens (F ahey et al., 2001). In the
present study, weed competition was eliminated in all treatments with regular hand
weeding. The population of plant pathogenic nematodes was low in the oilseed radish
treatment (data not shown). However, nematode suppression alone may not account for
the high yield observed. Through rapid growth and production of a large root system,
oilseed radish can recycle N 157.2 kg ton'l (N gouaj io and Mutch, 2004). Studies have
documented the ability of oilseed radish to scavenge residual soil N after crop harvest
(N gouaj io and Mutch, 2004). This recycled N is then released slowly to the following
crop with several beneﬁts to the crop and the environment (Baggs et al., 2000).

This work suggests that cover crops especially oilseed radish, could be integrated
into celery production with associated increase in yield and reduction in fertilizer inputs.
The contribution of the cover crops on soil fertility should be quantiﬁed and credited
while developing fertilization programs. It is also important to determine the nutrient
release curve of the cover crops in order to optimize their contribution to cropping
’ systems. Finally, establishing and maintaining a cover crop requires investments by the
farmer. Therefore a cost study would help determine the proﬁtability of the different

systems.

40

ACKNOWLEDGEMENTS

Funding for this work was provided in part by USDA CSREES Risk Avoidance and
Mitigation Program. Grant N9: 2002-51101-01908. We also would like to thank the MSU
Muck Research Farm and Eding Brothers Celery Inc. for access to facilities. Finally, we
duly thank MSU College of Agriculture and Natural Resources ALAN A Graduate

Fellowship to the principal author.

41

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43

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Table 2.8.

Effects of cover crop and fertilizer rate on celery stalk length at different dates in Houghton muck
soil in Laingsbm and Hamilton during}003 and 2004.

 

 

 

 

 

 

Cover crop and fertilizer 2003 2004
ratex
Laingsburg site 23 1) AT: 43 DAT 64 DAT 23 DAT 43 DAT 64 DAT
cm
Oilseed radish plus Half. 14.5 25.8 a 48.8 ab 20.8 41.5 a 64.0 a
Cereal rye plus Half. 14.0 24.0 ab 50.0 a 20.0 40.5 ab 63.5 a
Hairy vetch plus Half. 14.5 22.8 abc 48.0 ab 20.0 41.8 a 62.8 ab
Oilseed radish plus Low 14.3 22.0 abc 46.0 abc 20.0 38.0 be 56.0 c
Cereal rye plus Low 14.2 21.0 abc 46.8 ab 20.3 36.8 d 58.0 c
Hairy vetch plus Low 13.3 17.0 c 42.8 be 20.2 37.3 d 58.5 c
Control plus Full 13.5 20.8 abc 46.8 ab 19.8 40.8 a 65.0 a
Control plus Half. 13.0 19.5 be 45.5 abc 19.5 40.0 abc 64.3 a
Control plus Low 13.5 18.0 c 40.5 c 17.8 37.5 cd 58.8 bc
P-value NS * * NS " “*
Hamilton site 32 DAT 44 DAT 64 DAT 31 DAT 52 DAT 72 DAT
cm
Control 37.3 54.3 79.3 18.7 be 45.0 66.3 ab
Hairy vetch 37.0 53.3 74.0 - - -
Oilseed radish 39.3 54.3 77.0 21.7 a 47.3 69.3 ab
Cereal rye 38.7 55.7 78.3 14.7 d 42.7 65.3 b
Oriental mustard - - - 20.0 ab 47.3 70.3 a
Yellow mustard - - - 17.7 c 46.0 70.3 a
P-value NS NS NS "* NS "

 

x Fertilizer rates are Full, Half, and Low. The full rate was 180, 90, 450 kg ha'1 of N,
P205, and K20, respectively. The Half rate corresponded to 50% of the full rate. The
low rate was 50% of the N applied in the full rate and no P205and K20. All P205, K20,
and 25% of N were top dressed and the remaining N side dressed in three equal
applications during the season.

2 All numbers within a column and year followed by the same letter are not statistically
different (a = 0.05).

52

.0000 0.0.0 00 A00 c. 000$ .00 000w00 0.0 00 .00 .5308 00003. 800.0 00000000

.900 00000000 0 800038080 000803 0000000000 A 000.0.» ...-00 030.0 .0800... 0.0 00 .0 000000000000 .00 000005000 000 00 N0 0

000000 0.0 $0000 000000030 .0000 00000 5 0000000 0000 Z 800000.000 0.0 0.00 0000000 000 0003 Z .00 $3

0:0 .030 800.. =< .000. 0.00 000.. 0.0 0.00 0.00 :..-.0 0.0 E 000.000 Z 0.0 .00 000m 003 0000 30— 0.2- .0000 :...0 0.0 .00 000m 00 0000000000000
800 :03 000. 5030000000 .000 000 .0000. .Z .00 0.0.. wx 0m.» .00 .00. 003 0000 =3 0.0... .>>3 0.00 .000: £00. 000 00000 0000.000”. x

 

 

 

 

 

 

 

0.8 0.0- 30. 00.. 088:. 30:80

0.00 0.0. 0.00. 00.. - - - - .888 .8800

..00 0.0- 0.00. 00.. 0.00 0. .- 0.0... 00.. or .880

0.8 0.0- 0.3.. 00.. 0.00. N. .- 0.000 00.. 0.0.8. 88:0

- - - - 0. . 0 0. .- 0.00. 00.. 88> 0.0..

0.00 0.0- 0.... . 00.. - - - - .0080

8.0 80:50..

0:00 0. .- 0.03. 00.. mm. 0.00.. ... .- 0.". 0.00 00.0 30-. 00... .0080
mm 0.0... N. .- 0... 0.00. 00.0 mm. 0.000 0..- mm 0.00.. 00.0 0.0.. 8.0 .0080
00 0.0.. N. .- 0 m 0.000 00.. m. 0.0.... 0. .- 0.. 0.000 8.0 :00 8.0 .0080
00 0.0:. ...- 0.. 0.000 00.0 mm 0.000 0. .- 0.. 0.00.. 00.0 >>0.. 8.0 80> 0:0:
0... 0.000 ...- 00 0.00. . 00.0 0... 0.000 0. .- 00 0.0. 0 00.0 80.. 8.0 00 .880

0. . 00 ...- 0.000 00.. mm 0.000 ... .- 0... 0.000 8.0 33 0.... 8.8. 88:0

... .. ... .- 0.00. 00.. 0 m 0.0.. ... .- 0.. 0.00.. 00.0 0.0.. 2.... 88> 08:
..m. 0.000 ...- 0.. 0.000 00.. 0 m 0.00.. 0. .- 0.. 0.000 00.0 0.0.. 8... 00. .880
.m 0.0.. ...- .0 0.0... 00.. 0. m 0.000 0. .- 0m. 0.0.... 00.0 0.0: 8.0 8.8. 88:0

00.0 “000000....—
muaomoEooo 382
can D a N.— S D a N.—
vocm 088 00000 0000—0000 000 0000 0000
.0000 08

0000 ... 80:50: .08 008000.80 00 58 .008. 0:08 08.8 5.: 80.. :... 00 + .0 + .0 + a. u 0 8.08.8 0.8.00. 2.. 80 .8808 08.00080
.0." 0.0a...

53

Table 2.10.

Eﬂ‘ects of cover crop and fertilizer on total and marketable celery yield (weight and stalk number)
in Laingsburg duringl003 and 2004.

 

 

 

 

Cover crop and fertilizer Before trimming yield After trimming yield
ratex

Total 1 Marketable Marketable Marketable

stalks”
ton ha" — stalks ha“ —
2003
Oilseed radish plus Half. 73,3 (2,3)T ,- 70.5 (4.0) a 46.0 (3.0) a 66.1 (2.3) a
Cereal rye plus Half. 65.6 (4.5) a 57.4 (6.7) ab 37.8 (5.3) ab 55.2 (4.7) abc
Hairy vetch plus Half. 63.9 (5.7) abc 57.1 (7.5) ab 36.2 (4.3) ab 59.0 (3.4) ab
Oilseed radish plus Low 62.1 (4.4) abcd 53.7 (6.4) 34.8 (4.7) ab 57.2 (4.4) abc
abc
Cereal rye plus Low 53.3 (0.9) bcd 45.4 (3 .4) bc 29.2 (2.2) b 54.5 (4.9) abc
Hairy vetch plus Low 49.0 (4.8) d 37.4 (5.4) c 23.9 (4.1) b 46.5 (2.5) be
Control plus Full 57.1 (6.8) bcd 49.1 (9.4) be 38.5 (11.1) ab 51.8 (7.4) bc
Control plus Half. 59.0 (5.5) bcd 48.4 (6.7) bc 30.5 (4.1) ab 48.2 (1.8) bc
Control plus Low 50.7 (6.5) cd 38.0 (7.8) c 24.4 (5.5) b 44.7 (5.6) c
P-value * * * *
2004

Oilseed radish plus Half. 96.9 (5.9) ab 86.5 (7.1) a 59.0 (5.6) a 60.7 (2.9) a
Cereal rye plus Half. 101.0 (4.2) a 87.6 (5.7) a 56.3 (3.6) ab 57.2 (2.5) ab
Hairy vetch plus Half. 95.7 (6.0) ab 83.5 (9.3) a 54.4 (6.3) abc 56.3 (5.1) ab
Oilseed radish plus Low 89.9 (4.0) abc 74.8 (8.4) ab 48.8 (6.0) abcd 54.5 (5.5) abc
Cereal rye plus Low 82.5 (4.0) be 62.6 (6.5) be 40.1 (4.6) cd 49.1 (4.7) bcd
Hairy vetch plus Low 78.5 (1.4) c 56.4 (3.7) be 37.0 (3.3) d 44.7 (2.3) cd
Control plus Full 98.9 (5.1) a 85.4 (6.8) a 56.5(63) ab 56.3 (3.4) ab
Control plus Half. 97.0 (3.7) a 86.5 (3.8) a 57.6 (3.0) ab 59.9 (0.9) ab
Control plus Low 78.5 (4.0) c 51.3 (8.8) c 42.1 (8.3) bed 40.2 (5.9) d
P'Value it it t **

 

 

 

x Fertilizer rates are Full, Half, and Low. The full rate was 180, 90, 450 kg ha'1 of N,
P205, and K20, respectively. The Half rate corresponded to 50% of the full rate. The
low rate was 50% of the N applied in the full rate and no P205 and K20. All P205, K20,
and 25% of N were top dressed and the remaining N side dressed in three equal
applications during the season. 2 All numbers within a column and year followed by the
. same letter are not statistically different (on = 0.05). T Standard errors of the means are
parenthesized. ” Number of stalks (x1000 stalks ha’l).

54

Table 2.11.

Effects of cover crop and fertilizer on total and marketable celery yield (weight and stalk
number) in Hamilton durirg 2003 and 2004.

 

 

 

 

 

 

Cover crop and Before trimming yield Aﬁer trimming yield
fertilizer ratex ‘
Total ' Marketab 1e Marketable Marketable
stalks
ton ha'l - stalks ha'l —
x1000
2003
Control 160.0 (8.9)t 142.0 (16.9) 94.9 (9.4) 107.2 (15.5)*
Hairy vetch 170.5 (13.4) 155.3 (15.9) 103.6 (10.4) 111.5 (11.3)
Oilseed radish 161.7 (2.7) 133.6 (10.5) 90.0 (7.3) 98.6 (8.6)
Cereal rye 163.6 (22.0) 141.9 (26.4) 92.4 (18.7) 98.6 (8.6)
P-value NS NS NS NS
2004
Control 169.1 (10.9) ab 146.2 (14.3) ab 102.2 (11.4) ab 105.0 (5.67)
Oilseed radish 182.0 (5.6) a 167.0 (10.1) a 118.6 (7.7) a 111.5 (7.73)
Cereal rye 159.4 (1.3) b 131.4 (10.7) b 89.0 (7.7) b 96.5 (11.13)
Oriental mustard 171.1 (5.3) ab 149.4 (3.6) ab 104.5 (2.4) ab 105.0 (2.14)

Yellow mustard 184.8 (7.8) a 163.7 (13.9) a 115.4 (9.4) a 107.2 (7.73)

P-value * "‘ "‘ NS
All numbers followed by the same letter are not statistically different (a = 0.05).
1 Standard errors of the means are parenthesized.

55

Table 2.12.
Effects of cover crop and fertilizer on total soluble solids on Houghton muck
soil in Laingsburg and Hamilton during 2003 and 2004.

 

 

Cover crop and fertilizer ratex 2003 2004
Total soluble solids %'
Laingsburg site
Oilseed radish plus Half. 3.4 3.2
Cereal rye plus Half. ‘ 3.3 3.6
Hairy vetch plus Half. 2.4 3.6
Oilseed radish plus Low 3.6 3.6
Cereal rye plus Low 3.4 3.5
Hairy vetch plus Low 3.0 3.6
Control plus Full 3.3 3.5
Control plus Half. 2.9 3.5
Control plus Low 3.5 3.6
P-value NS NS
Hamilton site

Control 3.1 3.4
Hairy vetch 3.1 -
Oilseed radish 3.3 3.5
Cereal rye 3.4 3.4
Oriental mustard - 3.4
Yellow mustard - 3 .5
P-valuey NS NS

 

" Fertilizer rates are Full, Half, and Low. The Full rate was 180, 90, 450 kg ha'1 of N,
P205, and K20, respectively. The Half rate corresponded to 50% of the full rate. The
Low rate was 50% of the N applied in the full rate and no PzOsand K20. All P205, K20,
and 25% of N were top dressed and the remaining N side dressed in three equal
applications during the season.

y P-values are P > 0.05 (NS Non signiﬁcant)

56

§

Laingsburg
- - — 2003 Season
.............. 2004 Season '3' /

§
\

Growing degree days (GDD base 10 °C)
"’ §
8
\
\
\

 

o 20 4o 60 i so 100
DAT

Hamilton

— — — 2003 Season /
.............. 2004 Season /

200 . /

Growing degree days (GDD base 10 °C)
\

 

O 20 4O 6O 80 100
DAT

Fig. 2.1. Growing degree days (GDD base 10 °C) during celery growth in 2003 and 2004
at Laingsburg and Hamilton. Celery was transplanted on 23 May 2003 and 28
June 2004 in Laingsburg and on 13 May 2003 and 10 May 2004 in Hamilton.
DAT is days after celery transplanting.

57

2003 Laingsburg Celery Gmwth 2004 Laingsburg Celery Growth

3

 

 

   

 

 

 

 

 

 

 

 

 

 

 

60 1
50 : oilseed radish + half
A ‘ -'- '- oilseed radish+low 50 .
Ta -..-:-.... control+full A
.3 40 ' control + half 40 .
h .....- .... control+ low
gw‘ so«
a 20‘ 2o
5
10 < 10 .
OJ 0 .p
60 .
a. cereal rye + half
A5°‘ ...... "'Ecerealrye-How B
'35 ° control+full
%‘O‘ - -"-control+half
Bo m """" control+ low
v 30 1
é
a 20‘
E
10 4
’ #7
60.
A 501 -O' hairy vetch + half C
"' —' O '- hairy vetch+ low
E 40 control+ full
E" ‘ -”--"— control+half
3 30< ”WOW" control + low
‘-
§ 20-
E
E10-
!9- .
o 600

   

Fig. 2.2. The relationship between celery dry matter accumulation and growing degree days
(GDD base 10 °C) under different cover crop: oilseed radish (a), cereal rye (b), and
hairy vetch (c) and fertilization treatments during 2003-04. Observed data were fitted
to a 3 parameter equation. Regression coefficients are indicated in Table 2.3.

58

Hamilton Celery Growth

60 1 + control
:‘ —"'—‘ oilseed radish
"a — "- ‘ cereal rye .
. .' I
a ...... o ...... hall'y vetch ... I,/
0 4O -1 '/ .
M ' '
h
:3
E
20 r
E‘
'5

 

 

 

_'+ ' '— oilseed radish

A 50 . — 4 — cereal rye t.’
1 ........ . ....... oriental mUStard / .
5 — "— yellow mustard .-/, "
a .90 e

' 40 .1 '. . '

3 .5’

3

33

a

E 20 .

E‘

w:

 

 

 

Fig. 2.3. The relationship between celery dry matter accumulatiOn and growing degree
days (GDD base 10 °C) as effected by cover crop treatments. Observed data were
ﬁtted to a 3 parameter equation. Regression coefficients are indicated in Table
2.3.

59

14 . 2003 Laingsburg Cele-y Growth 14 1 2004 Laingsburg Celery Growth

 

 

 

 

 

 

 

 

 

 

 

 

 

 

-,_ ,_ oilseed radish + half
12‘ o oilseed radish + low 12 *
: -..-_,._ control + full A
3; 1° ‘ ...... -.--.. control + half 10 .
0; control + low
is 8 ‘
‘3 6 .
I
8 4‘
2 .
O.
14
-.-. -....cereal rye + half
12 ‘ a cereal rye + low 12 .
A 10 _,. _,,_control+ ﬁll]
'7 ‘ control + half 10 .
s ......+... control + low
'a B 8
3 61
ﬂ
8 4.
2 1
0
12 4 T hairy vetch + half 14 ‘
: _°—‘ l- hairy VCtCh + low 12 .
:.:, 101 ...... _ control+full
e; 8 control + half C 10 .
'E '“"'“"”" control + low 8 ‘
in
Z 6 4
(D
u 4 .
2 .
v o ' ,
600 o zoo 400 600
GDD GDD

Fig. 2.4. Crop growth rate versus growing degree days under cover crop: oilseed radish (a),
cereal rye (b), and hairy vetch (c) and fertilizer treatments. Observed (symbols)
predicted (lines) of celery dry plant at Laingsburg. Observed data were ﬁtted to a 3
parameter equation. Regression coefficients are indicated in Table 2.5.

60

 

Hamilton Celery Growth

 

 

      

 

30 q + control
25 . -"'-" oilseed radish 9
.7? — 'V— ‘ cereal rye '
: 20 t ...... g ...... hairy VClCh .
a 15 « ,
V a
g 10 ~ ,
U
5 . 9
A 2003
0 .
30 . __ ° .___ control ‘
25 ‘ oilseed radish ,./
A — "' _ cereal rye ../
2 m d ........ . ....... oriental mustard ./
N " "‘ ‘‘‘‘ yellow mustard/é.
a 15 . r"
on
a: .
U 10
U
5 .
B 2004
0 l l I
O 200 4CD 6m
GDD

Fig. 2.5. Crop growth rate versus growing degree days under cover crop: 2003 (a) and
2004 (b) for Hamilton. Observed (symbols) predicted (lines) of celery dry
plant. Predicted values for 2003 (a) regression were not ﬁtted to logistic
equation. Observed data were ﬁtted to a 3 parameter equation Regression
coefﬁcients are indicated in Table 2.5.

61

RGR(lng-kg'l'd'l) RGR(|ns'ks"°d'1)

RGR(lng°kg’l°d'l)

120 1 2003 Laingsburg Celery Growth 120 . 2004 Laingsburg Celery Growth

      

 

 

 

 

  
 
  

 

  

 

 

 

 

 

 

 

 

 

100‘ """ ‘ '100 4
A
30* so «
60 ‘ 60 .
“J “' -..: .. oilseed radish+ half 4° '
j orlseedlradﬁlsll; + low
. -.. -..- contro + .
2° ’ ”:.--.. control + half 2°
control + low
0 . O a
120 -
B 120 l
100 ‘
100 <
80 4
60 ..
____n_,__cerea}rye+111:1f 4o .
a cerea rye+ w
1 _..._”_control + ﬁrll 20 .
.... ’H . control+ half
0 ' ' control + low . 0
120 l C 120 .
100 i 100 .
80 q .- ................... 80 ‘
60 4 .' III 60
.-:'/' +4 hairy vetch + half
. ' —' '. hairy vetch+ low .
4° —°— control+ full 4°
20 . -"'--"- control+ half 20 ‘
.... "”7 control + low
0 . . . 0 . ‘ .
O 200 4CD 600 0 200 400 600
CD” con

Fig. 2.6. Mean predicted relative growth rate as a function of the cumulative growing degree
(GDD) alter celery transplanting under cover crop: oilseed radish (a), cereal rye (b), and
hairy vetch (c) and fertilizer treatments in 2003 and 2004 at Laingsburg. Regression
coefﬁcients are indicated in Table 2.7.

62

a?

   

 

 

 

 

 

Hamilton Celery Growth
A 120 i
‘1‘
2:: 100 -
Fl
3° 80‘
Be
.a 60‘
m 40 . + control \.
g —"'—' Oilseed radish °
_ —v— -
20 ‘ cereal rye
...... °. . hairy vetch 2003
0 j . .
+ control
""" oilseed radish
-"— cereal rye
140 ....... § ...... oriental mustard
1 - +—- yellow mustard
3 120 ~
'1'" 1001
‘1‘
5‘ 80*
90 J
.5 60
a ”l
m 20 -
o 1 ' ' I
0 200 400 600 80°
GDD

Fig. 2.7. Mean predicted relative growth rate as a function of the cumulative
growing degree days (GDD) after celery transplanting in 2003 and
2004 at Hamilton Regression coefficients are indicated in Table 2.7.

63

2003 Laingsbng Celery Growth

   

 

 

   

 

 

   

 

2004 Laingsburg Celery Growth

 

 

 

 

 

 

 

60 1 . oilseed radish + half A 60 ‘
"1'" oilseed radish + low
A control + Hill
5 """" control+half
E 40 . ‘ ..-. control + low 40 l
E
2
:5
a 20 l 20 .
0 0
_. _ ._.cerea1rye+half B
50‘ -:- cerealrye+low 60-
A _u-_u_control+ﬁlll
E ”M’s“..- control + half
3, control + low
a 40 ‘ 4o .
.§ . ..
a
*2 20 . 20 .
I
o . 0
+ ' hairy vetch + half C
60 —‘ O '- ha' vetch+ low .
A con 1+ full 60
5 _.. -..- control+half
V 40 . """'“'" control + low
% 4° ‘
E
a
g 20 ‘ 20 .
I
O . . . 0 r f
0 20 40 60 0 20 4O
DAT DAT

Fig. 2.8. Day alter transplanting (DAT) predicted function and observed means of celery stalk
length under cover crop: oilseed radish (a), cereal rye (a), and hairy vetch (c) and fertilizer
treatments at Laingsburg, MI (2003 and 2004). Regression coefﬁcients are indicated in
Table 2.9.

Hamilton Celery Growth

is

—"'_’ oilseed radish

.__'_-

(,3
cereal rye //-°'
...... on... hairy vetch (4!.

9.3

f.

stalk length ( cm )
8

 

 

  
   
 

 

 

20 .
2003
0
w ‘ _.+._ COHtl‘Ol
oilseed radish
_ "‘ _ cereal rye
A m ‘ ........ . ....... oriental mu Star d /
E ”"“ '''' yellow mustard
8. . /
g . /
E” 4° x"
2 ‘ /
£5
3 20 .
m /
2004
0 .
O 20 40 60 80

DAT
Fig. 2.9. Day after transplanting (DAT) predicted function and observed means of celery

stalk length under cover crop treatments at Hamilton, MI (2003 and 2004).
Regression coefﬁcients are indicated in Table 2.9.

65

Chapter 3: The effects of cover crops and fertilization on soil properties and celery

(Apium graveolens L.) on Houghton muck soil.

ABTRACT

A 2-year study conducted in Laingsburg and Hamilton, MI showed that soil nutrient
composition improved under cover crop rotation system. Further, the practice of
integrating cover crops was compatible with celery production. In Laingsburg, cropping
systems included cover crop and fertilizer rates. The cover crops were oilseed radish,
cereal rye, hairy vetch, and a bare ground control. The fertility rates were full (180, 90,
and 450 kg ha'1 N, P205, K20), half (90, 45, and 225 kg ha'1 N, P205, K20), and low rate
(90 kg ha'1 N). In Hamilton, the cover crops were oilseed radish, cereal rye, hairy vetch,
yellow mustard, oriental mustard, and a bare ground control. Total dry matter production
averaged 114 to 719 g rn'2 in Laingsburg and 147 to 1599 g m'2 in Hamilton. There was
no measurable change in soil phosphorus content. However, cover crops inﬂuenced
magnesium, calcium, and potassium concentrations. Soil nitrate content was higher in
plots where oilseed radish was grown. Cover cropped plots sustained higher N levels than
the fallow control. The subsequent celery crop was affected by the cover crops
treatments. Within individual fertilization levels, higher celery yields were recorded in
the oilseed radish plots. The results of this experiment indicate the inclusion of cover
cr0ps can successfully improve the magnitude of soil mineral composition, sustain celery

yield on muck soils, and can potentially reduce fertilizer inputs.

66

INTRODUCTION

Celery is an important commodity of vegetable production in the state of
Michigan. However, intensive practices of celery cultivation with high nitrogen (N)
fertilization can increase nitrate (N 03' N) leaching. Additionally, leaving the soil bare
aﬁer harvest can increase soil erosion. Therefore, it is possible to improve soil quality and
enhance celery yield by developing sustainable techniques that prevents soil erosion and
reduces leaching.

Past conventional farming systems used synthetic inputs as a key component in
soil fertility to improve yields (Liebman and Davis, 2000). Nitrogen as the primary
limiting nutrient is an essential growth element in crop production (Di and Cameron,
2002). However, liberal nitrogen (N) fertilization in conventional vegetable farming
during the early half of the twentieth century has resulted in excess-fertility conditions in
many situations. Consequently, leaching and erosion has led to the loss of soil nutrients
resulting in N03’ N accumulation of surface water and groundwater (Di and Cameron,
2002). These N0; N concentration levels have generally increased in the recent past
(Pang and Letey, 2000) and have in most cases exceeded acceptable contamination limits
(Strebel et al., 1989; EU, 1991; Fletcher, 1991). Furthermore, developing a sustainable
management strategy that reduces potential groundwater contamination resulting from
leaching can conserve residual soil N and in turn, can maintain water quality and improve
soil health (Muller et al., 1987; Sainju et al., 2000; Shipley et al., 1992).

A sustainable approach of managing crop residue to protect soils from erosion and
nutrient leaching can provide beneﬁts to cropping systems (Ruffo and Bollero, 2003).

Replacing applied inorganic N with organic N from cover crops can reduce nitrate

67

leaching from agricultural soils (Burket etal., 1997; Stute and Posner, 1995). Many
studies have shown that N can be retained in agricultural systems by various crop
management strategies such as cover crops, crop rotation, interseeding, and accessory
cropping (Ditsch and Alley, 1991; Ebelhar etal., 1984; Hargrove, 1986; Hesterman et al.,
1986). Thus, plant residue can play an important role in cycling of nutrients essential to
Inoducﬁon.

In addition to preventing soluble nutrients from leaching (Kelly, 1990), the use of
winter cover crops in crop rotation systems can be a valuable asset in improving nutrient
retention in the surface layer of intensively managed crop systems (W yland et al., 1966).
Using cover crops can potentially reduce nutrient movement within cropping systems
during the winter season by increasing the amount of time the land is covered with
growing vegetation (Strock et al., 2004). The rapid growth and establishment of cover
crop vegetation following the fall harvest of the cash crop can reduce NO3'N (Meisinger
et al., 1991), and thereby limit leaching. Nitrate reductions are achieved by cover crop
sequestration and retention of soil residual N that can result in N provisions the following
spring (Kuo et al., 1996). A number of studies have found that non-leguminous cover
crops can reduce soil N03' N leaching below the root zone (Lamb et al., 1985; Powlson,
1988, Martinez and Guiraud, 1990; Meisinger et al., 1991). Without vegetative cover
during the winter period, precipitation increases the possibility of nutrient leaching. -
Therefore, using cover crops as a nutrient conservation tool can reduce groundwater
contamination, and improve N-use efﬁciency (Baggs et al., 2000; Power and Doran,

1988).

68

Celery is an important vegetable crop in Michigan. Nationally, Michigan ranks
second after California in celery production (6.2 % of total national production) with c.
890 ha of celery harvested value at $18.8 million in 2004 (USDA, 2004).

In Michigan, it is possible to integrate cover crops into celery cropping systems to
establish a vegetative cover prior to the onset of frost.

The purpose of this study was to evaluate winter annual cover crops that would ﬁt
into celery production system and to assess cover crop effects on nutrient cycling.
Speciﬁc objectives were to: (i) measure the effects of different cover crops on soil
fertility and the possibility of reducing inorganic fertilizer inputs, (ii) determine the
effects of the cover crops and fertilizer rates on celery yield, and (iii) evaluate the effect

of cover crops or soil microbial activity.

2. MATERIALS AND METHODS
2.1. Experimental site

Studies were conducted during 2002 through 2004 on two sites at Michigan State
University (MSU) Muck Soils Research Farm in Laingsburg, MI and at a commercial
farm in Hamilton, MI. Both experiments were initiated in late summer of 2002. The soil
was Houghton muck with 80 % organic matter and a range pH of 6.2 - 6.9. Temperature
and rainfall data were collected from Bath and Hudsonville weather stations for
Laingsburg and Hamilton studies, respectively (Fig. 3.1 and 3.2). In Laingsburg during
both years, cover crops were planted in the same plot following harvests and celery was

transplanted in late spring. The Hamilton experiment was conducted in different ﬁelds

69

each year. In May of 2004, planned celery transplanting in Laingsburg was delayed due

to severe rainfall (Fig. 3.2).

2. 2. Laingsburg Study

The experiment had four cover crops and three fertilizer rates. The cover crops
were oilseed radish (cv. diakon), cereal rye (cv. VNS), hairy vetch (cv. common), and
bare ground. Establishment occurred in late summer (26 August 2002 and in 25 August
2003) following the celery crop harvest, using a broadcast method and incorporated by
shallow discing. Oilseed radish, cereal rye, and hairy vetch were seeded at rates of 28,
112, and 39 kg ha“, respectively.

The 3 rates of fertilizer were: full rate (180, 90, and 450 kg ha" N, P205, K20), half
rate (90, 45, and 225 kg ha" N, P205, K20), and low rate (90 kg ha" N). The full rate was
the recommendation for commercial celery production on muck soils in Michigan. Each
year, 25% of N and all of P, and K were broadcast during land preparation (20 May 2003
and 28 June 2004); equal amounts of the remaining N rates were applied at three
subsequent side dressings during the growing season (13 June, 3 July, 25 July in 2003
and 21 July, 10 August, and 31 August in 2004). The experimental design was a
randomized complete block with four replications. Treatments were combinations of
cover crop and fertilizer rate and consisted of the four cover crops plus low or half rate of
fertilizer. A bare ground plus high rate of fertilizer (normal practice) was also included
for a total of 9 treatments. Individual plots were 4.1 m by 10.7 m and contained four rows
of celery at 0.15 m in-row spacing and separated by 1.5 m buffer. Individual plots were

hand weeded during the season. Celery was transplanted on 23 May 2003 and 28 June

70

2004. At maturity, 20 plants were harvested on 12 August 2003 and 20 September 2004.
All cover crop plus fertilizer treatments were maintained in the same location throughout
the duration of the study.

Soil samples were collected prior to the fertilizer top dress application on 20 May
2003, and 14 May 2004. Soil sampling was conducted by collecting 8 random cores from
the top 10 cm depth in each plot. Analyses was conducted to determine soil available
N03’ N, P, K, Mg, Ca, and total N. Celery was transplanted on 23 May 2003, and on 28
June 2004.

Microbial respiration and biomass C analysis was conducted during 2004.
Biological activity potential was determined using soil microbial respiration (CO2),
(Kumar and Goh, 2000). Refrigerated soil samples were preincubated at room
temperature for 15 days. Then 40 g of soil (dry weight equivalent) was put in a 500 mL
jar sealed with a lid containing a rubber septum. Each sample was processed in
duplicate, with one set fumigated (with chloroform) and the other non-fumigated. All
samples whether fumigated or non-fumigated were opened and ventilated aﬁer 24h. A
ﬁnal incubation period lof 5 days was observed, after which 1 mL of head space air was
injected into an infra-red C02 (Quibit System). Soil respiration was calculated as the
amount of C02 evolved from the non-fumigated samples. Soil microbial biomass carbon
was calculated by subtracting the amount of C02 in the non-fumigated sample ﬁom that

in the corresponding fumigated sample, and a correction factor.

71

2. 3. Nitrogen Leaching Assessment

In Laingsburg, ion exchange resin (IER) bags were used to measure N03‘N leaching
beyond celery root zone (from May 21“ until August 12‘“, 2003). [BR bags were buried
in the soil to accumulate ions by binding (Binkley and Matson, 1983). The extent of
accumulation of N03' N enables us to estimate the relative effects of experimental
treatments on N pools that have been mineralized but not immediately taken up by plant
roots (Binkley et al., 1986). In 2003, IER bags were prepared by placing 4 g of
equivalent weight resin (A0“ 3 Anion Exchange Resin, Bio-Rad Laboratories, Hercules,
CA, USA,) in nylon mesh material. At the beginning of the season, the IER bags were
placed in each plot c. a 30 cm depth from soil surface by tunneling vertical channels near
celery row, then burrowing a perpendicular tunnel beneath the row with care to avoid

disturbing developing root systems and its surrounding soil environment.

2. 4. Hamilton Study

The experiment was a complete block design with three replications. Plot sizes were
12.2 m long by 18.3 m wide. In 2003, cover crop levels, seeding rates, and sampling
methods were identical to the Laingsburg site previously discussed above. In 2004,
yellow mustard (cv. tilney) [Sinapis alba L.] and oriental mustard (cv. forge) [Brassica
juncea (L.) Cosson] cover crops were also used at 22 kg ha“ and 13 kg ha'1 seeding rates,
respectively. In 2004, hairy vetch was excluded from the experiment. Cover crops were
planted on 9 August 2002 and 30 August 2003. Celery transplanting dates were 13 May
2003 and 10 May 2004 in a double row raised bed system with spacing of 101 cm

between consecutive beds, 31 cm between row, and 15 cm in-row spacing. Similar to the

72

 

Laingsburg site, microbial respiration and biomass C analysis was conducted during 2004

to determine biological activity potential.

DATA COLLECTION

In Laingsburg, all cover crops were sampled from two 2500 cm’2 areas within each
plot for biomass evaluation. Cover crop dry matter (DM) was determined after drying at
75 °C until constant weight was achieved. Freezing temperatures during the winter kills
oilseed radish, therefore its biomass samples were estimated prior to the October frost of
each year. On the other hand, winter hardy cereal rye and hairy vetch continued grth
through spring, and were killed with glyphosate [N — (phosphonomethyl)- glycine)]. In
both years, cereal rye and hairy vetch biomass samples were collected prior to land
preparation for celery transplanting. Celery plants were sampled at 23, 43, 64, and 84
days aﬁer transplanting (DAT) in 2003 and 2004. During each sampling, dry celery
tissue was ground and screened through 1 mm sieve; 1 g of sieved tissue was used to’
extract N03'N with 50 ml of 2 M KCl. Sampling was not conducted in thecenter two
rows of each plot, as these were allocated for ﬁnal crop yield estimation. Twenty plants
were collected at harvest on 12 August 2003 and 20 September 2004. At harvest, celery
stalks were sorted into marketable and non-marketable standards, accordingly (USDA,
1959). General marketable standards qualify as well developed, well-formed plants with
stalk lengths of c. 0.36 m. Stalk lengths were measured from soil surface to plant crown.
Processing included recording marketable before and after trimming stalk weights.

In Laingsburg during 2003, IER resin bags from each plot were collected at harvest.

The bags were placed in sample cups, and the N03'N was extracted with 50 ml of 2 M

73

KCl per bag. The extract was ﬁltered and the concentration of N03'N in the extract was
determined colorimetrically (Flow Solution IV, ).

In Hamilton, celery plants were sampled on the 32, 44, 64, and 75 DAT in 2003 and
on the 31, 52, 72, and 88 DAT in 2004. Celery dry tissue N03'N was extracted with 50
ml of 2 M KCl identical to the Laingsburg extraction method. At harvest, 10 plants were
collected on 29 September 2003 and 20 plants on 6 August 2004. At harvest, sorting and
processing techniques were conducted similar to those discussed in the Laingsburg
methodology. Soil samples were collected from each plot and underwent the similar

methodologies outlined for Laingsburg in 2004.

Statistical Analysis

All data was analyzed using analysis of variance (ANOVA) PROC GLM of SAS (SAS
institute, Inc. 1999). The least-square means test was used to determine the signiﬁcant
differences between the treatment means. Differences were deﬁned at P < 0.05 for all

data sets.

RESULTS
3.]. Climate

The weather conditions during the two celery-growing seasons differed greatly
(Fig. 3.1). At Laingsburg, both maximum and minimum air temperatures were higher in
2004 than in 2003 (Fig. 3.1). This was due to the delay in celery transplanting until early
June (warmer month) in 2004 because of high precipitation that made ﬁeld operations

difficult in May (Fig. 3.2).

74

In Hamilton, air temperatures in both years were different even though celery was
transplanted at similar times. The 2003 season was warmer earlier and cooler late
compared to the 2004 season.

In Laingsburg (Fig. 3.2), total rainfall from 0 to 84 DAT was 112 and 163 mm in
2003 and 2004. In 2004, most of the rainfall occurred in May during the planned
‘ transplanting that, in turn delayed ﬁeld activities in Laingsburg. In Hamilton, total

rainfall from transplanting to harvest was 178 (2003) and 285 (2004) mm.

3. 2. Cover crop biomass production

In Laingsburg, total biomass production varied with cover crop species and growing
season (Table 3.1 and Fig. 3.3). Means across cover crop biomass were lower in 2004
than in 2003. In‘both years, the higher cover crop biomass production was observed in
the oilseed radish treatment and was statistically different from biomass measured from
hairy vetch and cereal rye, respectively. In Laingsburg, oilseed radish produced the
greatest biomass in both years with 719 and 480 g m‘2 for 2003 and 2004, respectively.
For cereal rye, biomass was 284 (2003) and 270 g m‘2 (2004). Hairy vetch produced the
lowest biomass with 181 g m‘2 in 2003 and 114 g m'2 in 2004.

In Hamilton, the highest DM biomass yield with oilseed radish (585 g mi) in 2003
and in cereal rye (1599 g m") treatment in 2004. In Hamilton, oilseed radish, yellow
mustard and oriental mustard biomass production were similar and ranged from 691 to
822 g m’z.

Generally, cereal rye biomass was lower than expected in Laingsburg and Hamilton

during 2003 due to poor germination in the fall.

75

3.3 Soil mineral concentration

In 2003, at Laingsburg, differences in the magnitude of soil mineral concentrations
were observed among fall planted cover crops in early spring soil sampling (Table 3.2).
Similarly, in 2004, increases in the magnitude indicate cover crop and fertilization
affected soil mineral levels. Cover crops grown in 2002 had no inﬂuence on phosphorus
(P), calcium (Ca), and magnesium (Mg). However, the effects of cover crops were seen
in potassium (K), residual soil nitrate (NO3'N) and total N.

Although, higher soil P values were observed in oilseed radish (47.0 mg kg'l) and
cereal rye (46.8 mg kg"'), they were not different from the control (43.5 mg kg'l).
Magnesium concentrations ranged ﬁ'om 579.8 to 633.3 mg kg]. Oilseed radish cover
crop increased soil K concentration. A value of 264.3 mg kg'l and 167.3 mg kg'1 of K
was found in the oilseed radish and control treatments, respectively. Plots where oilseed
radish was previously grown provided signiﬁcantly greater concentrations of N03'N.
Means averaged across cover crop indicate 65.0 mg kg’1 of N03'N was produced in the
oilseed radish treatment compared to 38.8 and 45.3 mg kg’1 in other treatments. Results
indicate 131 kg ha'lof N was recycled by the oilseed radish treatment in comparison to 91
kg ha'1 of N observed in the control.

In 2004, at Laingsburg, the effects of cover crop and fertilizer regimes did not
inﬂuence phosphorus (P) concentrations (Table 3 .2). The pattern of soil K indicates the
oilseed radish plots receiving both low and half rate of fertilizer provided higher
concentrations (444 and 473 mg kg ") in comparison to other cropping systems. As in
2003, oilseed radish increased the concentration of NO3'N in the soil, with 159 and 158

mg kg '1 in the low and half rate of fertilizer, respectively. These were signiﬁcantly

76

different from the cropping systems of control with full rate of fertilizer and cereal rye
with half rate of fertilizer. Similarly, statistically greater total N accumulation was
observed in the oilseed radish plots in comparison to control half and full rate of
fertilizer. These differences are partly attributed to the ability of oilseed radish to recycle
residual soil N.

Soil analysis was not conducted in Hamilton in 2003 because the grower cooperator
applied fertilizer early. In 2004, at Hamilton, concentration of Ca and P were not
signiﬁcant in cover crop treatments as shown in Table 3.3. There was a signiﬁcant effect
of cover crop on soil K, Mg, and NO3'N concentrations. Soil K was increased under
oriental mustard (125.4 mg kg ") and yellow mustard (109 mg kg "). Oilseed radish
greatly increased the concentration of soil Mg (130.8 mg kg ") which was statistically
higher than that of control (120.3 mg kg “) treatment. Oilseed radish, yellow mustard,
and oriental mustard increased N03' N concentration by 11 to 12 fold compared with the

control. Cereal rye did not affect N concentration in the soil.

3. 4. Soil microbial respiration and microbial biomass C

In Laingsburg, there were no signiﬁcant differential effects of cropping systems on
soil microbial respiration or on soil microbial carbon (Table 3.4 and Fig. 3.4). Soil CO2
evolution ranged from12.4 to 16.1 pg g soil'1 day'1 and soil microbial biomass carbon
ranged ﬁom 273.8 to 348.1 ug g soil".

In Hamilton however, there was measurable differential effect of cover crops on both
soil microbial respiration as well as soil microbial carbon (Table 3.4 and Fig. 3.4).

Greater soil microbial respiration was observed in the cereal rye (18.4 pg g soil'l day")

77

treatment. This was statistically different from the control (14.0 pg g soil'l day'l) and
yellow mustard (9.5 pg g soil'l day'l) treatments. Soil samples ﬁ'om the yellow mustard
cover crop had the lowest rate of respiration. Similar to microbial respiration, soil
microbial carbon was inﬂuenced by cover crop. This may result from the rate of cover
crop decomposition. Both yellow mustard (400.7 pg g soil'l) and cereal rye (389.6 pg g
soil’l) treatments provided higher microbial carbon compared to oilseed radish and the
control treatments. These values were signiﬁcantly greater than those measured in the

control (321.2 pg g soil'l) as well as in the oilseed radish (305.0 pg g soil'l) treatments.

3. 5. IER N0; N accumulation

In 2003, at Laingsburg, there were no statistical differences in accumulation of NO,“
N in IER among the cover crop-fertilizer treatments at harvest (Table 3.5). Nitrate
leaching is a serious problem in agricultural systems. Our results indicate that under our
experimental conditions, little NO; N leaching occurred during celery growing season.
Nutrient leaching of organic soils occurs from runoff or leaching. This observation was
true regardless of the fertilizer rate used. Therefore, most of the N0; N leaching to
ground water may occur between growing seasons. This hypothesis was not tested in our
study. However, if that was true, it would support the use of cover crops between
growing seasons to recycle residual soil NO3' N. Oilseed radish was very efﬁcient at

recycling NO; N.

78

3. 6. Tissue N0; N concentration

In 2003 and 2004, at Laingsburg, there were no signiﬁcant effects of cover crop-
fertilizer cropping system on celery tissue nitrate (N 03' N) concentration during the
growing season (Table 3.6). The lack of difference in celery tissue NO; N concentration
among the fertilizer rates in the control plots and among the different combinations of
cover crops and fertilizer rates suggests that celery accumulate little N0; N. The
additional soil available nitrogen in the system with high fertility was probably take up by
celery and used for growth rather than accumulated as NO; N. This was reﬂected in the
difference in celery growth and development among the treatments.

In 2003, at Hamilton, no effects of cover crop on celery NO; N were detected (Table
3.6). In 2004, however, nitrate tissue concentrations varied across treatments during the
ﬁrst sampling date at 31 DAT. The control plot had the lowest tissue N0; N
concentration (58.0 mg kg ") and yellow mustard treatment the highest concentration
(347.5 mg kg "). No differences among treatments were found during the remainder of
the season. This result further supports the hypothesis of nitrogen utilization for celery

growth rather than accumulation in tissue.

3. 7. Celery yield

In Laingsburg, celery yield was affected by the different treatments in both 2003 and
2004 (Table 3.7 and Fig. 3.5, 3.6 and 3.7). This was observed for total and marketable
yield, of the untrimmed and trimmed stalks, as well as for the number of marketable
stalks. Across years and treatments, a higher number of marketable stalks were observed

in Laingsburg during 2003.

79

In 2003, yields of the bare ground and hairy vetch treatments with low fertilizer rate
produced the lowest values of all categories. The evaluation suggests an importance of
adequate soil fertility measures in celery production. For example, plant weights of the
untrimmed marketable stalks were only 38.0 ton ha'1 (in the control plus low fertilizer
treatment) and 37.4 ton ha" (in the hairy vetch plus low fertilizer treatment), in
comparison to 45.4 to 70.5 ton ha" in other treatments. The system with oilseed radish
and the half rate of fertilizer signiﬁcantly increased yields. Moreover, yields in the
' oilseed radish plus half rate were greater or equal to the yields produced by the control
and full fertilizer rate. Similar observations were with marketable stalks. The highest
numbers of marketable stalks were recorded in the plots previously occupied by oilseed
radish (66,000 plants ha") that received the half rate of fertilizer.

In 2004, low yields were observed in the bare ground plots receiving the low fertilizer
rate. In those plots, increased yields correlated with increasing rates of fertilizers.
However, cover crop systems performed similarly when receiving either the half or low
fertilizer rates. The entire plot was ﬂooded after heavy rain, which probably canceled all
cover crop effects.

In Hamilton during 2003, there were no observed effects of cover crops on celery
yields (Table 3.7). In 2004, the yields observed were higher than those of 2003. There
was a greater variation in total yields among the treatments. Yields from cereal rye plots
were reduced considerably. Total trimmed stalk weights were 102.2 ton ha" in the
control and only 89.0 ton ha'l in the cereal rye plots. The yield penalty associated with '

cereal rye was observed in both the marketable before and after trimming yields, although

80

the latest was not evident. Higher yields were observed in the oilseed radish and yellow
mustard treatments but weren’t different from yields of the control plot.
DISCUSSION

Our objective was to determine whether winter annual cover crops following
intensely produced celery could ﬁt into a rotational system. Also, we sought to assess effects
of cover crop and fertilization on nutrient management. Understanding how cropping system
inﬂuences soil mineral composition can provide important information used in developing
nutrient management strategies for Michigan celery producers.

The results presented in this paper were generated from a two year study and suggests
a probable ﬁt of the cover crops investigated. When seeded in late summer following celery
harvests, a considerable cover crop stand was established and production of signiﬁcant
biomass occurred during early spring of the next year. The rapid establishment and growth
can potentially reduce soil erosion (Bowman et al., 1998) and accumulate soil nitrogen
(Odhiambo and Bomke, 2001). Schomberg and Endale (2004) reported the availability of
soil N is highly dependant upon the amount of cover crop biomass produced. Additionally,
Clark et al. (1995) reported a correlation with increased N content and cover crop biomass
production.

Under muck soil conditions, cover crops used in this study produced signiﬁcant
biomass before being killed by frost (oilseed radish), or by herbicide or cultivation the
following season (cereal rye, hairy vetch). Hairy vetch and oilseed radish biomass
production was consistent during both seasons. However, cereal rye biomass productivity
varied with growing conditions. The difference between years was more rainfall following

rye planting in 2004. Low soil moisture content during germination and seedling

81

establishment may be adverse to cereal rye growth on muck soils. Excessive moisture can
however, result in poor rye establishment (Strock et al., 2004). In vegetable production,
minimal residue and ease of incorporation are desirable cover crop characteristics during
spring planting (Jackson et al., 1993). In this study, we observed considerable hairy vetch
surface litter following incorporation that may interfere with celery transplanting. Also,
timing cereal rye incorporation and celery transplanting is key to management practices.

Following the 2003 ﬁeld season, beneﬁcial effects of cropping systems were
observed as an increase of soil mineral concentrations were seen. In 2004, although
phosphorus remained constant across years, an increase in soil nutrient content occurred
across treatments.

Soil microbial activity was affected by the cover crop treatments in Hamilton, but not
affected by the treatments in Laingsburg. This differential response at the two sites is likely
due to the cropping history of the sites. The Hamilton site was in continuous celery for over
10 years while Laingsburg was fallow for many years prior to the establishment of the
experiment. It was therefore easier to affect soil microbial activity in the long term
monoculture in Hamilton than in Laingsburg. These results support the importance of crop
rotation and biodiversity in cropping systems.

While no differences in celery tissue NO; N content were detected in treatments,
growth and development were enhanced in the systems with high fertilizer rates. Also
oilseed radish improved nitrate recycling and celery growth.

Cereal rye enhanced celery yield. However, high residue production may be
detrimental to celery. When large cereal rye biomass was produced (Hamilton 2004), this

resulted in stunting, yellowing, and low celery yield. The inhibition of growth may be

82

attributed to either N immobilization or allelopathic potential. Cereal rye is known to
produce allelochemicals (Barnes et al., 1987) that affect the growth of several species
(Barnes and Putnam, 1983). Therefore, when using cereal rye as a cover crop, sufﬁcient time
should be allowed for residue breakdown prior to celery transplanting.

Oilseed radish increased celery yield both under the low and half rates of fertilizer.
Oilseed radish produced large amounts of biomass which can create an environment more
conducive to celery growth. This is in contrast to cereal rye. A study conducted by Ngouajio
and Mutch, (2004) documented the ability of oilseed radish to scavenge residual soil N after
crop harvest. Through rapid growth and production of a large root system, oilseed radish
recycled 157.0 kg ton" of N (N gouajio and Mutch, 2004). This recycled N is then released
slowly to the following crop with several beneﬁts to the crop and the environment (Baggs et
al., 2000).

The results of this work suggests that cover crops evaluated, particularly oilseed
radish, could be integrated into celery production with improved soil fertility, reduced
fertilizer inputs, and increase yield. The effects of the cover crops on contribution to soil
fertility between growing seasons should be further measured. Results will prove vital in
development of nutrient management to address nitrate leaching. Finally, it is also important
to determine the nutrient release curve of the cover crops in order to synchronize with celery
crop demand and optimize their contribution to crop rotation systems.

Acknowledgements

Funding for this work was provided in part by USDA CSREES Risk Avoidance and
Mitigation Program. Grant No: 2002-51101-01908. We also would like to thank the MSU
Muck Research Farm and Eding Brothers Celery Inc. for access to facilities. Finally, we duly

thank MSU College of Agriculture and Natural Resources ALANA Graduate Fellowship to
the principal author of this work.

83

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90

Table 3.4.

Effects of cover crop and fertilizer on soil microbial activity in Laingsburg and
Hamilton during 2004.

Cover crop and fertilizer ratex Soil microbial respiration Soil microbial C
coz' c (pg - g‘ soil" 'day'l) coz'c (pg - g - soil“)

Laingsburg

Control plus Low 15.9 (3.1)* 293.8 (17.8)
Hairy vetch plus Low 16.1 (3.8) 322.2 (56.7)
Cereal rye plus Low 14.2 (2.9) 304.9 (68.3)
Oilseed radish plus Low 15.1 (2.3) 316.4 (33.1)
Control plus Half 15.9 (3.0) 329.6 (26.3)
Hairy vetch plus Half 13.3 (2.5) 311.1 (58.8)
Cereal rye plus Half 14.6 (3.0) 348.1 (53.7)
Oilseed radish plus Half 12.4 (3.8) 273.1 (47.8)
Control plus Full 13.6 (3.1) 301.8 (33.5)
P-value NS ' NS
Hamilton

Control 14.0 (1.1) by 321.2 (17.8) bc
Oilseed radish 15.6 (0.2) ab 305.0 (6.6) c
Cereal rye 18.4 (0.8) a 389.6 (35.1) a
Oriental mustard 15.9 (1.2) ab 371.6 (10.6) ab
Yellow mustard 9.5 (0.7) c 400.7 (9.3) a
P-value 0.0020 0.0277

 

" Fertilizer rates are Full, Half, and Low. The full rate was 180, 90, 450 kg ha'1 of N,
P205, and K20, respectively. The half rate corresponded to 50% of the full rate. The low
rate was 50% of the N applied in the full rate and no P205 and K20. All P205, K20, and
25% of N were top dressed and the remaining N side dressed in three equal applications
during the season. In Laingsburg, soils were collected on September 20, 2004. No
fertilizer treatments were used in Hamilton. In Hamilton, soils were collected on August
6, 2004.

3’ All numbers within a column and year followed by the same letter are not statistically
different (a = 0.05, LSD). '

1‘Standard errors are parenthesized.

NS Nonsigniﬁcant at P > 0.05.

91

Table 3.5.

NO; N accumulation by IER“ in Laingsburg
during 2003.

Cover crop and fertilizer ratey

mg N03' N kg'l resin

 

Control plus Low 927 (230)‘
Hairy vetch plus Low 731 (408)
Cereal rye plus Low 623 (349)
Oilseed radish plus Low 1102 (362)
Control plus Half 493 (143)
Hairy vetch plus Half 898 (321)
Cereal rye plus Half 941 (362)
Oilseed radish plus Half 794 (404)
Control plus Full 680 (107)
P-value NS

 

’ IER refers to Ion Exchange Resin.

yFertilizer rates are Full, Half, and Low. The full rate was 180, 90, 450 kg ha'1 of
N, P205, and K20, respectively. The half rate corresponded to 50% of the full rate.
The low rate Was 50% of the N applied in the full rate and no P205and K20. All
P205, K20, and 25% of N were top dressed and the remaining N side dressed in three
equal applications during the season.

‘Standard errors are parenthesized.

NS Nonsigniﬁcant at P > 0.05.

92

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93

Table 3.7.

Eﬂ'ects of cover crop and fertilizer on marketable celery yield in Laingsburg and
Hamilton during 2003 and 2004.

 

 

 

 

Cover crop and 2003 2004
fertilizer rate“ '
number of yield number of yield
stalks,"r (ton ha") stalks” (ton ha'l)
(x1000 ha") @1000 ha")
Laingsburg
Control plus Low 44.7 (5.6) c 24.4 (5.5) b 40.2 (5.9) d 42.1 (8.3) bcd
Hairy vetch plus Low 46.5 (2.5) be 23.9 (4.1) b 44.7 (2.3) cd 37.0 (3.3) d
Cereal rye plus Low 54.5 (4.9) abc 29.2 (2.2) b 49.1 (4.7) bcd 40.1 (4.6) cd
Oilseed radish plus 57.2 (4.4) abc 34.8 (4.7) ab 54.5 (5.5) abc 48.8 (6.0) abcd
Low
Control plus Half 48.2 ( 1.8) be 30.5 (4. 1) ab 59.9 (0.90) ab 57.6 (3.0) ab
Hairy vetch plus Half 59.0 (3.4) ab 36.2 (4.3) ab 56.3 (5.1) ab 54.4 (6.3) abc
Cereal rye plus Half 55.2 (4.7) abc 37.8 (5.3) ab 57.2 (2.5) ab 56.3 (3.6) ab
Oilseed radish plus 66.] (23) T 3" 46.0 (3.0) a 60.7 (2.9) a 59.0 (5 .6) a
Half
Control plus Full 51.8 (7.4) be 38.5 (11.1) ab 56.3 (3.4) ab 56.5 (6.3) ab
P-value " * " *
Hamilton

CODU'OI 107.2 (15.5)T ax 94.9 (9.4) a 105.0 (5.67) a 102.2 (11.4) ab
Hairy vetch 111.5 (11.3)a 103.6 (10.4)a - -
Oilseed radish 98.6 (8.6) a 90.0 (7.3) a 111.5 (7.73) a 118.6 (7.7) a
Cereal rye 98.6 (8.6) a 92.4 (18.7) a 96.5 (11.13) a 89.0 (7.7) b
Oriental mustard - - 105.0 (2.14) a 104.5 (2.4) ab
Yellow mustard - - 107.2 (7.73) a 115.4 (9.4) a
P-value NS NS NS *

 

x Fertilizer rates are Full, Half, and Low. The full rate was 180, 90, 450 kg ha'1 of N,
P205, and K20, respectively. The half rate corresponded to 50% of the full rate. The low
rate was 50% of the N applied in the full rate and no P205 and K20. All P205, K20, and
25% of N were top dressed and the remaining N side dressed in three equal applications
during the season. y All numbers within a column and year followed by the same letter are
not statistically different (a = 0.05, LSD). TStandard errors for the before and aﬁer
category means are parenthesized. "stalks ha'l (x1000).

94

Laingsburg Maximum Temperature

40 n
........ 2004 A
—— 2003
30 - o 0 :- ~ .05.:
20'l .. :,‘ 5
1O -
O l l ﬁr I l I I I I

 

 

10 20 30 40 50 60 70 80 90

Temperature ( °C )
c

40 ' Laingsburg Minimum Temperature
........ 2004
—— 2003 B

30 .1

20 " 0. .- 3

1O " :.:: : .. 10:..- o.

l
0 .

 

 

0 10 20 30 40 50 60 70 80 90
Days after Transplanting (DAT )

Fig. 3.1. Daily maximum (A) and minimum (B) temperature of Laingsburg
during celery growth season in 2003 and 2004. Celery transplanted
on 23 May 2003 and 28 June 2004 in Laingsburg. Data recorded

in Bath weather station.

95

Hamilton Maximum Temperature

 

 

 

 

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A U. v 9.522558

Days after Transplanting (DAT )

Hamilton during celery growth season in 2003 and 2004.
Celery transplanted on 13 May 2003 and 10 May 2004 in

Hamilton. Data recorded in Hudsonville weather station.

Fig. 3.2. Daily maximum (A) and minimum (B) temperature of

96

Laingsburg

    
 

 

    

 

 

 

 

250 -
[:1 Long Term Mean
I - 2003
ﬂ 5221 2004
200 - y
f
é
150 +
3
wo- ? 7
% é
% i
so % é
- é a '
a a
a 0 4 a « 4 I
E Aprll May June July August September
i
E Hamilton
250 T [:1 Long Term Mean
- 2003
2004
200 .
150 ~
100 ~
. 50 - [E
0

 

 

 

 

 

 

 

 

Aprll May June July August September

Fig. 3.3. Total monthly rainfall at Laingsburg and Hamilton during celery growth
season in 2003 and 2004. Data recorded in Bath. and Hudsonville weather
stations. The long term means are from 2001-2003 in Laingsburg and
Hamilton.

97

dry matter ( g ' m‘2 )

1800
1600]
1400 -
1200 —
1000 -
800 _.
600 -
4oo -

200-

 

1800 -

1600 -

1400 -

1200 -

1000-

800 1

600 -

400-

200-

 

Laingsburg Cover Crop Biomass Production

L\\‘ 2003

C C
§ﬂ

Hairy vetch

EE 2003
:1 2004

III/IIII/A 3’

 

B b
Cereal rye Oilseed radish-

Hamilton

1

Q”

U'

 

 

 

L
8’56 4m 0

tr 4‘

f”
a o...»

.3 sf
0 9 00

"as III/IA w

’b

489

Fig. 3.4. Cover crop (total) biomass yield in 2003 and 2004 growing seasons.
In Hamilton, mustards were not seeded in 2003 nor was hairy vetch

in 2004.

98

  

5.5.2....
. "D‘L

5 wwwwwwwmwwwwwwwwwwwwwwww

  

 

 

 

‘7
..L

'11-

 

 

2004 Lamgsburg Soul Microbial Respiration

 

 

d

20-

?».S ..-—::.whavuuou

 

. .
5 0 5 O
1 4|

 

TE

 

.llTl.

 

2004 Laingsburg Soil Microbial C

TIT.

 

TT

 

 

mwmm

::.:.uhéuﬂoo

.m.

 

99

Fig. 3.5. Laingsburg microbial soil respiration (A) and microbial
biomass C (B) during celery growing season in 2004.

COzC(ug'g’soil"' day")

COzC(ug‘g'soil'1)

2004 Hamilton Soil Microbial Respiration

:3 Control A
E Oilseed radish
20 Cereal rye

 

     
 
 
    

EEEED Orientalmustard
Yellow mustard
2004 Hamilton Soil Microbial C
500 [:2 Control B
E Oilseed radish
Cereal rye
400 55533 Oriental mustard
Yellow mustard
300
200
100

0

Fig. 3.6. Hamilton microbial soil respiration (A) and microbial biomass C (B)

during celery growing season in 2004.

100

2003 Laingsburg Celery Yield

...».wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww . $¢
.sx

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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w.

1%, m

a

& m.

.w

a ..m.

L

.1 m
TT. .

 

 

 

 

 

 

120 1
100 .
80 -‘

60«
40«
20-
0
120-
100-
80-
60~
40...
20-
o
f

Fig. 3.7. Celery total yield before trimming stalks as inﬂuenced by cover

an: . no.

101

crop and fertilization in 2003 (A) and 2004 (B) at Laingsburg.
Means separation by the least squares means test, P < 0.05.

2003 Hamilton Celery Yield
[:1 Control A
200 5223: Hairy vetch
E Oilseed radish
22m Cereal rye

 

150

100

2004 Hamilton Celery Yield

I: Control B
E Oilseed radish

Cereal rye

BEES Oriental mustard

Yellow mustard

ton ' ha'1

200

150

100

50

 

0

Fig. 3.8. Celery total yield before trimming stalks as influenced by cover
crop and fertilization in 2003 (A) and 2004 (B) at Hamilton.
Means separation by the least squares means test, P < 0.05.

102

 

 

 

 

 

 

 

 

m ,
.v... 1%.
m e
a 1%
m 1%.
g
..m. TI
u
w u
2
TH.
_ z . -

_- a:

2004 Laingsburg Celery Yield

 

 

 

 

 

 

 

 

 

 

 

80-

...e.

20-

Fig. 3.9. Celery marketable yield after trimming stalks as influenced

by cover crop and fertilization in 2003 (A) and 2004 (B) at
Laingsburg. Means separation by the least squares means

test, P < 0.05.

103

ton ' ha'1

100

2003 Hamilton Celery Yield

140 E Control

m Hairy vetch

120 = Oilseed radish

[22E Cereal rye

80

60

40

20

 

2004 Hamilton Celery Yield

[:1 Control
[:1 Oilseed radish
Cereal rye
EDIE Orientalmustard
BESS! Yellow mustard

140

      

120

 
   

100

80

60

4O

20

Fig. 3.10. Celery marketable yield after trimming stalks as inﬂuenced

by cover crop in 2003 (A) and 2004 (B) at Hamilton. Means
separation by the least squares means test, P < 0.05.

104

2003 Laingsburg Celery Yield

0

onosononononono .

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2004 Laingsburg Celery Yield

 

 

 

TT
93
TIT . TITI. . .RGN i

 

 

 

 

4O
20
0

m o m m
28:: 12.2.2;

604
40

Laingsburg. Means separation by the least square means
105

crops and fertilization in 2003 (A) and 2004 (B) at
test, P < 0.05.

Fig. 3.11. Number of marketable celery stalks as influenced by cover

Stalk8° ha'l (x1000)

2003 Hamilton Celery Yield

 

  
   
 
    

A

[:1 Control
140 m Hairy vetch

[:1 Oilseed radish

EZZZJ Cereal rye
120
100
80
60
4O
20

0
2004 Hamilton Celery Yield
B
140 :1 Control
1:] Oilseed radish
VII/z Cereal rye
12° Oriental mustard
ellow mustard

100 -

80
60
40
20

0
Fig. 3.12. Number of marketable celery stalks as influenced by cover crops

in 2003 (A) and 2004 (B) at Hamilton. Means separation by the least
square means test, P < 0.05.

106

Chapter 4: Integration of cover crops and fertilizer rates for weed management in

celery (Apium graveolens L.).

ABSTRACT

A number of studies have shown that weed suppression can be improved using
cover crops and different fertilization strategies. However, little is known about these
effects on weed population dynamics on high organic matter (>80% OM) soils. Field
studies were carried out in Laingsburg, MI from 2002 to 2004 on Houghton muck soil to
assess the impacts of cover crops and soil fertility regimes on weed populations and
celery yield. The cover crops were oilseed radish, cereal rye, hairy vetch, and a bare
ground control. The fertility rates were full (180, 90, and 450 kg ha‘1 N, P205, K20), half
(90, 45, and 225 kg ha‘1 N, P205, K20), and low rate (90 kg ha'1 N). Each cover crop
treatment was combined with the low or half rate of fertilizer. An additional treatment
with bare ground plus the full rate of fertilizer was added as standard practice. Treatments
were maintained in the same location for the duration of the study. Maj or weed species
were common chickweed, prostrate pigweed, shepherd’s-purse, common purslane, and
yellow nutsedge. Each year, oilseed radish consistently produced the greatest biomass
and provided over 98% early season weed suppression. Hairy vetch and cereal rye
provided over 75% weed suppression in early spring. Unlike the 2003 season, weed
populations were affected by the soil fertility level during the 2004 growing season.
Weed biomass increased as fertilizer rate increased, but total density was not affected.
Within individual fertility levels, higher celery yields were recorded in the oilseed radish

plots. For example, in the low fertility rate, celery yield was 34.8, 29.2, 23.9, and 24.4 ton

107

ha'1 in the oilseed radish, cereal rye, hairy vetch, and control plots, respectively in 2003.
Overall, the results of this experiment indicate that cover crops can successfully improve
weed management and celery yield on muck soils, while allowing reduction of fertilizer

inputs.

108

INTRODUCTION

Michigan is the second largest producer of fresh market and processing celery
after California (USDA 2005). In 2004, 931 ha of celery were planted in Michigan, and
total crop value was estimated at $19 million. Michigan growers rely on intensive celery
production systems. Most of the production is conducted on Houghton muck soil with
short-term rotations. The lack of long-term rotations has led to a resurgence of
troublesome weeds and has diminished soil fertility levels. Currently, Michigan
producers are becoming increasingly interested in a more comprehensive weed and
fertility management approaches that address these concerns. Cover crops have shown
many beneﬁts when used between growing seasons (Mutch and Snapp 2003; Ngouajio
and Mennan 2005; Teasdale 1998). One of the objectives of using annual cover crops in
temperate regions is to manage the soil with over-wintering species that produce
considerable biomass during the spring. Winter annual cover crops are planted in late
summer or fall, become established before winter, and produce most biomass during
early spring before planting a summer crop (Teasdale 1996).

Cover crops can be used as a potential tool in restbring soil fertility and reducing
weed competition in cropping systems. However, due to the short growing season,
Michigan producers are limited to selection and timing options of cover crop as a
planting challenge. Early transplanting of celery is harvested in mid July to early August
and can allow for rapid establishment of vegetation prior to the fall frost. Therefore,
selection of cover crops is critical. Oilseed radish is a cool season cover crop that can be
planted in Michigan after harvest of a warm season cash crop. Cereal rye and hairy vetch

are winter annual cover crops that can consistently perform well in Northern climates.

109

Winter annual cover crops are best adapted to areas where there is a sufﬁcient
establishment period in the fall and soil moisture is not limiting in the spring (Teasdale
1996). In Michigan, there is a small window following harvest of most vegetables when
cover crops can be introduced and established prior to the onset of cool climates.
Exploiting these cover crop niches could allow improving weed control and soil fertility
management approaches (Snapp et al. 2005).

The use of cover crops in sustainable farming systems has been a common practice
for many years (Burket et al. 1997). Cover crop usage is well documented and includes:
erosion control, reduced runoff, improved inﬁltration, soil moisture retention, and
improved soil tilth, (Blevins et a1. 1990; Hall et al. 1984; Robinson and Dunham 1954;
Teasdale 1996; Teasdale and Mohler 1993; Utomo et al. 1990). In addition to the many
beneﬁts, cover crops can also provide weed control (Gallandt et al. 1999; Ngouajio and
Mutch 2004; Williams et al. 1998), and improve soil fertility (Kuo and Jellum 2002;
Ranells and Wagger 1996).

The management of weeds is vital to the success of sustainable farming systems. The
principal goal of using cover crops for weed control is replacing an unmanageable weed
population with a manageable cover crop (Teasdale, 1996). Cover crops effectively
suppress weeds by competition and changing environmental factors that affect moisture
used for weed germination (Fisk et al. 2001), emergence, and establishment (Liebman
and Davis 2000). Residue biomass in the form of plant litter alters physical parameters of
soils and can signiﬁcantly inﬂuence plant communities (F acelli and Pickett 1991) by
inhibiting the emergence of most plant species (Teasdale and Mohler 2000). Cover crop

residue can also modify environmental conditions that have an impact on weed

110

communities. Altered envirOnmental conditions include changes in soil temperature,
decrease in soil moisture, as well as release of allelopathic chemicals and/or physical
impediments to weed seedlings (F acelli and Pickett 1991; Fisk et al. 2001; Teasdale
1996; Teasdale and Mohler 1993).

Nitrogen (N) fertilizers are important nutrient input sources used in vegetable
production to enhance crop yields. However, nutrients may promote growth of crops
(Everaats 1992) as well as weeds (Sindel and Michael 1992; Teyker et al. 1991). The
ability of weeds to efﬁciently use and assimilate minerals can lead to interference with
crops (Blackshaw et al. 2004; DiTomaso 1995; Sibuga and Bandeen 1980). The ensuing
competition favoring weeds in most scenarios results from vigorous weed seedlings and
is a detriment to crop yields (Dhima and Eleﬁherohorinos 2001). Increasing crop
competitiveness during such interactions is an important component of strategic fertility
systems, particularly within weed management programs. Cultural practices using
reduced fertility levels (Dyck and Liebman 1994) and fertilizer placement (Melander and
Jorgensen 2003) have been used successfully to manage weeds.

To our knowledge, no study has focused on the effect of cover crops and fertilizer
regimes on weed population on muck soil in general and celery in particular. Because of
the high organic matter content of muck soil and the high soil fertility requirements of
celery, integration of cover crops and fertilization regimes may have signiﬁcant effects
on weed populations and celery yield. For this reason, this research was conducted to: (i)
evaluate the potential for integrating cover crops into a celery production system, (ii)
measure the. effects of cover crops and soil fertility on weed populations, and (iii)

evaluate celery yield as affected by cover crops and fertilization.

111

MATERIALS AND METHODS
Experimental Site

This study was conducted on a Houghton muck soil with 80 % organic matter and
pH of 6.2-6.9 from 2002 to 2004. The experimental site was located on Michigan State
University’s Muck Soils Research Farm in Laingsburg, MI. The initial experiment was
established in summer of 2002 on land that was previously fallow during the summer.

The experiment had four cover crops and three fertilizer rates. Cover crop
treatments were oilseed radish (cv. diakon), cereal rye (cv. VNS), hairy vetch (cv.
common), and bare ground. Establishment occurred in late summer (26 August 2002 and
in 25 August 2003) following the celery crop harvest, using a broadcast method and
incorporated by shallow discing. Oilseed radish, cereal rye, and hairy vetch were seeded
at rates of 28, 112, and 39 kg ha", respectively.

The 3 rates of fertilizer were: full rate (180, 90, and 450 kg ha" N, P205, K20), half
rate (90, 45, and 225 kg ha" N, P205, K20), and low rate (90 kg ha‘1 N). The full rate was
the recommendation for commercial celery production on muck soils in Michigan. Each
year, 25% of N and all of P, and K were broadcast during land preparation (20 May 2003
and 28 June 2004); equal amounts of the remaining N rates were applied at three
subsequent side dressings during the growing season (13 June, 3 July, 25 July in 2003
and 21 July, 10 August, and 31 August in 2004). The experimental design was a
randomized complete block with four replications. Treatments were combinations of
cover crop and fertilizer rate and consisted of the four cover crop plus low or half rate of
fertilizer. A bare ground plus high rate of fertilizer (normal practice) was also included

for a total of 9 treatments. Individual plots were 4.1 m by 10.7 m and contained four rows

112

of celery at 0.15 m in-row spacing and separated by 1.5 m buffer. Individual plots were
hand weeded during the season and a 1m'2 area was maintained undisturbed throughout
the season for weed assessment. Celery was transplanted on 23 May 2003 and 28 June
2004. At maturity, 20 plants were harvested on 12 August 2003 and 20 September 2004.
All cover crop and fertilizer treatments were maintained in the same location throughout

the duration of the study.

DATA COLLECTION

Cover crop total biomass was collected from each plot in 2003 and 2004 growing
seasons using a randomly placed 50- by SO-cm quadrat. Oilseed radish is ill adapted to
freezing temperatures thus; biomass sampled on October 2002 and 2003 prior to being
frost killed. Because hairy vetch and rye are winter hardy, their biomass was sampled the
following spring (8 May 2003 and 6 May 2004). Cereal rye, hairy vetch, and weeds in
other treatments were then killed with glyphosate prior to land preparation. Cover crop
biomass was determined after oven drying at 75 °C until constant weight was achieved.

Winter annual weed density was assessed in all plots using a randomly placed 50-
by 50-cm quadrat per plot each year (May 6 in 2003, and May 8 in 2004) prior to cover
crop incorporation, fertilizer application, and land preparation. The effect of cover crops
and fertilizer on weed populations was determined during the growing season. Weed
density and dry weight were assessed twice: following celery transplanting (on June 18,
and July 9 in 2003 and July 21, and August 18 in 2004) before each fertilizer side
dressing. Sampling was conducted as described above. The Weeds were separated by

species, and then all species were combined and dried at 75 °C until constant weight was

113

obtained for dry biomass measurement. To avoid weed interference with celery, weed
evaluations were conducted on undisturbed, permanently established microplots within
each experimental unit. During the 2003 and 2004 growing season, hand weeding and
hoeing were used to maintain weed free celery plots following each weed survey.

Celery harvest was manually conducted in the two center rows of each plot in 2003
and 2004. At harvest, plants were separated into marketable and non-marketable yields,
according to market standards. Generally, marketable plants are qualiﬁed as well
developed; well-formed plants with a minimum stalk length of 30 cm (USDA 1959).
Stalk length was measured from soil surface to plant crown. Stalk weight was measured

before trimming and aﬁer trimming in each category.

Statistical Analysis

Data on weed density and species composition were transformed to the logmto meet
homogeneity of variance and normality assumptions of AN OVA (Laufenberg et al.
2005). A value of 0.001 was added to all data to adjust zero for transformation. All data
were then back transformed for clarity of presentation and tables. AN OVA was
conducted on all data using the PROC GLM of SAS and means separated using Fisher’s
Protected LSD at 5 % probability level (SAS Institute, Inc. 1999). Species richness was
determined by using the number of weed species retrieved from respective plots
(N gouaj i0 and Mennan 2005). Cover crop biomass, weed variables, and celery yield data
are presented separately for each year because of signiﬁcant year by treatment

interactions.

114

RESULTS AND DISCUSSION
Climate

The weather conditions during the two celery-growing seasons differed greatly
(Figures 4.1 and 4.2). Because of excessive rainfall (234 mm) in May of 2004, celery
transplanting was delayed until June 28. Consequently, both daily maximum and
minimum temperatures were higher in 2004 than in 2003 (Figure 4.2). At celery
transplanting, maximum daily temperature was below 15 °C in 2003 and above 20 °C in

2004.

Cover Crop Biomass Production

Oilseed radish produced the greatest biomass in both years, with 7,186 and 4,797 kg
ha '1 in 2003 and 2004, respectively (Figure 4.3). Cereal rye and hairy vetch produced
2,839 and 1,808 kg ha", respectively in 2003, and 2,699 and 1,044 kg ha", respectively
in 2004. Unlike oilseed radish that was killed by frost in late fall, both cereal rye and
hairy vetch continued growth until spring killed with glyphosate. Hairy vetch developed

an extensive root system that persisted aﬁer land preparation and interfered with celery

transplanting.

Effects of Cover Crop and Fertilizer on Weed Density and Species Composition
Weed density varied with year (Table 4.1). However, oilseed radish provided the

greatest weed suppression in both 2003 and 2004 for evaluations conducted in May prior

to land preparation. In 2003, weed density was 264 plants m'2 in the control plot and only

21 plants m'2 in the oilseed radish plot. Weed density in the cereal rye, and hairy vetch

115

plots was 91 and 117 plants m'2, respectively, and were signiﬁcantly lower than weed
density in the bare ground plot. Similar results were obtained in 2004 during the ﬁrst
evaluation in May 6. Oilseed radish plots had the lowest weed densities, regardless of the
fertility level. Densities ranged from 49 to 51 plants In’2 in the oilseed radish plots
compared with 200 to 313 plants m'2 in the control plots. The fertilization regime used in
the previous crop did not translate into signiﬁcant differences in weed infestations in r-
2004. However, there was a general tendency in all treatments (except cereal rye) for

greater weed densities as the fertility levels increased

 

In-season weed suppression also varied with year (Table 4.1). In 2003, evaluations }
conducted in June 18 (28 DAT, days after transplanting) showed more weeds in the
oilseed radish plots, compared with the control plots with high rate of the fertilizer. Weed
densities were 853 m'2 in the oilseed radish plus low fertilizer, 723 plants in the oilseed
radish plus half fertilizer, and only 309 in the control plus full fertilizer. All other
treatments had equivalent weed infestations. No differences in weed densities were
observed for second in-season evaluation in 2003 and both in-season evaluations in 2004.

The prevalent species during the growing season were common chickweed
(Stellaria media), common purslane (Portulaca oleracea), prostrate pigweed
(Amaranthus blitoides), shepherd’s-purse (Capsella bursa-pastoris), and yellow nutsedge
(Cyperus esculentus) (Figure 4.4). During the growing season, the major weed species
present in the experimental plot and their relative contribution to total populations
changed as the season progressed (Figure 4.4). In May and early June when maximum air
' temperature was below 15 °C, the prominent species was common chickweed. By the end

of June, a signiﬁcant shift in weed population occurred. Most of the chickweed

116

populations Were replaced by prostrate pigweed and common purslane. From July to
August the population of pigweed declined while that of common purslane increased.
Finally, in August when air temperature started to decline, the population of chickweed
started to increase again in the plots. It is important to note that weed populations
observed at successive dates were ﬁ'om different ﬂushes since the entire plot was weeded
after each evaluation. The simultaneous presence of both winter annual and warm season
weeds on Michigan organic soils makes weed control highly challenging. Common
chickweed, prostrate pigweed, and common purslane were the most important species.
Yellow nutsedge is another troublesome weed in muck soil in Michigan (Zandstra 2005),
but was only recorded in signiﬁcant numbers in May of 2004. Early in the season,
common chickweed accounted for 52 and 84 % of the total population in 2003 and 2004
(Figure 4.4). Common purslane although less, contributed 21 and 47 % (2003) and 84
and 76 % (2004) of the total weed population.

In 2003, oilseed radish signiﬁcantly reduced the density of common chickweed and
shepherds purse in early spring (Table 4.2). Cereal rye also reduced the density of
shepherd’s-purse. However, during the growing season, none of the major weed species
was affected by the treatments. In 2004, weed suppression in early spring was similar to
2003 observations (Table 4.3). Common chickweed was suppressed in the oilseed radish
plots, and yellOw nutsedge in both oilseed radish and cereal rye plots. During the season,
the only weed that was affected by the treatments was common chickweed for evaluation
conducted on August 18, when its density was lowest in plots previously grown with

oilseed radish and subjected to the low fertilizer rate regime.

117

Weed species richness (number of species) was not affected by the treatments in
2003 (Table 4.4). The largest number of weed species was observed for evaluations
conducted in mid season (June 18) in 2003. In 2004, the number of weed species in early
spring was affected by the treatments. Irrespective of the fertilizer rate, oilseed radish and
cereal rye plots had fewer species (1 to 1.3) than the other treatments (1.8 to 2.3 species).
As in 2003, no treatment effect was observed on weed species richness during the

growing season.

Effects of Cover Crop and Fertilizer on Weed Dry Biomass

Weed biomass varied with year, cover crop, and fertilizer treatments (Table 4.5).
The effects of cover crop on winter annual weeds were more pronounced during the ﬁrst
evaluations in both years (P S 0.05). In 2003, the ﬁrst weed evaluation conducted on May
8 showed high level of weed suppression by the cover crops, with oilseed radish
exhibiting the greatest suppressive effects. Weed biomass was 101.2 g m'z, in the bare
ground treatment, compared to 0.3, 15.3, and 31.3 g m'z, respectively in the oilseed
radish, cereal rye, and hairy vetch treatments. Since this was the ﬁrst year of the
experiment, no effect of fertilizer level was possible. During celery growing season, weed
biomass in all treatments was similar, indicating no carryover effects of the cover crops
and no effect of soil fertility levels.

In 2004, the ability of the cover craps to reduce spring weed populations was
conﬁrmed with May’s evaluation. The greatest weed biomass (193 g m'z) was observed
in the bare ground plot where the highest rate of fertilizer was applied the previous

season. This veriﬁes Dhima and Eleﬁherohorinos (2001) results of a weed dry weight

118

increase with nitrogen fertilization. Oilseed radish showed the least weed biomass,
regardless of the applied fertilizer rate. Unlike 2003, there was a carryover effect of the
cover crops and fertilizer effects during the celery growing season in 2004. Weed
biomass assessed on July 21 (23 DAT) showed the greatest weed biomass in the bare
ground treatment that received the full rate of fertilizer (225 g m'z). This was followed by
hairy vetch and the bare ground treatments, each combined with 50% fertilizer rate. All
other treatments had comparable weed biomass. The ﬁnal weed evaluation conducted on

August (72 DAT) show no differences among treatments.

Effects of Cover Crop and Fertilizer on Celery Yield

Celery yield was affected by the different treatments in both 2003 and 2004
(Figures 4.5 and 4.6). This was observed for total and marketable yield, of the untrimmed
and trimmed stalks, as well as for the number of marketable stalks.

In 2003, yields from the control and hairy vetch plots receiving the low fertility
rate, produced the lowest values in all categories. This observation indicates the
importance of adequate soil nutrient amendment in intensely grown celery production.
For example, total marketable plant weight before stalk trimming was 38.0 ton ha" (in the
control plus low fertility treatment) and 37.4 ton ha’1 (in the hairy vetch plus low fertility
treatment), compared to 45.4 to 70.5 ton ha" in other treatments. The combination of
oilseed radish and half rate of fertilizer signiﬁcantly increased yield. Moreover, yields in
the oilseed radish plus the half rate were greater than or equal to yield of the control and

full fertility rates. Similar results were observed with the number of marketable stalks

119

 

(Figure 4.7). The highest numbers of marketable stalks were recorded in the oilseed
radish (66,000 plants ha") that received the half rate of fertilizer.

In 2004, low yields were observed in all systems receiving the low fertility rate.
Oilseed radish cover crop increased yield in those treatments. For example, total
marketable yield (before stalk trimming) was 89.9 ton ha" with oilseed radish and the low
fertility rate in comparison to 78.5 ton hall with the bare ground system. Similar results
were found true for the number of marketable stalks. However, in 2004, there was no E

observed yield beneﬁt noted when the cover crops were combined with the halfrate of

fertility. Similarly, applying a full rate of fertilizer to the bare ground plot did not ”‘-

 

improve yield over the cover crop systems with half rate of fertilizer.

The objective of this work was to improve celery cropping systems with cover
crops. Also, we sought to determine how weed populations and celery yield are affected
by different cover crops and soil fertility levels. Results of this study indicate a possible
ﬁt of the evaluated cover crops in celery production, particularly, in systems where
harvests occur in July or early August. In this study, cover crops sown in late August
rapidly established, providing considerable soil cover during winter and biomass in the
following spring. Teasdale and Daughtry (1993), documented early spring weed control
by cover crops that were used in their study. Mohler and Teasdale (1993), and Ngouajio
et al. (2003) in their respective studies showed increase in weed control as cover crop
biomass increased. Additionally, Fisk et al. (2001) observed cover crop biomass
negatively affected weed density. A dense carpet of cover crop mechanically inhibits

weed germination and emergence (Teasdale 1996).

120

Under muck soil conditions, cover cr0ps used in this study produced signiﬁcant
biomass before being killed by frost (oilseed radish), or by herbicide or cultivation the
following season (cereal rye, hairy vetch). Oilseed radish did not over-winter, while the
other cover crops continued growth to the following spring. Oilseed radish and hairy
vetch biomass was stable across years. On the other hand, cereal rye biomass productivity
varied with growing conditions. The primary difference between the years was more
rainfall following rye planting in 2004. Apparently, adequate soil moisture during
germination and subsequent seedling establishment may be critical for cereal rye on
muck soils.

Although, the cover crops reduced weed densities in spring, there was no signiﬁcant
effect of the cover crops and level of soil fertility on weed density during celery growing
season. Most studies documenting low weed densities in the cover crop systems during
cash crop growth had normally leﬁ high residue on the soil surface (Williams et al.
1998). In this study, all residues were incorporated into the soil, therefore reducing their
physical effects on weed seed germination. In 2004 however, the high fertilizer rate
favored weed growth as indicated by the greater biomass in the control plots early in the
growing season. This observation suggests that high fertility does not affect seed
germination but seedling growth. This is in contrast to observations of Agenbag and
Villiers (1989) who suggested that fertilization, may affect weed seed dormancy. Several
studies have reported reduced weed infestations under low fertilization programs
(Alkamper 1976; AmpongNyarko and DeDatta 1993; Banks et al. 1976; DiTomaso
1995). Following those studies, fertilizer banding as a weed control strategy has been

recommended in weed management programs (DiTomaso 1995). Crimson clover, hairy

121

 

 

 

vetch, and other cover crops have been reported to reduce weed infestations in cropping
systems (Dka and Liebman 1994; Ngouajio and Mennan 2005; Williams et al. 1998).
These are legume cover crops that increase soil N fertility. However, the mechanism of
weed suppression may be more complex than simple soil fertility modiﬁcation.

Therefore, by using different cover crop and fertilization practices, Michigan
producers can reduce weed densities in celery production that, in turn will increase crop
competitiveness and thereby increase their potential for optimal crop yields. Increased
vegetative growth by cover crops during the winter season can also provide soil N
(Hargrove 1986; Kuo et al. 1997). Oilseed radish increased celery growth and yield both
under the low and half rates of fertilizer. By producing large amounts of biomass, oilseed
radish can improve microbial activity and create an environment more conducive to
celery growth. Oilseed radish has been shown to produce glucosinolates (F ahey et al.
2001), secondary metabolites, that suppress weeds, nematodes, and some soil borne plant
pathogens.

Cereal rye enhanced celery growth and yield. However, high residue production
may be detrimental to celery. When large cereal rye biomass was produced (data not
shown), this resulted in stunting, yellowing, and low celery yield. Those grth
inhibitory conditions may be attributed to either nutrient immobilization or
allelochemical interactions. Cereal rye is known to produce allelochemicals (Barnes et a1.
1987) that interfere with normal growth of several species (Barnes and Putnam, 1983).

This work suggests that cover crop, especially oilseed radish, could be integrated
into celery production with associated weed suppression, increase in yield, and reduction

in fertilizer inputs. The effects of the cover crops on weed populations and contribution to

122

soil fertility should be quantiﬁed and credited while developing weed management and
fertilization programs. It is also important to determine the nutrient release curve of the
cover crops in order to synchronize with crop demand and optimize their contribution to
celery crop rotation systems. Finally, establishing and maintaining a cover crop requires
investments by the farmer. Therefore a cost study would help determine the proﬁtability

of the different systems. r

ACKNOWLEDGEMENTS

 

Funding for this work was provided in part by USDA CSREES Risk Avoidance and
Mitigation Program. Grant No: 2002-51101-01908. We also would like to thank the MSU
Muck Research Farm and Eding Brothers Celery Inc. for access to facilities. Finally, we
duly thank MSU College of Agriculture and Natural Resources ALANA Graduate
Fellowship to the principal author of this work.

123

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127

 

 

 

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_ 2004

Monthly precipitation (mm)

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F IGURB 4.1. Total monthly precipitation. Data recorded in Bath

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Days after transplanting

FIGURE 4.2. Daily maximum (A) and minimum (B) temperature at different days aﬁer
transplanting (DAT) during celery growth in 2003 and 2004. Celery transplanted on 23

May 2003 and 28 June 2004 in Laingsburg and. Data recorded in Bath weather station
located at the experimental site.

134

 

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- 2003
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Cover crop species

FIGURE 4.3. Biomass production (kg - ha") by the cover crops prior to incorporation
and transplanting of celery in 2003 and 2004. Vertical bars represent standard errors of
the means. Biomass of oilseed radish was measured in October of the year preceding
the growing season (before they were killed by frost). Cereal rye and hairy vetch ~
biomass was estimated in May prior to land preparation.

135

 

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FIGURE 4.4. Major weed species and contribution to total weed density in 2003 (A) and
2004 (B). Other includes all species contributing less than 10 % to total weed density.

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FIGURE 4.5. Total before trimming celery yield as inﬂuenced by cover crop and
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FIGURE 4.6. Marketable aﬁer trimming celery yield as inﬂuenced by cover crop and

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FIGURE 4.7. Number of marketable celery stalks as

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