- gar.
1145774 2‘3:
”2.33:4?“
3",." 1

«pa. ,

‘ _, ~ . . .

cu;..2..',‘5' .
.‘ .14.
~.

 

. .t ray
1 . m.

.'\ “'6' ‘
4,311.3 V'

;! ,4. L.
1

.E
ca

11. fl.

‘1“ .

if 3

4.7V
'n—n

‘ . .. "kgkfn‘éh
{35‘2“ 4: 5'
Mi:

 

 

THEM?

This is to certify that the
thesis entitled
£151:le C'gkaN AND N (T? CHLL’N YlCL~D
”'D .--- '." . , -7 .
“L '> RFNDG LC.‘ LELLLMWE (’(MIE‘F’, (E70?
ll u. L ’DA’I’E' A ND «Marmara ATlele
presented by

’Pk’i’é‘R LEONA’K‘WLJ "Tiff/1N

has been accepted towards fulfillment
of the requirements for

"’1‘ “)2 degree in m" 1r we ’x‘iL- ac (was

@éigféma)

Major professor

Date l/fld/ql-f

0-7639 MS U is an Affirmative Action/Equal Opportunity Institution

IlllllllllllllllllllllIUIHHIIIllllllllllllllllllllll

3 1293 01033 0417

 

USRARY
Bfiachigan Siam
Univeraity

 

 

 

PLACE ll RETURN BOX to romovo this checkout from your record.
TO AVOID FINES mum on or baton «to duo.

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MSU In An Afflrmdlvo Action/Equal Opportunity IMRNOI'I
. Wanna-m

CORN GRAIN AND NITROGEN YIELD RESPONSE TO LEGUME COVER CROP
KILL DATE AND SUBIRRIGATION

BY

Peter Leonard Tiffin

A THESIS

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

MASTER OF SCIENCE

Department of Crop and Soil Sciences

1994

ABSTRACT

A field study was conducted to determine the effect of
timing of killing a legume cover crop on the yield and N
uptake of a following corn crop in subirrigated and non-
irrigated systems. Corn grain yield following red clover
(RC) with no N fertilizer applied was similar to grain yield
with no cover crop and 140 kg N ha’1 applied. A ten day
difference in killing the RC cover crop had no effect on
grain yields or total N uptake of a following corn Crop.
Soil water contents at the time of corn planting were higher
in the early- than in the late-kill RC systems. Timing of
RC kill may be an effective technique for managing soil
water content in spring without sacrificing N contribution.
The legume based cropping systems were as profitable as
systems with no cover crop. 'Subirrigation did not

significantly affect corn grain yields.

TABLE OF CONTENTS

List of Tables

Lsit of Figures
Introduction

Materials and Methods
Results and Discussion
Conclusions

Refrences

iii

Page
iv

vi

24
62

64

Table

LIST OF TABLES

Phosphorous and potasium content and pH of soil sampled
from the subirrigated and non-irrigated experiments in
fall 1991 and spring 1993.

Grain dry matter yield and N concentration of wheat
grown with and without interseeded red clover in
subirrigated and non-irrigated experiments in 1992 and
1993.

Effect of seeding method and time of kill on red clover
plant population, shoot and root N content in fall,
1992, and shoot and root dry matter, N concentration,
and N content in spring 1993, and calculated plowdown N
for the subirrigated and non-irrigated experiments.

Effect of N fertilizer (1992) and cover crop/N
fertilizer combinations (1993) on corn ear-leaf N
concentration in the subirrigated and non-irrigated
experiments.

Effect of cover crop treatment and N fertilizer on corn
grain and stover dry matter, N concentration, and N
content, and total N in above ground biomass at harvest
for the subirrigated experiment in 1993.

Effect of cover crop treatment and N fertilizer on corn
grain and stover dry matter, N concentration, and N
content, and total N in above ground biomass at harvest
for the non-irrigated experiment in 1993.

Effect of N fertilizer on corn grain and stover dry
matter, N concentration, and N content, and total N in
above ground biomass at harvest for the subirrigated
and non-irrigated experiments in 1992.

Regression equations for corn grain yield (GR), grain N
content (GRN), and total N in above ground biomass at
harvest (TN) as a function of N fertilizer applied (x)
for the subirrigated and non-irrigated experiments
during 1992 and 1993.

iv

10

11

12

Fertilizer replacement values of red clover cover crop
in 1993 based on corn grain yield, grain N content, and
total plant N content at harvest reported as kg N ha“.

Significance of cover crop treatment and N fertilizer
on volumetric water content in the O to 14.5 and 14.5
to 44.5 cm soil layers after corn was planted for the
subirrigated and non-irrigated experiments in 1993.

Variable costs, gross revenue, and net return of
subirrigated and non-irrigated corn produced in
fertilizer (no-cover crop)- and red clover cover crop-N
based cropping systems. Corn grain price was 1993
government support price, costs were provided by the
county extension service in Huron County, Michigan.
Information is not provided for materials and
activities common to all systems (eg corn seed,
herbicide). Cost of N fertilizer is $.35 kg'1 N.

Variable costs, gross revenue, and net return of
subirrigated and non-irrigated corn produced in
fertilizer (no-cover crop)- and red clover cover crop-N
based cropping systems. Corn grain price was 1993
government support price, costs were provided by the
county extension service in Huron County, Michigan.
Information is not provided for materials and
activities common to all systems (eg corn seed,
herbicide). Cost of N fertilizer is $.70 kg'1 N.

LIST OF FIGURES

Figure

1

Daily precipitaion and subirrigated and non-irrigated
water table depths from 19 May through 12 September
1992.

Daily precipitaion and subirrigated and non-irrigated
water table depths from 20 May through 27 September
1993.

Nitrate-N conentrations of soil sampled between 14 May
and 12 September 1993 from 0 to 15, 15 to 30, and 30 to
45 cm soil layers of corn following no cover crop and
early- and late-kill frost seeded red clover cover
crops with no N fertrilizer applied in the subirrigated
and non-irrigated experiments.

Corn grain yield response to fertilizer N in
subirrigated (SI) and non-irrigated (NI) experiments in
1992. Plotted points are means of six replications for
the SI experiment and eight replications for the NI
experiment.

Corn grain N content response to fertilizer N in
subirrigated (SI) and non-irrigated (NI) experiments in
1992. Plotted points are means of six replications for
the SI experiment and eight replications for the NI
experiment.

Total N in above ground corn biomass at harvest
response to fertilizer N in subirrigated (SI) and non-
irrigated (NI) experiments in 1992. Plotted points are
means of six replications for the SI experiment and
eight replications for the NI experiment.

Corn grain yield response to fertilizer N in
subirrigated and non-irrigated experiments in 1993.
Corn followed either no- cover crop or red clover cover
crop. Plotted points for red clover are means of
early- and late-kill, drilled and frost seeded
treatments. No-cover crop points are means of four
replications.

vi

10

11

12

13

14

vii

Corn grain N content response to fertilizer N in
subirrigated and non-irrigated experiments in 1993.
Corn followed either no-cover crop or red clover cover
crop. Plotted points for red clover are means of
early- and late-kill, drilled and frost seeded
treatments. No-cover crop points are means of four
replications.

Total N in above ground corn biomass at harvest
response to fertilizer N in subirrigated and non-
irrigated experiments in 1993. Corn followed either
no-cover crop or red clover cover crop. Plotted points
for red clover are means of early- and late-kill,
drilled and frost seeded treatments. No-cover crop
points are means of four replications.

Volumetric soil water content in the 0 to 14.5 and 14.5
to 44.5 cm soil layers for no-cover, red clover early-
kill, and red clover late-kill treatments and daily
precipitaion between 1 May and 19 May 1993 in the
subirrigated experiment. Each point is the mean of
four measurements, unless otherwise noted.

Volumetric soil water content in the 0 to 14.5 and 14.5
to 44.5 cm soil layers for no-cover, red clover early-
kill, and red clover late-kill treatments and daily
precipitaion between 1 May and 19 May 1993 in the non-
irrigated experiment. Each point is the mean of four
measurements, unless otherwise noted.

Monthly precipitation during the growing season in
Huron County, Michigan 1979 through 1993.

Volumetric soil water content in the O to 14.5 and 14.5
to 44.5 cm soil layers in the subirrigated experiment
and daily precipitaion between 20 May and 28 July 1993.
Corn followed no-cover red clover early kill or red
clover late-kill cover crop treatments. No fertilizer
N was applied to corn. Each point is the mean of four
measurements.

Volumetric soil water content in the 0 to 14.5 and 14.5
to 44.5 cm soil layers in the subirrigated experiment
and daily precipitaion between 20 May and 28 July 1993.
Corn followed no-cover red clover early kill or red
clover late-kill cover crop treatments. Fertilizer N
was applied to corn at 210 kg N had. Each point is
the mean of four measurements.

15

16

viii

Volumetric soil water content in the 0 to 14.5 and 14.5
to 44.5 cm soil layers in the non-irrigated experiment
and daily precipitaion between 20 May and 28 July 1993.
Corn followed no-cover red clover early kill or red
clover late-kill cover crop treatments. No fertilizer
N was applied to corn. Each point is the mean of four
measurements.

Volumetric soil water content in the O to 14.5 and 14.5
to 44.5 cm soil layers in the non-irrigated experiment.
and daily precipitaion between 20 May and 28 July 1993
Corn followed no-cover red clover early kill or red
clover late-kill cover crop treatments. Fertilizer N
was applied to corn at 210 kg N ha“. Each point is
the mean of four measurements.

INTRODUCTION

Including legume cover crops in a cropping system may
provide benefits of reduced soil erosion (Smith et al,
1987), increased water infiltration (McVay et al. 1989),
improved soil tilth (Marten and Touchton, 1983),
contribution of biologically fixed nitrogen (Heichel et a1,
1985), and increased yield of a subsequent crop (Baldock et
al., 1981, Holderbaum et al., 1990). The N contributed by
legume cover crops is often the most important reason
growers include them in cropping systems.

Two common methods of measuring the N contributed by a
legume to a cropping system are total N content of the
legume biomass (TNLB) and the fertilizer replacement value
(FRV) (Hesterman, 1988). For red clover, alfalfa, and hairy
vetch the TNLB at the time of incorporation is commonly
reported to exceed 100 kg/ha (Wagger, 1989; Oyer and
Touchton, 1990) and has been reported as high as 350 kg/ha
(Groya and Scheaffer, 1985). Because the TNLB method
measures only that N present in the plant biomass at the
time of incorporation into the soil, Griffin and Hesterman
(1989) modified the TNLB method to include the N content of

the legumes prior to winter dieback. The plowdown N yield

2
(PDN) was defined as N contained in herbage and roots in the
fall plus N contained in herbage at the time of spring
incorporation. The FRV is defined as "the quantity of
fertilizer N required to produce a yield in a crop that does
not follow a legume that is identical to that produced by
incorporation of the legume" (Hesterman, 1988). Reported
FRVs typically are in the 70-170 kg N/ha range (Oyer and
Touchton, 1990; Utomo et al. 1990) and have been reported to
be as high as 225 kg N/ha (Harris, 1993). Corn yield
increases of up to 100 percent (Holderbaum et al., 1990;
Voss and Shrader, 1979) have been reported following
plowdown of a legume compared to corn grown under similar
conditions without the legume.

Non-legume crops following a legume do not always show
yield increases, and under certain conditions legume cover
crops actually can have a negative effect upon a subsequent
crop. Under water-limiting conditions, corn crops following
a legume cover crop have exhibited reduced emergence
(Holderbaum et al., 1990a; Hesterman et al., 1992), limited
early growth (Holderbaum et al., 1990a; Corak et al., 1991;
Hesterman et al., 1992), and reduced grain and stover yield
(Touchton and Whitwell, 1984; Hesterman et al. 1992). The
likely cause of this negative effect is depletion of soil
water by an actively growing legume (Ebalhar et al., 1984;
Frye et al., 1988; Badarrudin and Meyer, 1990; Hesterman et

al., 1992).

3
Corak et al. (1991) reported that, in Kentucky, a

hairy vetch winter cover crop compared to a no cover crop
control reduced soil water in the top 30 cm by approximately
30% at the time of no-till corn planting in the spring.
Ebalhar et al. (1984) compared four winter cover crops in a
no-tillage system in Kentucky and found that, compared to
corn residue, hairy vetch depleted soil water in the 7.5 to
15 and 15 to 30 cm soil profiles by 16 and 25%,
respectively. The other cover crops they studied, each of
which produced less biomass than hairy vetch, did not
significantly deplete soil water content. The results of
these studies with vetch in the Eastern and South-eastern
U.S. may not be directly applicable to a conventionally
tilled system in the north-central U.S. because of the
importance of climate (Briggs and Shantz, 1916) and plant
species (Fairbourn, 1982) in determining moisture
utilization and soil moisture depletion. Information about
the extent, dynamics, and affect of legume cover crops on
soil water depletion in the north-central U.S. is limited.

Irrigation may be effective at alleviating legume
induced soil water deficits without sacrificing legume
nitrogen contribution. Corak et al. (1991) used irrigation
to successfully alleviate moisture stress in corn which
followed a hairy vetch cover crop.

Killing a cover crop two to three weeks prior to

planting a subsequent crop has also been recommended by

4
several researchers (Hargrove and Frye, 1987; Utomo et al.,
1987; Munawar et al., 1990) as a way to minimize the risk of
yield loss from cover crop induced soil-water deficits.
Munawar et al. (1990) found timing of killing a rye cover
crop to have no effect on soil water content at the time of
no-tillage corn planting. However, beginning one week after
corn planting soil water contents were greater with early-
killed than late—killed rye. These researchers attributed
the differences in soil water content to the early killed
rye, which flattened against the soil surface, being a more
effective barrier than the late killed rye, which remained
standing.

Terminating spring growth of a legume cover crop will
limit biomass and N accumulation (Ngalla and Eckert, 1987;
Ebalhar et al., 1984). The effects of early termination of
legume growth may be especially pronounced in northern
climates, where active spring growth is characterized by
rapid increases in dry matter accumulation and nitrogenase
activity (Rice, 1980). Holderbaum et al. (1990) reported
that hairy vetch grown in Maryland added 2 kg N/ha/day
between the onset of spring growth and early to mid-May.
Although incorporating a larger quantity of N results in a
potentially larger available N pool, changes in chemical
composition associated with maturity may reduce the rate of
decomposition, resulting in similar quantities of N being

available to a subsequent crop (Wagger, 1989)

5

Timing of cover crop desiccation or incorporation may
be an effective technique for managing green manure water
use. When water is plentiful, cover crops could be allowed
to grow until the desired time of planting a subsequent
crop. Under conditions of water surplus, cover crop spring
growth may actually reduce soil water content, potentially
reducing leaching of N03-N (McCracken et al., 1988) and
allowing earlier field operations. During years when water
is expected to be limited, terminating cover crop growth
earlier could minimize soil water depletion by the cover

crop.

Water table management using combined sub-surface
drainage—irrigation (subirrigation) systems is‘a method of
regulating soil water conditions for improved crop growth.
Reported effect of subirrigation on corn grain yields has
varied. Nemon et al. (1987) reported that subirrigating
corn on a sandy soil increased grain yields by 40 and 86% in
two years. Belcher (1992) reported a 26% increase in corn
grain yields averaged across 16 year/locations in Michigan.
In contrast, Chieng et al. (1987) found subirrigation to
have little effect on corn grain yields during three years
of research. Woodruff et al. (1987) reported lower corn
yields with a 0.35- and 0.70- compared to l-m water table

depth with 0 or 112 kg N ha“1 applied but no difference in

6
yield with 224 or 336 kg N ha“. The varied effects of
subirrigation on corn yield may be due to different soil
types and/or precipitation.

Subirrigation systems are easily adapted to existing
tile drain systems and can be particularly effective in some
humid areas where uneven seasonal rainfall distribution
leads to water surpluses and deficits during the same season
(Nemon et al. 1987). Potential advantages of subirrigation
compared to other methods of irrigation include efficiency
at providing water to crops growing on soils having low
water holding capacities, low labor requirements, minimal
evaporative loss (Criddle and Kalisvaart, 1967), and reduced
energy requirements (Strickland et a1. 1981). The potential
disadvantages of subirrigation include possible limitation
of crop choice dependent upon rooting characteristics and
the limited adaptability to sites with a relatively flat
soil surface and a naturally high water table or a water
impermeable soil layer close to the soil surface (Criddle
and Kalisvaart, 1967).

Subirrigation may result in a considerably different
soil environment than that found under rain-fed conditions.
Chieng et al. (1987) stated that the soil environment
created by subirrigation will result in reduced leaching of
nutrients from the upper root zone. However, Woodruff et
al. (1984) found reduced N uptake by fertilized corn and

lower concentrations of soil NO3-N when water tables were

7

maintained at 35 or 70 cm in comparison to 100 cm depths.

Because soil water content strongly affects microbial
reaction rates (Paul and Clark, 1989), rates of legume
decomposition, N mineralization, and denitrification may be
altered under subirrigated conditions. Slower rates of
legume decomposition under wet conditions have been reported
for laboratory (Bartholomew and Norman, 1946) and field
(Wagger, 1989) experiments. The potential for subirrigation
to alter rates of legume decomposition and the movement of N
within a system may result in differing relative performance
of legume- versus fertilizer-N based systems under
subirrigated compared to non-irrigated systems. Previous
research on subirrigation has concentrated on the management
of the subirrigation system for optimizing crop production

in fertilizer-N based systems.

miles

The goal of this research was to determine the effect
that timing of killing a legume cover crop had on grain
yield and N uptake of a following corn crop in subirrigated
and non-irrigated systems.

Specific objectives were to i) compare the N
contributed by early- and late-kill red clover cover crops,
ii) compare grain yield and N uptake of corn following
early- and late-kill red clover cover crops, iii) determine

the effect of subirrigation on grain yield and N uptake of

8
corn grown in red clover- and fertilizer-N based cropping
systems, iv) quantify water content in the soil surface
layers prior to corn planting and during early season
growth, and v) determine which crop sequence/management

combination provided the highest net revenue.

MATERIALS AND METHODS‘

This research was conducted in 1992 and 1993 on a
cooperating farmer's field near Pigeon, Huron County,
Michigan. Soil type was Kilmanagh loam (fine-loamy, mixed,
nonica, mesic Aeric Haplaquepts). The field was chosen
because of existing subsurface drainage and reverse-flow
subirrigation systems. Drain lines were at 7.6-m intervals.
Two parallel experiments were established. One experiment
received irrigation water through the reverse flow
subirrigation (SI) system and the second experiment was non-
irrigated (NI). Subirrigation was not a randomized
treatment. Water table depths in both experiments, measured
weekly during the period the subirrigation system was used,
are shown in Figures 1 and 2. Water table measurements were
taken between 11:00 am and 1:00 pm. Measurements reported
are the average of one reading taken a tile line and one
reading taken midway between two tile lines.

The entire field had been planted to sugar beets, dry
beans, and barley in 1989, 1990, and 1991, respectively. To
break an existing hardpan a shank was used to subsoil the
field to a depth of 45 cm after barley harvest in 1991. No

N fertilizer was applied in 1991. Results from soil tests

10

140 1 60 1 80 200 220 242

 

 

N
O

 

.b
O

 

 

O)
O

 

 

 

 

 

 

 

Water table depth (cm)
(I:
O

 

 

 

 

 

 

 

100

 

 

 

 

 

120

m
_. m
01 m 01
l l 1

Precipitation (0

 

 

 

 

 

 

 

.0
o 0:
l

I '1 [ll ll II III I I
r r

 

 

 

ill ll
2

140 160 180 200 2éo 40

Julian Date

 

non-irrigated I sub-irrigated
1 Last date on which water table measurements were taken.

Figure 1 Daily precipitation and subirrigated and non-irrigated water table
depths from 19 May through 12 September 1992.

11

200 220 2 2401 260
q ; _ : l r

 

A
O
l

O)
O
J

 

 

 

 

 

 

m
C
L

 

\
N
O O
l

. f A
_L
, O)
O
l : - _L
(D
l j o

 

 

 

 

 

 

 

 

 

Water table depth (cm)

 

 

 

 

 

 

 

 

 

 

 

 

Precipitation (cm)

 

 

 

 

 

140 160 180 200 220 240 260
Julian Date
non-irrigated I subirrigated

 

1 Last date on Mich water table measurements were taken.
2 Water table depth observation tube was dry alter this date.

Figure 2 Daily precipitation and subirrigated and non-irrigated water table
depths 19 May through 27 September 1998.

12
performed on samples taken during the fall of 1991 and
spring of 1993 are in Table 1. No P, K, or lime were added
because soil tests indicated that P, K, and pH were suitable
to obtain maximum grain yields.

Precipitation data were collected from a weather

station located on site during the 1992 season (Figure 1)
and from a location five miles north of the site during the

1993 season (Figure 2).

r in m an E rim n l D i
Five 2-year cropping systems were studied. Each system
was defined by the cropping sequence and management of the
cover crop. The five cropping systems were:
i) wheat (no-cover crop)-corn
ii) wheat (RC-FS early—kill)-corn
iii) wheat (RC-FS late-kill)-corn
iv) wheat (RC-DR early-kill)-corn
and v) wheat (RC-DR late-kill)-corn
where RC = red clover cover crop

FS frost seeding used to establish red clover

DR drilling used to establish red clover,

early-kill = red clover killed 13 days prior to
planting corn
late kill = red clover killed three days prior

to planting corn

13

Table 1 Phosphorous and potasium content and pH of soil sampled from
the subirrigated and non-irrigated experiments in fall 1991
and spring 1993.

 

 

 

Time of
Experiment sampling P' K pH
--- kglha ---
Subirrigated Fall 1991 115 305 7.5
Spring 1993 120 260 7.5
Non-irrigated ' Fall 1991 155 280 6.8
Spring 1993 145 230 6.7

 

t Phosphorous measured as Bray P-l.

14

Data from a complete cycle of each cropping system were
collected from spring 1992 through fall 1993. In this
complete cycle, winter wheat was planted in October 1991,
and harvested in July 1992, RC was seeded in spring 1992 and
killed in spring 1993, and corn was planted after RC kill in
May 1993. In addition, data were collected and are
presented for corn grown in 1992 and wheat grown in 1993.
These two crops were not part of a complete cropping system
cycle.

Comparing methods of red clover establishment was not a
specific objective of this study. In May 1992 drilling was
used to establish a second set of RC plots in each block.

It was intended that the two sets of RC plots would be used
for the early- and late-kill treatments. However, plant
populations in fall 1992 were significantly higher in the FS
than DR plots. To avoid confounding the effect of RC kill
date with plant population, RC-DR and RC-FS plots were kept
separate. Early- and late-kill treatments were established
by splitting each RC plot. For statistical analysis, early-
and late-kill treatments were treated as whole plots. Red
clover-DR and RC-FS data were used to determine effects of
kill date.

Each of the two experiments (SI and NI) was a
randomized complete block split-plot design with four
blocks. Whole plots were cover crop management (no-cover,

RC-FS early-kill, RC-FS late-kill, RC-DR early-kill, and RC-

15
PS late-kill). Four rates of fertilizer N, 0. 70, 140, and
210 kg N ha”, were applied to corn plots as a split
treatment. No-cover plots were 13.4 by 15.2 m, RC plots
were 13.4 by 7.6 m. Split plots were 3.35 by 15.2 m for no-

cover treatments and 3.35 by 7.6 m for RC treatments.

r n m n n 'n
Winter Wheat Wheat (Triticum aestivium L. var.

’Frankenmuth’) was drilled at 0.17 m row spacing at 200
kg/ha in early October of each year. In the fall of 1991,
the entire field was planted with wheat, and wheat growing
in plots to be planted with corn was killed by tillage in
the spring of 1992. Three wheat plots per replication
remained during the 1992 season; one plot was wheat only,
red clover was drilled into one plot, and red clever was
frost-seeded into the remaining plot. In 1992, all wheat
plots were fertilized with 67 kg N/ha applied on June 10,
after grain heads had formed. No herbicide was applied to
wheat plots. Wheat was harvested on 28 July 1992. Grain
yields were determined by sampling three 1-ufi quadrats from
each plot.

For the 1993 growing season, two wheat plots per
replication were established; one plot was not interseeded
and red clover was frost-seeded into the other plot. In
1993 wheat plots received 28 kg N/ha on October 11, 1992 and

100 kg N/ha on April 11, 1993. No herbicide was applied to

 

16
wheat plots. On 28 July 1993, wheat grain yields were
determined by machine harvesting a 1.15 by 15.2-m strip from

each plot.

Red Clever Red Clover (Trifolium pratense L. ‘medium’)
was frost-seeded using a fertilizer spreader into one wheat
plot per replication on 28 March in 1992. Red clover was
drilled into the RC-DR plots on 13 May 1992. Equipment for
all seedings was calibrated to apply 16.8 kg seed/hectare.
However, in 1992 the fertilizer spreader used to broadcast
the seed leaked, and the estimated seeding rate was 22.4 kg
seed/ha. Red clover was inoculated with the appropriate
inoculant two weeks before planting. At the beginning of
the second season of RC growth, early- and late-kill clover
treatments were established by splitting each RC plot. The
RC early-kill plots in both experiments were sprayed with
3.5 L glyphosate + 2.3 L crop oil concentrate ha'1 on 6 May
1993. Glyophosate was also applied to the no-cover
treatment in the NI. No herbicide was applied to late-kill
plots. In 1992, the entire field was moldboard-plowed on 17
May 1993.

Red clover crops established in the spring of 1992 were
sampled after a hard frost and apparent cessation of growth
on 17 October 1992. Spring sampling occurred on 4 May and

14 May 1993. The earlier sampling date was two days prior

17
to early-kill, the later sampling date was three days prior
to late-kill.

In 1993, RC was frost seeded into one wheat plot per
replication on 28 March. Seeding rate for frost-seeded RC
was 16.8 kg/ha. Red clover was inoculated with the
appropriate inoculant two weeks before planting. Red clover
established in the spring of 1993 was sampled after a hard
frost and apparent cessation of growth on 17 October 1993.

In both years, RC biomass was sampled by hand—
harvesting three 0.33 x 0.33-m quadrats per plot. Plants
were excavated to a depth of 0.3 m. Plant herbage and
roots-crowns were separated by cutting 3 cm above the
crowns. Root-crown samples were washed with tapwater to
remove soil. Plant populations were determined by counting
the number of plants within each quadrat and are reported as
number of plants m". All samples were dried at 60°C to

constant water content.

EDIE Corn (Zea mays L. Pioneer cv. 3751) was planted
in 55-cm rows at 71,500 seeds/ha on 14 May in 1992 and 20
May in 1993. In both years, weed control was achieved by
cultivation. In 1993, hand hoeing augmented machine
cultivation. Each year, four rates of ammonium-nitrate
granular fertilizer; 0, 70, 140, and 210 kg N ha“, were
applied as a split treatment to all corn plots. Nitrogen

fertilizer was broadcast at planting. Corn grain was

 

 

18
harvested from a 6.1 and 4.6-m section of the center two
rows in each split plot in 1992 and 1993, respectively.
Grain yields were adjusted to 155 g kg“ moisture. Plant
populations were determined by counting the number of plants
in this yield area and calculating populations on a per
hectare basis. Corn stover was sampled by harvesting ten
stalks from the yield rows of each subplot. These stalks
were weighed, and three stalks were subsampled. Subsamples
were dried at 60°C to constant water content. Dried stalks
were ground and analyzed for total N. Corn ear-leaves from
two (1992) or three (1993) randomly selected plants from
each plot in the 0 and 140 kg N ha“ plots were sampled when
plants were at silking. Corn ear-leaves were analyzed for N

concentration.

Plen; Anelyeis end N Caleuleeion

All wheat, red clover, and corn samples were weighed
before and after drying and moisture content was calculated
to express yield measurements on a dry matter (DM) basis.
After drying, all samples were ground to pass through a 1—mm
screen using a cyclone mill. Total N concentration of
ground samples was determined by micro-Kjeldahl digestion of
0.100 9 plant material in 12 M H2804 with 1.5 g K280, and
0.075 g Se catalyst. Following digestion, total NHZ4+ in
samples was determined by Lachat Quik—Chem Method no. 10-

107-06-2-E (Lachat Chemicals, Inc. Mequon, WI). Total N

19
content of materials was calculated as the product of DM
content and N concentration.
Red clover plowdown nitrogen (PDN) was calculated

according to Griffin and Hesterman (1991) using equation 1:

PDN = fall(herbage + root)N + spring herbage N [1]

Grain yield-based FRV of the RC cover crops was
calculated by setting the regression equation describing the
N fertilizer response of corn grain yield with no-cover
equal to the corn grain yield following RC with no N
fertilizer applied. The regression equation was then solved
for N. The calculated N value equals the FRV. Fertilizer
replacement values based on corn grain N content and total

plant N content were calculated in a similar manner.

Seil Weeer Meeeugemenee

Volumetric soil water content (VWC) under no-cover and
RC-FS early- and late-kill treatments were measured using a w
Tektronics model 1502B time domain reflectometer [TDR] (Topp
and Davis, 1985). For each TDR reading, dielectric
constants and associated soil water contents were calculated
using equations developed by Topp et al. (1980).
In fall 1992, parallel pair transmission lines (rods)
made from 4.96 mm diameter stainless steel were installed

vertically, 5 cm apart, to 14.5, 29.5, and 44.5 cm depths in

 

20
each no—cover and RC-FS late-kill plot. Rods were pushed or
hammered into the soil using a wooden frame as a guide.
Pairs of rods were placed approximately 10 cm apart from
each other. All rod pairs were placed in corn rows. On 1
May 1993 all rods were re-established to proper depth and
TDR readings were initiated. On 11 May, four days after RC
early-kill, rods were installed in each RC early-kill plot.
All rods were removed from the field on 17 May before
plowing and corn planting. On 20 May, after corn was
planted, rods were reinstalled in the 0 and 210 kg N-rate
split plots in corn following three cover crop treatments;
no-cover, RC-FS early-kill, and RC-FS late-kill. Because of
variability in measurements of VWC in the 14.5 to 29.5 and
29.5 to 44.5-cm soil layers data from these layers were
integrated and analyzed as a single soil layer.- Results of
analysis of data from two soil layers, 0 to 14.5-cm and 14.5

to 44.5-cm, are presented.

W e.
In 1992, soil was sampled from the 0 to 15, 15 to 30,

and 30 to 45-cm layers from the 0 and 140 kg N/ha treatments

of each corn plot on July 22, October 12, and November 11.

In 1993, soil was sampled from the 0 to 15, 15 to 30, and 30

to 45 cm.layers from the 0 N-rate corn plots of NC and FS-RC

early and late-kill plots on five dates: 14 May, 2 June, 24

June, 20 July, and 12 September. Soil was sampled using a

 

21
2.5 cm diameter soil corer. Two or three cores were taken
from each plot sampled. Inorganic nitrogen (NH: and NO;)
was extracted from the soil samples by shaking 20 g dry soil
in 100 ml of 2 M KCl for one hour. Inorganic N in filtered
KCl extracts was assayed colormetrically on a Lachat flow
injector analyzer using Lachat QuikChem Method 12-107-04-1—A.
Only total inorganic-N data are presented. Soil samples were
pooled by treatment across replication prior to analysis,

precluding statistical analysis of the data.

Eeenemie Anelyeie

The net income of each cropping system/N fertilizer
combination was calculated by subtracting selected variable
costs from gross income. Selected variable costs included
the cost of red clover seed, N fertilizer, fertilizer
application, operation, maintenance, and depreciation of the
subirrigation system. Gross income was calculated by
multiplying corn grain yield from each treatment by the 1993
government target price for corn grain. The costs of N
fertilizer and fertilizer application were obtained from the
Huron County, MI Cooperative Extension Service. The hauling
and drying costs are from Schwab, 1994. Shrinking of grain
caused by drying was not accounted for. Depreciation cost
was calculated by dividing the $740 ha“ cost of installing
the subirrigation system by the 20 year expected life of the

system. Operation, maintenance, and installation costs, and

 

 

22
expected life of the subirrigation system are from Belcher

(1992).

S i i 1 al i

Each of the two experiments (SI and NI) was analyzed as
a randomized complete block split-block design with four
blocks. Cover crops were whole plots. In 1993, N-rates were
applied across early- and late-kill treatments within each RC
plot. Because N-rate was not applied as a randomized
treatment within each early- and late-kill plot, N-rate was
analyzed as a split block treatment. When more than one sub-
sample was analyzed, the mean of the sub-samples was used for
statistical analysis.

Data was analyzed using analysis of variance (ANOVA).
Soil VWC data were analyzed separately by date and soil
layer. Comparisons between VWC treatment means were made
using the Least Significant Difference test (LSD) (Petersen,
1985) when the ANOVA indicated a significant F (P < 0.05).
Corn ear-leaf N concentration, grain and stover dry matter, N
concentration and N content, and total plant N content means
were partitioned using orthogonal contrasts. The contrasts
were RC versus no-cover crop and RC early-kill vs RC late-
kill. The REG procedure of SAS was used to test the
significance of linear and quadratic equations describing the
response of corn grain yield, dry matter, and total N

content to N fertilizer applied. A t-test was used to

 

23
compare data from the SI experiment to data from the NI

experiment.

.41":

RESULTS AND DISCUSSION

Reg Clever Biemeee end N Centen;

Interseeding red clover into a standing wheat crop did
not significantly affect wheat grain yields or grain N
concentration in either the SI or NI experiment (Table 2).
These results are similar to results reported by Hesterman et
a1. (1992), Janke et al. (1987), and Ngalla and Eckart
(1987), but contrast with Brandt et al. (1989) who reported
that interseeding subterranean clover into winter wheat had a
significant effect upon wheat grain yield. Results reported
by Brandt et al. (1989) may have been due to either not
fertilizing the wheat or aggressive growth of the interseeded
legume. The data reported here corroborate the conclusion
reached by Hesterman et al. (1992), that interseeding a small
seeded forage legume into a standing small grain crop may be
an effective method of incorporating a legume cover crop into
a rotation without sacrificing a revenue-producing grain crop
during the establishment phase.

Killing RC early limited the quantity of N accumulated
in RC shoots by as much as 70 kg ha“ (Table 3). Lower
spring RC shoot N content resulted in significantly and near-

significantly (P<0.07) lower PDN in the early- compared

24

 

 

255

Table 2 Grain dry matter yield and N concentration of wheat grown with and without
interseeded red clover (RC)' in subirrigated and non-irrigated experiments
in 1992 and 1993.

 

 

1992 1993

Experiment Seeded DM N 0M N

Mg/ha X Mglha X
Subirrigated Hithout RC 2.2 2.1 7.0. 1.6
r Hith RC 2.4 1.9 7.7 1.5
Significance NS NS NS NS
CV(%) 10.6 6.2 10.4 4.6
Non-irrigated without RC 2.6 1.8 7.3 1.6
With RC 2.3 1.6 6.7 1.6
Significance NS NS NS NS
CV(%) 10.9 8.4 5.4 2.5

 

I’Red clover was frost-seeded on 28 March in 1992 and 1993.
Significant difference (t-test, P<0.0S) between subirrigated and non-irrigated
experiments.

226

.muoozm mcmcdm + Amuoot + muoocmvddaw cm acoucoo 2 ma vouadaudou mm: 2 cropzo.a .
s h

.>.o>_cuaaawt .aza>az .oo.o ecu .Fo.o .mo.o use “a acau_c_cm_m ... .. .

 

 

 

—.mr Fm v.6 m.NN o.mN F.m F.0N o.M~ N.flw MQ ARV >u
m: a are m: as at we r. u- u- .dmx *0 Gem»
m: m: m: m: m: m: m: we we ace nonuoe mamboom
oucmummmcm_m
wNm 0v m.~ o.w vmw N.M 0.M r: r . mum.
MON hm N.m m.w mo P.v Q.N cm mmw Fm >dcmo Buddmco
NON mm <.~ ¢.— «FF N.M o.m .. - . mama
now me o.~ m.F No N.¢ m.P mm mN— m¢~ >~Lmo Umfloow umoLu
voumm_tt_-coz
0.0 m.kw P.m m.¢— o.¢~ n.m 0.QN w.m M.NP NM ARV >u
we we tee m: use {a ate it u- .: .dmx *0 OEmh
«C c mc a a m: m: mc m: a; nozuoe mc_uoom
oocmu_wmcm_w
—0N me m.N N.F M~— 0.M M.M u- r . vumd
Q¢N Fm N.M 0.F wk F.c o." no NN— om— >dcao Daddmuo
mom km m.N m.F FF— 0.M F.m .. r a Quad
mMN on —.m N.— Nq N.¢ 0.? em nor com >dumo bovmmm quLu
Umummmggmnsm
msxmx m:\mx. x anxm: mc\mx x mc\mx mcxmx mcxmx Lexmucedd .Ir
zom mxmuQ: z z to mxmuQD z z to z duper z Laue» .comumdanon ddmx voguoz ucosmcoaxm
mUOOK WUOOSM $900M wHOOp—w UC@d& W0 gwh OCmuflflm

 

 

hoop .mcmcmw moor «.Lmu

 

.mucoemtuaxo pouam_ttm-coc ace pouam_ct_b:m toe

.Azoav z crousodn bouaLDodnu pea .noop unmade cm acoucou 2 new .comuncucoucou z .touune xcu uooc new uoocm new
.moo— .ddaw c_ ucoucou 2 ~66; use uoocm .comuodaaod acadd to>odu pot co ddmx Co oemu new rogues mcmvoom wo uuomwm n canoe

27
to late-kill RC system in the SI and NI experiments,
respectively. However, timing of RC kill did not
significantly affect corn ear-leaf N concentrations in 1993
(Table 4), or corn grain yield and grain N content (Table 5
and 6) in 1993 suggesting that kill date did not affect the N
available to the succeeding corn crop. Wagger (1989) also
reported no effect of cover crop kill date on the yield and N
status of a following corn crop. Possible reasons that lower
PDN may not have resulted in less N being available to the
succeeding corn crop are (i) more N was immobilized by
microbial activity in the late- than early-kill system, (ii)
more N was leached from the late- than early-kill system,
(iii) changes in RC chemical composition resulting from
advanced maturity resulted in late-kill RC to be more
resistant to decomposition and N contained in the late-kill
RC to be less available than N contained in early-kill RC
(Wagger, 1989), and (iv) the higher N content of late—kill RC
shoots may have resulted from uptake of soil N rather than
biologically fixed atmospheric N (Rice, 1980). That early-
kill did not limit the amount of N available to the
succeeding corn crop suggests that, in systems where a cover
crop accumulates the majority of N the season before
incorporation, there may be a large range in the period of
time during which a cover crop could be killed without
limiting the N available from that cover crop. These results

are in contrast to warnings made by several

 

228

Table 4 Effect of N fertilizer (1992) and cover crop/N fertilizer combinations
(1993) on corn ear-leaf N concentration in the subirrigated and non~
irrigated experiments.

 

 

 

Cover N coneeptration
Experiment crop N-rate 1992 1993
kg/ha -------- x N -------
Subi rri gated No-cover o 1.32 1.27‘
140 2.43 2.54
RC-early' 0 -- 2.42
140 -- 2.81
RC-late 0 -- 2.43
140 -- 2.89
Significance
No-cover vs RC -- ***
RC-early vs -late -- NS
N-rate *** ***
(No-cover vs RC) x Nrate -- **
CV (X) 4.9 9.8
Non-irrigated no-cover 0 1.27 1.50
140 2.40 2.61
RC-early 0 -- 2.48
140 -- 2.75
RC-late 0 -- 2.30
140 -- 2.78

Significance

No-cover vs RC -- *4.
RC-early vs -late -- NS
N-rate *** tit
(No-cover vs RC) x Nrate -- 4*.
CV (X) 4.3 5.2

 

**, *** Significant at the 0.01 and 0.001 levels, respectively.

' Red clover (RC) was frost seeded. RC-early was sprayed with glyphosate 13
days before planting corn. Both RC-early and RC-late were moldboard plowed
on 17 May 1993, three days before planting corn.

Significant (P<0.05, determined by t-test) difference between subirrigated
and non-irrigated experiment.

 

259

Table 5 Effect of cover crop treatment and N fertilizer on corn grain and stover dry matter,
N concentration, and N content, and total N in above ground biomass at harvest for
the subirrigated experiment in 1993.

 

 

 

 

Cover Grain Stover'
crop' N-rate on N n on N N Plant u
kg/ha Mg/ha X kg/ha Ng/ha X kg/ha kg/ha
no-cover 0 3.6 1.2 37 4.5 0.42' 19' 56
r 70 6.6 1.0 57 5.7' 0.50' 29 86
140 8.6 1.1 80 5.8 0.77 41 121
210 10.4 1.2 105 5.8 0.66 41 145
RC-FS early 0 8.5 1.3 91 6.1 0.61 39 132
70 9.6 1.4 112 5.5' 0.75 41 152
140 11.5 1.4 134 7.5 0.82 60 194
210 10.5 1.3 113 6.3 0.81 50 164
nc-rs late 0 8.4 1.4 99 6.4' 0.76 48 147
70 10.4 1.3 116 6.0 0.72 44 159
140 10.9 1.4 126 6.7 0.88 59' 185'
210 11.3 1.2 117 8.2 0.70 59 176
RC-DR early 0 8.2 1.1 79 6.2 0.82 50 129
70 10.1 1.3 114 5.9 0.61 36 150
140 10.0 1.4 115 5.9 0.80 47 161
210 10.2 1.3 115 6.1 0.86 52 167
RC-DR late 0 8.6 1.3 94 6.6' 0.67 45 139
70 10.5 1.3 118 7.0 0.85 61 179
140 9.6 1.2 101 6.1 0.76 45 147
210 11.1 1.3 126 8.4' 0.82 70 195
Significance
N-rate * us NS us as as us
no-cover vs RC *** ** *** NS NS NS *
RC-E vs RC-L us as us NS us us NS
N-rate X cover crop * NS * NS NS NS NS
CV (11 13 11 15 19 19 26 15
LSD for cover crops’ 0.6 0.11 16 -- -- -- 50
LSD for N-rates‘ 1.4 0.28 38 -- -- -- 56

 

*, **, *** Significant at the 0.05, 0.01, and 0.0001 levels, respectively.

1 Significant difference (t-test, P<0.5) between subirrigated and non-irrigated experiments,

compared within a treatment.

# RC-FS, RC-DR stand for red clover frost seeded and drilled into winter wheat, respectively.
Early kill was sprayed with glyphosate 13 days before planting corn.

kill were moldboard plowed on 17 May, 3 days before planting corn.
’ Least significant difference to compare cover crop treatment means within a N-rate.
Least significant difference to compare N-rate means within a cover crop treatment.

Both early- and late

3()

Table 6 Effect of cover crop treatment and N fertilizer on corn grain and stover dry matter,
N concentration, and N content, and total N in above ground biomass at harvest for
the non-irrigated experiment in 1993.

 

 

 

 

Cover Grain Stover
crop N-rate ON N N on N N Plept N
kg/ha Ng/ha X kg/ha Ng/ha X kg/ha kg/ha
no-cover 0 4.8 0.95 46 4.2 0.72' 30' 76
70 7.2 0.91 65 4.2' 0.76' 32 98
140 9.6 1.02 99 4.9 0.82 40 139
210 9.5 1.16 111 5.0 0.67 33 144
nc-rs early 0 9.2 1.10 100 4.1 0.81 33 133
70 9.9 1.18 116 5.3' 0.76 41 156
140 10.6 1.10 115 6.3 0.72 46 162
210 9.9 1.15 114 5.5 0.83 46 160
nc-rs late 0 9.2 1.16 107 4.7' 0.91 43 150
70 10.5 1.14 119 5.0 0.72 36 155
140 10.0 1.09 110 5.1 0.73 37' 146'
210 11.1 1.12 124 5.2 0.86 45 169
RC-DR early 0 8.8 1.07 95 5.1 0.60 31 124
70 9.3 1.10 104 5.5 0.74' 40 144
140 9.8 1.18 116 5.3 0.82 42 158
210 9.2 1.07 99 5.2 0.97 50 150
RC-DR late 0 8.4 1.04 88 5.2' 0.72 37 125
70 9.5 1.09 105 5.1 0.78 41 145
140 9.9 1.14 114 5.5 0.83 46 159
210 10.5 1.08 114 5.1' 0.80 41 154
Significance
N-rate NS NS NS NS NS NS NS
no-cover vs RC NS NS NS NS NS NS NS
ac-e vs RC-L us as us us us us as
N-rate X cover crop *** NS ** NS NS NS NS
CV(X) 10 9 14 17 19 28 12
LSD for cover cropss 2.2 -- 28 -- -- -- --
LSD for N-rates 2.0 -- 35 -- -- -- --

 

*, **, *** Significant at the 0. 05, 0. 01, and 0. 0001 levels, respectively.

1 Significant difference (t- test, P<0. 5) between subirrigated and non irrigated experiments,
compared within a treatment.

3 RC-FS, RC-DR stand for red clover frost seeded and drilled into winter wheat, respectively.
Early kill was sprayed with glyphosate 13 days before planting corn. Both early- and late
kill were moldboard plowed on 17 May, 3 days before planting corn.

§ LSD to compare cover crop treatment means within a N-rate.

1 LSD to compare N-rate means within a cover crop treatment.

31
researchers (Ebalhar et al., 1984; Ngalla and Eckert, 1987)
that early kill of a cover crop may limit the N benefit

derived from that cover crop.

Seil N geneen;

Nitrate-N concentrations of soil sampled on 14 May
(Julian date 135), prior to RC incorporation, from the 0 to
15 cm layer of the RC-FS early—kill, RC-FS late-kill and no-
cover plots were 15, 8.8, and 5.6 ppm, respectively, in the
SI experiment, and 12.9, 8.4, and 8.9 ppm, respectively, in
the NI experiment (Figure 3). The higher nitrate-N
concentrations in the RC early-kill indicate that N in the
early-kill RC began to be mineralized prior to the time corn
was planted (Figure 3). Although earlier mineralization of
early-killed cover crops may increase the potential for N to
leach from the system, in this study increased inorganic
concentrations were measured in only the surface 0 to 15 cm
layer. Similarly, Sarrantonio and Scott (1988) found N from
legume cover crops was mineralized within 7 days of killing
but that the N remained in the surface soil layer. Prior to
incorporating the cover crops, inorganic N concentrations
were similar in the late-kill RC and no-cover systems.

Nitrate-N concentration in soil sampled from the 0 to 15
and 15 to 30 cm layers from early- and late-kill RC systems
on 24 June were 17 and 17 ppm respectively, in the SI

experiment, and 24 and 28 ppm, respectively in the NI

 

ppm N as N03-

32

 

35

25'
20‘

15

0-15 cm soil layer

10

 

15—30 cm soil layer
1

 

 

 

15—

 

30-45 cm soil layer

 

 

 

 

*1 l l

l l l l
1 20 1 40 1 60 180 200 220 240 260 280
Julian Date

no-cover RC early-kill RC late-kill
subirrigated: - ~0- - - o- - - a. .
non-irrigated: “' + +

1 Early-kill BC was sprayed with glyphosate 18 days before corn planting. Both early- and
late-kill RC were moldboard plowed on 17 May. three days before planting corn.

Figure 3 Nitrate-N concentrations of soil sampled between 14 May and 12 September 1993
from 0 to 15, 15 to 30, and 30 to 45 cm soil layers of corn following no cover crop
and early- and late-kill frost seeded red clover cover crops with no N
fertilizer applied in the subirrigated and non-irrigated experiments.

 

33
experiment. In the SI experiment, nitrate-N concentrations
from the RC 0 N-rate systems were lower than the 21 ppm pre-
sidedress soil nitrate test critical level. Corn grain
yields (Table 5) from the RC-FS early- and late-kill 0 N-rate
plots in the SI experiment were significantly lower than
yields from the fertilized plots (Table 5). Nitrate-N
concentration in soil from the NI experiment exceeded the
pre-sidedress soil nitrate test critical level of 21 ppm (Fox
et al., 1989; Bundy and Andrasski, 1993), indicating that in
both early- and late-kill RC systems there was no need for
additional fertilizer to be applied to the corn crop. In the
NI experiment, corn grain yields from RC-FS early- and late-
kill 0 N-rate systems were not significantly lower than grain
yields from the fertilized plots (Table 6). In the no-cover
systems soil nitrate-N concentrations were 9 ppm in both SI
and NI experiments. In both experiments, corn grain yields
from the no-cover systems responded significantly to
fertilizer N. In this study, the 21 ppm nitrate-N critical
level was an effective predictor of the availability of soil
N to corn grown in both legume- and fertilizer-N based

cropping systems.

Cern Dex Mateer and N Yield end Legdme N Centribdeien

In 1992, ear-leaves from corn grown with 140 kg N ha“
had significantly higher N concentrations than ear-leaves

sampled from corn that was not fertilized (Table 4). In

34
1993, N-rate significantly affected the N concentration of
ear-leaves from corn grown in both the no-cover and RC-FS
systems (Table 4). Time of RC kill did not significantly
affect ear-leaf N concentration in any case. The significant
interactions between cover crop and N-rate reported for both
experiments are a result of the greater response of ear-leaf
N concentration to N fertilizer in the no-cover than in the
RC systems.

Corn ear-leaf N concentration has been reported by
several researchers as a means of assessing the N status of
corn (James et al., 1967; Melsted et al., 1969; Asghari and
Hanson, 1984; Cerrato and Blackmer, 1991). Reported corn
ear-leaf N concentrations at which grain yield is maximized
(the critical level) are generally above 2.75% (James et al.,
1967; Asghari and Hanson, 1984; Melstead et al. 1969). Some
researchers have suggested that a corn ear-leaf N
concentration of 2.75% overestimates the quantity of N
necessary to achieve maximum yield (Cerrato and Blackmer,
1991) while data from Asghari and Hanson (1984) suggest that
critical values may be difficult to determine for legume-N
based systems. In the SI experiment in this study, maximum
corn grain yields (Table 5) were not obtained when corn
earleaf N concentration was below 2.75% (Table 4), suggesting
the 2.75% critical level was appropriate. In the NI
experiment corn earleaf N concentrations from the no-cover

140 kg N ha“ N-rate and RC-FS 0 N-rate systems were below

35
the 2.75% critical level (Table 4) but corn grain yields from
these systems were not significantly different from.maximum
yields (Table 6), suggesting that the 2.75% critical level
was too high.

The response of corn grain dry matter and grain N
content, and total N in above ground biomass at harvest to
fertilizer N—rate in 1992 indicate that available soil N
limited corn growth (Figures 4, 5, and 6, respectively, and
Table 7). Corn grain dry matter in the SI experiment in 1992
was not different with 210 compared to 140 kg N ha“ applied
(Table 8). In contrast, grain N content and total plant N
were higher with 210 kg N ha“ than with 140 kg N ha“
applied. Greater response of grain N (Hargrove, 1986,
Hesterman et al., 1992) and total plant N content (Hesterman
et al., 1992) reflect the greater sensitivity of these
parameters to available N.

In the SI experiment in 1993 there was a highly
significant difference in corn grain yield and grain N
content between no-cover and RC systems but no difference
between early- and late—kill RC systems (Table 5). The
significant N-rate by cover crop interaction for corn grain
dry matter yield and N content in the SI experiment reflects
the greater response of corn grain to fertilizer N in the no-
cover system than the RC systems (Figure 7 and 8,
respectively, and Table 7). Total plant N was not

significantly affected by N-rate (Figure 9 and Table 7) but

 

36
was significantly higher in the RC systems than in the no-

cover system .

Grain yield Mg/ha

37

 

10..

>1
‘1‘

.01
‘1’

 

 

 

 

l l l l
0 70 140 210

N rate kg N/ha

Subirrigated Non-irrigated

O O

 

Figure 4 Corn grain yield response to fertilizer N in subirrigated (SI) and
non-irrigated (NI) experiments in 1992. Plotted points are means
of six replications for the SI experiment and eight replications
for the NI experiment.

 

\

grain N content kg/ha

38

 

100 —

(D
O
l

O)
O
l

h
0
l

 

 

 

0 l l l
0 70 140 210
N-rate kg N/ha

 

Subirrigated Non-irrigated

O O

 

Figure 5 Corn grain N content reponse to fertilizer N in subirrigated (SI) and

non-irrigated (NI) experiments in 1992. Plotted points are the means
of six replications for the SI experiment and eight replications
for the NI experiment.

 

Total N in above ground biomass kg/ha.

39

180

 

160— O

_ O
140—
120-

100*

O)
O
l

O)
O
l

.h
C
J

 

 

 

 

N
O

l l l
0 70 140 210

N-rate kg N/ha

Subirrigated Non-irrigated

O O

 

Figure 6 Total N in above ground biomass at harvest response to fertilizer
N in subirrigated (SI) and non-irrigated (NI) experiments in 1992.

Plotted points are the means of six replications in the SI
experiment and eight replications in the NI experiment.

40

Table 7 Regression equations for corn grain yield (GR), grain N content (GRN), and total N in
aboveground biomass at harvest (TN) as a function of N fertilizer applied (x) for the
subirrigated and non-irrigated experiments during 1992 and 1993.

 

Experiment Year Cover Crop Equation R2 Si nificance
441__ _ 9.

 

Subirrigated

1992 No-cover GR = 2.7 + .032(X) 0.88 .0001
can = 14 + 0.37rx) 0.90 .0001

1» = 27 + 0.58(x) 0.83 .0001

1993 No-cover GR = 4.0 + .031(x) 0.67 .0001
can = 30 + 0.28(x) 0.66 - .0001

TN = 56 + 0.44(x) 0.72 .0001
RC-DR-early can = 68 + 0.45 (x) - 0.0017(x2) 0.63 .0015

RC-DR-late GRN = NS

RC-FS-early can = 76 + 0.4800 - 0.0018(x2) 0.61 .0022
RC-FS-late GRN = NS

ac combined' GR = 8.5 + .026(x) - 7.3*10‘(x2) 0.50 .0001

1» = 142 + 0.18(x) 0.25 .0001

Non-Irrigated

1992 No-cover on = 3.4 + .053(X) - .00014(x2) o 83 .0001
can = 26 + 0.31(x) 0.87 .0001

1» = 48 + 0.57(x) 0.86 .0001

1993 No-cover GR = 4.7 + .052(x) - .00013(x2) 0 88 .0001
can = 39 + 0.27(x) 0.86 .0001

IN = 77 + 0.35(x) 0.80 .0001
ac combined as = 9.1 + .060(x) 0.17 .0006

can = 86 + 0.06(x> 0.12 .0054

ru = 137 + 0.117(x) 0.21 .0002

 

1 RC combined represents frost seeded and drilled early and late kill red clover, except for
GRN in the subirrigated experiment in which RC drilled early kill (RC-DR-early) in which grain
yield was significantly lower than when corn follwoed other covers. There were no significant
differences between any of the red clover cover crop systems at any N rates for GRN or TN.

 

41

Table 8 Effect of N fertilizer on corn grain and stover dry matter, N concentration, and
N content, and total N in above ground biomass at harvest for the subirrigated and

non-irrigated experiments in 1992.

 

 

 

 

Grain Stover
Exper'ment Nrrate 0M N N on N N Plant N
kg/ha Ng/ha X kg/ha Ng/ha X kg/ha kg/ha
Subirrigated
0 2.6 0.9' 22 4.3 .37' 16 38
- 70 4.9 0.9' 42' 6.6 .35' 23 60'
140 7.8 1.0. 77 7.3 .47 28 109'
210 9.1 1.2 112 7.7 .66 43 164
Signiiissnss
N'rate *** *** iii *** *** * *tt
cv (x) 16 6.1 19 11 15 21 18
LSD 1.8 0.1 15 1.3 .01 9 24
Non-irrigated
0 3.3 0.9' 28 4.5 .43' 19 44
70 6.7 0.9' 62' 6.6 .43' 30 92'
140 8.0 1.0 83 8.1 .55 45 128'
210 8.6 1.3 107 7.7 .83 64 164
Significance
N'rate iii *ti tit *tt *ti *** ti".
c.v.<x) 15 7.5 18 15 20 27 13
LSD 1.6 0.1 14 1.6 0.18 11 14

 

*,*** Significant at 0.05, 0.001 probability levels, respectively, NS = not significant

at P=0.05.

l, 1 Significant difference at 0.05, 0.01 probability levels (t-test) between subirrigated

and non-irrirrigated experiments.

42

In the NI experiment in 1993 there was a highly
significant N—rate by cover crop interaction for corn grain
yield and grain N content (Table 6). This interaction
reflects the significant response of grain yield to
fertilizer N in the no-cover system and the lack of response
where corn followed RC (Figure 7 and 8, Table 7). Asghari
and Hanson (1984b), Hargrove (1986), and Hesterman et al.
(1992) all reported no response of yields from grain crops
when those crops followed a legume. The lack of yield
response is most likely a result of the RC contributing
sufficient N to supply the N demand of the corn crop. In the
NI experiment, total plant N was not significantly affected
by N-rate or cropping system (Table 6 and Figure 9).

In 1993, corn grain yield, grain N content, and total N
differed significantly between corn grown in the no-cover
crop system and corn grown in the RC systems where no
fertilizer N was applied, allowing FRV of the red clover to
be calculated based on each of these parameters. Fertilizer
replacement values based on grain yield are more commonly
reported (Baldock et al. 1981, Ebalhar et al. 1984, Hesterman
et al. 1986) but FRV based on grain N content (Hargrove,
1986, Hesterman et al., 1992) or total plant N (Hesterman et
al. 1992) may be more sensitive to N available from a cover
crop. There were no consistent patterns relating FRVs to RC

seeding method or kill date (Table 9).

43

 

10—

 

.‘l
01
1

Grain dry matter yield Mg/ha
'1"

 

2.5-n

 

 

 

l l l l
O 70 140 210

N-rate kg N/ha

 

 

No-cover subirrigated No-cover non-irrigated
--1:5--
Red clover subirrigated Red clover non-irrigated
I El

Figure 7 Corn grain yield response to fertilizer N in subirrigated and
non-irrigated experiments, 1993. Corn followed either no-cover crop
or red clover cover crop. Plotted points of red clover are means of early-
and late-kill, drilled and frost seeded treatments. No-cover crop points
are means of four replications.

44

 

 

 

 

120
.......................... [:1
100— ,8" I
Il” . "5
rm ’I” "' I
£ II” ""
3’ 80— O
H El” ,""
c . ,.
q) ."
up; a
c "'l
o x.
0 ."
z 60‘ ,v’
e O
9. "x.
C) "’5
40—3"
20—
l r l l
o 70 140 210

N-rate kg N/ha

No-cover subirrigated

O
Fled clover subirrigated

 

 

No-cover non-irrigated

Figure 8 Corn grain N content response to fertilizer N in subirrigated and
non-irrigated experiments, 1993. Corn followed either no-cover crop

or red clover cover crop. Plotted points for red clover are means of early-
and late-kill, drilled and frost seeded treatments. No-cover crop points

are means of four replications.

45

 

 

 

 

 

 

 

200
:11
£ 180
U)
x’.
8
m 160
E
.2
.o 140
.0
5
9 120
o:
9
o 100
.o
(0
.E 30
Z
Ts
o 60
l-

40 l l l 1

0 70 140 210
N-rate kg N/ha
No-cover subirrigated No-cover non-irrigated
e "'0'"
Red clover subirrigated Red clover non-irrigated
I "'lj'"

Figure 9 Nitrogen in above ground corn biomass at harvest response to

fertilizer N in subirrigated and non-irrigated experiments in 1993. Corn

followed either no-cover or red clover cover crop. Plotted points for

red clover are means of early-and late-killed, drilled and frost seeded
treatments. No-cover crop points are means of four replications.

46

Table 9 Fertilizer replacement values of red clover cover crops in 1993 based on corn grain
yield, grain N content, and total plant N content at harvest.

 

FRV Subirrigated experiment Non-irrigated experiment

 

Red clover based on: Grain Grain N Total Grain Grain N Total
Nanagement' Yield Content Plant N Yield Content Plent N
------------------------- kg N/ha -------------------------
FS early-kill 146 170 175 131 186 167
FS late-kill _ 142 194 223 138 205 167
DR early-kill 138 133 148 114 173 155
DR late-kill 150 179 168 95 154 144
early-kill mean 142 152 162 123 180 162
late-kill mean 146 187 196 117 180 156
Significance
Early- vs late-kill NS * NS NS NS NS

 

1 FS, DR stand for red clover frost seeded and drilled into wheat, respectively.
Early kill was sprayed with glyphosate 13 days before planting corn. 80th early-
and late-kill were molboard plowed on 17 May, 3 days before planting corn.

* Significant at 0.05 probablity level.

47
The lower FRVs from the NI experiment are a result of higher
grain yields from the no-cover system in the NI than in the
SI experiment.

The effect of subirrigation on corn grain yield and N
uptake were similar for the no-cover systems in both 1992 and
1993. At lower N rates, corn grain yield, N content, and
total plant N were consistently lower in the SI than the NI
system (Tables 5 and 6), suggesting either a loss of N from
or lower N availability in the SI system. Decreased corn
grain yield and N concentration were reported by Chaudhary et
al. (1975) when water table depths were at 60 or 90 cm
compared to 120 cm depths and by Woodruff et al. (1984) when
water tables depths were 0.70 m or less. Measured water
table depths in the SI experiment in this study varied
between 0.38 m and 1.1 m in 1992 (Figure 1) and 0.45 and 1.1
m in 1993 (Figure 2). Woodruff et al. (1984) concluded that
less N was available to corn with higher water table depths
due to loss of N from denitrification or leaching.

In the RC systems in 1993 corn grain yields and corn
grain N content differed little between the SI and NI systems
(Table 5 and 6). Chieng et al. (1987) also reported little
effect of subirrigation upon corn grain yields. These
results contrast with the 26% increase in corn yields
averaged across 16 year/locations reported by Belcher (1992);
although, during some years yield increases reported by

Belcher were minor. Higher grain yields may not have

48

occurred in the SI experiment in this study due to
precipitation and soil storage supplying sufficient water for
corn to obtain maximum grain yields in the NI experiment.

Corn stover yields were consistently higher in the SI
than the NI system (Tables 5 and 6). Higher stover yields
are evidence of greater above ground vegetative growth in the
SI experiment. It is possible that the greater above ground
growth in the SI experiment resulted from a more consistent
water supply or to less partitioning of C to below ground
growth.

In 1992, corn plant population means were 66,500 and
67,500 plants ha“ in the SI and NI experiments,
respectively. In 1993, corn plant population means were
63,000 and 62,900 plants ha“ in the SI and NI experiments,
respectively. Fertilizer N-rate did not have a significant
affect on plant population in either experiment in 1992 or

1993.

Seil Weeer Centen;

Prior to cover crop incorporation (Julian date 138),
there was a tendency for soil water content to be lower in
the RC late-kill plots than in either the RC early-kill or
no-cover plots, particularly in the lower soil layer (Figures
10 and 11). Water content in the surface soil layer of the
RC plots may not have been significantly less than VWC in the

no-cove plots due to greater water evaporation from the

Soil water content v/v

14.5-44.5 cm horizon

'81

.°
60
re

0.28

0—14.5 cm horizon

0.24

p
00
re

9
to
m

p
[0
.§

0.20

Precipitation in cm

0.8 '
0.6 .
0.4 .
0.2 .

49

 

 

 

 

 

 

 

 

 

     

..l
"l
1 r r
120 1 30
Julian Date
no-cover red clover late-kill red clover early-kill
-.- - -.. - - . ....A ......

1 Red clover was frost seeded. Red clover early-kill was sprayed with
glyphosate on 7 May. The field was moldboard plowed on 1 May (Julian date 137).
2 Only one measurement for no-cover. mean of two measurements for red clover
at each horizon on this date.

Figure 10 Volumetric soil water content in the 0 to 14.5 and 14.5 to 44.5 cm

soil layers for no-cover, red clover early-kill, and red clover late-kill
cover crop treatments hnd daily precipitation between 1 May and 19

May 1998 in the subirrigated experiment. Each point is the mean of
four measurements, unless noted otherwise.

50

 

 

 

 

 

 

    

 

 

 

 

 

c 0.36 a
O
N
'C
O
.C 0.32 r
'0. ..
i <1- 0.28 r e- ..... ‘a ...........
Y— ‘-.' ......... A
H 6 .°‘--
C
.92, 0.24 -
C
O ' i ' l T l '
0 v * a“
5 0.32 a ' ................. v
a C a, ........... .
g o \‘ "-.,-‘ ........ a
= .N ‘\ ....... t
o 8 0.28 — x
a) .c ' ....... b
E ‘~
0
m- 0 24 -
i . “\b
e
:3:
0.2 -
E l l l
O
.5 0.6 ~
g 0.4 .
O 0.2 ~ 1%
9
120 125 .130 135
Julian Date _
no-cover red clover late-kill red clov‘er early-kill
--I--. ......

Figure 11

1 Red clover was frost seeded. Red clover early-kill was sprayed with
Iyphosate on 7 May. The field was moldboard plowed on 17 May Julian date 137).
2 can of three measurements at each horizon for no-cover on this ate.
', " Data points labeled with the same letter within each sam ling date and horizon
are not significantly different at P-0.10 and 0.05, respe vely. according to
pairwise comparisons using Fisher's LSD.

Volumetric soil water content in the 0 to 14.5 and 14.5 to 44.5 cm
soil layers for no-cover red clover early-kill and red clover late-kill
cover crop treatments land daily precipitaiton between 1 May and 19

May 1993 in the non-irrigated ex eriment. Each point is the mean of
four measurements unless note othenrvrse.

51
unprotected soil surface of the no-cover plots. The greater
difference in water content in the deeper soil layer may also
have been due to greater water uptake by RC roots from the
deeper soil layer. Ebalhar et al. (1984) also reported a
cover crop to affect the water contents of deeper soil layers
greater than the surface layer.

The greatest difference in VWC in the different systems
was between the no-cover and RC late-kill plots in the 14.5
to 44.5-cm layer in the NI experiment. This difference was
approximately 30% of the total water content of that soil
horizon, corresponding to 3 cm of water. Precipitation in
May, 1993 was 1.2 cm less than the ten year average (Figure
12) and less than May precipitation during 9 of the past 15
years in this area of Michigan. High early season
precipitation in this part of Michigan suggests that a cover
crop is seldom likely to reduce soil water contents to a
level significantly lower than with no cover crop.

Prior to RC incorporation, there was a smaller
difference between VWC in the late-kill RC and no-cover
treatments in the SI experiment than in the NI experiment.
The relative difference between treatments in the two
experiments may be a result of not controlling weeds in the
no-cover plots in the SI experiment. Corack et al. (1991)
reported smaller differences in VWC between vetch cover crops

and no cover crops in a year when weeds on the no-cover crop

 

52

6.: :o pupa—"E Lo: m_ 82 :_ :owmgdfiea Eo mdm P

 

 

 

 

e 4 I o
:mmE 28> me name Name mam 722
5:05.
tenEmEmm “mam—é. >3... 8:2. >92
_ _ _ I _ _ o
o
o o
o o o
o
o 0 do w I@ m
o o @ l
o O O 4m
o a m 66 m
. w I o
a . W . ...
a r e...
6 do .0 o m or m
O l.
. U
a .w a a
o o o w
l m—
0
PO
om

.89 .5325 23:332.). 5:300 :05: :_ common 9565 65 05:6 :o_§_d_omad 25:22 NP 2391..

53
plots were not controlled than in two years when weeds were
controlled.

The difference in soil VWC between early- and late-kill
RC suggests that killing cover crops early may be an
effective means of limiting water use by spring growth.
During dry years, an early-kill cover crop may conserve more
water than no cover crop by providing a mulch which retards
evaporation from the soil surface (Fry et al., 1988). In
contrast, living covers may offer a management tool for
removing excess water from the soil profile.

After corn planting (Julian date 141), VWC showed very
similar trends in the different cropping systems within both
the 0 to 14.5 and 14.5 to 44.5 cm soil layers. The trends
were similar with either 0 or 210 kg N ha“ applied within
both the SI (Figures 13 and 14) and NI (Figures 15 and 16)
experiments. Within each soil layer, VWC was lower after corn
planting than before corn planting. Differences in VWC
before and after corn planting likely resulted from changes
in soil bulk density caused by moldboard plowing before
planting. In the SI experiment VWC in the RC early-kill
system was higher than in the no—cover or RC late-kill
system, especially at the 0 kg ha“ N-rate (Figure 14).
During the period that VWC were measured, this difference
deviated little at either soil horizon or N-rate. Since TDR
rods were not moved after initial post corn planting

installation, it is probable that this difference resulted

54

 

 

 

 

 

 
   

 

 

 

 

 

0.4
‘:0.35 r
O
N
.5 _
c 0.3
> 5
E 19.0.25 -
+- <1-
8 S
-r-l 0.2 r
C
O
0
‘6
4—1
E
= § 0.3 a
O 't:
<0 .8
E025 -
o
in.
i 0.2-
3'
E l l r
o
.E
1:
£3.
a. i .. ... a ,_
. 180 200 220
Jullan date
no-cover red clover late-kill red cloverzarly- -kill

Within each horizon and s amspllngrd date data points labeled with the e leu— ot
filgnlflcantly different (.P-O 0 )racco ding alrwls e comps r son usfigher'LS sLS
o points are labeled. there were no sign cant differences tween crops.

Figure 13 Volumetric soil water contents in the 0 to 14.5 and 14.5 to 44.5 cm soil layers
in the subirrigated experiment and daily precipitation between 20 May and
28 July 1993. Corn followed no-cover, red clover early-kill or red clover late-
kill cover crop treatments. No fertilizer N was applied to corn.
Each point Is the mean of four measurements.

55

 

 

 

 

 

0.35 —
C
O
N
'8 03 .
c .
> E
3 100.25 ~
E’i
.9, 0.2 -
c:
O
O
5
...:
(0
3 5 0.3—
% .u
a) .8
E025 -
O
m.
i 0.2 -
3'
E l l l
0 l
.E
C r
.9 if
313'
ICI-
0 “ F
01
a ,

 

 

 

 

   

 

160

   

. 180
Julian date
no-cover red clover late-kill red clover early-kill
+ - - l - - ..... ‘W

* Within each horizon and sampling date data points labeled with the same let- not
significantly different (P-0.0 ) according to pairwise comparison usfigher’s LSD.

Figure 14 Volumetric soil water contents in the 0 to 14.5 and 14.5 to 44.5 cm soil layers
in the subirrigated experiment and daily precipitation between 20 May and
28 July 1993. Corn followed no-cover, red clover early-kill or red clover late-

kill cover crop treatments. Fertllzer N was applied to corn at 210 kg/ha.
Each point is the mean of four measurements.

Soil water content v/v

56

 

O O

ie .0 ' .0

0| 0) 8 «h
l r l

0145 cm horizon

.0
M
r

 

 

.°
0
1

0.25 ‘

14.5-44.5 cm horizon
o
to

 

 

N

l

o .5
our-ethanol

Precipitation in cm

 

1

 

  

 

u‘llllfrlljlll‘rlllflllllttll'rr.

  

1 40 1 80 200 220

Julian date
no-cover red clover late-kill red clover Karly-kill

Within each horizon and sampling date data points labeled with the same lett- not
significantly different (P=0.0 ) according to pairwise comparison uslfiwer s LSD.

Figure 15 Volumetric soil water contents in the 0 to 14.5 and 14.5 to 44.5 cm soil layers
in the non-irrigated ex eriment and daily precipitation between 20 May and
28 July 1993. Corn fo lowed no-cover, red clover early-kill or red clover late-

kill cover crop treatments. No N fertilizer was applied to corn.
Each point is the mean of four measurements.

 

 

57

 

 

 

 

 

 
   

 

   

 

 

 

: 0.35%
O
..u
‘5 -
c 0.3
g 1
z to 0.25 -
> er'
-1- 1- 1
r: 6 02“
9 .
C -l
O
O
1—
9
(U C
3 o 0.3—
N
:-.: ~:
(3 2
$0.25 -
*0.
i, 0.2 -
5!.
E
U -
.E
C
S
(U
3: .;
0- E
a e .
. 180 200 220
Julian date
no-cover red clover late-kill red cloverze‘arly-kill

1 Within each horizon and sam ling date data points labeled with the same Ietternot
significantly different (P-0.0 according to pairwise comparison uwer’s LSD.

Figure 16 Volumetric soil water contents in the 0 to 14.5 and 14.5 to 44.5 cm soil layers
in the non-irrigated experiment and daily precipitation between 20 May and
28 July 1993. Corn followed no-cover, red clover early-kill, or red clover late-

kill cover crop treatments. Fertilizer N was applied to corn at 210 kg/ha.
Each point is the mean of four measurements.

 

 

58
from the soil characteristics at the specific locations where
VWC was measured.

A significant affect of N-rate on VWC during the later
stages of corn growth was reported by Corak et al. (1991) and
was expected in the NI experiment in this study. However,
significant effects due to N rate occurred only during the
first three weeks after planting in the surface horizon of
the SI experiment (Table 10). The lack of a significant N-
rate effect may be due to regular precipitation events, the
amount of precipitation, and/or the shallow depth to which

water contents were measured.

Eeenomie Perfegmenee
In 1993, the RC-N system.produced significantly higher

net return than the no-cover system at the 0, 70, and 140 kg
N ha“ N-rates in the SI experiment and at the 0 and 70 kg N
ha“ N-rates in the NI experiment (Table 11). The
differences in net return between the two systems were due to
significantly higher gross revenues in the RC system. The SI
system had lower economic returns than the NI system, except
at the highest N rates. Differences between SI and NI
systems were only significant with no N fertilizer applied.
Doubling the price of fertilizer N (Table 12), from $0.35 to
$0.70 kg“, had no effect on the relative performances of the

cropping systems.

£59

.>ez ON :6 poucedd we: ceou .

 

 

 

 

 

mz m2 mz m: e m: mz m2 m2 eaae-zeaoeu
m2 a: ma m2 m2 m2 m2 m2 mz abet-z
m2 mz m2 m2 mz m2 m2 mz m2 aoeu so m.ee-m.eF
mz wz wz m2 mz m2 m2 m2 m2 auee-zaaeeu
m2 m2 mz mz m2 m2 m2 m2 m2 aaae-z
m2 mz «2 m2 m2 mz m2 m2 m2 aoeu Eu m.ep-o
uamwm_LLCHMMz
m2 m2 m2 mz m2 m2 m2 m2 - abet-zeaoeu
m2 m2 m2 mz mz mz m2 m2 - euae-z
m: a. mz mz m2 m2 m: a - aaeu so m.ee-m.eF
m2 m2 m2 m2 mz e mz m2 - oaae-zeeoeu
m2 m2 m2 m: a a m: a - auee-z
mz m2 mz m2 as a use as t QOLU Eu m.c—to
peummmec_
‘53—. FN >:.:. a»... 0:33 QN 065—. or 0:3... m >mt PM >0! ON >02 «N >2. ON "mum—u .3210ch conmgoc ucoEmgoflxw
mo~ ea? on. No, Amp ~mp new mew Pep “abet ce_.:4 ._em
puma
.62 E

mucoemeedxe pou6m_::_-co: ace veuam_tc_n:m ecu tow .peucedn mm: :toe cones meo>o. ._om Eu m.eq o» m.c—
be» m.e— ea c as» :_ aceucou team: o_:uoeado> :o ecum._ueow 2 6:6 unusuaeeu deco ee>ou we ouceu_e_:u_m op e.na»

Table 11

60

Variable costs, gross revenue, and net return of subirrigated and non-irrigated corn
produced in fertilizer (no-cover crop)- and red clover cover crop-N based cropping systems.
Corn grain price was 1993 government support price, costs‘ were provided by the county
extension service in Huron County, Michigan. information is not provided for materials and
activitieslwhich are common to all systems (eg corn seed, herbcide). Cost of N fertilizer
is $.35 kg' N.

 

 

 

 

 

 

1993
r Fertilizer-N Red clover-Ns
0 70 140 210 0 70 140 210
Subirrigated ----------------------------- 5 ha" -----------------------------
Variable Costs
Red clover seed - - - - 53 53 53 53
N-Fertilizer - 25 49 74 - 25 49 74
Fertilizer application - 8 8 8 - 8 8 8
Drying 15 27 35 42 34 41 46 44
Hauling 7 13 17 20 17 20 22 21
Depreciation 38 38 38 38 38 38 38 38
Electricity 38 38 38 38 38 38 38 38
Total variable costs 98 149 185 220 180 223 254 276
lncm I I I O I I
Gross Revenue 395 715 925 1115 910 ' 1080 1215 1180
Net Return 295" 565' 740' 895 730" 860' 960' 905
Non-irrigated
Variable Costs _
' Red clover seed - - - - 53 53 53 53
N-Fertilizer - 25 49 74 - 25 49 74
Fertilizer application - 8 8 8 - 8 8 8
Drying 19 29 39 39 37 41 42 42
Hauling 9 14 19 19 18 20 20 21
Total variable costs 28 76 115 140 108 147 172 198
income ' . ' '

Gross Revenue 515 780 1045 1035 990' 1095 1115 1130
Net Return 485" 705' 930 895 880" 950' 945 930
§ Yields for legume N system are the mean of frost-seeded red clover early- and late-kill. Variable

costs do not include the price of chemical or application for herbicide dessication in the early-

kill system.

1 Prices used were: corn grain S 127 llg'1 dry matter (equal to $2.75/bushel at 15.5X moisture).

Red

Clover seed, 17 kg ha'1 a S 3.10 kg. N-Fertilizer, a S .35 kg'1 N. Fertilizer application $7.70 ha“.
Drying and hauling costs were calculated for grain harvested at 200 kg lllg'l moisture. Depreciation
was calculated as cost of system establishment divided by system life. Cost of establishment used
was $740 ha'l system life was considered to be 20 years. This method of calculating depreciation
includes no return on investment. Cost and estimated life of system are from Belcher (1992).
Installation cost was the lowest of the given range.

* Significant difference (P<0.05) between fertilizer and legume N systems within an N-rate, comparisons

1

made using LSD.
Significant difference (P<0.05) between St and Ni experiments, comparisons made using t-test.

Table 11

61

Variable costs, gross revenue, and net return of subirrigated and non- irrigated corn

produced in fertilizer (no- cover crop)- and red clover cover crop- N based cropping systems.
Corn grain price was 1993 government support price, costs were provided by the county
information is not provided for materials and

extension service in Huron County, Michigan.
activities which are common to all systems (eg corn seed, herbcide).

is S. 35 kg N.

Cost of N fertilizer

 

 

 

 

 

 

1993
r Fertilizer-N Red clover-N’
0 70 140 210 0 70 140 210
Subirrigated ----------------------------- S ha'I -----------------------------
Variable Costs
Red clover seed - - . - 53 53 53 53
N-Fertilizer - 25 49 74 - 25 49 74
Fertilizer application - 8 8 8 - 8 8 8
Drying 15 27 35 42 34 41 46 44
Hauling 7 13 17 20 17 20 22 21
Depreciation 38 38 38 38 38 38 38 38
Electricity 38 38 38 38 38 38 38 38
Total variable costs 98 149 185 220 180 223 254 276
InCO‘ne I I I I I I
Gross Revenue 395 715 925 1115 910' 1080 1215 1180
Net Return 295" 565' 740' 895 730" 860 960' 905
Non-irrigated
Variable Costs
Red clover seed - - - - 53' 53 53 53
N-Fertilizer - 25 49 74 - 25 49 74
Fertilizer application - 8 8 8 - 8 8 8
Drying 19 29 39 39 37 41 42 42
Hauling 9 14 19 19 18 20 20 21
Total variable costs 28 76 115 140 108 147 172 198
income . . _ _
Gross Revenue 515 780 1045 1035 990' 1095 1115 1130
Net Return 485" 705' 930 895 880" 950' 945 930
§ Yields for legume N system are the mean of frost-seeded red clover early- and late-kill. Variable

costs do not include the price of chemical or application for herbicide dessication in the early-
kill system.

Prices used were: corn grain S 127 Mg dry matter (equal to lS2. 75/bushel at 15. 5X moisture). Red
Clover seed, 17 kg ha a S 3.10 kg. N- Fertilizer, 0 S .35 kg N. Fertilizer application S7. 70 ha .
Drying and hauling costs were calculated for grain harvested at 200 kg Mgl moisture. Depreciation
was calculated as cost of system establishment divided by system life. Cost of establishment used
was S740 ha'1 system life was considered to be 20 years. This method of calculating depreciation
includes no return on investment. Cost and estimated life of system are from Belcher (1992).
installation cost was the lowest of the given range.

* Significant difference (P<0.05) between fertilizer and legume N systems within an N-rate, comparisons

1

made using LSD.
Significant difference (P<0.05) between Si and Ni experiments, comparisons made using t-test.

 

CONCLUSIONS

Red clover incorporated the spring after the seeding
year contributed between 235 and 328 kg N ha“ when N
contribution was measured as total N in legume biomass.
Although early spring kill of RC limited the N content of RC
biomass, no effect of RC kill date was seen on the grain dry
matter or N yield of a following corn crop. It is possible
that long term benefits of including a legume crop in a
cropping system may be enhanced by greater spring growth and
N accumulation. Early-kill RC also depleted soil water
content less than RC late-kill. The effect of RC kill date
on soil water content suggests that cover crop kill date may
be effectively used for managing soil water contents in
spring. These results also suggest that a delay in killing a
legume cover increases the risk of soil water depletion by
the cover crop and does not enhance the N contribution to a
succeeding crop.

Subirrigating corn did not increase grain yields, most
likely due to adequate rainfall and soil water storage
supplying adequate water for corn to obtain maximum yields in
the non-irrigated experiment. There was evidence for greater

N loss from the subirrigated than from the non-irrigated

62

63
experiment. Nitrogen loss from a subirrigated system.may be
minimized by maintaining a lower water table. The effect of
subirrigation on grain yield and N uptake would likely be
different during a year with lower precipitation.

The economic analysis suggested that at least in some
years in both subirrigated and non-irrigated systems RC-N
based cropping systems can be as profitable as systems which
do not include a legume cover crop. In addition, the greater
importance of high fertilizer inputs in the SI system should

be considered when assessing the economics of these systems.

 

REFERENCES

Asghari, M. and R.G. Hanson. 1984. Nitrogen, climate, and
previous crop effect on corn yield and grain N. Agron. J.
76:536-542.

Badarrudin, M., and D.W. Meyer. 1990. Green-manure legume
effects on soil nitrogen, grain yield, and nitrogen
nutrition of wheat. Crop Sci. 30:819-825.

Baldock J.0., R.L. Higgs, W.H. Paulson, J.A. Jackobs, and
W.D. Shrader. 1981. Legume and mineral N effects on crop

yields in several crop sequences in the upper Mississippi
Valley. Agron. J. 73:885-890.

Bartholomew, W.V. and A.G. Norman. 1946. The threshold
moisture content for active decomposition of some mature
plant materials. Soil Sci. Soc. Am. Proc. 270-279.

Belcher, H.W., 1992. Economics of subirrigating row crops.
Paper presented at the Irrigation Associations 1992
International Irrigation Exposition and Technical
Conference. New Orleans, LA, November 1-4, 1992.

Binford, G.D., A.M. Blackmer, and N.M. 31-Hout. 1990. Tissue
test for excess nitrogen during corn production. Agron J.
82:124—129.

Boawn et al, 1963. Residual N from ammoniumrnitrate
fertilizer and from alfalfa plowed under. Agron. J. 55:231-
235.

Briggs, L.J., and H.L. Shantz. 1916. Daily transpiration
during the normal growth period and its correlation with the
weather. Journal of Agriculture Research. 7:155-212.

Bundy, L.G. and T.W. Andraski. 1993. Soil and plant nitrogen
availability tests for corn following alfalfa. J. Prod.
Agric. 6:200—206.

Cerrato, M.E. and A.M. Blackmer. 1990. Relationships between

grain nitrogen concentrations and the nitrogen status of
corn. Agron. J. 82:744-749.

64

65

Cerrato, M.E. and A.M. Blackmer. 1991. Relationships between
leaf nitrogen concentration and the nitrogen status of corn.
J. Prod. Agric. 4:525-531.

Chaudhary, T.N., V.K. Bhatnager, and 8.8. Prihan. 1975. Corn
yield and nutrient uptake as affected by water table depth
and soil submergence. Agron. J. 67:745-748.

Chieng, S.-T., J.Keng. amd M.G. Driehuzen. 1987. Effects of
subsurface drainage and subirrigation on the yields of four
crops. Canadian Agricultural Engineering. 29:21-26.

Corak, S.J., W.W. Frye, and M.S. Smith. 1991. Legume mulch
effects on soil water and corn production. Soil Sci. Soc.
Am. J. 55:1395-1400.

Criddle, W.D. and C. Kalisvaart. 1967. Subirrigation
systems. p. 905-921. In R.M. Hagan, H.R. Haise, and T.W.
Edminster (eds.). Irrigation of Agricutural Lands. American
Society of Agronomy, Madison, WI.

Doty and Parson. 1979. Water requirements and water table
variations for a controlled and reversible drainage system.
Trans. ASAE 22(3):532-536,539.

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

Fairbourn, M.L. 1982. Water use by forage species. Agron. J.
74:62-66.

Fox, R.H., G.W. Roth, K. V. Iversen, and W.P. Piekielek.
1989. Soil and tissue nitrate tests for predicting soil
nitrogen availability to corn. Agron J. 81:971-974.

Frye, W.W., J.H. Herbek, and R.L. Blevins. 1983. Legume
cover crops in production of no-tillage corn. p. 179-191. in
W. Lockerentz (ed.) Environmentally sound agriculture.
Praeger Publishers, New York.

Groya and Sheaffer, 1985. Nitrogen from forage legumes:
harvest and tillage effects. Agron. J. 77:105-109.

Hargrove, W.L. 1986. Winter legumes as a nitrogen source for
no-till grain sorghum. Agron. J. 78:70-74.

Hargrove, W.L., and W.W. Frye. 1987. The need for legume
cover crops in conservation tillage production. In J.F.
Power (ed.) The role of legume in conservation tillage
systems. Soil Conservation Society of America, Ankeny, IA.

 

 

66

Heichel, G.H., C.P. Vance, D.K. Barnes, and K.I. Henjum.
1985. Dinitrogen fixation and N dry matter distribution
during 4 year stands of birdsfoot trefoil and red clover.
Crop Sci. 25:101-105.

Hesterman, O.B., C.C. Sheaffer, D.K. Barnes, W.E. Lueschen,
and J.H. Ford. 1986. Alfalfa dry matter and nitrogen
production, and fertilizer nitrogen response in legume-corn
rotations. Agron. J. 78-19-23.

Hesterman, O.B.. 1988. Exploiting forage legumes for
nitrogen contribution in cropping systems. p. 155-166. In
W.L. Hargrove (ed). Cropping Strategies for Efficient Use of
Water and Nitrogen. ASA-CSSA-SSSA Special publication no
51. ASA-CSSA-SSSA. Madison, WI.

Hesterman, O.B., T.S. Griffin, P.T. Williams, G.H. Harris,
and D.R. Christenson. 1992. Nitrogen production by forage
legumes seeded into small grains and response of a following
Corn Crop. J. Prod. Agric. 5:340-348.

Holderbaum, J.F., A.M. Decker, J.J. Meisinger, F.R. Mulford,
and L.R. Vough. 1990. Fall-seeded legume cover crops for no-
tillage corn in the humid east. Agron. J. 82:117-124.

Holderbaum, J.F., A.M. Decker, J.J. Meisinger, F.R. Mulford,
and L.R. Vough. 1990. Harvest management of a crimson clover
crop for no-tillage corn production. Agron. J. 82:918-923.

Jones, J.B. Jr. 1967. Interpretation of plant analysis for
several agronomic crops. p. 49-58. In Soil Testing and Plant
Analysis part II Plant Analysis. SSSA Special Publication
Series no. 2. SSSA, Madison, WI.

Levin, A., D.B. Beegle, and R.H. Fox. 1987. Effect of
tillage on residual nitrogen availability from alfalfa to
succeeding corn crops. Agron. J. 79:34-38.

Marten, G.W. and J.T. Touchton. 1983. Legumes as a cover
crop and source of nitrogen. J. Soil Water Conserv. 38:214-
216.

McCracken, D.V., S.J. Corack. M.S. Smith, W.W. Frye, and
R.L. Blevins. 1988. Residual effects of N fertilizer and
winter cover cropping on N availability. Soil Sci. Soc. Am.
J. 53: 1459—1464.

McVay, K.A., D.B. Radcliff, and W.L. Hargrove. 1989. Winter
lwegume effects on soil properties and nitrogen fertilizer
requirements. Soil Sci. Soc. Am. J. 53: 1856-1862.

67

Mitchell, W.H., and M.R. Teel. 1977. Winter annual cover
crops for no-tillage corn production. Agron. J. 69:569-573.

Munawar, A., R.L. Blevins, W.W. Frye, and M.R. Saul. 1990.
Tillage and cover crop management for soil water
conservation. Agron. J. 82:773-777.

Nemon, M.A., B. von Hoyningen Huene, J. Gallichand, and R.S.
Broughton. 1987. Subsurface irrigation and drainage on
sandy soil in southern Quebec. Canadian Agricultural
Engineering. 29:137-142.

Ngalla and Eckert, 1987. Wheat-red clover interseeding as a
nitrogen sourvce for no-tillage corn. In J.F. Power (ed.)
The role of legume in conservation tillage systems. Soil
Conservation Society of America, Ankeny, IA.

Paul, E.A. and F.E. Clark. 1989. Soil Microbiology and
Biochemistry. Academic Press. San Diego, California. pp 273.

Pierre, W.H., L. Dumenil, Von D. Jolley, J.R. Webb, and W.D.
Shrader. 1976. Relationship between corn yield, expressed
as a percentage of maximum, and the N percentage in the
grain. I. Various N-rate experiments. Agron. J. 69:215-220.

Rice, W.A., 1980. Seasonal patterns of nitrogen fixation and
Dry matter production by clovers grown in the peace river
region. Can. J. Plant Sci. 60:847-858.

Sarrantonio, M. and T.W. Scott. 1988. Tillage effects on
availability of nitrogen to corn following a winter green
manure crop. Soil Sci. Soc. Am. J. 52:1661-1668.

Schwab, G. 1994. Michigan custom rate. Michigan State
University extension bulletin. unpublished.

Smith 1956. Influence of fall cutting in the seeding year on
the dry matter and nitrogen yields of legumes. Agron. J.
48:236-239.

Smith, M.C., R.W. Skaggs, and J.B. Parsons. 1985.
Subirrigation system control for water use efficiency. ASAE
Paper No. 82-2520. ASAE St. Joseph, MI. 49085. Transactions
of the ASAE. 489-496.

Smith, M. Scott, W.W. Frye, and Jac J. Varco. 1987. Legume
winter cover crops. p. 95-139. In. Advances in Soil Science.
Vol. 7. Springer—Verlag New York Inc.

Smith, S.J. and A.N. Aharpley. 1993. Nitrogen availability
from surface—applied and soil-incorporated crop residues.
Agron. J. 85:776-778.

nrcwrcnu STATE UNIV. LIBRARIES
llllllllllllllllllllIllllllllllllllllllllllllllll
31293010330417