The effects of different autumn-seeded cover crops on subsequent irrigated corn response to nitrogen fertilizer

doi:10.4236/as.2010.13018

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Vol.1, No.3, 148-153 (2010) Agricultural Sciences

doi:10.4236/as.2010.13018

The effects of different autumn-seeded cover crops on

subsequent irrigated corn response to nitrogen

fertilizer

Gholam Reza Mohammadi*, Mohammad Eghbal Ghobadi

Department of Crop Production and Breeding, Faculty of Agriculture, Razi University, Kermanshah, Iran; *Corresponding Author:

mohammadi114@yahoo.com

Received 13 May 2010; revised 30 September 2010; accepted 3 October 2010.

ABSTRACT

A common crop rotation in the west Iran is

wheat-fallow-corn. The fallow period after wheat

harvest (during fall and winter) can lead to soil

erosion, nutrient losses (e.g. nitrate leaching)

and offsite movement of pesticides. This period

is an ideal time to establish a cover crop. In or-

der to investigate the effects of different au-

tumn-bseeded cover crops on subsequent irri-

gated corn response to nitrogen fertilizer, field

studies were carried out during the 2007-2008

growing season at the Agricultural Research

Farm, Razi University, Kermanshah, Iran. The

experiment was conducted in a split plot ar-

rangement based on a randomized complete

block design with three replications. The main

plots consisted of four cover crops including

alfalfa (Medicago sativa L.), berseem clover

(Trifolium alexandrinum L.), common vetch (Vi -

cia sativa L.) and winter rye (Secale cereale L.)

and a control (no cover crop). The sub plots

consisted of two fertilizer N rates (0 and 250 kg

ha-1). Cover crops were grown for nearly 5

months and then were incorporated into the soil

as green manures. The results indicated that

corn plant traits including seed yield, the num-

ber of seeds per ear and leaf chlorophyll con-

tent were significantly influenced by cover

crops. Whereas, the cover crops had no sig-

nificant effects on the number of ears per plant,

100-seed weight and harvest index of corn.

Among the cover crop species, common vetch

produced higher dry weight and showed the

highest positive effects on the corn plant traits.

Dry weight produced by this cover crop was

56.41, 120.16 and 124.19% higher than those of

winter rye, berseem clover and alfalfa, respec-

tively. Common vetch enhanced seed yield, the

number of seeds per ear and leaf chlorophyll

content of corn by 46.30, 21.95 and 8.52%, re-

spectively, compared to control. All of the corn

traits under study, except the number of ears

per plant and harvest index were significantly

improved by nitrogen fertilizer. In general, this

study revealed that the autumn-seeded cover

crops, especially common vetch can be used to

improve corn yield. However, the cover crops

should be supplemented with nitrogen fertilizer

to obtain optimal results.

Keywords: Corn; Cover Crop; Nitrogen Fertilizer

1. INTRODUCTION

A common crop rotation in the west Iran is wheat-fal-

low-corn. The fallow period after wheat harvest (during

fall and winter) can lead to soil erosion, nutrient losses

(e.g. nitrate leaching) and offsite movement of pesticides.

In addition, weeds can germinate and grow without

competition [1]. This period is an ideal time to establish

a cover crop. Cover crops can be readily incorporated

into crop rotations that include cereals [2]. A well-cho-

sen cover crop can intercept raindrops and reduce water

runoff, soil erosion and protect streams from pollution

[1]. However, the protection that such vegetation pro-

vides against erosion is influenced mainly by the amount

of biomass that covers the ground (differs with each spp)

[3]. Cover crops have also been shown to increase the

number of organisms which are natural enemies of some

crop pests [1]. These crops offer habitat or resources for

beneficial organisms [4,5]. For example, populations of

ground-dwelling predators were greater in a corn and

soybean rotation with alfalfa and kura clover cover crops

than without a cover crop [6]. Studies focusing on leg-

ume cover crops establishment following cereals have

reported considerable N contribution to a subsequent

G. R. Mohammadi et al. / Agricultural Sciences 1 (2010) 148-153

149

corn crop [7,8].

Brophy et al. [9] suggested that when cover crops are

turned over into the soil as green manures, they contrib-

ute nutrients to the main crop so that less chemical fer-

tilizer required. However, the amount of the contribution

depends on the biomass which varies over time and de-

pends on rainfall and other factors. Lehman et al. [10]

also noted that the legume cover crops have imported

positive effects on the nutrient cycling in three ways: 1)

recycling soil nutrients 2) enhancing soil nutrient avail-

ability for the main crop and 3) fixing the atmospheric

N2 that is important for the main crop. However, crop

yield responses to additional fertilizer N continue to oc-

cur in some environments and certain management sys-

tems [11,12].

Nonlegume cover crops, primarily winter rye, are also

used during the overwinter period to reduce wind ero-

sion and potentially recover residual N from the soil or

provide other benefits to subsequent crops [13]. Several

studies [14-16] showed that significant amounts of N can

be accumulated by nonlegume cover crops. Bundy and

Andraski [13] reported that corn grain yields at below

optimum N rates (0 and 112 kg ha-1) were significantly

higher where the rye cover crop was grown. However,

legume cover crop species are often preferable to

nonlegumes because they supply their own N. In general,

biological N fixation (for legumes) and overall N accu-

mulation during growth are primary factors governing

the adequacy of a cover crop as an N source. Moreover,

genetic differences (species and variety) may dictate that

some legumes grow larger and accumulate more N than

others. Environment (temperature, soil type and nutrient

and water availability) and management (e.g., planting

density and timing, mowing, and pest control) may fur-

ther alter performance of individual cover crop species

[17-19]. Because they do not derive direct sales profit,

cover crop species are often chosen that require accepta-

bly low levels of nutrient, irrigation, and pest control

inputs and often fit into otherwise unplanted fallow pe-

riods. However, despite the positive effects often pro-

duced by winter annual cover crops in corn production,

there is also a potential for reduction in corn yield [20].

Therefore, the success of these kinds of cropping system

is largely determined by the selection of the most appro-

priate cover crop species and there is no consensus as to

which cover crops import more positive effects on corn

yield.

The present study was conducted to evaluate the ef-

fects of different cover crops (non-legume and legume

species) planted during the fallow period (after wheat

harvest) on subsequent irrigated corn response to nitro-

gen fertilizer in the west Iran.

2. MATERIALS AND METHODS

The study was carried out during the 2007-2008 grow-

ing season at the Agricultural Research Farm of Razi

University, Kermanshah, west Iran. The soil type was a

silty clay with a pH of 7.9–8.3 and 0.8% organic matter.

The field was planted with wheat (Triticum aestivum L.)

the previous growing season. The land was plowed and

disked before crops planting. Fertilizers were applied

according to the soil test recommendations. For all crops,

irrigation was applied at germination and thereafter to

prevent water stress. Weeds were controlled as needed

during all of the growing season.

The experiment was conducted in a split plot ar-

rangement based on a randomized complete block de-

sign with three replications. The main plots consisted of

four cover crops and a control (no cover crop). The

cover crop species evaluated were alfalfa (Medicago

sativa L.), berseem clover (Trifolium alexandrinum L.),

common vetch (Vicia sativa L.) and winter rye (Secale

cereale L.). These cover crop species were selected ac-

cording to environmental conditions and economic con-

siderations of the region. Before corn planting, each

main plot was split into two sub plots. The sub plots

consisted of two fertilizer N rates (0 and 250 kg ha-1)

applied in the form of urea. Cover crops were seeded on

12 October 2007 by surface broadcasting at seeding rates

of 50 kg ha-1 alfalfa, 50 kg ha-1 berseem clover, 250 kg

ha-1 common vetch and 220 kg ha-1 winter rye. The

seeding rate of each cover crop treatment was based on

the recommended forage seeding rate for that crop in the

region. Cover crops were grown for nearly 5 months and

then were incorporated into the soil as green manures on

16 March 2008. Before incorporation cover crop dry

weights were determined by harvesting them at ground

level in three random 0.5 × 0.5 m quadrats in each sub

plot. Then cover crop plants were dried at 80ْC to the

constant weights and weighed.

The corn cultivar used was ‘KSC 704’ (a grain corn

cultivar that is commonly planted in the region). In order

to protect against soil-borne diseases, prior to seeding,

the corn seeds were treated with benomyl at 0.2% (w/w).

Corn was planted in the sub plots on 2 May 2008. Each

sub plot consisted of five corn rows of 5 m long with a

row spacing of 75 cm and with 20 cm between plants in

the same row. At tasselling stage leaf chlorophyll content

of corn plants was determined on 10 randomly selected

plants of each plot using a chlorophyll meter (SPAD-502;

Minolta, Osaka, Japan).

At maturity, the corn plants located 2 m from the three

center rows of each sub plot were harvested by hand,

allowed to dry at 80ْC to a constant weight, then threshed

and seed yield (g m-2) was obtained and reported based

G. R. Mohammadi et al. / Agricultural Sciences 1 (2010) 148-153

150

on a moisture content of 15.5%. Before final harvesting

corn yield components including the number of ears per

plant and the number of seeds per ear were determined

on five randomly selected plants in the center rows of

each sub plot. Additionally, 100-seed weight was meas-

ured according to the recommendation of the Interna-

tional Seed Testing Association (ISTA) [21]. Harvest

index was calculated as the ratio of seed weight to total

shoot weight [22]. The data analyses were carried out

using SAS software [23].

3. RESULTS AND DISCUSSION

According to analysis of variance (data not shown)

there was a significant difference (at the 0.01 level of

probability) between the dry weights produced by dif-

ferent cover crop species under study. Moreover, corn

plant traits including seed yield, the number of seeds per

ear, 100-seed weight and leaf chlorophyll content were

significantly influenced by nitrogen fertilizer treatment.

Whereas, the effect of cover crop treatment was statisti-

cally significant for seed yield, the number of seeds per

ear and leaf chlorophyll content. Both nitrogen fertilizer

and cover crop treatments had no significant effects on

the number of ears per plant and harvest index of corn.

Moreover, the two way interaction (cover crop treatment

× nitrogen fertilizer level) was not significant for all of

the traits under study.

Among the cover crop species, common vetch pro-

duced higher dry weight at the time of the incorporation

into the soil (Table 1). Dry weight produced by common

vetch was 56.41, 120.16 and 124.19% higher than those

of winter rye, berseem clover and alfalfa, respectively

(Table 1). Alfalfa produced the lowest dry weight, al-

though there was no significant difference between this

cover crop and berseem clover for the dry weight pro-

duced (Table 1). Although, winter rye produced higher

dry weight than those of berseem clover and alfalfa, but

the corn plant traits were not significantly improved by

this cover crop (Table 1). According to Ranells and

Wagger [24] non leguminous cover crops typically have

low N contents and high C/N ratios, showing litter or no

beneficial effects on the succeeding crop yield. As de-

termined visually, common vetch also produced a dense

canopy on the ground surface throughout the growing

season. This can be attributed to the better establishment

and growth of this cover crop under environmental con-

dition of the region as compared with other cover crops

under study. In temperate environments winter-hardy

legumes such as vetch are capable of accumulating large

amounts of biomass and N and delivering substantial N

benefit to subsequent spring-planted crops [25].

All of the corn plant traits under study except the

number of ears per plant and harvest index were signifi-

cantly improved by nitrogen fertilizer applied at 250 kg

ha-1 (Table 2). Overall, this treatment increased seed

yield, the number of seeds per ear, 100-seed weight and

leaf chlorophyll content by 61.24, 96.83, 12.05 and

19.23%, respectively, when compared with the treatment

in which no nitrogen fertilizer was applied (Table 2).

According to Thonnissen et al. [26] with respect to sea-

son and location, green manure N should be supple-

mented with N fertilizer to ensure optimal yields.

Among the cover crop species, common vetch showed

the highest positive effects on the corn plant traits. This

cover crop enhanced seed yield, the number of seeds per

ear and leaf chlorophyll content by 46.30, 21.95 and

8.52%, respectively, compared to control (no cover crop)

(Table 1). However, the number of ears per plant,

100-seed weight and harvest index of corn were not sig-

nificantly affected by common vetch or other cover

crops (Table 1). Moreover, there were no significant

differences between other cover crops and control for

Table 1. Means comparison of the traits under different cover crop treatments.

Corn

Cover crop

treatment Seed yield

(g m-2)

Seeds per

ear (N)

100-seed

weight (g)

Ears per

plant (N)

Leaf chloro-

phyll content

(SPAD value)

Harvest index

Cover crop

dry weight

(g m-2)

Common vetch 924.14 a 548.61 a 24.92 a 1.02 a 53.51 a 0.39 a 306.29 a

Alfalfa 734.49 b 462.29 b 24.03 a 1.00 a 47.20 bc 0.37 a 136.62 c

Berseem clover 737.26 b 448.76 b 25.18 a 1.01 a 47.07 bc 0.37 a 139.12 c

Rye 702.17 b 449.89 b 26.00 a 0.94 a 44.28 c 0.37 a 195.82 b

Control (no

cover crop) 631.68 b 449.85 b 23.11 a 0.94 a 49.31 b 0.37 a 000.00 d

LSD (0.05) 174.79 53.88 5.19 0.10 3.69 0.03 42.54

The same letters at each column indicate an insignificant difference at the 0.05 level of probability. LSD, least significant difference; SPAD, refers to the chlo-

rophyll meter.

G. R. Mohammadi et al. / Agricultural Sciences 1 (2010) 148-153

151

Table 2. Means comparison of corn plant traits under different nitrogen fertilizer levels.

Corn

Nitrogen fertilizer

level (kg ha-1) Seed yield

(g m-2)

Seeds per

ear (N)

100-seed weight

(g)

Ears per plant

(N)

Leaf chlorophyll

content

(SPAD value)

Harvest index

250 920.80 a 623.16 a 26.04 a 0.99 a 52.51 a 0.38 a

0 571.08 b 316.60 b 23.24 b 0.97 a 44.04 b 0.37 a

LSD (0.05) 87.42 63.29 2.08 0.04 6.26 0.02

Dissimilar letters at each column indicate a significant difference at the 0.05 level of probability. LSD, least significant difference; SPAD, refers to the chloro-

phyll meter.

seed yield and the number of seeds per ear of corn. Corn

seed yields were improved by 16.71, 16.28 and 11.16%

following berseem clover, alfalfa and winter rye, respec-

tively, when compared with control, but theses im-

provements were not statistically significant (Table 1).

Leaf chlorophyll content of corn was significantly lower

in winter rye treatment than control, so that, this cover

crop caused the reduction of 10.20% in leaf chlorophyll

content of corn plant as compared with control (Table 1).

This can be attributed to the higher C/N ratio in plant

tissues of non-legume cover crops such as winter rye [27]

that consequently lead to the slower decomposition and

N release of their plant tissues [28] and strong N immo-

bilization after these crops are added as green manures

into the soil [29]. This can result in reduced N availabil-

ity to corn.

The enhancement of leaf chlorophyll content by com-

mon vetch can be due to the improved soil nitrogen con-

dition by incorporated common vetch plants. This can be

led to the increased leaf nitrogen content [30]. Nitrogen

is a substantial element of the chlorophyll structure, so

that, a positive correlation between leaf nitrogen and

chlorophyll content is well documented for a number of

plant species [31-34]. Moreover, the positive significant

correlations between photosynthesis and leaf nitrogen

content have been proved for a large number of species

[35-40]. The improvement of photosynthesis due to in-

creased leaf chlorophyll content ultimately can result in

the enhancement of corn growth and yield.

Moreover, higher corn seed yield in the plots in which

common vetch was incorporated into the soil can be as a

result of the higher dry weight produced by this cover

crop that consequently led to the improvement of soil

condition and nutrient supplement to corn plants. This

was supported by a significant and positive correlation

between corn seed yield and cover crop dry weight (r =

0.67; P < 0.01). According to Brophy et al. [9] when

cover crops are turned over into the soil as green ma-

nures they contribute nutrients to the main crop. The

amount of the contribution depends on the biomass

which varies over time and depends on cover crop spe-

cies and other factors.

Nitrogen fertilizer applied at the level of 250 kg ha-1

increased corn seed yield by 129.03, 71.59, 59.08, 47.25

and 33.62% following control (no cover crop), winter

rye, alfalfa, berseem clover and common vetch treat-

ments, respectively, when compared with the treatment

in which no nitrogen fertilizer was applied (Figure 1). In

other words, nitrogen application improved corn seed

yield following all of the cover crop treatments. How-

ever, the highest improvement occurred at the control

plots (Figure 1). Moreover, there were lower corn seed

yield responses to nitrogen fertilizer following legume

cover crops than rye, so that, the highest and the lowest

enhancements of corn seed yields due to the applied ni-

trogen fertilizer were obtained following winter rye and

common vetch cover crops, respectively (Figure 1).

Overall, improvements of the corn plant traits in re-

sponse to the applied nitrogen fertilizer indicated that the

nitrogen released from the incorporated cover crops was

not sufficient to support the potential corn growth and

yield. Griffin et al. [41] also reported that cover crops

can supply all or most of the N required by a subsequent

crop if cover crop biomass is of sufficient quantity and N

mineralization is approximately synchronous with sub

Figure 1. The effect of different cover crop treatments on

corn seed yield under two nitrogen fertilizer levels (0 and 250

kg ha-1).

G. R. Mohammadi et al. / Agricultural Sciences 1 (2010) 148-153

152

sequent crop demand. However, studies evaluating the

effect of 15N from legume residues decomposing under

field conditions lead to the conclusions that < 30% of

legume N was recovered by a subsequent nonlegume

crop and large amounts of legume N were retained in

soil, mostly in organic forms [42-44]. Kuo and Jellum

[45] also found that corn yields were affected by N fer-

tilizer applied irrespective of cover crop species.

In general, this study revealed that the autumn-seeded

cover crops, especially common vetch can be used to

improve corn yield. However, the cover crops should be

supplemented with nitrogen fertilizer to obtain optimal

results.

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