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American Journal of Experimental Agriculture
11(6): 1-19, 2016, Article no.AJEA.24385
ISSN: 2231-0606
SCIENCEDOMAIN international
www.sciencedomain.org
Influences of Some Preceding Winter Crops and
Nitrogen Fertilizer Rates on Yield and Quality of
Intercropped Maize with Cowpea
Sherif I. Abdel-Wahab
1*
, Wael M. El Sayed
2
and Amal M. El Manzlawy
3
1
Department of Crop Intensification Research, Field Crops Research Institute, Agricultural Research
Center, Giza, Egypt.
2
Department of Maize Research, Field Crops Research Institute, Agricultural Research Center, Giza,
Egypt.
3
Department
of Seed Technology Research, Field Crops Research Institute, Agricultural Research
Center, Giza, Egypt.
Authors’ contributions
This work was carried out in collaboration between all authors. Author SIAW designed the study,
wrote the protocol, carried out the field experiments and wrote the first draft of the manuscript. Author
WMES reviewed the experimental design, wrote the results and managed the literature searches.
Author AMEM tested quality of maize grains and managed the analyses of the study. All authors read
and approved the final manuscript.
Article Information
DOI: 10.9734/AJEA/2016/24385
Editor(s):
(1)
Mirza Hasanuzzaman, Department of Agronomy, Sher-e-Bangla Agricultural University,
Bangladesh.
Reviewers:
(1)
Maria Jose Alves Bertalot and Eduardo Mendoza, Instituto Elo de Economia Associativa, Botucatu, Brazil.
(2)
Veronica Makuvaro, Midlands State University, Zimbabwe.
Complete Peer review History:
http://sciencedomain.org/review-history/13753
Received 18
th
January 2016
Accepted 12
th
February 2016
Published 18
th
March 2016
ABSTRACT
A field study was conducted in Mallawi Agricultural Experiments and Research Station, Agricultural
Research Center (ARC), El-Minia governorate, Egypt to decrease mineral nitrogen (N) inputs of
maize with good yield quality and increase farmers' benefit. Local maize cultivar T.W.C. 310 was
grown under intercropping and sole cultures in one row/ridge that received three mineral N fertilizer
rates (75, 87.5 and 100% of the recommended N rate of maize), while local cultivar of cowpea
seeds Keraim – 1 were drilled in one row and two rows/ridge under intercropping and sole cultures,
respectively. A split split plot design with three replicates was used. Quality of maize grains was
tested in the laboratories of Seed Technology Research Department, Field Crops Research
Original Research Article
Abdel-Wahab et al.; AJEA, 11(6): 1-19, 2016; Article no.AJEA.24385
2
Institute, ARC. Maize grain yield and its attributes were increased after harvest of legume crops
compared to those grown after wheat harvest. Intercropping cowpea with maize increased grain
yields per plant and per ha by 4.00 and 1.94%, respectively, in comparison with sole culture in
addition to yielding 16.85 ton/ha of cowpea forage. Cowpea improved yield quality and N use
efficiency (NUE) of intercropped maize after berseem cutting. Land equivalent ratio and land
equivalent coefficient values for intercrops were much greater than 1.00 and 0.25, respectively,
indicating less land requirements of intercropping system than sole maize. Farmer's benefit was
achieved by intercropping cowpea with maize that received 87.5% of the recommended mineral N
fertilizer rate of maize after berseem cutting.
Keywords: Crop sequence; intercropping; maize; cowpea; mineral N fertilizer; yield quality.
1. INTRODUCTION
There is a strong global tendency to reduce the
amount of mineral nitrogen (N) fertilization of
maize (Zea mays L.). Some of the major causes
of low maize yield are declining soil fertility and
insufficient use of mineral fertilizers resulting in
severe nutrient depletion of soils [1]. It is known
that maize plant development is strongly
dependent on the availability of N in the soil and
the efficiency of N utilization for biomass
production and yield [2]. It is a strategic crop and
it is used for human consumption, animal and
poultry feeding and industrial purposes. Demand
for the maize grains in the Egyptian market is
intensively increasing where maize cultivated
area reached about 814435 ha in 2013 with an
average yield of 7.64 ton per ha [3].
Certainly, maize provides high yield with good
quality in terms of dry matter, but always there is
a shortage in green forage supply during the
summer season. Accordingly, intercropping a
legume forage crop such as cowpea (Vigna
unguiculata L.) with maize is very important tool
for minimize the mineral N – fertilizer rates of
maize in addition to cowpea could be a
successful practice in cattle feeding that is
severely limited by marked seasonal feed deficits
in the summer season. Cowpea facilitates N
uptake of the intercropping maize [4] and
consequently, N symbiotic fixation has
contributed to facilitate N uptake for intercropped
maize [5]. Cowpea is promising double purpose
forage and seed crop for its green canopy or
using it in animal diets as dry seeds, as well as, it
is a primary source of plant protein for humans
and animals [6] in the summer season.
Quality of maize grains is primarily related to
grain endosperm properties. Endosperm
characteristics, although principally determined
by genetics, may be influenced by the growing
environment and agronomic practices, especially
N fertilizer inputs [7]. The role of fertilizers,
especially N is most importance in improving the
yield and quality of maize [8]. It is know that
endosperm accounts for approximately 85% of
total grain dry weight at maturity and contains
about 70% of grain protein [9].
Certainly, crop residue is a good source of
nutrients in many agr – ecosystems for
sustainable crop production and environment
[10]. These observations led to integration of
crop sequence and intercropping must be related
to soil nutrient availability, especially there are
strategic food crops such as wheat (Triticum
aestivum L.), berseem (Trifolium alexandrinum
L.) as a forage crop and faba bean (Vicia faba)
grown during the winter season in Egypt.
Therefore, the main objective of the present
research was to decrease N inputs of maize crop
with good yield quality and increase farmers'
benefit.
2. MATERIALS AND METHODS
A research was carried out at Mallawi
Agricultural Experiments and Research Station,
El-Minia governorate (31°06'42" N, 30°56'45" E,
17 m a. s. l.), Egypt, during 2013/2014 and
2014/2015 seasons. Chemical analysis of the
soil (0 – 30 cm) was done by General
Organization for Agricultural Equalization Fund,
Agricultural Research Center, Giza, Egypt (Table
1). Methods of chemical analysis employed were
as described by Chapman and Pratt [11].
This experiment included eighteen treatments
which were the combinations of three preceding
winter crops (berseem cv. Giza 6, faba bean cv.
Misr 1 and wheat cv. Beni – Sweif 1), two
cropping systems (intercropped maize with
cowpea and sole maize) and three mineral N
fertilizer rates of maize (285.6 kg N/ha, 249.9 kg
N/ha and 214.2 kg N/ha were expressed as 100,
87.5 and 75% of the recommended mineral N
fertilizer rate of maize), in addition to sole culture
of cowpea.
Abdel-Wahab et al.; AJEA, 11(6): 1-19, 2016; Article no.AJEA.24385
3
Table 1. Soil nitrogen content of the experimental soil in 2014 and 2015 seasons after harvest
of the winter field crops and before growing maize and cowpea
The preceded
crop
Growing season
2014
2015
N (ppm)
P (ppm)
K (ppm)
N (ppm)
P (ppm)
K (ppm)
Berseem 42.00 34.00 222.00 48.00 30.00 237.00
Faba bean 32.00 23.00 197.00 36.00 18.00 210.00
Wheat 12.00 10.00 158.00 15.00 11.50 172.00
Maize cultivar T.W.C.310 and cowpea cultivar
Keraim-1 were used in this study. Water was
supplied by furrow irrigation. Calcium super
phosphate (15.5%P
2
O
5
) at rate of 357 kg/ha and
potassium sulfate (48.0%K
2
O) at rate of 119
kg/ha were applied during soil preparation in the
two winter seasons. The previous rates were
applied during soil preparation in the two
summer seasons. Water was supplied by furrow
irrigation. In the two winter seasons, berseem
and faba bean seeds were inoculated by
Rhizobium trifolii and Rhizobium leguminosarum,
respectively, before seeding it and Arabic gum
was used as a sticking agent. Faba bean and
berseem seeds were sown on October 20
th
in
2013 season and October 16
th
in 2014 season.
Wheat grains were sown on November 11
th
and
8
th
in 2013 and 2014 seasons, respectively.
Wheat grains and berseem seeds were drilled at
the rate of 166.6 and 59.5 kg per ha,
respectively. Faba bean seeds were grown in
both sides of the ridge and were distributed to
two plants/hill spaced at 20 cm. Mineral N
fertilizer was applied at rate of 35.7 kg N/ha for
each of berseem and faba bean at 15 days from
sowing. Mineral N fertilizer of wheat was applied
at rate of 178.5 divided into three equal doses at
sowing, 15 and 30 days from sowing. Berseem
and faba bean plants were harvested on April
22
nd
in 2014 season and April 19
th
in 2015
season. Wheat plants were harvested on May 7
th
and 5
th
in 2015 season.
In the two summer seasons, cowpea seeds were
sown on May 20
th
and 17
th
in 2014 and 2015
seasons, respectively, meanwhile, maize grains
were sown on June 10
th
and 8
th
in 2014 and
2015 seasons, respectively. Maize was sown in
one side of ridge (70 cm width) with growing one
plant/hill spaced at 30 cm under intercropping
and sole cultures, meanwhile, cowpea seeds
were inoculated by Rhizobium melitota before
seeding it and Arabic gum was used as a
sticking agent. Cowpea seeds were grown in the
other side of maize ridge (two plant/hill spaced at
20 cm) under intercropping culture. Growing
cowpea in both sides of the ridge (two plant/hill
spaced at 20 cm) under sole culture. In other
words, the planting densities of intercropped
maize with cowpea were equal to 100 and 50%
of sole maize and cowpea plant densities,
respectively. Mineral N fertilizer of cowpea was
applied at rate of 35.7 kg N/ha at 15 days from
cowpea sowing. Sole crops were used to
estimate the competitive relationships. All the
tested crops were grown in accordance to local
agricultural practice. Cowpea plants were cutting
on August 4
th
and 1
st
in 2014 and 2015 seasons,
meanwhile maize plants were harvested on
October 3
rd
and 1
st
in 2014 and 2015 seasons,
respectively.
A split-split-plot design with three replications
was used. The preceded winter field crops were
randomly assigned to the main plots, cropping
systems were allotted in sub plots and mineral N
fertilizer rates were allotted in sub sub plots. The
area of sub sub plot was 12.6 m
2
, it consisted of
six ridges, and each ridge was 3.0 m in length
and 0.7 m in width.
2.1 The Studied Traits
2.1.1 Yield and its attributes
The following traits were measured on ten plants
from each sub sub plot at harvest; plant height
(cm), stem diameter (cm), number of ears/plant,
ear length (cm), ear diameter (cm), ear weight (g)
and grain yield per plant (g). Maize grain yield/ha
(ton) and cowpea forage yield/ha (ton) were
recorded on the basis of experimental plot area
by harvesting all plants of each sub sub plot.
2.1.2 Quality of maize grains
Samples of 50 grams from maize grains were air
dried, then ground and the fine powder stored
in brown glass bottles. All the chemical
determinations were estimated in ground grains
dried at 70°C till constant weight. The total N of
maize grains was determined using Micro-
kjeldahl apparatus according to A.O.A.C. [12].
Crude protein content of maize grains was
Abdel-Wahab et al.; AJEA, 11(6): 1-19, 2016; Article no.AJEA.24385
4
calculated by multiplying total N by 6.25 [13].
Crude oil content of maize grains was
determined using Soxhlet apparatus and N-
hexane as a solvent [12]. These analyses were
done by Seed Technology Research
Department, Field Crops Research Institute,
ARC.
2.1.3 Nitrogen Use Efficiency (NUE)
NUE for each treatment was determined using
the agronomic efficiency (AE) and partial factor
productivity (PFP) indices [14]: AE = (Y – Y
o
)/ F
and PFP = (Y
o
/ F) + AE, where F = amount of
(fertilizer) nutrient applied (kg/ha); Y = Crop yield
with applied nutrients (kg/ha) and Y
o
= crop yield
(kg/ha) in a control treatment with application of
214.2 kg N/ha. A basic assumption was that N
uptake is the same in fertilized and unfertilized
plots. This assumption was made with a caution
since soil N transformations and root
development may differ between fertilized and
unfertilized plots [15,16].
2.1.4 Competitive relationships
2.1.4.1 Land equivalent ratio (LER)
LER defines as the ratio of area needed under
sole cropping to one of intercropping at the same
management level to produce an equivalent yield
[17]. It is calculated as follows: LER = (Y
ab
/ Y
aa
)
+ (Y
ba
/ Y
bb
), where Y
aa
= Pure stand yield of crop
a (maize), Y
bb
= Pure stand yield of crop b
(cowpea), Y
ab
= Intercrop yield of crop a (maize)
and Y
ba
= Intercrop yield of crop b (cowpea).
2.1.4.2 Land equivalent coefficient (LEC)
LEC is a measure of interaction concerned with
the strength of relationship [18]. It is calculated
as follows: LEC = L
a
x L
b
, where L
a
= relative
yield of crop a (maize) and L
b
= relative yield of
crop b (cowpea).
2.1.5 Monetary Advantage Index (MAI)
The price of maize was 309.1 US$ per ton [3],
meanwhile the price of cowpea was 17.1 US$
per ton (market price). MAI suggests that the
economic assessment should be in terms of the
value of land saved; this could probably be most
assessed on the basis of the rentable value of
this land. MAI was calculated according to the
formula, suggested by Willey [19]. MAI= [Value
of combined intercrops x (LER–1)]/LER.
2.2 Statistical Manipulation
Analysis of variance of the obtained results of
each season was performed. The homogeneity
test was conducted of error mean squares and
accordingly, the combined analysis of the two
experimental seasons was carried out. The
measured variables were analyzed by ANOVA
using MSTATC statistical package [20]. Mean
comparisons were done using least significant
differences (L.S.D) method at 5 % level of
probability to compare differences between the
means [21].
3. RESULTS AND DISCUSSION
3.1 Yield and Its Attributes
3.1.1 Effect of the preceding crop
Ear length, diameter and weight, grain yields per
plant and per ha were affected significantly by
the preceding crop in the combined data across
2013/2014 and 2014/2015 seasons, meanwhile,
plant height, stem diameter, number of ears per
plant and forage yield of cowpea per ha were not
affected (Table 2). Ear length, diameter and
weight, grain yields per plant and per ha were
increased significantly by the preceding legume
crop (berseem or faba bean) compared to those
followed by wheat. As a result of crop sequence,
grain yield per plant was increased (P ≤ 0.05) by
18.28 and 12.40% after berseem cutting and
faba bean harvest, respectively. Also, grain yield
per ha was increased by 8.97 and 7.23% after
berseem cutting and faba bean harvest,
respectively. These results could be due to soil
N, P and K contents were more available to
subsequent maize plant after the preceding
legumes (Table 1). Consequently, there was an
increase in dry matter accumulation that reflected
on ear characteristics (length, diameter and
weight) during maize growth and development
(Table 2), especially grain yield per plant was
positively and significantly correlated with ear
length [22].
Therefore, it is recommended that cereal should
be grown after legumes, which would enable
using the accumulated biological N for their
nutrition in more rational way [23]. These results
reveal that the preceding cereal crop (wheat)
decreased soil nutrient availability and increased
intra-specific competition between maize plants
which decreased measurements of ear
characteristics (length, diameter and weight)
Abdel-Wahab et al.; AJEA, 11(6): 1-19, 2016; Article no.AJEA.24385
5
compared with the preceding legume crops.
Cobs may be considered as temporary sink and
the stored photosynthates were translocated to
grains during their development. Accordingly,
yield potential of maize plant could be affected
positively or negatively by choice of the
preceding winter field crop; especially grain yield
per plant had positive and highly significant
correlation with fresh ear weight, cob length and
ear diameter [24]. So, it may be possible that
there was better soil environment for the and
nutrient cycling [25] as a result of a mix of living
rhizobia and dead berseem or faba bean roots
near the experimental soil surface. Legumes, in
contrast to cereals, have a beneficial effect on
grain yield of subsequent cereal crops [26].
These results are in accordance with those found
by Bloem and Barnard [27] who found that maize
yields after rotation with legumes were generally
higher than the control treatments. They added
that after the effect of N was accounted for via
the N – corrected yield, it was evident that
additional yield increases of 10% (average).
Moreover, Ali et al. [28] showed that legumes as
a preceding crop had increased significantly
grain yield (5104 ka/ha) compared to fallow as
preceding practice (3185 kg/ha). Finally, Lamlom
et al. [29] concluded that the preceding berseem
crop had positive chemical and biological effects
on soil fertility that improved growth and
development of maize in the following season
compared to those grown after wheat harvest.
3.1.2 Effect of cropping systems
Ear length, diameter and weight, grain yields per
plant and per ha and forage yield of cowpea per
ha were affected significantly by cropping
systems in the combined data across 2013/2014
and 2014/2015 seasons, meanwhile, plant
height, stem diameter and number of ears per
plant were not affected (Table 2). Ear length,
diameter and weight, grain yields per plant and
per ha were increased significantly by
intercropping cowpea with maize in the same
ridge compared to those of sole culture. As a
result of intercropping, grain yields per plant and
per ha were increased (P ≤ 0.05) by 4.00 and
1.94%, respectively, compared with sole maize.
It is known that the population of plants per
square meter (density) and arrangement of
individual plants within a square meter determine
nutrient use and grain yield of maize [30].
Although plant density was identical between
mixed pattern and sole culture, however, mixed
pattern increased grain yields per plant and per
ha compared to sole culture. Growing cowpea
with maize in the same ridge had higher grain
yield per plant and per ha than those of sole
culture. In this concern, Gao et al. [31] found that
the grain yield of maize as an intercrop were
significantly greater than those of maize as a
sole crop.
These results could be attributed to maize plant
benefited from biological N fixation process
(BNF) by cowpea during maize growth and
development. These results indicate that the
fixed N of cowpea could be used by intercropped
maize during growth and development. There is
evidence that leguminous plants can benefit the
intercrop cereals in the same season through N
excretion [32] and nodule decomposition [33].
Clearly, mixed pattern played an important role to
improve edaphic environmental conditions in
rhizosphere of intercropped maize roots [34].
Accordingly, mixed pattern had positive effect on
grain yield and its attributes of the plant (Table 2)
through maximized carbon assimilation and crop
productivity [35] compared to sole maize.
Moreover, HamdAlla et al. [6] showed that
intercropping cowpea with maize played as a
reservoir for the naturally occurring biological
control agents of maize plants which contributed
positively in improve maize yield compared to
sole maize.
With respect to cowpea yield, it was decreased
by 52.45% as compared to sole cowpea (Table
2). These results could be attributed to spatial
arrangement of mixed pattern increased inter-
specific competition between the intercrops for
basic growth resources where efficiency of C
4
crops for N and water use was higher than C
3
crops [36]. These results are in agreement with
those obtained by HamdAlla et al. [6] who
concluded that fresh and dry forage yields of
cowpea were lower in intercropping with maize
than sole cowpea.
3.1.3 Effect of mineral N fertilizer
Plant height, stem diameter, number of
ears/plant, ear length, diameter and weight, grain
yields per plant and per ha were affected
significantly by mineral N fertilizer in the
combined data across 2013/2014 and 2014/2015
seasons, meanwhile, forage yield of cowpea per
ha was not affected (Table 2). It is observed that
plant height and stem diameter of maize plant
were increased by increasing mineral N fertilizer
rate from 75 to 100% of the recommended
mineral N fertilizer rate. Increasing mineral N
Abdel-Wahab et al.; AJEA, 11(6): 1-19, 2016; Article no.AJEA.24385
6
fertilizer rate from 214.2 to 285.6 kg N/ha
increased plant height and stem diameter by
9.66 and 9.59%, respectively. Naturally, there
was growth disadvantage of maize when maize
plants received 249.9 or 214.2 kg N/ha than
those received 285.6 kg N/ha. It is expected that
growth and development of maize plant was
affected negatively by decreasing mineral N
fertilizer rate from 285.6 to 214.2 kg N/ha which
reflected on growth resources such as soil N and
water and converted to the lowest growth
regulators and dry matter accumulation.
Consequently, the increase in plant height and
stem diameter might be due to the positive effect
of N element on plant growth that led to
progressive increase in internodes length and
number during maize growth and development.
It is known that plant height has been described
as a measure of growth related to the
efficiency in exploitation of environmental
resources [37].
Also, yield attributes of maize was increased by
increasing mineral N fertilizer rate from 75 to
100% of the recommended mineral N fertilizer
rate. Increasing mineral N fertilizer rate from
214.2 to 285.6 kg N/ha increased number of
ears/plant, ear length, diameter and weight, grain
yields per plant and per ha were increased by
8.42, 3.58, 13.94, 23.90, 31.98 and 12.57%,
respectively. These results could be due to 285.6
kg N/ha increased the strength of physiological
source such as chlorophyll [38], effective age of
leaves [39] and ear leaf N content [40] that
contributed greatly in photosynthetic process
during maize growth and development. These
results show that the decreasing mineral N
fertilizer rate from 285.6 to 214.2 kg N/ha
decreased soil N availability and increased intra-
specific competition between maize plants for
basic growth resources especially soil N which
restricted the ear characteristics (length,
diameter and weight). These results are in
agreement with those obtained by Bojović and
Marković [41] who found that N content
influenced from presence and ratio mineral
elements in the soil and it was close link with
chlorophyll content. Also, Hokmalipour and
Darbandi [42] revealed that chlorophyll was
increased significantly by increasing N fertilizer
levels.
With respect to cowpea, from self-evident there
was no relationship between mineral N fertilizer
rates of maize and yield of cowpea. Similar
results were obtained by El-Shamy et al. [43]
who reported that mineral N fertilizer rates of the
cereal component had not any relationship with
all the studied traits of the legume component
under intercropping conditions.
3.1.4 Response of the preceding crop to
cropping systems
Ear length, diameter and weight, grain yields per
plant and per ha were affected significantly by
the preceding crop x cropping systems in the
combined data across 2013/2014 and 2014/2015
seasons, meanwhile, plant height, stem
diameter, number of ears per plant and forage
yield of cowpea per ha were not affected
(Table 2). There was a positive interaction
between the preceding legume crops and
intercropped maize with cowpea on ear length,
diameter and weight, grain yields per plant and
per ha compared to the other treatments.
Accordingly, the preceding cereal crop (wheat)
decreased soil nutrient availability (Table 1) and
increased intra-specific competition between
maize plants for above and under-ground
conditions which reduced potential yield of sole
maize. So, these results indicate that BNF
process of cowpea (the legume component)
could be integrated with the residual effect of the
preceding berseem or faba bean crop and
thereby contributed mainly to fulfill the N
requirement of maize (the cereal component) by
enhancing the rhizobia growth in rhizosphere of
maize roots during maize growth and
development. Naturally, the fixed N by legume
can be use by intercropped cereals during their
growing period and this N is an important
resource for the cereals [44].
3.1.5 Response of the preceding crop to
mineral N fertilizer
Plant height, stem diameter, number of
ears/plant, ear length, diameter and weight, grain
yields per plant and per ha were affected
significantly by the preceding crop x mineral N
fertilizer in the combined data across 2013/2014
and 2014/2015 seasons, meanwhile, forage yield
of cowpea per ha was not affected (Table 2).
Growing maize that received 100% of the
recommended mineral N fertilizer rate (285.6 kg
N/ha) after harvest of the legume crops had the
highest studied traits of maize compared to the
other treatments. Certainly, N is the key element
in increasing yield and mediates the utilization of
potassium, phosphorus and other elements in
plants [45]. Also, the soil fertility status is
improved by activating the soil microbial biomass
[46].
Abdel-Wahab et al.; AJEA, 11(6): 1-19, 2016; Article no.AJEA.24385
7
Table 2. Effect of the preceding crop, cropping systems, mineral N fertilizer rates and their interactions on maize yield and its attributes, as well as, cowpea yield, combined data
across 2013/2014 and 2014/2015 seasons
Treatments
Plant height (cm)
Stem diameter
(cm)
Ears/plant (no.)
100%
87.5%
75.0%
Mean
100%
87.5%
75.0%
Mean
100%
87.5%
75.0%
Mean
Berseem Intercropping culture 292.37 287.71 268.58 282.88 2.26 2.12 2.01 2.13 1.07 1.04 0.99 1.03
Sole culture 294.04 287.02 269.59 283.55 2.24 2.12 2.04 2.13 1.05 1.02 0.98 1.01
Mean 293.20 287.36 269.08 283.21 2.25 2.12 2.02 2.13 1.06 1.03 0.98 1.02
Faba bean Intercropping culture 285.46 281.99 264.31 277.25 2.21 2.07 2.00 2.09 1.05 1.02 0.98 1.01
Sole culture 287.68 283.25 266.16 279.02 2.19 2.05 1.98 2.07 1.03 1.00 0.96 0.99
Mean 286.57 282.62 265.23 278.14 2.20 2.06 1.99 2.08 1.04 1.01 0.97 1.00
Wheat Intercropping culture 274.14 269.41 244.67 262.74 2.07 2.01 1.95 2.01 1.01 1.01 0.92 0.98
Sole culture 275.79 271.16 245.55 264.16 2.05 1.97 1.93 1.98 1.00 0.99 0.91 0.96
Mean 274.96 270.28 245.11 263.45 2.06 1.99 1.94 1.99 1.00 1.00 0.91 0.97
Average of cropping
systems Intercropping culture 283.99 279.70 259.18 274.29 2.18 2.06 1.98 2.07 1.04 1.02 0.96 1.00
Sole culture 285.83 280.47 260.43 275.57 2.16 2.04 1.98 2.06 1.02 1.00 0.95 0.98
Average of mineral N fertilizers 284.91 280.08 259.80 274.93 2.17 2.05 1.98 2.06 1.03 1.01 0.95 0.99
L.S.D. 0.05 Preceding crop (P)
L.S.D. 0.05 Cropping systems (S)
L.S.D. 0.05 Mineral N fertilizer rates (N)
L.S.D. 0.05 P x S
L.S.D. 0.05 P x N
L.S.D. 0.05 S x N
L.S.D. 0.05 P x S x N
N.S.
N.S.
21.31
N.S.
23.82
N.S.
N.S.
N.S.
N.S.
0.18
N.S.
0.24
N.S.
N.S.
N.S.
N.S.
0.05
N.S.
0.08
N.S.
N.S.
Table 2. Continued…
Treatments
Ear length (cm)
Ear diameter (cm)
Ear weight (g)
100%
87.5%
75.0%
Mean
100%
87.5%
75.0%
Mean
100%
87.5%
75.0%
Mean
Berseem Intercropping culture 21.54 21.38 20.86 21.26 5.43 5.30 4.81 5.18 222.47 209.43 186.69 206.19
Sole culture 21.42 21.15 20.69 21.08 5.38 5.21 4.72 5.10 215.16 200.97 177.22 197.78
Mean 21.48 21.26 20.77 21.17 5.40 5.25 4.76 5.14 218.81 205.20 181.95 201.98
Faba bean Intercropping culture 21.49 21.30 20.78 21.19 5.40 5.20 4.73 5.11 216.14 202.38 179.86 199.46
Sole culture 21.35 21.09 20.62 21.02 5.34 5.15 4.64 5.04 210.05 196.01 171.25 192.43
Mean 21.42 21.19 20.70 21.10 5.37 5.17 4.68 5.07 213.09 199.19 175.55 195.94
Wheat Intercropping culture 21.31 21.10 20.52 20.97 5.21 4.99 4.61 4.93 206.56 191.89 160.12 186.19
Sole culture 21.22 20.97 20.41 20.86 5.13 4.90 4.49 4.84 199.12 184.73 149.45 177.76
Abdel-Wahab et al.; AJEA, 11(6): 1-19, 2016; Article no.AJEA.24385
8
Treatments
Ear length (cm)
Ear diameter (cm)
Ear weight (g)
100%
87.5%
75.0%
Mean
100%
87.5%
75.0%
Mean
100%
87.5%
75.0%
Mean
Mean 21.26 21.03 20.46 20.91 5.17 4.94 4.55 4.88 202.84 188.31 154.78 181.97
Average of cropping
systems Intercropping culture 21.44 21.26 20.72 21.14 5.34 5.16 4.71 5.07 215.05 201.23 175.55 197.28
Sole culture 21.33 21.07 20.57 20.98 5.28 5.08 4.61 4.99 208.11 193.90 165.97 189.32
Average of mineral N fertilizers 21.38 21.16 20.64 21.06 5.31 5.12 4.66 5.03 211.58 197.56 170.76 193.30
L.S.D. 0.05 Preceding crop (P)
L.S.D. 0.05 Cropping systems (S)
L.S.D. 0.05 Mineral N fertilizer rates (N)
L.S.D. 0.05 P x S
L.S.D. 0.05 P x N
L.S.D. 0.05 S x N
L.S.D. 0.05 P x S x N
0.25
0.23
0.11
0.26
0.28
0.24
0.32
0.25
0.21
0.08
0.27
0.28
0.22
0.31
19.15
15.33
6.54
20.93
22.28
17.09
23.75
Table 2. Continued…
Treatments
Grain yield/plant (g)
Grain yield/ha (ton)
Forage yield of cowpea (ton/ha)
100%
87.5%
75.0%
Mean
100%
87.5%
75.0%
Mean
100%
87.5%
75.0%
Mean
Berseem Intercropping culture 232.71 218.23 184.56 211.83 8.04 7.60 7.18 7.60 16.52 17.83 17.53 17.29
Sole culture 223.93 210.34 174.13 202.80 7.89 7.44 7.05 7.46 35.42 35.89 35.11 35.47
Mean 228.32 214.28 179.34 207.31 7.96 7.52 7.11 7.53 25.97 26.86 26.32 26.38
Faba bean Intercropping culture 221.10 204.76 174.33 200.06 7.87 7.56 7.01 7.48 16.50 16.76 16.91 16.72
Sole culture 215.12 200.71 166.05 193.96 7.73 7.41 6.90 7.34 35.61 35.12 35.08 35.27
Mean 218.11 202.73 170.19 197.01 7.80 7.48 6.95 7.41 26.05 25.94 25.99 25.99
Wheat Intercropping culture 204.37 187.03 145.84 179.08 7.41 6.99 6.56 6.98 15.71 16.89 16.42 16.34
Sole culture 197.72 180.44 136.24 171.46 7.27 6.83 6.41 6.83 35.29 35.11 35.02 35.14
Mean 201.04 183.73 141.04 175.27 7.34 6.91 6.48 6.91 25.50 26.00 25.72 25.74
Average of cropping
systems Intercropping culture 219.39 203.34 168.24 196.99 7.77 7.38 6.91 7.35 16.24 17.16 16.95 16.78
Sole culture 212.25 197.16 158.80 189.40 7.63 7.22 6.78 7.21 35.44 35.37 35.07 35.29
Average of mineral N fertilizers 215.82 200.25 163.52 193.19 7.70 7.30 6.84 7.28 25.84 26.26 26.01 26.03
L.S.D. 0.05 Preceding crop (P)
L.S.D. 0.05 Cropping systems (S)
L.S.D. 0.05 Mineral N fertilizer rates (N)
L.S.D. 0.05 P x S
L.S.D. 0.05 P x N
L.S.D. 0.05 S x N
L.S.D. 0.05 P x S x N
28.42
17.07
6.91
31.55
33.14
19.78
36.23
0.60
0.42
0.12
0.64
0.69
0.45
0.76
N.S.
14.79
N.S.
N.S.
N.S.
N.S.
N.S.
Abdel-Wahab et al.; AJEA, 11(6): 1-19, 2016; Article no.AJEA.24385
9
3.1.6 Response of cropping systems to
mineral N fertilizer
Ear length, diameter and weight, grain yields per
plant and per ha were affected significantly by
cropping systems x mineral N fertilizer in the
combined data across 2013/2014 and 2014/2015
seasons, meanwhile, plant height, stem
diameter, number of ears per plant and forage
yield of cowpea per ha were not affected (Table
2). Obviously, intercropped maize that received
285.6 kg N/ha gave the highest ear length,
diameter and weight, grain yields per plant and
per ha compared to the other treatments.
Conversely, sole or intercropped maize that
received 214.2 kg N/ha increased intra and inter-
specific competition between cowpea and maize
plants, respectively, for basic growth resources
especially soil N. Accordingly, the rate of
photosynthetic process could not be maintained
high during grain filling which reflected on grain
yield of sole or intercropped maize plant as a
consequence of decrease in soil N availability
compared to the other treatments.
These results show that intercropping cowpea
with maize interacted positively with 87.5% of the
recommended mineral N fertilizer rate (249.9 kg
N/ha) to decrease inter-specific competition
between intercropped maize plants for basic
growth resources especially soil N. It is important
to mention that there were no significant
differences between 285.6 and 249.9 kg N/ha on
maize plants of mixed pattern. These findings
imply that application of 249.9 kg N/ha for
intercropped maize with cowpea furnished
suitable environmental resources for maize plant
to increasing inter-specific competition between
maize and cowpea for fixed N. Clearly, the
greater competition of maize plant for available
soil N at high bean populations, when legumes
were nearer to maize rows, might have
stimulated root nodulation of intercropped beans
[47]. Consequently, maize plant of mixed pattern
that received 249.9 kg N/ha could be enhanced
BNF process of cowpea to fix about 12.5% N of
maize requirements where nodulation and N
fixation by legumes is adversely affected by
higher rates of fertilizer N [48]. Finally, El –
Shamy et al. [40] showed that maize plant of
mixed pattern that received the recommended N
rate did not achieve the highest grain and total
yields/ha. They added that the recommended N
rate to maize plant of mixed stand affected
negatively rhizobia activity in rhizosphere of
maize roots and efficiency of BNF by adjacent
legume plants.
3.1.7 Response of the preceding crop to
cropping systems and mineral N
fertilizer
Ear length, diameter and weight, grain yields per
plant and per ha were affected significantly by
the preceding crop x cropping systems x mineral
N fertilizer in the combined data across
2013/2014 and 2014/2015 seasons, meanwhile,
plant height, stem diameter, number of ears per
plant and forage yield of cowpea per ha were not
affected (Table 2). Intercropping cowpea with
maize that received 100 or 87.5% of the
recommended mineral N fertilizer rate after
legume crops harvest gave the highest ear
length, diameter and weight, grain yields per
plant and per ha compared to the other
treatments. It is important to mention that
intercropped maize plants that received 249.9 kg
N/ha after harvest of the legume crops reached
the same significance level of intercropped maize
plants that received the highest mineral N
fertilizer rate after harvest of the legume crops.
These results reveal that there was positive
interaction effect of the preceding legume crops
and intercropped maize plants that received
249.9 kg N/ha because of nitrate could be
inhibited nitrogenase activity in the legume plant
nodules [49]. It is known that legumes have two
sources of N nutrition – symbiotic N fixation of
atmospheric molecular N in symbiosis with
Rhizobium or Bradyrhizobium sp. and
assimilation of soil N (mainly in the form of
nitrates), using the enzyme nitrate reductase
[50]. Thus, the bacteria that actually fixed the N
become lazy and N fixing declines [51].
Accordingly, the efficiency of BNF process could
not be enhanced by the interaction among the
preceding legume (berseem or faba bean) crop,
intercropped maize and the highest mineral N
fertilizer rate.
3.2 Quality of Maize Grains
3.2.1 Effect of the preceding crop
Quality of maize grains (N, oil and protein
contents) was affected significantly by the
preceding crop in the combined data across
2013/2014 and 2014/2015 seasons (Table 3).
Berseem residues increased grain N and protein
contents but it decreased grain oil content
compared to those by faba bean or wheat. These
results could be due to the increase in soil N
content after berseem cutting (Table 1) which
increased absorption N uptake from soil by
maize roots to sink tissues (grains), especially N
Abdel-Wahab et al.; AJEA, 11(6): 1-19, 2016; Article no.AJEA.24385
10
supply to maize grains influences on the
accumulation of proteins [52].
3.2.2 Effect of cropping systems
Quality of maize grains (N, oil and protein
contents) was affected significantly by cropping
systems in the combined data across 2013/2014
and 2014/2015 seasons (Table 3). Growing
cowpea in the other side of maize ridge
increased grain N and protein content by 1.47
and 1.16%, respectively, compared with those of
sole maize, but it decreased grain oil content.
These results could be due to maize plant
benefited from BNF process of cowpea which
reflected positivity on grain N and protein
contents.
3.2.3 Effect of mineral N fertilizer
Quality of maize grains (N, oil and protein
contents) was affected significantly by mineral N
fertilizer in the combined data across 2013/2014
and 2014/2015 seasons (Table 3). It is observed
that Increasing mineral N fertilizer from 214.2 to
285.6 kg N/ha increased grain N and protein
contents by 5.26 and 6.00%, respectively.
Naturally, there was growth disadvantage of
maize plant with the application of 249.9 or 214.2
kg N/ha as a result of decreasing soil N
availability and hence these rates of mineral N
fertilizer were not able to satisfy the requirement
of maize growth and development. Similar results
were obtained by Sarwar [8] who indicated that
the protein content was increased significantly
with the successive increase of N.
3.2.4 Response of the preceding crop to
cropping systems
Quality of maize grains (N, oil and protein
contents) was affected significantly by the
preceding crop x cropping systems in the
combined data across 2013/2014 and 2014/2015
seasons (Table 3). It seems that there was a
positive effect of the preceding berseem crop
interacted with cowpea on quality of maize
grains. Berseem residues improved soil N
availability (Table 1) that decreased intra-specific
competition between maize plants for above and
under-ground conditions and increased potential
yield of intercropped maize. So, these results
indicate that BNF process of cowpea (the legume
component) could be integrated with the residual
effect of the preceding berseem crop and
thereby contributed mainly to fulfill the N
requirement of maize (the cereal component) by
enhancing the rhizobia growth in rhizosphere
of maize roots during maize growth and
development.
3.2.5 Response of the preceding crop to
mineral N fertilizer
Quality of maize grains (N, oil and protein
contents) was affected significantly by the
preceded winter field crops x mineral N fertilizer
in the combined data across 2013/2014 and
2014/2015 seasons (Table 3). Growing maize
with the application of 285.6 kg N/ha had the
highest grain N and protein contents and the
lowest grain oil content compared to the other
treatments.
3.2.6 Response of cropping systems to
mineral N fertilizer
Quality of maize grains (N, oil and protein
contents) was affected significantly by cropping
systems x mineral N fertilizer in the combined
data across 2013/2014 and 2014/2015 seasons
(Table 3). Intercropped maize plants with the
application of 285.6 kg N/ha gave the highest
grain N and protein contents and the lowest grain
oil content compared to the other treatments.
Conversely, maize plants of sole culture 214.2 kg
N/ha increased inter-specific competition
between maize plants for basic growth resources
especially soil N which reflected on grain N, oil
and protein contents. It is expected that
intercropping cowpea with maize plants that
received 87.5% of the recommended N rate
(249.9 kg N/ha) promoted rhizobia growth in
rhizosphere of maize root. Vegetative growth and
development of maize plant benefited from the
available fixed N by intercropped legume which
reflected positively on the ear leaf N content [40].
3.2.7 Response of the preceding crop to
cropping systems and mineral N
fertilizer
Quality of maize grains (N, oil and protein
contents) was affected significantly by the
preceding crop x cropping systems x mineral N
fertilizer in the combined data across 2013/2014
and 2014/2015 seasons (Table 3). Intercropping
cowpea with maize that received 100 or 87.5% of
the recommended mineral N fertilizer rate after
berseem cutting had the highest grain N and
protein contents and the lowest oil content
compared to the other treatments. These data
show that there was effect (P ≤ 0.05) of the
preceding crop x cropping systems x mineral N
fertilizer rates on quality of maize grains.
Abdel-Wahab et al.; AJEA, 11(6): 1-19, 2016; Article no.AJEA.24385
11
Table 3. Effect of the preceding crop, cropping systems, mineral N fertilizer rates and their interactions on quality of maize grains, combined data across 2013/2014
and 2014/2015 seasons
Treatments Grain N content (%) Grain oil content (%) Grain protein content (%)
100% 87.5% 75.0% Mean 100% 87.5% 75.0% Mean 100% 87.5% 75.0% Mean
Berseem Intercropping culture 1.45 1.44 1.38 1.42 10.22 10.25 10.32 10.26 9.06 9.00 8.62 8.89
Sole culture 1.45 1.42 1.36 1.41 10.27 10.29 10.38 10.31 9.06 8.87 8.50 8.81
Mean 1.45 1.43 1.37 1.41 10.24 10.27 10.35 10.28 9.06 8.93 8.56 8.85
Faba bean Intercropping culture 1.42 1.40 1.36 1.39 10.32 10.34 10.43 10.36 8.87 8.75 8.50 8.70
Sole culture 1.41 1.40 1.32 1.37 10.38 10.42 10.49 10.43 8.81 8.75 8.25 8.60
Mean 1.41 1.40 1.34 1.38 10.35 10.38 10.46 10.39 8.84 8.75 8.37 8.65
Wheat Intercropping culture 1.38 1.36 1.31 1.35 10.52 10.54 10.60 10.55 8.62 8.50 8.18 8.43
Sole culture 1.36 1.34 1.27 1.32 10.56 10.60 10.68 10.61 8.50 8.37 7.93 8.26
Mean 1.37 1.35 1.29 1.33 10.54 10.57 10.64 10.58 8.56 8.43 8.05 8.34
Average of cropping
systems Intercropping culture 1.41 1.40 1.35 1.38 10.35 10.37 10.45 10.39 8.85 8.75 8.43 8.67
Sole culture 1.40 1.38 1.31 1.36 10.40 10.43 10.51 10.44 8.79 8.66 8.22 8.55
Average of mineral N fertilizers 1.40 1.39 1.33 1.37 10.37 10.40 10.48 10.41 8.82 8.70 8.32 8.61
L.S.D. 0.05 Preceding crop (P)
L.S.D. 0.05 Cropping systems (S)
L.S.D. 0.05 Mineral N fertilizer rates (N)
L.S.D. 0.05 P x S
L.S.D. 0.05 P x N
L.S.D. 0.05 S x N
L.S.D. 0.05 P x S x N
0.03
0.02
0.01
0.04
0.06
0.03
0.07
0.09
0.05
0.03
0.11
0.13
0.08
0.15
0.17
0.12
0.08
0.19
0.21
0.15
0.24
Abdel-Wahab et al.; AJEA, 11(6): 1-19, 2016; Article no.AJEA.24385
12
3.3 Nitrogen Use Efficiency (NUE)
3.3.1 Effect of the preceding crop
Partial factor productivity (NUE–PFP) expressed
as crop yield per unit of N applied (Roberts,
2008) are indicative of the degree of economic
and environmental efficiency in use of nutrient
inputs. In this study, NUE ranges from 101.81 to
212.88 kg grain yield per kg nutrient applied (Fig.
1). NUE values of 40–80 kg/kg are usual with
values > 60 kg/kg for NUE being common in
well–managed systems or at low levels of N use,
or at low soil N supply [14]. Berseem residues
increased NUE of maize plants compared to that
of the other preceded crops (Fig. 1). These
results could be due to the increase in soil N
content after berseem cutting (Table 1) which
increased absorption N uptake from soil by
maize roots. Consequently, this status led to
more assimilation into amino acids that serve as
N carriers throughout the plant and N transport
from source to sink tissues throughout plant
development, especially during the grain filling
period (Table 2).
3.3.2 Effect of cropping systems
NUE was affected significantly by cropping
systems in the combined data across 2013/2014
and 2014/2015 seasons (Fig. 1). Growing
cowpea in the other side of maize ridge
increased NUE by 2.06% compared with that of
sole maize. These results could be due to maize
plant benefited from BNF process of cowpea that
reflected positively on grain N content (Table 3).
Similar results were obtained by Gao et al. [31]
who showed that N uptake of maize as an
intercrop was significantly greater than those of
maize as a sole crop. Also, El-Shamy et al. [40]
showed that legume crop improved N use
efficiency (NUE) for maize plant of mixed pattern.
Finally, Zhang et al. [53] indicated that
intercropping systems reduced use of N fertilizer
per unit land area and increased relative
biomass of intercropped maize, due to promoted
photosynthetic efficiency of border rows and N
utilization during symbiotic period.
3.3.3 Effect of mineral N fertilizer
NUE was affected significantly by mineral N
fertilizer in the combined data across 2013/2014
and 2014/2015 seasons (Fig. 1). Maize plants
with the application of 87.5% of the
recommended mineral N fertilizer rate increased
(P≤0.05) NUE by 89.70 % compared to that of
maize plants with the application of 100% of the
recommended mineral N fertilizer rate. It is
observed that NUE values emerging from this
study apply to low levels of N use, or at low
soil N supply and contributed positively in
increase of photosynthesis process efficiency
and consequently grain yield/plant (Table 2).
Fig. 1. NUE as affected by the preceding crop, cropping systems, mineral N fertilizer rates and
their interactions, combined data across 2013/2014 and 2014/2015 seasons
Abdel-Wahab et al.; AJEA, 11(6): 1-19, 2016; Article no.AJEA.24385
13
Similar results were obtained by El-Shamy et al.
[40] who found that adding 83.33% of the
recommended mineral N fertilizer rate N to maize
plant increased (P≤0.05) NUE by 97.74 percent
compared to those that received 100% of the
recommended mineral N fertilizer rate.
3.3.4 Response of the preceding crop to
cropping systems
NUE was affected significantly by the preceding
crop x cropping systems in the combined data
across 2013/2014 and 2014/2015 seasons (Fig.
1). There was a positive effect of berseem
residues with cowpea on NUE of intercropped
maize compared to the other treatments. So,
these results could be attributed to BNF process
of cowpea integrated with the residual effect of
the preceding berseem crop and thereby
contributed mainly to fulfill the N requirement of
maize.
Conversely, maize plants that followed wheat
crop had the lowest NUE compared to the other
treatments. These results could be due to the
preceding wheat crop decreased soil nutrient
availability (Table 1) which increased intra-
specific competition between maize plants for
above and under-ground conditions and reduced
potential yield of sole maize.
3.3.5 Response of the preceding crop to
mineral N fertilizer
NUE was affected significantly by the preceding
crop x mineral N fertilizer in the combined data
across 2013/2014 and 2014/2015 seasons (Fig.
1). Growing maize with the application of 100%
of the recommended mineral N fertilizer rate
(285.6 kg N/ha) after berseem cutting had the
highest NUE, meanwhile, maize plants that
received 75% of the recommended mineral N
fertilizer rate (214.2 kg N/ha) after wheat harvest
had the lowest NUE compared to the other
treatments. It is expected that the preceding
wheat crop interacted with 214.2 kg N/ha and
resulted in a greater competition between maize
plants for available soil N which affected
negatively N uptake of maize plant.
3.3.6 Response of cropping systems to
mineral N fertilizer
NUE was affected significantly by cropping
systems x mineral N fertilizer in the combined
data across 2013/2014 and 2014/2015 seasons
(Fig. 1). Intercropping cowpea with maize plants
with the application of 87.5% of the
recommended mineral N fertilizer rate had the
highest NUE compared to the other treatments.
These data may be due to the application of 87.5
% of the recommended mineral N fertilizer rate
promoted rhizobia growth in rhizosphere of
intercropped maize roots which reflected
positively on N uptake and IAA content in tissues
of maize plant and contributed strongly with
enhancing efficiency of photosynthesis process.
Intercropping cowpea with maize that received
100% of the recommended mineral N fertilizer
rate could be affected negatively rhizobia activity
in rhizosphere of intercropped cowpea roots
which reflected negatively on NUE of
intercropped maize plant. These results are in
parallel with those obtained by El-Shamy et al.
[40] who found that adding 83.33% of the
recommended N rate to maize plants promoted
rhizobia growth in rhizosphere of maize roots and
increased N uptake and IAA content in tissues of
maize plant which increased NUE of
intercropped maize compared to those received
the full mineral N fertilizer rate.
3.3.7 Response of the preceding crop to
cropping systems and mineral N
fertilizer
NUE was affected significantly by the preceding
crop x cropping systems x mineral N fertilizer in
the combined data across 2013/2014 and
2014/2015 seasons (Fig. 1). Intercropping
cowpea with maize that received 100 or 87.5% of
the recommended mineral N fertilizer rate after
berseem cutting had the highest NUE,
meanwhile, maize plants of sole culture that
received 75.0% of the recommended mineral N
fertilizer rate after wheat harvest had the lowest
NUE compared to the other treatments. These
results reveal that there was advantage of
intercropping cowpea with maize that received
87.5% of the recommended mineral N fertilize
rate after berseem cutting as a result of
increasing efficiency of BNF process of cowpea.
Intercropping cowpea with maize that received
100% of the recommended mineral N fertilizer
rate after berseem cutting did not achieve the
highest NUE because of nitrate could be
inhibited nitrogenase activity in the legume plant
nodules [49].
3.4 Competitive Relationships
3.4.1 Land equivalent ratio (LER)
3.4.1.1 Effect of the preceding crop
The values of LER were estimated by using data
of recommended sole cultures of both crops.
Abdel-Wahab et al.; AJEA, 11(6): 1-19, 2016; Article no.AJEA.24385
14
Intercropping cowpea with maize increased LER
as compared to sole cultures of both crops in the
combined data across 2013/2014 and 2014/2015
seasons (Fig. 2). It was ranged from 1.36 (by
intercropping cowpea with maize that received
214.2 kg N/ha after wheat harvest) to 1.47 (by
intercropping cowpea with maize that received
285.6 kg N/ha after berseem cutting). The results
showed that maize was superior in the intercrop
system where the relative yield was increased
than those of sole culture, meanwhile cowpea
was inferior companion crop where the relative
yield was decreased than those of sole culture in
the combined analysis.
LER was affected significantly by the preceding
crop in the combined data across 2013/2014 and
2014/2015 seasons (Fig. 2). The advantage of
the highest LER by intercropping cowpea with
maize after harvest of the legume crops over the
others could be due to residual effect of the
legume crops improved soil nutrient availability
(Table 1) for intercropping cowpea (50 % of sole
cowpea plant density) with maize (100% of sole
maize plant density) and reflected positively on
relative yields of both crops. These results are in
accordance with those obtained by HamdAlla et
al. [6] who concluded that the actual productivity
was higher than expected productivity. Also, Abd
El-Salam and Abd El-Lateef [54] concluded that
maize-cowpea intercropping increase land use
efficiency by 12- 14% compared with each crop
grown alone.
3.4.1.2 Effect of mineral N fertilizer
LER was affected significantly by mineral N
fertilizer in the combined data across 213/2014
and 2014/2015 seasons (Fig. 2). LER was
increased by increasing mineral N fertilizer rates
from 214.2 to 285.6 kg N/ha. These results show
that the decreasing mineral N fertilizer rate from
285.6 to 214.2 kg N/ha decreased soil N
availability (Table 1) and increased intra-specific
competition between maize plants for basic
growth resources especially soil N.
3.4.1.3 Response of the preceding crop to
mineral N fertilizer
LER was affected significantly by the interaction
between the preceding crop and mineral N
fertilizer in the combined data across 2013/2014
and 2014/2015 seasons (Fig. 2). LER was
increased by application of 285.6 or 249.9 kg
N/ha to maize plants after the preceding legume
crops. These results may b due to the interaction
between the preceding legume crops and 285.6
or 249.9 kg N/ha increased N content in tissues
of maize plants especially N is the key element in
increasing yield and mediates the utilization of
potassium, phosphorus and other elements [45].
Fig. 2. LER as affected by the preceding crop, cropping systems, mineral N fertilizer rates and
their interactions, combined data across 2013/2014 and 2014/2015 seasons
Abdel-Wahab et al.; AJEA, 11(6): 1-19, 2016; Article no.AJEA.24385
15
3.4.2 Land Equivalent Coefficient (LEC)
3.4.2.1 Effect of the preceding crop
LEC was a measure of interaction concerned
with the strength of relationship. LEC is used for
a two- crop mixture the minimum expected
productivity coefficient (PC) is 25 percent, that is,
a yield advantage was obtained if LEC value was
exceeded 0.25. LEC was affected significantly by
the preceding crop in the combined data across
2013/2014 and 2014/2015 seasons (Fig. 3).
Intercropping cowpea with maize increased LER
as compared to sole cultures of both crops. The
advantages of the highest LEC by intercropping
cowpea with maize that followed legume crops
over the others could be due to the preceding
legume crops improved soil nutrient availability
(Table 1) for intercropping cowpea with maize
which reflected positively on relative yields of
both crops.
3.4.2.2 Effect of mineral N fertilizer
LEC was affected significantly by mineral N
fertilizer in the combined data across 2013/2014
and 2014/2015 seasons (Fig. 3). LEC was
increased by increasing mineral N fertilizer rates
from 214.2 to 285.6 kg N/ha. These results show
that the decreasing mineral N fertilizer rate from
285.6 to 214.2 kg N/ha decreased soil N
availability (Table 1) and increased intra-specific
competition between maize plants for basic
growth resources especially soil N.
3.4.2.3 Response of the preceding crop to
mineral N fertilizer
LEC was affected significantly by the interaction
between the preceding crop and mineral N
fertilizer in the combined data across 2013/2014
and 2014/2015 seasons (Fig. 3). LEC was
increased by application of 285.6 or 249.9 kg
N/ha to maize plants after the preceding legume
crops. These results may b due to the interaction
between the preceding legume crops and 285.6
or 249.9 kg N/ha increased N content in tissues
of maize plants especially soil N (Table 1).
3.5 Intercropping Economic Advantage
The economic performance of the intercropping
was evaluated to determine if maize and cowpea
combined yields are high enough for the farmers
to adopt this system. The averages of monetary
advantage index (MAI) values of intercropping
cowpea with maize that received 100 or 87.5% of
the recommended mineral N fertilizer rate after
berseem cutting were higher than the other
treatments (Fig. 4). Differences between the
highest and the lowest values of MAI were 274
US$ in the combined data across 2013/2014 and
2014/2015 seasons. On the other hand, there
were gradual and consistent decreases in MAI
values with deceasing mineral N fertilizer rate
from 100 to 75% of the recommended mineral N
fertilizer rate of intercropped maize with cowpea.
Intercropping cowpea with maize that received
87.5% of the recommended mineral N fertilizer
Fig. 3. LEC as affected by the preceding crop, cropping systems, mineral N fertilizer rates and
their interactions, combined data across 2013/2014 and 2014/2015 seasons
Fig.
4. MAI as affected by the preceding crop, cropping systems, mineral N fertilizer rates
their interactions, combined data across 2013/2014 and 2014/2015 seasons
rate after berseem cutting resulted in high MAI
and could be recommended. These results are in
parallel with those observed by
HamdAlla
[6]
who concluded that values of MAI were
2097.28, 2607.95 and 2360.80 in both seasons
and the combined analyses.
4. CONCLUSION
It could be concluded that intercropping cowpea
with maize that received 87.5% of the
recommended mineral N fertilizer after
cutting compensated 12.5%
N
requirements and achieved desirable yield with
good
yield quality under Egyptian conditions.
COMPETING INTERESTS
Authors have declared that no competing
interests exist.
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