INTRODUCTION
In the interval between the two sequential cropping such as wheat-wheat,
wheat-rape, etc., considering the time when the farm gets free of the
previous crop and the time required for land preparation for the next
crop in autumn, there is no sufficient time for cultivation of a grain
plant as the main crop. From the other hand, very high temperature and
prolonged summer of the arid and semi-arid regions like as varamin (30
km apart in SE of Tehran) justify the optimum use of water. Studying on
cultivation of a plant with profitable and short growing season as well
as high potentials for benefiting such a high heat and radiation of summer,
would lead to increment of resources utilization efficiency.
Sweet corn (Zea mays L. var. Saccarata) is among tropical Gramineae,
of which the growing period up to economic product harvest (ear in soft
dough stage) is 75-80 days by average and which leaves a remarkable bulk
of green biomass with high rate of protein, used as a byproduct for feeding
purposes.
Multiple cropping is considered as one of the methods of environment-friendly
and sustainable agriculture. In a tropical and subtropical region such
as Iran, water is a limiting factor for planting date, which influence
crop yields, intercropping is one of the strategies for optimum resources
utilization efficiency and realization of objectives of sustainable agriculture
(Vandrmire, 1989). Intercropping, including corn and bean which was popular
in Mexico during 900 to 1500 BC (Francis, 1982), causes the enhancement
of potential yield. In this case, according to plant diversity principle
in farm, the grounds are prepared for increment of production, maintenance
of soil fertility, erosion control and altogether optimum utilization
of the resources (Mazaheri, 1998).
In many experiments of intercropping, in which the components are composed
of one species of legumes and one species of cereals the yield of intercropping
shows advantage over that of the sole cropping (Morris and Garrity, 1993).
In this regard, such instances as intercropping of soybean/corn (Elomre
and Jackobs, 1986), corn/cowpea (Mandhal et al., 1996), corn/garden
bean (Atri et al., 2000), can be mentioned.
The yield in intercropping systems depends on selection of compatible
genotypes with suitable characters for establishment of a minimum competition
and maximum assistance as well as application of appropriate inputs and
farm operations (such as crop density, mixing ratio and intercropping
pattern) (Mutungamiri et al., 2001). Mazaheri (1998) believes that
intercropping may be useful when the crops have the roots of different
depths; from the other hand, the stem length and plant growth pattern,
play role in competition of two species for light. If two plants are similar
with respect to stem length and growth manner, such issues as shading
and competition for light would be effective on their yield. Inter specific
variation in intercropping prevents the probable yield loss through reducing
the pests and diseases as well as asphyxiating the weeds (Hosseini and
Kolar, 1988).
In corn/soybean intercropping, the highest yield is resulted from a mixing
ratio of 25% corn and 75% soybean (Pookpakdi, 1985, quoted by Danaeifar
et al., 2001). Similarly, Mazaheri (1998), having mixed 75% corn
with 25% bean, produced 16% more yield in comparison with sole cropping
of these two species. According to findings of Zand and Ghafari Khaligh
(2002), mixing ratio of 50:50 (1 to 1) for cowpea and grain sorghum showed
19% profitability in comparison with their sole cropping. Having estimated
the aggresivity index in intercropping treatments, they stated that cowpea
was the dominant species and has used the environmental conditions more
efficiently.
Barzegari et al. (2004) expressed that intercropped pop corn and
cowpea, leaved very significant differences in yield components of pop
corn and bean. According to LER for grain yield, intercropping showed
superiority over sole cropping.
Rahimi et al. (2004), having compared the three different ratios
of intercropping of corn and soybean with their sole cropping, determined
that the maximum yields are, respectively for treatments related to 50%
intercropping of both crops and then 25% corn and 75% soybean. Also, they
indicated that reducing the number of corn rows, the length of ear, number
of ears in each plant, kernel number per ear, soybean pod number, 1000
weight of grain soybeans and crude protein percent of soybean increased,
probably as a result of less shading and dominance of corn.
According to Danaeifar et al. (2001), high plant density, increased
the dry matter in both pure stand and intercropping.
In a research on the effect of density and planting arrangement on qualitative
and quantitative yield of forages in intercropping of Egypt clover and
barley forage, Shahrivar et al. (1996) stated that in all intercropping
cases, with enhancement of density, the dry matter yield increases and
the maximum yield of dry matter is related to 50:50 (barley/clover) intercropping
in high density that has caused equal to 6.06% overproduction in comparison
with maximum yield of sole cropping. In addition, with the rise of density,
LER increases, in such a manner that the maximum LER was reached in high
density and 50:50 (barley/clover) intercropping. Also the highest rates
of crude protein were reached in this ratio.
Since researches made on different resources have put emphasis on profitability
of intercropping of one legume and one cereal, the general objectives
of this study are considered as evaluation of the impact of mung bean
(Vigna radiata L.)/Sweet corn mixing ratios and plant density on
the yield of sweet corn as the main crop.
MATERIALS AND METHODS
Experiment was carried out in summer 2006 in an agricultural area located
in Varamin region (30 km apart from South East of Tehran, 35°20` N,
51°31` E, 1050 masl).
Soil texture was determined as clay loam with pH = 7.65 and OC = 0.71%.
The farm had been under wheat crop the previous year. Therefore, preparation
works including tillage, basic fertilization, disc harrow, leveler, making
ridges and furrows, etc., were fulfilled after wheat harvest in early
July. Experiment was carried out in a split plot design based on randomized
complete blocks with 4 replications. Plant density with 3 levels (6, 8
and 10 plant m-2 for sweet corn, cultivar S.C.403 and 10, 20
and 30 plant m-2 for mung bean cultivar, Partow) were arranged
in main plots and 5 mixing ratios (0:100, 25:75, 50:50, 75:25, 100:0 for
Mung bean/Sweet corn) were arranged in subplots. Seeds of the two crops
were simultaneously planted on July 28, 2006. Each experimental unit was
composed of 6 cropping rows, each 6.5 m long, 0.75 m apart. Within each
plot, alternative cropping lines 2, 3, 4 and 5 were allocated to sweet
corn or mung bean with intended mixing ratios and in marginal lines of
each experimental unit (lines 1 and 6) sweet corn was planted.
All measures of crop management were taken, including distribution of
top-dressing, weeding out, pests and probable diseases control and irrigation
with common method of the region, if necessary. Soil fertilization works
were performed in two stages on September 6 and October 3, on the basis
of needs of crops for nitrogen as was shown by results of soil analysis
and in the form of row banding. Harvest of sweet corn was done on October
31 in soft dough stage (economic maturation). In this stage, sampling
was made on four middle lines with a length of 4 m, indeed of total fresh
weight of biomass in harvest area (9.6 m-2), 10 plants of sweet
corn and 10 plants of mung bean were prepared as explants, to determine
oven dried weight. Some morphological parameters such as length of ear,
number of suckers per plant, diameter of corn stem, height of corn plant
and height of mung bean plant, were examined before sampling.
Also yield components of both sweet corn and mung bean were determined.
Statistical analysis of experimental data was done using SAS program
using (PROC ANOVA). Then the means of traits under study were compared
through Duncans multiple range test.
RESULTS AND DISCUSSION
Corn biomass (biologic yield): Results of data variance analysis
indicated that the total dry matter, forage yield after ear harvest as
well as dry matter of different organs of sweet corn (leaves, stem, ear)
have not been impacted by the plant density (Table 1).
The mixing ratio of the two components crop, however, has left a significant
effect (p≤0.01) on the mentioned traits. Although the interaction of
these traits was not significant, Pillai et al. (1990), having
reviewed the ecologic benefits of forage corn/cowpea intercropping, stated
that such an intercropping has increased significantly the yield of green
forage and dry matter. Means comparison indicates that total dry matter
in medium density D2 (8 plants m-2) has shown the
highest yield and in such a density of the dry matter distributed in different
plant organs, the ear has had more share in comparison with other organs
(Table 2) Francis et al. (1982) explained that
corn in the density of about 6 plant m-2 would show the highest
yield. In this experiment with the rise of density, the dry matter distributed
between leaf and stem has increased, but the ear yield has declined (Table
2) because in high density the lower leaves, being placed under the
shade, usually show the higher rates of respiration than those of photosynthesis
and act as a parasite for the plant and especially for the upper leaves.
In sweet corn, just like most of other agricultural species, inflow and
utilization of soluble carbohydrates together with amino acids, as a source
of reduced nitrogen, is necessary for vegetative and reproductive growth,
therefore, in this stage of plant growth, partitioning of assimilates
to the ear is more than the other organs that has caused increment of
dry matter in the ear. In this stage, the carbohydrates required for filling
the kernel are originated from current photosynthesis and transition from
temporary sources of stems, leaves, cob and husk. But the change in density
results in change in the yield.
In some states of plant density, the yield will be turned from positive
state to negative state; in such a case, competition and assistance make
impressions simultaneously. This state is seen in medium density (D2),
in such a manner that with the rise of density, we would witness the yield
loss. In other words, it can be understood that in medium density, corn
has used the environmental conditions better and by the rise of density
as a result of intensification of intraspecies competition, the increment
of biomass yield has stopped and/or even has encountered the reduction
of dry weight.
| Table 1: |
Analysis of variance of Mean squares of sweet corn
biomass (final harvest) |
|
*and **: Significant at the 5 and
1% levels of probability, respectively |
| Table 2: |
Means comparison of sweet corn biomass in soft dough
stage (final harvest) affected by plant density and mixing ratio |
|
Means with the same letter(s) in each
column are not significantly different at 5% probability level using
Duncan`s multiple range test |
As to dry weight of fodder corn after harvest of ear, it is seen that
with the rise of plant density, forage dry matter has shown an upward
trend as a result of plant density increasing as well as increment of
stem and leaf dry matter. Therefore, a positive relation between plant
density and dry matter accumulation in sweet corn forage could be expected.
As can be shown in Table 2, the highest dry matter
of sweet corn has reached in sole cropping and as a result of reduction
of corn portion, sweet corn dry matter decreased and such reduction of
yield has not been changed equally and has been in such a manner that
the total sweet corn dry matter has shown 24 and 19% reduction in comparison
with control treatment, respectively in 75/25 and 50/50 sweet corn/mung
bean treatments. Also in 25/75 sweet corn/mung bean intercropping, we
see a 21% loss in ear dry matter, but in 50/50 sweet corn/mung bean, only
a 10% yield loss has occurred. That is to say that the rate of ear dry
matter has been reduced by reduction of ear portion at intercropped treatment.
Tripathi et al. (1987) studied on forage yield in sole cropping
and legume/cereal intercropping in summer, observed that in sole cropping,
sorghum (Pioneer 988 cultivar) and corn (African tall cultivar) produced
significantly more fresh forage and dry matter in comparison with other
treatments.
Having examined the intercropping of chick pea and barley for forage
production, Daryaei et al. (2006) concluded that chick pea forage
yield was influenced by mixing ratio (p≤0.01) and chick pea pure stand
showed the highest forage yield. According to the records of Danaeifar
et al. (2001), with the rise of density, the dry matter produced
in both sole cropping and intercropping increased. They high plant density
particularly as to forage crops, creates a suitable microclimate and results
in the rise of total dry matter yield. Similarly Shahrivar et al.
(1996) stated that in all cases of barley/clover intercropping, with the
rise of density, dry matter yield has increased and the highest yield
of dry matter was related to 50/50 mixing ratio in high density.
Ear yield: Plant density has caused no significant difference
on ear, kernel, cob and husk dry weight. The impact of mixing ratio, however,
on these traits was so significant (p≤0.01) and interaction of density
and mixing ratio has resulted in a significant difference only in cob
dry weight (Table 1).
As indicated by the table of comparison of means of traits (Table
2), the highest rate of kernel dry matter is in density D2
(mean), but as to cob and husk dry weight, has decreased with the rise
of dry matter density. Although, there is no statistically significant
difference between the rates achieved, however, the fluctuation of yield
is resulting from such issues as shading of plants and competition in
high densities and such an effect is related to reduction of sun radiations
to lower parts of plants in high densities. Also it can be seen that with
the rise of corn portion in experimental plots, dry matter increases in
such a manner that the corn sole cropping has had the highest dry matter
in kernel and with increment of mung bean portion, corn yield has decreased
due to interspecies competition.
Relative Crowding Coefficient (RCC): This index determines the
rate of competition between two species, which has been intercropped through
replacement series. Treatments with RCC<1 are interpreted as non-profitability
of intercropping in comparison with sole cropping. Such conditions can
be seen for total biomass yield both before and after ear harvest, but
the mixing ratio 75/25 (sweet corn/mung bean) in low density (D1P2)
and mean density (D2P2), respectively with RCC of
1.20 and 1.11 and also this same density and mixing ratio of 25/75 (sweet
corn/mung bean) with RCC = 1.43 are considered as the most profitable
intercropping states with respect to total dry matter yield before harvest.
In general, in sweet corn/mung bean intercropping, mung bean is always
the recessive species, in such a manner that in most of the cases, its
RCC (Km) for the yield both before and after corn ear harvest
is less than RCC for sweet corn (Ks).
Considering the morphological difference and physiological properties
of these two species, appearance of such a result is expectable because
sweet corn, as a C4 crop possesses a relatively high growing
rate and has overcome the second component of intercropping (mung bean)
in utilizing the sources especially the light. More RCC of sweet corn
(Ks which is more than 1) in comparison with that of mung bean,
supports this conclusion.
On the basis of Mazaheri (1993) report, profitability in intercropping
is resulted when the partners are different from each other with respect
to growth form and manner and absorption rate of inputs (light, water
and food), in such a case, interspecies competition will be less than
intraspecific competition and with reduction of competition, profitability
of intercropping is guaranteed. Should after ear harvest, the remainder
of biomass is considered as forage, the superior treatment can be selected
with more accuracy in RCC rates for experiment units. In this experiment,
D1P2 with RCC = 1.98 was the best intercropping,
treatment.
| Table 3: |
Land equivalent ratio for total biomass and forage
yield in intercropping of mungbean and sweet corn |
|
(D 1) 1, (D 2) 2
(D 3) 3; (P 1)*, (P 2)**,
(P 3)***, (P 4*)***, (P 5)*****, 1Relative
Yield of sweet corn; 2Relative Yield of mung bean; 3Land
Equivalent Ratio; 1Low plant density; 2Mean
plant density; 3High plant density; *(100/0), **(75/25);
***(50/50); ****(25/75); *****(0/100); percents for sweet corn/mung
bean, respectively |
Land Equivalent Ratio (LER): The highest LER for total yield before
ear harvest was reached in D2P4 equal to 1.08; followed
by D1P2 with LER = 1.03 (Table 3).
On such a basis, total biomass dry matter yield, resulting from intercropping
in mentioned treatment, has respectively shown 8 and 3% increment in comparison
with sole cropping. Meanwhile, in evaluation of dry biomass yield after
ear harvest, it is seen that D1P2 treatment, leaving
LER equal to 1.09 and 9% yield rise in comparison with sole cropping,
followed by D2P4 with LER = 1.01.
For the purpose of reviewing the forage production in sorghum/cowpea
intercropping. Sharifi et al. (2006) reported the highest LER (1.26)
in 75/25 (sorghum/cowpea) mixing ratio.
Also Daryaei et al. (2006), having intercropped black chick pea
and barley for forage production through dry-farming, recorded the highest
LER as 1.25 in a dense population of intercropped chick pea/barley.
In many of similar researches which have been performed as to intercropping
of corn with such legumes as cowpea (Ennin et al., 2001), bean
(Raja and Reddy, 1990; Francis et al., 1982; Hikam et al.,
1992; Bigonah et al., 1996, cowpea (Barzegari et al., 2004),
soybean (Carrutherset et al., 2000; Danaeifar et al., 2001),
intercropping has always an advantage over sole cropping, in such a manner
that in the mentioned experiments, LER was always more than unit.
According to Mazaheri (1993, 1998), difference in height and growth periods
of two plants are among the main reasons for advantage of intercropping
of such plants in comparison with sole cropping of each of them. In this
regard, ecological niche for the purpose of absorption of sources and
establishment of competition reduction mechanism can be discussed as a
scientific justification for profitability of sweet corn/mung bean intercropping
in comparison with their sole cropping.
CONCLUSION
As the conclusion of different sections of this study and considering
the main objective of the experiment, mixing ratio of 25/75 (mung bean/sweet
corn) is introduced as the superior mixing ratio, because this treatment
produced the highest rate of total sweet corn biomass. It is worth mentioning
that the highest rate of forage sweet corn yield and yield components
of ear was achieved in above mentioned treatment.
Intercropping profitability indices support this claim, because mixing
ratio of 25/75 (mung bean/sweet corn) in low density (D1P2),
leaving the LER = 1.03 and =1.09 for total biomass yield before ear harvest
and total dry forage yield after harvest, have stood at the first place
in comparison with sole cropping. In reviewing the rate of competition
index, it can be stated that with the mentioned mixing ratio in low densities,
sweet corn which had shown the highest LER, left the least competition
index of 0.83 and 0.5, for total biomass and forage yield, respectively.
In order to increasing the green chop forage yield of sweet corn as a
by product in summer cropping in such a warm condition, mung bean/sweet
corn intercropping with 25/75 mixing ratio in severely recommended.
In this case we can produce enough fresh ear yield as vegetable for us
and additional green forage for our livestoks.
