Abstract:
Grain legumes are used widely in intercropping systems. However,
quantitative and comparative data available on their Nj fixation and N beneficial
effect on the companion crop in intercropping systems are scarce. Hence, studies
were conducted to ascertain the above when cowpea (Vigna unguiculata (L.)
Walp), mungbean (Vigna radiata L.) and groundnut (Arachis hypogaea L.) were
intercropped with maize (Zea mays L.). Attempts were also made to investigate
the effect of K on the competitive ability of grain legumes in legume+cereal
intercropping systems.
The first experiment was aimed at ascertaining the effects of K application
on the growth and N-fixation of groundnut ( cv. No.45), when intercropped with
maize (cv. Badra). The study was conducted in basins (30 liters), at three K
levels viz. 0, 20 and 40 mg K/kg of soil. The soil used was tagged by
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incorporating N-labelled plant material. When grown as a monocrop, K had no
effect on the per cent N derived from atmosphere, amount of N., fixed, dry matter
production, pod yield and total N content of groundnut. However, when
intercropped with maize, lack of K application affected the above parameters
significantly which was overcome by improving K level. Thus, the optimum level
of K for groundnut was greater when intercropped than monocropped. There
were evidence for possible interactions between K level and cropping system,
with regard to Ng fixation, pod yield and total dry matter production of
groundnut. Intercrop maize derived 30-35% of its N content from the associated
groundnut plants which amounted to 13-22 mg N/plant. The amount of N supplied
by groundnut to associated maize plant was not affected by K level. It appears
that there is a scope for alleviating growth depression of legume component in legume-cereal intercropping systems by developing appropriate K fertilizer
practices.
H
The second experiment was 'N-aided and done outdoors in basins at two
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locations. N labelling was done either by incorporating N-tagged plant material
or by applying ^N-labelled fertilizer along with sucrose. Intercropped
groundnut fixed the highest amount of nitrogen from the atmosphere (i.e. 552 mg
plant *), deriving 85% of its N from the atmosphere. Intercropped cowpea and
mungbean fixed 161 and 197 mg N plant \ obtaining 81% and 78% of their N
content from the atmosphere, respectively. The proportion of N derived by maize
from the associated legume varied from 1-11% for mungbean, 11-20% for cowpea
and 12-26% for groundnut which amounted to about 19-22, 29-45 and 33-60 mg
N maize plant \ respectively. The high nitrogen fixation potential of groundnut
in duel stand and its relatively low harvest index for N have apparently
contributed to greater N-beneficial effects on the associated crop.
The third experiment, which was planned for monitoring the time course of
nitrogen fixation/nitrogen transfer in groundnut and cowpea in maize based
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intercropping systems, in two potassium regimes. This ”N-aided study was carried
out in the dry zone, in similar type of basins used previously. Estimates were
made on 30, 60 and 76 DAP (Days After Planting) for both legume and non-legume
components. Groundnut fixed more nitrogen than cowpea at all three samplings.
K application had no significant effect on the amount of nitrogen fixed by
legumes at final harvest. Intercropping has resulted in a significant increase in
dry matter yield, nitrogen yield and amount of nitrogen fixed by both legumes.
A tendency to increase the nitrogen transfer from legume to companion crop was
evident from 60 - 76 DAP. At the final harvest, groundnut fixed higher amount of nitrogen (677rag plant *), however, less amount was transferred to maize
(33mg plant * or 5% of groundnut nitrogen ) compared to cowpea which fixed less
amount of N (348mg plant and transferred more (48mg plant * or 16% or 19% of
cowpea nitrogen) at K^q. Intercropping significantly increased the nitrogen yield
of maize except for maize in raaize+cowpea mixture at *40. The peak nitrogen
fixation was observed to be around 60 DAP for both legumes.