RA 00015.pdf - OAR@ICRISAT

during the rainy season-which were based on
growth-stage sensitivity to drought stress and on
rainfall probabilities-were not applied because
the rainfall was adequate in quantity and distribution.
This is the second time in succession that
this situation has occurred. It appears necessary
to explore the possibility of conducting
supplemental-irrigation research on a multilocation
basis during the rainy season. Through
employment of cooperative programs, one can
cover a wider range of rainfall conditions and
obtain the necessary data more rapidly.
C r opping Systems
Intercropping has again received major attention
this season. Another major effort involved moredetailed
investigations in areas of particular
promise, notably plant population and genotype
evaluation. In the intercropping work, the aims
are to identify the various aspects of population
and spacing, and to assess their independent
effects as well as their interrelationships. In the
work with genotypes, the aims are to identify
desirable genotype characteristics and to examine
the problems of evaluating relatively large
numbers of genotypes.
Intercropping performance is assessed by a
"Land Equivalent Ratio" (LER) which is the
relative area of sole crops required to produce the
yield or yields obtained in intercropping. This
permits direct comparison of crops with different
yield levels and it can be used either for an
individual crop or for the total of all crops. In the
latter case, a total greater than unity indicates a
yield advantage for intercropping, e.g. a LER of
1.2 indicates a yield advantage of 20 percent.
There has also been a further examination of
the possibility of growing two successive crops
on deep Vertisols where traditionally only a
single postrainy season crop is grown. Again,
both "sequential" sowing (seeding following
harvest of the first crop), and "relay" sowing
(seeding shortly before harvest of the first crop)
have been examined.
The influence of legume/cereal intercropping
on the development of pest populations has been
examined with particular emphasis on the important
pest, Heliothis armigera (Hubner). Information
on the pest/parasite relationship in intercrops
has also been obtained.
Plant Population and Spatial
Arrangement in Intercropping
In maize/pigeonpea intercropping, response to
total plant population (i.e., both crops combined)
at various row-arrangement patterns was
examined. It was found that to achieve maximum
advantage from intercropping, the total
population had to be higher than that for either
sole crop alone. For either sole crop, the optimum
population was six plants per square
meter. At this level in intercropping, the yield
advantage was 30 percent (Table 52). Although
this is quite a substantial advantage, it was
increased to 45 percent at a total population of
nine plants/m 2 . The data indicate that this might
be further increased at even higher populations
and this will be investigated further next season.
A particularly interesting aspect of this experiment
was the effect of maize competition on the
efficiency of the pigeonpea plant (Table 53). The
absence of substantial reproductive growth of
the pigeonpea until after maize harvest is considered
to be due to maize competition. After
maize harvest there was considerable compensation
in reproductive growth, especially in number
of pods per plant. Thus compared to the sole
crop, the harvest index (HI) of the pigeonpea was
substantially increased by intercropping. In the
treatment with the highest proportion of maize
the HI value was increased from 17.2 to 30.4
percent.
In the postrainy season, a new intercropping
design permitted examination of population
changes in either crop. Four chickpea populations
were established in main plots and the
population of a safflower intercrop was systematically
changed within these. A 10-percent
change between each safflower population gave a
fourfold change in 15 steps. These population
effects were distinguished from spatial arrangement
effects by examining all population treatments
at each of two row arrangements.
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