RA 00048.pdf - OAR@ICRISAT

grown after maize compared with sorghum
showed very drastic reductions of 4 9 - 8 7 % in 1
year (which the authors consider must have
involved some phytotoxic effect) but only moderate
reductions of 1 0 - 1 5 % in another 2 years
(Fig. 3).
Further work on this subject would seem to be
desirable. In the meantime it should be recognized
that in some cropping systems the net
contribution of the sorghum crop may not be as
high as its own yield indicates because of lower
yields in subsequent crops.
Genotypes for Specific
Cropping Systems
It is often stated that genotypes should be
selected specifically for the systems in which they
are to be grown. While this is no doubt true, it
does not necessarily mean that different systems
have very different genotype requirements. Some
systems may have little in the way of special
requirements beyond the need for an appropriate
maturity period, and this presents no particular
conceptual or technical difficulties. But the notable
exception to this is the intercropping system
where genotype selection must recognize that
genotypes will ultimately be grown in competition
with another crop. For this system much more
consideration needs to be given to the identification
of desirable plant characters and the formulation
of appropriate screening procedures.
Unfortunately, intercropping systems are
almost infinitely variable, and the sorghum
genotype required is likely to vary according to the
nature of the associated crop and the exact way
the crops are combined. This can be illustrated
with reference to two types of intercropping
systems. The first is where the sorghum is grown
as a very high proportion of the system and it is
the dominant crop. This is typified by the sorgum/
pigeonpea combination in which, as seen earlier,
the sorghum is grown at its full sole crop
population and the objective is to produce at least
9 0 - 9 5 % of a sole crop yield. In this system, it is
particularly easy to predict how a given sorghum
genotype will behave since it virtually behaves as
a sole crop. Moreover, because of the dominance
of the sorghum, it is not difficult to predict that
pigeonpea yield will be increased as height and/or
maturity of the sorghum is decreased, and this
has been verified in field studies. Thus this
system represents one of the simpler situations
where the desired plant characters, the sorghum
intercrop performance, and the performance of
1 9 7 7
Mean of 1978 and 1 9 7 9
3
Sorghum
After maize
After sorghum
Sorghum
2
Chickpea
Chickpea
1
Pigeonpea
Pigeonpea
0
-79% -87% -49% -14% -10% - 1 1 %
Depression in yield (%)
Figure 3. Yield of postrainy-season crops after a rainy-season crop of maize or sorghum (ICRISAT data).
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