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ILC 1929 at Tel Hadya and ILC 482 at Kafrantoon and Jinderis subsitcs of
ICARDA during the 1979-80 cropping season. At Jinderis, which represents
typical chickpea- growing area in northern Syria, a spring planting variable was
also introduced in the study. The total seasonal rainfall and potential evapotranspiration
at these three locations as well as the grain yield response to various
levels of plant population are given in Fig. 4. It is evident that the yield of winterplanted
chickpea increased conspicuously at all locations when plant population
was raised from 16.6 plants/m2 to up to 33.3 plants/m2. Increasing the population
beyond this level resulted in significant reduction in the yield at Jinderis,
whereas at Tel Hadya the yield showed an increasing trend up to 50 plants/m2.
Even the spring crop at Jinderis responded positively to increased population up
to 33.3 plants/m2; the magnitude of increase was, however, not as high as in the
case of winter-planted crop. From these data, it is evident that a population level
of about 33.3 plants/m2 appears to be optimum for a situation having a seasonal
precipitation around 400 mm.
In order to test the interaction between plant population responsc and moisture
supply in greater detail, these studies are being carried out again at four
ICARDA subsites during the 1980-8 1 cropping season. The data collected on the
percent interception of the photosyntheti,:ally active radiation (PAR) by the
canopy of ILC 482 chickpea at Tel Hadya at the advanced podding stage as
affected by plant population and planting season are shown in Fig. 5. The
seasonal precipitation has been a;ound 350 am. Under this condition, the increase
in plant population from 16.6 to 50 plants/m2 has shown almost a linear
increase in PAR interception in winter- planted crop as against an asymptotic
trend beyond 25 plants/m2 in case of spring- planted crop. The latter might be
attributed to increased inter-plant competition for limited available moisture
supply at levels higher than 25 plants/m2. The differences in the interception of
PAR by the winter- and spring-planted crop should reflect in the overall phytomass
and economic yield.
Response to Nutrient Application
Since the yield levels of a winter-planted crop are much higher than those of the
spring- planted crop, it is logical to expect that the mineral nutrient requirement
of the former would also be considerably higher than that of the latter. Whereas
on a soil of high native fertility this additional requirement of the nutrient may
easily be met, on the soils with poor fertility status the limitation of the mineral
nutrients might prove a significant constraint to the realization of the yield
potential of a winter- planted crop.
An important dimension to the mineral nutrition of the crop is the fact that the
crop is capable of meeting a major part of its nitrogen requirement by symbiotic