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SUMMARYThe effect on soil fertility and crop performance of different organic fertilizers; paddy straw (PS), farmyard manure (FYM), water hyacinth compost (WHC) and tank silt (TS), at different rates of application and in combination with N fertilizer, was studied in a rice-based cropping system on an acid lateritic soil at Kharagpur, India, during 1985/86. Organic manuring of wet-season rice (first crop) with 5 t PS/ha 10 days before transplanting and 10 t FYM or 10 t WHC/ha at transplanting increased grain yield as much as the application of 30 kg N/ha. Increasing the rates of FYM and WHC application up to 15 t/ha increased yield but increasing the rate of PS beyond 5 t/ha did not. Response to increasing amounts of N was not linear; there was a significant increase up to 90 kg N/ha and a decrease when N was applied in conjunction with organic fertilizers. There was a significant increase in the N uptake of the rice but a decrease in the recovery of applied fertilizer N with the application of increasing rates of organic and N fertilizer.The organic C content of the soil after the rice harvest increased significantly after PS application, whereas there was more available N after WHC and FYM. Increasing the rate of application of PS up to 15 t/ha increased organic C but not available N. Mineral N fertilizer had little effect on fertility build-up. Grain yields of wheat and gram (Cicer arietinum), grown after rice without any additional fertilizer, increased significantly. The residual N effect of the previous crop on wheat or gram yield was small and adding fertilizer directly is considered essential for higher productivity in these crops in a rice-based cropping system.

Peanuts (Arachis hypogaea L.) which are commonly grown in intercropping systems often suffer from shading caused by the associated crop. Through this study an attempt has been made to estimate the effect of different levels of shade at different growth stages on crop yield. Field experiments were laid out during monsoon and winter seasons of 1985 and 1986 by creating artificial shading up to 25 and 50 per cent of the day/natural light at flowering‐pegging, pod filling and maturity stages of a Spanish bunch type peanut. Dry matter production has shown linear response to light intensity and due to 50 per cent shading it was reduced by 55 per cent. Vegetative growth rate during pod filling stage was very poor as a result of increase in shading at this stage. In shaded plants the nodulation was less and some reduction in chlorophyll content was also observed. However, oil content in kernel was not affected by shading. Shading caused significant reduction in pod number and kernel weight and thus there was decrease in pod yield. Flowering to pegging and pod filling stages seemed to be sensitive to shading while increase in shading at maturity stage did not cause any reduction in yield. It could be possible to obtain about 90 per cent pod yield by avoiding shading during flowering to pegging stage (45 DAS).

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