EFFECTS OF WINGED BEAN ON A FOLLOWING MAIZE CROP

The effects of winged bean (Psophocarpus tetragonolobus) on a following crop of maize were assessed in two agroecological zones of Sri Lanka. Maize was grown after maize with variable rates of nitrogen fertilizer (0-150 kg N ha-1) or after winged bean or soyabean (Glycine max). Where it could be extrapolated from the nitrogen response curve, the apparent nitrogen contribution by winged bean was 70 kg N ha-1. However, in some cases maize after winged bean yielded more than the maximum yield predicted by the Mitscherlich N-response curve, suggesting the effect of some yield-enhancing mechanism in addition to nitrogen contribution. Where no fertilizer nitrogen was used, maize yields on land which had previously grown winged bean were 52-91% higher than those where maize was the previous crop. Winged bean proved to be an effective green manure crop even when all above-ground plant parts were harvested for food and fodder.