Use of Green Manure Crops in Control of Hirschmanniella mucronata and H. oryzae in Irrigated Rice.

Four field experiments were conducted to study the effect of Sesbania rostrata and Aeschynomene afraspera as rotational and green manure crops on the population dynamics of Hirschmanniella mucronata and H. oryzae, and subsequent rice yields. The sequential cropping of the legumes with rice controlled both nematode species. In two experiments, yield of rice was related to the nematode population denisites at planting and harvesting of the second rice crop (R(2) = 0.391, P < 0.001, and R(2) = 0.57, P < 0.001), regardless of the treatments. Rice yield increases were attributed to nutritional effect of the green manure and the reduction of the nematode populations or the modification of a factor(s) linked to the nematode populations induced by their cropping. As the two leguminous crops do not generate direct return, using them to control the rice-root nematodes was not economical, despite the significant yield increase obtained.