On-farm assessment of Sesbania green manure in a rainfed rice system in northeast Thailand

Rainfed rice yields on middle-to-upper paddy terraces in "mini-watershed" landscapes of Northeast Thailand are low, limited by poor soil fertility and erratic rainfall distribution. Farmers do not apply mineral fertilizers to these paddies because of the high risk on returns associated with uncertain soil water conditions.;On-farm field experiments were conducted during two cropping seasons (1990 and 1991) at Hin Lad village in Khon Kaen Thailand to determine: (1) growth potential of Sesbania rostrata on a series of middle-to-upper paddy fields, under rainfed soil and water conditions, with existing soil fertility (1990) and with phosphorus fertilization at 45 kg-P ha;Soil moisture on middle-to-upper paddies was sufficient for establishment and growth of the green manure crop in both years.;In 1990, Sesbania biomass production was low, averaging 320 kg ha;In 1991, phosphorus fertilization increased Sesbania biomass production over four-fold, to 5600 kg ha;Seed production is possible on middle paddy fields with minimal labor and material inputs, but involves reduction of the rice cropping area by 8% and considerable labor inputs.;Low input management strategies which lead to production of moderate quantities of S. rostrata green manure biomass can increase rice yields with reasonable labor inputs that are acceptable to farmers engaged in traditional rainfed rice cropping systems on mid-to-upper paddy terraces in Northeast Thailand.