The use of Sesbania (Sesbania rostrata) and urea in lowland rice production in Sierra Leone

The suitability of sesbania (Sesbania rostrata) as green manure for lowland rice was evaluated in the Inland Valley Swamp (IVS) of Sierra Leone, and a ttempts were made to identify appropriate methods of its management in comb ination with urea. Sesbania - rice intercropping and sesbania - rice rotati on treatments were compared with 60 kg N ha(-1) applied in two splits and 3 0 kg N ha(-1) as basal or top dressed to rice grown in the two cropping sys tems. The N-15 isotope dilution technique was used to quantify N uptake fro m the green manure and urea and its utilization by rice. Rotating 40-50 day s old sesbania two days prior to transplanting and top dressing with 30 kg N ha(-1) as urea at nine weeks after transplanting gave highest rice grain yield (121% over the control without sesbania and urea). However intercropp ing sesbania with rice tended to increase N uptake and N fertilizer utiliza tion more than the rotation treatments. The higher grain yield of rice in r otation despite lower N uptake than intercropping shows that other effects than only N explain the beneficial effect of sesbania on rice.