Abstract

In Ethiopia, rice (Oryza sativa L.) grain yield is low party due to low nitrogen fertility status of the soil. An experiment was conducted from August to November, during main rainy season of 2010, in Gambella, Ethiopia, to determine grain yield and yield components and N efficiency responses of rice to five N rates (0, 3.5, 7, 10.5, 14 g m-2) in factorial combinations with three sowing methods (drilling, dibbling and broadcast) in a randomized complete block design with three replications using commonly grown rice variety, nerica-4. Grain yield increased from 302-469 g m-2, total biomass 786-1268 g m-2, tillers 477-661 m-2, panicles 456-612 m-2 and filled grains/panicle 80-100 when N rate increased from 0-14 g m-2. Maximum values for panicles (621 m-2) and filled grains/panicle (110) and that for grain yield (510 g m-2) were obtained at 7 and 10.5 g m-2 N rate, respectively. With the increase in N rate from 0-14 g m-2, grain N concentration increased from 1.44-1.53%, straw N concentration 0.79-0.93%, total grain N 4.36-7.18 g m-2, total straw N 3.82-7.45 g m-2 and total plant N 8.18-14.63 g m-2. Maximum values for grain N concentration (1.58%) and total grain N (8.04 g m-2) and total plant N (14.81 g m-2) were obtained at 10.5 g m-2 N rate. Agronomic efficiency decreased from 29 -12, apparent recovery 0.76-0.46 and physiological efficiency 38-26 when N rate increased from 3.5-14 g m-2. The present experiment suggests that soil nitrogen content should be considered in N fertilization recommendations.