Growth and Yield of Rice (Oryza sativa L.) as Affected by Time and Ratio of Nitrogen Application at Jimma, South-West Ethiopia

Abstract

– Insufficient nitrogen supply in inappropriate timing is an important constraint to productivity of upland rice (Oryza sativa L.), and there is limited information available on optimal timing of N application for upland rice in Ethiopia including Jimma area. Field experiment was conducted on three upland rice varieties (Gumara, Ediget and Nerica-4) in a completely randomized block design with 3 replications to determine the effects of timing and ratio of nitrogen application on growth and yield during the 2014 cropping season on acidic nitisol (soils possessing nitic property) at the Jimma University, College of Agriculture and Veterinary Medicine research site. The N-timing treatments were: N1 (50% at sowing and 50% at active tillering stage), N2 (25% at sowing + 50% at active tillering stage and 25% at panicle initiation), N3 (25% at sowing + 25% at active tillering stage and 50% at panicle initiation), and N4 (33% at sowing + 33% at active tillering stage and 33% at panicle initiation). The highest grain yields (1070 kg/ha), biomass yields (3333 kg/ha), total number of grains per panicle, and harvest index were recorded from ‘Ediget’ variety at the N2 combination (25% at sowing + 50% at active tillering stage and the remaining 25% at panicle initiation), followed by N3 and N4 combinations. The lowest grain yields (117 kg/ha) and biomass yields (767 kg/ha) were recorded from Nerica-4 variety at the N2 combination. Nerica-4 variety produced minimum grain and biomass yields across all the N combinations. Most of the parameters exhibited maximum performance under N2 and N3 combinations across all the varieties. The varietal treatments had highly significant (P<0.001) effects on the total number of panicles, grain yield, biomass yield and harvest index. Grain yield was positively correlated (P<0.01) with plant heights (r=0.68**), number of filled grains per panicle (r=0.52**) and thousand grains weight (r=0.61**) and negatively correlated with most of the traits. Number of panicles was the most important component of yield, accounting for about 87% of the variation in rice yield. Thus, rice cultivation and its nitrogen fertilizer management in the area is concerned, the variety ‘Ediget’ was recommended for higher grain and biomass yields regardless of the N-timing treatments. Concerning the N-timing treatments, the fa