Effects of nitrogen sources and application time on yield attributes, yield and grain protein of rain-fed NERICA-3 rice in Gambella, Ethiopia

Abstract A field experiment was carried out under rain-fed conditions at Imla, Gambella Agricultural Research Institute in 2008 and 2009 main cropping seasons in order to compare the effects of N sources [ammonium nitrate (NH4NO3), ammonium sulfate ((NH4)2SO4) and urea (CO(NH2)2)] and their time of application (½ at sowing + ½ at tillering; ⅓ at sowing + ⅓ at tillering + ⅓ at panicle initiation; ½ at sowing + ½ at panicle initiation, and ½ at tillering + ½ at panicle initiation) on growth, yield attributes and yield of rice (Oryza sativa L.) variety NERICA-3 (O. sativa x O. glaberrima), in a factorial experiment laid out in a RCBD replicated thrice. Nitrogen from each source was applied at the rate of 92 kg N ha-1, and the plots received uniform dose of 46 kg P and 20 kg K ha-1 at sowing. The results revealed that effects of year on rice days to flowering, panicle length, number of grains and grain weight panicle-1, grain yield, grain protein content (P ≤ 0.01), plant height, and straw yield (P ≤ 0.05) were only significant. The responses of rice growth and yield components and grain protein to sources of N were not significant (P > 0.05). Plant height, panicle length and grain weight panicle-1 to application time were significant (P ≤ 0.05) while the other growth and yield components and grain protein were not (P > 0.05). Only grain and straw yield significantly (P ≤ 0.01) influenced by interaction of N sources and application time whereas the other yield and growth components and grain protein not (P > 0.05). Effects of sources of N, interactions of year by sources of N, year by application time and year by sources of N by application time were insignificant(P > 0.05) on the rice growth, yield components and grain protein. Significantly increased rice grain yield (6.33 t ha-1) obtained with NH4NO3 applied ½ at sowing + ½ at tillering. The, results were subjected to economic analysis using the partial budget procedure to determine sources of N and application time that would give acceptable returns to farmers. Economic analysis showed that CO(NH2)2 applied ½ at sowing + ½ at panicle initiation and ½ at tillering + ½ at panicle initiation are superior and stable within a price variability range of 15%. Hence, it may be recommended for production of NERICA-3 rice under the climatic conditions prevailing in the study area.