The present study was conducted in 2009/10 to investigate the effect of N and S fertilization on yield, N uptake, N use efficiency, and grain protein content of the upland NERICA-4 rice variety. The layout of the experiments was randomized complete block designs with three replications, where in 2009 crop season, the effect of five N rates (N0 = 0, N1 = 36, N2 = 59, N3= 82 and N4 = 105 kg N ha-1) without S and in 2010 crop season, a factorial combination of the same N rates with three S rates (S0 = 0, S1 = 20 and S2 = 40 kg S ha-1) were used in 2.1 × 3 m2 plots to determine the response of the crop to N and S on irrigated Fluvisols. The application of N alone and in combination with S significantly affected (P < 0.05) the yield, yield components, N uptake, nitrogen use efficiency, and grain protein content of the rice crop. Nitrogen application alone increased the grain and total dry matter yield, average for both years by 0.7 and 2.5 Mg ha-1, compared to the controls (N0). The application of the same N rates, combined with S further improved the grain and total DM yield on average by 0.5 and 1.3 Mg ha-1, compared to those N rates without S. The leaf and grain N concentration, total DM and grain N-yield, and the grain protein content increased with N applications, but they were significantly enhanced when N was fertilized with S. Only the apparent N recovery was significant to N applications, but all the N use efficiency components were significantly affected when N was applied with S. Thus, this work showed the yield response of the crop could be improved with N and S fertilization with rice producing farmers benefiting from the application of S-containing N fertilizers to soils deficient in these nutrients.
Key words: Alluvial soils, semiarid, upland rice, N and S interactions, Nitrogen use efficiency.
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