Nitrogen use efficiency of upland rice in the humid tropics of southwest Ethiopia in response to split nitrogen application

Abstract

Background and Objective: Synchronizing timing of N-fertilizer application with rice crop nitrogen (N) demand is an important factor in determining soil N availability, crop N content and uptake capacity and yield of upland rice (Oryza sativa L.). Therefore, this study was designed to determine the effect of variations in N timing and splitting on grain yield, grain N content and N uptake and use efficiency in upland rice varieties on nitisols under rain-fed conditions of Jimma. Materials and Methods: A 2 years field experiment in rain-fed acidic soil was designed to study the effect of timing and splitting of nitrogen on N use efficiency of three improved rice varieties (Gumara, Ediget and NERICA-4) at Jimma, Southwest Ethiopia. A single rate of 64 kg N ha-1 was splitted in different growth stages of the crop in various proportions between sowing, active tillering and panicle initiation. The experiment was designed in randomized complete block with 3 replications. Results: Significant grain yield increases were achieved with split applications of N fertilizer when N was top dressed during active tillering and panicle initiation stages compared to all the remaining N-timing treatments. Nitrogen uptake efficiency was greatest with split application of N when N was top dressed at active tillering stage. Soil N concentration was significantly higher when N was applied at tillering stage compared to other applications. Conclusion: Application of N fertilizer to rice preferably as top dressing between active tillering and panicle initiation is a strategy to be recommended from the standpoint of both the environment and of farmer returns.