The effect of method, rate and time of urea application on nitrogen use efficiency and yield of wetland rice in Rwamagana district of Rwanda

Abstract

Rice is the staple food for more than half of the world population and for most low income people especially in Asia. In Africa, over 50 million people depend on rice farming. In Rwanda, the livelihood of nearly half a million individuals is rice-based. Rice is often very responsive to nitrogen fertilization and the high yield potential of modern varieties cannot be realized without adequate nitrogen supply to the plant during the entire growing period. The purpose of this study was to evaluate the effect of mode of application, rates, and timing of urea on rice productivity in Rwamagana marshland, Rwanda. IRRI28 variety was used in the experiment. Two separate experiments were conducted. The first one assessed the effect of fertilizer at different rates and at two modes of application i.e deep and surface placement. The N fertilizer rates were at 4 levels (0, 40, 80 and 120kg N/ha) resulting into a total of 8 treatments. The experiment was factorial and was arranged in a Completely Randomized Design (CRD).The second experiment assessed the effect of time and rates of nitrogen fertilizer applied in splits to the surface only. This second experiment was also arranged in a CRD with 11 treatments. All the treatments were replicated three times. For data analysis, JMP package statistical software was used to analyse data, and for means of separation, Fischer's protected LSD at the 5% significance level was used. Results of Grain yield components and grain rice yields were affected by different application methods but not significantly. Deep placement method appeared to be more effective and superior in rice performance, with grain yield of 5.6t/ha realized when 120kg/ha N was applied compared to 5.3tkg/ha with surface method, a difference of about 6%. Application of N in splits also influenced the rice yield components and grain yield but not significantly in relation to that of deep placement. In terms ofNUE (Nitrogen Use Efficiency), deep placement ofN again exhibited higher values than both surface and split methods which ranged between 7.5 and 13.5 kg grain/kg N applied. Nitrogen content in plant tissues and grain was generally low and less than 2% which is the recommended value in plant tissues. Again, deep placement exhibited higher % N content in plant tissues especially in Panicle Initiation where the content was more than 2 % than surface and split modes of application. In overall, deep method ofN application appeared more promising in rice productivity than surface and split modes of application in this study at Rwamagana, Rwanda.