Evaluation of ammonia volatilization from compacted urea-micronutrient fertilizers applied in rice (Oryza sativa L.) grown on a typic haplustept

Low efficiency of broadcast urea to flooded rice is mainly attributed to NH₃ volatilization. Slow N release and soil acidification can reportedly reduce NH₃-N losses. Pot experiments were conducted to test the efficacy of compacted urea-micronutrient fertilizers in flooded rice grown in a slightly alkaline sandy loam soil. In a controlled study in the laboratory, pH, urea hydrolysis and NH₃ volatilization were measured. The compacted urea + FeSO₄, urea + MnSO₄, urea + ZnSO₄ and urea + CuSO₄ showed 19.8, 10.1, 18.7 and 22.2% less NH₃-N loss, respectively over separate applications. This was reflected in enhanced grain yield of rice by 19.0, 13.2, 16.7 and 15.6% in compacted Urea + FeSO₄, urea + MnSO₄, urea + ZnSO₄ and urea + CuSO₄, respectively, over separate applications. Copper sulphate was most effective in reducing soil pH, regulating urea hydrolysis, decreasing NH₃ loss and improving apparent N recovery and grain yield of rice. The compacted urea + CuSO₄ may be promising fertilizers where farmers use CuSO₄ as algicide and algistat in lowland rice.