Yields and Nitrogen Use Efficiencies of Rice (Oryza sativa) at Different Sites Using Different Nitrogen Fertilizer Application Rates and Controlled-release Urea to Conventional Urea Ratios.

Rice yields and nitrogen use efficiencies were studied at five sites in southwest China using two nitrogen fertilization rates and five controlled-release urea (CRU) to ordinary urea (U) ratios. The fertilizer treatments significantly increased rice yields compared with the control (no nitrogen added) yields to different degrees at different sites. Applying CRU and U increased the rice yield more than adding the same amount of nitrogen as U only. Higher increasing production rate were found using a nitrogen application rate of 105 kg/hm² than 150 kg/hm². A 70:30 CRU:U ratio increased the yield more than other four ratios. Nitrogen use efficiency was 21.9% higher using a nitrogen application rate of 105 kg/hm² than 150 kg/hm², and 46.6%, 38.1%, 34.7%, and 22.2% higher than when only U was applied when CRU: U ratios of 70:30, 50:50, 100:0, and 30:70, respectively, were used. A 70: 30 CRU : U ratio gave the highest economic output (yuan/hm"). Applying both CRU and U gave an output 3078.87 yuan/hm² higher at a nitrogen application rate of 150 kg/hm² than at a nitrogen application rate of 105 kg/hm². Economic output was always higher using both CRU and U than using U only. The highest economic output was given using a 70:30 CRU:U ratio. Increasing the amount of nitrogen added decreased the output efficiency (per hm²) because CRU is expensive. Significant relationships were found between the yield increase rate and the proportion of CRU added (regression equation y = 7.429a; -185.7, R² = 0.663) and between the total rainfall over the whole growth period and the proportion of CRU added (y = --0.087 lx + 112.29, R³ = 0.6879). These regression equations can be used to determine the appropriate proportion of CRU that should be added at a site, depending on the rainfall and target rice yield. [ABSTRACT FROM AUTHOR]