Effects of Reducing Nitrogen Application on Yield and Nitrogen Utilization Efficiency of Paddy Field in Suburb of Guangzhou

【Objective】The study was conducted to explore the effects of reducing nitrogen （N） application measures on rice yield, N content in water and N application efficiency, and provide technical support and theoretical references for rice N fertilizer reduction in Guangzhou.【Method】Field experiment was carried out to analyze the effect of reduced application of slow-release nitrogen on N content in surface water, rice yield and N fertilizer utilization efficiency in the suburb of Guangzhou. Five treatments, namely, no nitrogen （CK）, conventional split fertilization （CF）, split application of slow-release fertilizer with N reduced by 25% （SFT）, one-off fertilization of slow-release fertilizer with N reduced by 25% （SFB）, and one-off fertilization of slow-release fertilizer with N reduced by 25% + organic substitution （SFB+OS）, were set.【Result】The N content in surface water after transplanting for 3 days under SFB treatment was higher than that under CF treatment, but then decreased quickly and remained at a relatively low level. The N contents in surface water under SFT treatment and SFB + OS treatment were similar with that under CF treatment after transplanting for 7 days, and then were significantly lower than that under CF treatment. The N contents of rice straw and grains under N fertilization treatments were significantly higher than that under CK treatment. Reduced N application had no obvious effect on N contents of rice straw and grains. Compared with CF treatment, different N reduction treatments had no significant effect on yields of rice grains. The agronomic efficiency, partial productivity and physiological utilization rate of N fertilizer under N reduction treatments were significantly higher than those under CF treatment, with the increased rates of 35.16%, 33.58% and 16.84%, respectively, among which the maximum increased rate was obtained under SFB+OS treatment.【Conclusion】SFT and SFB+OS treatments could improve the N utilization efficiency and reduce the risk of nitrogen loss on the premise of ensuring rice yield （especially for SFB+OS treatment）, which were the effective technical measures for rice N fertilizer reduction in the suburb of Guangzhou.