Effects of controlled-release urea on nitrogen uptake characteristics and yield of double-cropping rice around Dongting Lake area

Abstract

<p indent=0mm>The application of slow- and controlled-release fertilizer in rice production plays an important role in promoting the zero growth of fertilizer use and the sustainable development of agriculture in China. In this study, six consecutive years from 2013 to 2018 of controlled-release urea application in double-cropping rice in Hunan province were used to analyze the relationship between N uptake rate and N utilization in the above part of early- and late- rice in the main growth period by controlled-release urea application around the Dongting Lake district, and to explore the reasons for the sustained and stable yield increase of controlled-release urea on rice. The results showed that there was an obvious peak of N uptake rate in each stage of early rice by different N treatments, while N uptake in controlled-release urea (CRU) treatment was relatively delayed. And N accumulation was mainly from panicle initiation stage to heading stage, accounting for 35.31%–42.33%, followed by tillering stage to young panicle differentiation stage and heading stage to milk stage. Two obvious peaks of N uptake rates occurred in late rice from tillering stage to panicle initiation stage and from heading stage to milk stage, and the peak value was the highest at 1.0 CRU treatment. Large amount of N uptake from tillering stage to young panicle differentiation stage and heading stage to milk stage accounted for 35.92%–40.52% and 23.05%–24.58% of total amount of the whole growing period, respectively. Controlled-release urea could also significantly increase the yield of double-cropping rice, especially in early- and late- rice were treated with 0.9 CRU and 0.8 CRU respectively, and the yield increase of late rice was better than that of early rice with reduced application of controlled-release urea, and the N absorption efficiency, N agronomic efficiency and N partial productivity of early- and late- rice were significantly improved. The yield of early- and late-rice treated by CRU was significantly positively correlated with N accumulation and effective panicle number at panicle initiation stage, heading stage, milk stage and waxen stage, and the yield of late rice was significantly positively correlated with panicle length. The N accumulation of early and late rice at the panicle initiation stage was significantly negatively correlated with the agronomic and physiological rates of N fertilizer. The N partial productivity was significantly or significantly negatively correlated with the N accumulation of early rice at the panicle initiation stage, heading stage, milk stage and waxen stage, and significantly negatively correlated with the N accumulation at the heading stage of late rice. Therefore, application of controlled-release urea delayed the N uptake rate and N accumulation in the aboveground part of rice, which was beneficial to the later reproductive growth and seed setting, and could significantly improve the yield and nitrogen utilization efficiency of double-cropping rice. Combined with N absorption characteristics and grain yield of double-cropping rice, it was suggested that controlled release urea with a short release period should be used for early rice around the Dongting Lake area or applied with quick-availability N fertilizer to achieve further increase in yield level.