Effect of Nitrogen Application Timing on Grain Yield,Nitrogen Uptake and Use Efficiency of Hybrid Rice in South China

Four field experiments were conducted in four cropping seasons of two years(2004—2005) at Guangzhou,Guangdong Province,China and the effects of nitrogen application timing on grain yield,nitrogen uptake,and the recovery efficiency(RE),the agronomic efficiency(AE),the internal use efficiency(IE),the partial factor productivity(PFP) of fertilizer-nitrogen were investigated with Yueza 122,a two-line hybrid rice combination,as the material.The results showed that: a) Fertilizer-N applied at the early panicle differentiation(PD) and heading resulted in a grain yield increase in three out of four seasons,while N application as the basal or at tillering resulted in yield increase only in one of the four seasons.b) N application at PD and heading increased significantly the N uptake in all four seasons,while N application as the basal or at tillering did in only one season.For a given amount of fertilizer-N,RE and AE were greater when applied at PD and heading than as the basal or at tillering.c) The optimal N uptake increased with the number of sunshine hours during the grain-filling period.It is concluded that delaying the timing of fertilizer-N application by reducing N rate as the basal and/or at tillering and increasing N input at PD and heading are important to achieve a higher grain yield and N use efficiency for double-cropping hybrid rice in South China.