Effects of different nitrogen application rates on grain yields and nitrogen uptake and utilization by different rice cultivars

It is of great importance to identify the effects of nitrogen(N) fertilizer on grain yield and N utilization in rice production in terms of N economy and N ecology.Field experiments were conducted to analyze the various traits of yield components and N uptake and utilization by different rice cultivars under N application rates of 0,60,120,180,240,300,360 kg/ha.Two cultivars,ELIO and 4007,with similar agronomic traits were cultivated in the southeast in China in 2003 and 2004.Grain yields of 4007,well responding to N application,were significantly higher than those of ELIO at all N application rates.Yield components were significantly affected by N treatments,among which panicles per square meter had highest correlations with grain yields(0.839** and 0.933** for ELIO and 4007,respectively),suggesting the importance of number of panicles for obtaining high yields.Maximum grain yields were obtained at about 332 and 561 panicles per square meter for ELIO and 4007,respectively.N uptake by these two cultivars was generally increased with increasing of N application rates,but N utilization efficiency for grain yield(NUE) decreased with increasing N application rates.NUE of 4007 was significantly higher than that of ELIO at all N application rates,mainly resulting from its higher NHI potential.NUE was negatively correlated with stem and leaf N concentration at maturity,suggesting that the effective nitrogen translocation from the vegetative tissues to the grains during the post-anthesis period was one of main causes resulting in a higher NUE. In addition,4007 generally had higher partitioning parameters,such as agronomic N use efficiency,apparent recovery of applied N and partial factor productivity for applied N,than ELIO at all N application rates.Therefore,it was suggested that 4007 had advantages over ELIO under both N limited and sufficient conditions.It is feasible to optimize productivity and reduce the pollution risk for the environment in rice production systems through cultivating excellent rice cultivars.