Abstract:To explicit proper nitrogen fertilizer application of machine-transplanted double rice, a two-year (2013-2014) field experiment was conducted to study the effects of amount, ratio and period of nitrogen fertilizer application on the yield and nitrogen use efficiency of machine-transplanted double rice in double-cropping rice areas of the middle reaches of the Yangtze River (Shanggao of Jiangxi). The main results were as follows. Moderate amount of nitrogen fertilizer could increase effective panicle number and grain number per panicle, thereby increased spikelet number. For machine-transplanted double rice, the optimal nitrogen fertilizer application amount was 180 kg/hm2 for the early rice and 195 kg/hm2 for the late rice, which could maintain higher yield and utilization and absorption rate of nitrogen. Under the proper nitrogen application rate, ratio and period of nitrogen application had significant influences on yield and nitrogen utilization and absorption. The optimal ratio of basal tiller fertilizer and panicle fertilizer was 8:2 to 7:3 for the early rice, and 7:3 for the late rice. Appropriate time for top nitrogen application was 7 days after transplanting and the stage of the second leaf to top shooting out. The optimal ratio and time of nitrogen application was beneficial to maintain higher leaf area index (LAI) and dry matter accumulation, coordinated ratio of grain and leaf, sufficient panicle number, larger panicle type and high total spikelet quantity, while maintain high utilization and absorption rate of nitrogen.