Response of Grain Yield of Different Japonica Rice Cultivars to Amount of Nitrogen Application in High-Fertility Paddy Field

Nitrogen is the most important nutrition in rice production,and its function is affected by cultivar,fertilizer application and soil condition. In resent years,paddy field in Yangzi River has a trend of becoming fertile. In order to identify the optimal nitrogen application amount in high-fertility paddy field and to study the cultivar difference in nitrogen requirement,we planted 13 japonica rice cultivars with 5 nitrogen application levels in a high-fertility paddy field in China National Rice Research Insti-tute,Zhejiang province. The results were as follows:(1) Rice yield was significantly increased by nitrogen,most japonica rice cultivars reached their highest yield when nitrogen was applied at 150–225 kg ha-1. With the increase of nitrogen application amount,1 000-grain weight and seed setting rate decreased,while grains per panicle and effective panicle number increased till nitrogen application amount reached 225 kg ha-1.(2) There existed cultivar difference in optimal nitrogen application amount. According to the cultivar yield characteristics in none-nitrogen application treatment,low-yielding japonica rice cultivars were sensitive to N fertilizer,their yield increased largely even when small amount N fertilizer was applied,while the yield of high-yielding cultivars changed little when applied N fertilizer 75 kg ha-1;the optimal nitrogen application amount of cultivars with middle panicle number was larger than that with low( 220×104 per hectare) and high( 220×104 per hectare) panicle num-ber.(3) Most of the cultivars released before 1980 had the highest yield when 225 kg ha-1 nitrogen was applied,while the nitrogen needed for the highest yield in cultivars released after 1980 was different.