Effects of nitrogen application on yield and C/N of double-cropping rice

The experiment was conducted to study effects of different ratios of basic and tillering, and panicle nitrogen fertilization on yield, dry matter accumulation, nitrogen accumulation and the ratio of carbon and nitrogen of doublecropping rice. The results show that when the total nitrogen rate is N 225 kg/ha, the yield is the highest under the treatment which the ratio of basic and tillering nitrogen amount to panicle nitrogen amount is about 7∶3, the followings are the treatments of ratios of 6∶4 and 8∶2, which are all higher than that of the conventional nitrogen application pattern (10∶0). When the ratio of basic and tillering nitrogen application to total nitrogen application amount is from 60% to 70% of doublecropping rice, the dry matter accumulation, nitrogen accumulation, nitrogen utilization efficiency, N-agronomy efficiency are all increased under the ratio of 7∶3, the carbon metabolism and nitrogen metabolism are also in a good coordination. The usable carbohydrate including soluble sugars and starch of early rice leaf at booting stage is 17%-18%, C/N is 50-55, and the usable carbohydrate of late rice is 19%-21% and C/N is 50-60These would be the physiological base of getting higher rice yield when the ratios are 7∶3 and 6∶4In all, synthesizing the yield, nitrogen utilization efficiency and C/N of doublecropping rice, the ratio of nitrogen application at the panicle stage of rice to total nitrogen application amount is from 30% to 40%.