Effects of Different Nitrogen Fertilizer Rates on Agronomic Traits and Nitrogen Use Efficiency of Rice in Southern Hunan

By setting four different nitrogen levels for field trials and combining with laboratory analysis,the agronomic traits and nitrogen use efficiency of double-cropping rice under different nitrogen fertilizer rates in southern Hunan were researched.The results showed that increasing nitrogen fertilizer rate for early rice can increase effective panicle number and total grain number per panicle,but filled grain number,seed setting rate,1 000 grains weight had the decreasing tendency;increasing nitrogen fertilizer rate for late rice decreased effective panicle number,seed setting rate and 1 000 grains weight,but increased total grain number per panicle.Increasing nitrogen fertilizer rate can increase yield and net income of early rice,of which the highest yield and economical nitrogen fertilizer rate were 240.7 kg/hm2 and 220.1 kg/hm2 respectively;the yield and net income of late rice decreased with increasing nitrogen fertilizer rate,of which the highest in nitrogen reducing treatment,and the highest yield and economical nitrogen fertilizer rate were 122.3 kg/hm2 and 104.2 kg/hm2 respectively.Increasing nitrogen fertilizer rate also can increase nitrogen absorption and use efficiency of early rice,but had no significant effect on nitrogen absorption and use efficiency of late rice.