Genotypic variation in nitrogen use efficiency in summer maize

A field experiment was conducted to study the genotypic variation in nitrogen use efficiency in summer maize by quantify analyzing grain yield and biological yield,harvest index,nitrogen efficiency and responsiveness to nitrogen fertilizer.The results showed that there are significant genotypic variation in grain yield and biological yield among different summer maize varieties whatever nitrogen application rate.So did the harvest index,nitrogen efficiency and nitrogen responsiveness.The tested maize varieties could be classified into four different types based on their nitrogen efficiency and nitrogen responsiveness.Hudan 4,Shanzi 1 and Yedan 19 belonged to H-H type(high N use efficiency with high N responsiveness);Zhongdan 2,Yuyu 22 belonged to L-L type(low N use efficiency with low N responsiveness);Shandan16,Shandan 902 and Hudan 2000 belonged to H-L type(high N use efficiency with low N responsiveness),and Shandan 9 and Nongda108 belonged to L-H type(low N use efficiency and high N responsiveness).Comprehensive considering nitrogen efficiency and responsiveness,three representative genotypes(Hudan4,Yuyu 22 and Hudan 2000) were selected to determine their nitrogen accumulation,and compute their nitrogen utilization efficiency and nitrogen index.The results showed that the nitrogen accumulation couldn't reflect the nitrogen use efficiency in summer maize accurately.The contribution to nitrogen use efficiency was given by nitrogen utilization efficiency rely on nitrogen rate,and the nitrogen index can well reflected the nitrogen use efficiency whatever nitrogen application rate.