The effect of nitrogen application rate on carbon and nitrogen metabolism and nitrogen use efficiency of summer maize

Nitrogen fertilizer application rate has strong effects on carbon and nitrogen metabolism, which might influence the yield and recovery of N fertilizer of maize. However, at present, few reports have provided quantitative criteria for evaluating carbon and nitrogen metabolism of different maize cultivars. Therefore, a field experiment was conducted in Wuqiao Experimental Station of China Agricultural University (37°41′02″N，116°37′23″E) in 2006. The objective of this experiment was to establish such quantitative criteria for high yielding cultivars in North China Plain and to obtain high yield and high recovery of N fertilizer simultaneously through regulating carbon and nitrogen metabolism under suitable nitrogen fertilizer application rates. The split plot design was employed with main plot being nitrogen fertilizer rate (N 0, 90, 180 and 270 kg/ha) and sub-plot being cultivar (CF008, Zhengdan 958, and Jinhai 5), and each sup-plot replicated three times. The main results showed that C and N accumulation of stem/sheath and leaf and shoot N accumulation at maturity were higher under nitrogen fertilizer application rate 180 or 270 kg/ha, but C and N translocation rate, N uptake efficiency, N use efficiency, and recovery of N fertilizer were higher under nitrogen fertilizer application rate 90 kg/hm2. Positive correlation coefficient was observed between C translocation rate and grain yield, and between N translocation rate and recovery of N fertilizer, which provided evidence that high grain yield and recovery of N fertilizer could be obtained through increasing C and N translocation rate. Moreover, a series of quantitative criteria was obtained from this experiment suitable for Wuqiao area, which gave suggestions to farmers or scientists to evaluate the growth condition under similar field conditions: for CF008 and Jinhai 5, C/N ratio in stem and sheath were 22.11–22.91 at silking stage and 35.66–54.23 at maturity stage, and C/N ratio in leaf were 4.32–5.11 at silking stage and 9.06–10.57 at maturity stage under nitrogen fertilizer application rate of 90 kg/ha. For these three summer maize cultivars, yield reached 10688–11461 kg/ha, and recovery of N fertilizer of CF008 and Jinhai5 were 31.55%–49.33% under nitrogen fertilizer application rate of 90–180 kg/ha, while recovery of N fertilizer of Zhengdan 958 was 15.11%–19.20%.