Responses of roots distribution and nitrogen content of summer maize to nitrogen fertilization types and amounts

A fertilization experiment on different types and rates of N fertilizers was conducted in successive two years, the distribution of roots and N content of summer maize (Zea mays L., cultivar: Zhengdan958) were investigated and their correlations to yield and shoot N accumulation were analyzed. The main results show that：1）growth and downward extending of roots before the 9-leaf stage of summer maize are restrained by N application, and the restraining effect indicates a trend of compound fertilizer＞coated urea＞urea. Amounts of roots are increased in 0–25 cm and 50–80 cm soil layers, while decreased in 25–50 cm soil layer by N application at the silking stage. Total amount of roots indicates a trend of urea＞compound fertilizer＞coated urea, and significant differences among three types of N fertilizers are observed. 2）N contents in roots are improved significantly by N fertilization in 0–25 cm soil layer at the 9-leaf stage and 25–80 cm soil layer at silking stage. N content of roots is affected by type of N fertilizer, and significant differences among N fertilizers are observed. 3）Positive correlation at 0.05 and 0.01 probability level exist between yield, N accumulation amount of shoot and N content of roots in 25–80 cm soil layer at the silking stage, respectively. Correlations of roots density of fresh weight, volume and dry weight to yield and N accumulation amount of shoot are negative in 25–50 cm soil layer respectively, while they are positive in other soil layers, there into positive correlation at 0.05 probability level between yield and roots density of dry weight in 0–80 cm soil layer, and positive correlation at 0.10 probability level between yield and roots density of fresh weigh in 0–25 cm soil layer, and between N accumulation amount of shoot and roots density of fresh weigh in 0–80 cm soil layer are observed. These results show that root distribution and N content of summer maize are obviously affected by types and rates of N fertilization. The effects of N application on increasing of yield and N efficiency of summer maize are achieved mainly by improving fresh weight of roots in topsoil, total fresh weight and dry weight of roots and N content of roots in middle and lower soil layers.