Effect of Different Nitrogen Rates on Nitrogen Absorption and Allocation of Spring Maize in Double Ridges Mulched with Plastic Film

A field experiment was carried out on dryland of loess plateau to study the effect of different nitrogen rates on nitrogen absorption and allocation of spring maize in double ridges mulched with plastic film.Six nitrogen rates are 0,100,200,250,300and 400kg/hm2.The experimental results showed that:(1)The content of nitrogen and the nitrogen accumulation and kernel increased with the improvement of levels on nitrogen application,while the effect is not significant when nitrogen application exceed 250kg/hm2.(2)With the growing stage increasing,the nitrogen content of spring maize decreased while the nitrogen uptake of spring maize increased.(3)The nitrogen translocation amount and the transferred nitrogen contribution ratio of leaf and stem+sheath are higher than that of other organs.(4)With the increase of nitrogen application,the kernel yield increased firstly and then decreased.The kernel yield is the maximum when nitrogen rate is 250kg/hm2 and the kernel yield is 11 932kg/hm2.In addition,the nitrogen harvest index,nitrogenagronomic efficiency of the nitrogen level of 250kg/hm2 are higher than that of the nitrogen level of 300and 400kg/hm2.From the consideration of spring maize yield,nitrogen utilization point of view,250kg/hm2 is a reasonable nitrogen rate.