Effect of Fine Nitrogen Fertilization on Absorbance and Accumulation of Nitrogen in Cotton Drip-irrigated under Mulch

Under the same total nitrogen application,the experiment was conducted to explore the effect of different proportions of nitrogen topdressing strategy on nitrogen uptake and accumulation of cotton aboveground parts and to set a theoretical basis for fine nitrogen fertilization in cotton drip-irrigated under mulch.Five different nitrogen combinations,N1,N2,N3,N4,N5,were designed under the 390 kg·hm-2N application in mulch drip irrigation,and monitored nutrients uptake accumulation of different plant organs during the whole growth period of cotton,and analyzed the synchronous regulation effect between the yield and nutrients uptake accumulation.The results showed that the N4 treatment obviously enhanced single boll mass,and nitrogen accumulation reached 6 782.49 kg·hm-2;At budding stage,the leaf nitrogen content increased with the proportion increase in five nitrogen allocation.At initial bloom stage,when nitrogen treatment transformed from N1 and N2 to N3 and,N4,nitrogen content of cotton stem increased significantly from 2.67% to 3.89%.At full bloom stage,cotton leaf nitrogen content increased significantly from by 4.94% in N1 treatment to 6.81% in N4 treatment.At full boll stage,nitrogen content of cotton seed increased from 4.15% in N1 and N2 to 5.05% N3 and N4,Which increased more than those of leaf,stem,and boll shell;The nitrogen accumulation during the whole growth period in five treatments achieved respectively 199.29,197.18,201.74,218.88 and 192.79 kg·hm-2,which showed a consistent tendency with yield.The largest nitrogen accumulation during the whole period was detected in N4 treatment which had net nitrogen uptake 35.41 kg·hm-2 at initial bloom stage and 13.14 kg·hm-2 at early boll open stage.In conclusion,different proportion strategy nitrogen dressing under the same amount of nitrogen application had a significant impact on cotton yield and nitrogen accumulation.The strategy of Early-Heavy and Late-Light(N4 treatment) can raise nitrongen uptake at initial bloom stage of cotton,which can meet the nutrition need of stem organ,coordinate absorption nitrogen accumulation to reach the highest level during the whole period,and thus formed the high yield.