Study  on the nitrogen rate threshhold of  maize yield and nitrogen balance in Shihezi, Xinjiang

【Objectives】For reasonable application of nitrogen fertilizer and low risk of pollution from nitrogen fertilizer, accumulation of inorganic nitrogen and nitrogen balance under different N fertilizer application rates were investigated in gray desert soil. Correlation between accumulation of inorganic nitrogen in soils and yield of maize was also evaluated by conducting field experiments in 2011 and 2012, respectively. 【Methods】A field experiment was conduced in grey desert soil from 2011 to 2012. There were six treatments with N application levels of 0, 225, 300, 375, 450 and 600 kg/ha, accordingly, noted as N0, N225, N300, N375, N450 and N600, respectively. The local recommended N application rate was 300 kg/ha, P2O5 75 kg/ha, K2O 37.5 kg/ha. 【Results】The results show that the residual contents of NO-3-N and NH+4-N in soils are enhanced by the N application. The residualNO-3-N is mainly distributed in 0-60 cm soil depth and the residualNH+4-N in 0-20 cm soil depth. The residual nitrogen amounts are increased significantly with the increase of N application rate, and the increments are ranged from 12% to 102% when the N application rates are from 0 kg/ha to 225 kg/ha, and to 600 kg/ha in 2011. There are significantly exponential correlations between the residual nitrogen in soils and N application rates. The N application effect on soil residual nitrogen in 2012 is similar to that in 2011. The accumulation of inorganic nitrogen in the 0-100 cm soil layer is decreased, negative to the N application rate when it is less than 225 kg/ha. The accumulation amounts of inorganic nitrogen under N application rates of 0 and 225 kg/ha treatments are 165% and 170%, respectively, in 2011 and less in 2012, while the soil nitrogen accumlate significantly when N application rate is higher than 300 kg/ha. The accumulation amounts of inorganic nitrogen under N application rates of 375, 450, and 600 kg/ha treatments in 2011 are about 17%, 388%, and 170% higher than those in 2012. The regression equations of nitrogen accumulation with the N application rates are y2011=0.0001x2 + 0.1013x－22.537（R2 = 0.9288）, and y2012 = 0.0003x2 + 0.1417x - 52.78（R2 = 0.9583）, respectively. Both the loss of nitrogen and surplus are significantly increased with the increase of the N application rate. The accumulation amounts of inorganic nitrogen are balanced under the N application rates of 187 kg/ha in 2011 and of 245 kg/ha in 2012. The correlations between the yields of maize and the N application rate are parabolic or linear plus platform growth. There are no significant differences among the yield changes and the highest yields when the N application rate is higher than 300 kg/ha. The yield of maize is significantly lower than the highest yield when the net soil inorganic nitrogen accumulation equals zero can be expressed by. The nitrogen use efficiency is significantly reduced by an exponential relationship with the N application rate. There is an intersection point between the yield and the nitrogen use efficiency appeares at the N rate of 270 kg/ha, and that between residues of inorganic nitrogen and nitrogen utilization at the application rate of 340 kg/ha . 【Conclusions】It is an optimized method that using the production effect, environment effect and fertilizer effect to determine the nitrogen input threshold, and the reasonable nitrogen application rate can increase the yield of maize, reduce the risk of nitrogen non-point source pollution and improve the nitrogen use efficiency. Therefore, using three curves method, the N application rate of 270-340 kg/ha is the optimum nitrogen input threshold in maintaining maize high production.