新疆石河子地区玉米产量及氮素平衡的施氮量阈值研究

【目的】合理施用氮肥不仅会提高肥料利用率，还会降低氮素面源污染的风险。通过2年田间肥料定位试验，研究北疆灰漠土区不同氮肥用量下，土壤无机氮积累量、 氮素平衡和玉米产量间的相互关系，为氮肥合理施用提供依据。【方法】研究采用肥料田间定位试验，小区试验于2011-2012年开展，设计6个氮肥（N）用量水平: 0、 225、 300、 375、 450、 600 kg/hm2，分别以N0、 N225、 N300、 N375、 N450、 N600表示，其中300 kg/hm2为当地玉米农田氮肥推荐用量，磷肥（P2O5）施用量为75 kg/hm2，钾肥（K2O）施用量为37.5 kg/hm2。【结果】 1）施用氮肥增加了土壤硝态氮和铵态氮残留量，硝态氮主要残留于060 cm土层，铵态氮主要分布在020 cm土层深度。2011年试验中，土壤无机氮残留量随氮肥用量增加而显著增加，与对照相比，施氮处理无机氮残留量增幅为12%~102%，与施氮量呈指数增长关系。2012年氮肥用量对土壤无机氮残留量的影响与2011年相似。2）施氮量 225 kg/hm2时，0100 cm土层深度土壤无机氮积累量降低，表现为负积累效应，N0和N225处理下2012年土壤无机氮积累量分别较2011年降低165%和170%； 施氮量高于 300 kg/hm2时，土壤无机氮积累量显著增加，表现为富集现象，其中，N375、 N450和N600处理下2012年土壤无机氮积累量分别较2011年增加17%、 388%、 170%。土壤无机氮积累量与施氮量显著呈二次抛物线关系，2011年回归方程为y=0.0001x2 + 0.1013x－22.537（R2 = 0.9288），无机氮无积累时施氮量为187 kg/hm2； 2012年为 y = 0.0003x2 + 0.1417x - 52.78（R2 = 0.9583），无机氮无积累时施氮量为245 kg/hm2。土壤氮素表观损失量和氮素盈余量的增加幅度随氮肥用量增加而显著加大。3）氮肥投入可提高玉米产量，产量与施氮量呈显著的二次抛物线或线性加平台的关系，施氮量高于300 kg/hm2时，玉米产量与最高产量差异不显著； 产量与无机氮积累量呈二次抛物线形关系，当土壤无机氮达到平衡时，玉米产量显著低于最高产量，当玉米产量达到最大时，土壤无机氮有一定积累。氮肥利用率则随氮肥用量增加呈指数关系显著降低。施氮量270 kg/hm2为产量与氮肥利用率的交点，施氮量340 kg/hm2 是土壤无机氮残留量与氮肥利用率的交点。【结论】利用产量效应、 环境效应与肥料效应函数的交点确定氮肥投入阈值，是较为优化的方法。合理的氮肥投入不仅能获得玉米高产，降低氮素面源污染风险，还能获得较高的氮肥利用率。因此，施氮量260340 kg/hm2为本研究区玉米高产与环境友好的氮肥投入阈值。

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 residual NO^-₃-N is mainly distributed in 0-60 cm soil depth and the residual NH⁺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.