盐渍化灌区玉米施氮量阈值DNDC模型模拟

为了寻求保障农业生产和环境友好的适宜施氮量，利用内蒙古河套灌区2 a田间试验数据对脱氮-分解作用模型（Denitrification-Decomposition Model，DNDC）进行了率定与验证，模拟并研究了影响硝态氮淋失量和植株吸氮量的关键因素，以及玉米施氮量阈值。结果表明：1）DNDC模型可以较好地模拟玉米产量及氮素吸收利用情况，率定和验证过程中玉米产量、叶面积指数和收获时土壤0～20 cm土层土壤硝态氮累积量纳什效率系数与R2均不小于0.75，标准均方根误差为9.26%～21.48%。2）施氮量和追肥次数对硝态氮淋失量和植株吸氮量的影响较大，而耕作深度和灌水量对硝态氮淋失量和植株吸氮量的影响较小。且过多施用氮肥不会促进植株吸氮量和产量的增加，反而会增加硝态氮淋失量造成环境污染。3）植株吸氮量和玉米产量均随施氮量增加呈先增长后逐渐趋于稳定的趋势。此外，当追肥次数为3次时，生育期植株吸氮量较追肥1次和2次时的植株吸氮量平均高167.18%和31.27%。4）当追肥次数相同时，硝态氮淋失量随施氮量增加而增加；当施氮量相同时，随追肥次数增加，硝态氮淋失量逐渐降低。当追肥次数为2次和3次时，生长季硝态氮淋失量较追肥1次时平均减少41.96%、59.75%。综合考虑玉米产量、硝态氮淋失量和植株吸氮量，当施氮量为165.50～200 kg/hm2，且分别在拔节期、抽雄期和灌浆期进行追肥为较优的施肥方案。研究成果可为减少河套灌区地下水环境污染及资源浪费提供技术支撑。

Simulation of the threshold of maize nitrogen application using a DNDC model in salinized irrigation areas

Abstract: This study aims to determine the suitable nitrogen application rate for agricultural production and environmental protection in salinized irrigation areas. A two-year field experiment was carried out in the Hetao Irrigation District of Inner Mongolia in Western China. A Denitrification-Decomposition (DNDC) model was selected to simulate the key factors, including the amount of nitrate leaching loss, the amount of plant nitrogen uptake, and the threshold of maize nitrogen application rate. The results showed that: 1) The DNDC model accurately simulated the maize yield and nitrogen utilization. A better agreement between the measured and simulated data was achieved on the maize yield, leaf area index (LAI) and soil nitrate-nitrogen accumulation in the 0-20 cm soil layer, where the model Nash-Sutcliffe efficiency (ENS) and the coefficient of determination (R2) were all greater than 0.75, the normalized root mean square error (NRMSE) was 9.26%-9.57%, 13.49%-17.51%, and 19.84%-21.48%, respectively. 2) A sensitivity analysis of the model parameters showed that the nitrogen application rate (the sensitivity index of 1.92 and -0.89) and topdressing times (the sensitivity index of 0.11, and -0.85) presented significant effects on the amount of nitrate leaching loss and plant nitrogen uptake. However, the tillage depth (the sensitivity index of 0.03, and 0.09) and irrigation amount (the sensitivity index of -0.02, and -0.01) behaved little effect on the amount of nitrate leaching loss and plant nitrogen uptake. Whereas, the excessive application of nitrogen rate cannot promote the amount of plant nitrogen uptake and yield, but lead to the amount of nitrate leaching and even environmental pollution. 3) The amount of plant nitrogen uptake and maize yield increased firstly and then gradually stabilized, with the increase of nitrogen application rate. In addition, the amount of plant nitrogen uptake during the growth period increased by 167.18% and 31.27%, when the number of topdressing was three times, compared with one and two times. 4) Once the number of topdressing was the same, the nitrate leaching loss increased with the increase of nitrogen application rate. However, the leaching loss of nitrate decreased gradually with the increase of topdressing times, when the amount of nitrogen rate was constant. The nitrate leaching loss in the growing season decreased by 41.96% and 59.75%, when the number of topdressing was two or three times, compared with the single. As such, the optimal fertilization was 165.50-200 kg/hm2 nitrogen application rate, and top fertilization at the jointing, tasseling, and filling stages, considering the yield, the nitrate leaching loss, and the nitrogen rate applied with the maximum amount of plant nitrogen uptake. The finding can provide technical support to reduce the groundwater pollution and resource wastes in Hetao Irrigation District.