基于水量平衡下灌区农田系统中氮素迁移及平衡的分析

本文以于河套灌区典型灌域（前旗北疙堵乡塔布村）为研究对象，通过分析农田系统中水量平衡和氮素平衡，建立农田系统中氮素平衡和水分平衡的联立模型，并用此模型分析典型区域内农田系统中氮素随水分迁移的规律。分析表明：应用水量和氮平衡模型分析灌区农田系统中氮迁移及平衡，可以反映出农业面源污染物（氮）在整个农田系统中的去向，化肥使用量的降低和灌水量的减少，将有效的减少农田系统中氮素的输入量；秋灌—秋浇期间，玉米、番茄和葵花作物对氮的吸收率分别为17%、18%和32%，3种土壤中残留量分别为57%、60%和58%。依据河套灌区年施肥60万t计算，土壤残留量达到17.2万t。在秋灌-秋浇期间从黄河引入的氮总量达到1.21万t，随农田退水进入沟道的量为840 t。

Nitrogen balance in the farmland system based on water balance in Hetao irrigation district,Inner Mongolia

The influence of human activity on the nutrition circulation has essentially changed ecosystem processes, and chemical fertilizers and nitrogen-fixing plants further enhanced the nitrogen flux in agricultural ecosystem. When the input of nitrogen exceeds the crop assimilation capacity, surplus nitrogen in the farmland system will lead to the increase of nitrate leaching, ammonia volatilize and denitrification, and result in negative influence on the environment. The amount of absorbed N by the crop is from 26% to 36% in farmland system, and the most of the surplus N is lost by the NH₃ volatilization and denitrification, and some of the surplus N leached into groundwater. Hetao irrigation district (HID) is one of the three large-scale irrigation districts in China, the fertilizers amount used in the farmland of HID is increasing during the past ten years. This paper conducted a case study on the transport and balance of nitrogen in the farmland system based on water balance in Hetao Irrigation District (HID),Inner Mongolia. The cycle process of nitrogen and water in the farmland system was analyzed and a coupled model of the nitrogen and water balance was set up, by which the nitrogen transport rule in the farmland system was analyized. The results showed that the coupled model could reflect the relationship between water and N in farmland system by application of water-balance and N balance. The model not only reflected the migration paths of N in the farmland system, but also explained which could effectively increase the utilization of the fertilizers and which could reduce agricultural non-point pollution contribution. It could reduce the production of the agricultural non-point pollution by increasing the amount of straw returning, and it could reduce the output amount of N in farmland system by reducing the fertilizer amount. In autumn-irrigation period, the uptake rate of corn, tomato and sunflower is 17%, 18% and 32% respectively, and the soil residual rate is 57%, 60% and 58% respectively. In this period, the amount of N from the irrigation water is 12.1 thousand t, and the N discharge amount is 840 t. According to the fertilizer amount of 0.6 million t in year, the amount of soil residual of N is 0.17 million t. Because the fertilizer amount is higher and its utilization is lower, although the irrigation and drainage water amount is diseasing in the resent 10 years, the amount of N discharged into Wuliangsuhai Lake remains at about 330 t/a. So the effect of the agricultural irrigation non-point pollution of HID on the eutrophication of Wuliangsuhai Lake was significant.