中国农田施氮水平与土壤氮平衡的模拟研究

Simulation of nitrogen level and balance in cropland in China

为了估算全国尺度的农田土壤氮素的输入输出平衡状况,并探明土壤氮素的基本去向和氮素污染的可能性,以求合理施用氮肥、保护农田生态环境,该文主要运用农业生态系统生物地球化学模型(DNDC)方法,在GIS区域数据库支持下运行模型,并综合分析模拟结果。研究结果表明,以近20a来氮肥投入最多的1998年为例,全国农田土壤氮素平衡状况表现为总体过剩,总过剩量为456～962万tN,均值为709万tN。化肥态氮肥投入是土壤氮素收入的主要途径,占到氮素总收入量的近60%,其大量投入是造成农田土壤氮素过剩的主要原因;另外,从氮素的支出途径来看,除了作物生长从土壤中吸取大量的氮素以外,通过NH3挥发和氮淋溶丢失了大量的氮素,分别占总支出量的35%和15%,给环境造成了严重影响。模拟结果显示中国农田氮平衡存在较大的区域差异,减少氮素的无效丢失十分必要。

In order to estimate the nitrogen balance in cropland of China, identify the fate of nitrogen and the possibility of nitrogen pollution, and finally put forward strategies to keep rational nitrogen application in the cropland and to limit the environment problems arising from the overuse of N fertilizers. A computer simulation model of carbon and nitrogen biogeochemistry in ago-ecosystems （DeNitrification and DeComposition, DNDC） was applied to predict nitrogen balance in cropland in 1998 at national scale. Data on climate, soil properties, cropping systems, acreage, and management practices at county scale were collected from various sources and integrated into a GIS database to support the model. The model results reveal that the simulated balance of N is net surplus in the whole country＇s croplands in 1998 that range from 4.56 million t N to 9.62 million t N with an average of 7.09 million t N. Currently annual inputs of N mainly rely on the chemical fertilizer, and nearly 60% of N is input through fertilization. In terms of output of nitrogen in cropland, besides of the amounts uptake by plants growth, while nitrogen losses through volatilization of NH3 and leaching are the dominant occupying 35% and 15% of total output of N respectively, which will significantly affect the environment. The model results also indicate that the largest nitrogen surpluses distribute in the relatively developed provinces where the higher fertilizer are usually applied. Generally, it is urgent and necessary to hold back the inefficient losses of nitrogen.