牧草覆盖对坡面土壤矿质氮素流失的影响

利用室内模拟降雨试验，探讨了降雨、地表径流以及土壤矿质氮素有效作用深度（effective depth of interaction，EDI）的确定方法，研究了牧草覆盖对土壤矿质氮素EDI和地表流失的影响．结果表明，牧草覆盖增加了地表径流与表层土壤的相互作用，导致水土混合体深度增加，较深土层的土壤矿质氮通过溶解和解吸作用、对流-扩散作用等方式进入到地表径流中，矿质氮EDI增加．覆盖度越大，EDI值越大．与裸地相比，60％、80％和100％覆盖度处理中径流矿质氮平均浓度分别增加了34．52％、32．67％和6．00％，地表径流量分别减少了4．72％、9．84％和12．89％，侵蚀泥沙量分别减少了83．55％、87．11％和89．01％．60％和100％覆盖度处理的矿质氮地表流失总量分别为裸地处理的95．73％和84．05％，而80％覆盖度处理则为裸地处理的109．04％．草地植被对矿质氮素地表流失有“双重效应”：加剧了矿质氮向地表径流中的释放，使径流养分浓度高于裸地浓度；不同程度地减少了地表径流量和泥沙量及其养分含量．两种效应共同决定了土壤矿质氮素的地表流失量．

Runoff loss of soil mineral nitrogen and its relationship with grass coverage on Loess slope land

In a simulated rainfall experiment on Loess slope land, this paper determined the rainfall, surface runoff and the effective depth of interaction (EDI) between rainfall and soil mineral nitrogen, and studied the effects of grass coverage on the EDI and the runoff loss of soil mineral nitrogen. The results showed that with the increase of EDI, soil nitrogen in deeper layers could be released into surface runoff through dissolution and desorption. The higher the grass coverage, the deeper the EDI was. Grass coverage promoted the interaction between surface runoff and surface soil. On the slope land with 60%, 80% and 100% of grass coverage, the mean content of runoff mineral nitrogen increased by 34.52%, 32.67% and 6.00%, while surface runoff decreased by 4.72%, 9.84% and 12.89%, and eroded sediment decreased by 83.55%, 87.11% and 89.01%, respectively, compared with bare slope land. The total runoff loss of soil mineral nitrogen on the lands with 60%, 80%, and 100% of grass coverage was 95.73%, 109.04%, and 84.05% of that on bare land, respectively. Grass cover had dual effects on the surface runoff of soil mineral nitrogen. On one hand, it enhanced the influx of soil mineral nitrogen to surface runoff, and on the other hand, it markedly decreased the runoff, resulting in the decrease of soil mineral nitrogen loss through runoff and sediment. These two distinct factors codetermined the total runoff loss of soil mineral nitrogen.