土壤空间变异对滴灌水氮淋失风险影响的模拟评估

Assessing the influence of soil spatial variability on water leakage and nitrate leaching under drip irrigation through simulation

滴灌水氮淋失是系统设计和运行管理需要考虑的重要因素。本研究利用HYDRUS-2D软件构建了滴灌条件下的水氮运移模型,通过局部敏感性分析和全局敏感性分析方法研究了砂壤土土壤水力参数、初始含水率和土壤溶液中初始NO3--N浓度的空间变异对水分渗漏率和NO3--N淋失率的影响。结果表明,水分渗漏率和NO3--N淋失率随饱和含水率的增大而明显降低,随土壤初始含水率的增大而明显升高。弱变异条件下,水分渗漏率和NO3--N淋失率的变异性主要由土壤初始含水率、饱和含水率和饱和导水率的空间变异引起;中等变异条件下,初始含水率和土壤溶液中初始NO3--N浓度为影响水分渗漏和NO3--N淋失的最重要因素。当土壤达到中等变异程度时,忽略土壤参数空间变异的影响,可能会低估滴灌水分渗漏和NO3--N淋失的风险。因此,考虑关键土壤参数的空间变异特征,将有助于更准确地评估田间尺度滴灌水氮淋失风险。

It is of importance to consider the leaching of water and nitrogen in designing , operation and management of drip irrigation systems. A model simulating the transport of water and nitrate in soil was es tablished and solved numerically by using the HYDRUS-2D package. The local sensitivity analysis and glob al sensitivity analysis were carried out over the model to evaluate the influence of the spatial variability of soil hydraulic parameters , initial water content and nitrate nitrogen content on water leakage and nitrate leaching for a sandy loam soil under drip irrigation. The results indicate that the water leakage ratio and ni trate leaching ratio decreased greatly with an increase of saturated water content , while the ratios increased steadily with an increase of initial soil water content. For the sandy loam soil with a low spatial variabili ty , the majority of the variability of the water leakage and nitrate leaching can attribute to the spatial vari ability of initial and saturated water content and saturated hydraulic conductivity. However , water leakage ra tio and nitrate leaching ratio are mainly controlled by the initial water and nitrate content when the spatial variability of soil reached a medium level. The potential risk of nitrate leaching might be underestimated for a soil with medium spatial variability if the soil variability was neglected. It is therefore suggested that the spatial variability of soil should be considered when water leakage and nitrate leaching was assessed for a soil with a medium to high variability level.