土壤初始含水率对优先流的影响

Effect of initial soil water content on preferential flow

土壤中优先流的存在会造成肥料利用率降低以及土壤深层甚至地下水污染。为确定土壤初始含水率对优先流的影响,通过室内含大孔隙土柱定水头入渗实验,以长武黑垆土及渭河砂土为研究对象,分析不同土壤初始含水率对优先流的影响。结果表明:1)相同质地,当土壤初始含水率大于其斥水性的峰值含水率时,湿润锋运移深度随着土壤初始含水率的增大而增大,反之湿润锋运移深度随着初始含水率的增加而减少,不同质地土壤湿润锋运移速度随土壤粉粒质量分数升高而减慢;2)累积入渗量受到土壤储水性及斥水性的双重影响,导致与湿润锋的运移趋势并不一致,黑垆土对照CK组及优先流O-C-30组(除7.04%含水率外)累积入渗量随着土壤初始含水率的增大而减小,渭河砂土CK组及O-C-30组均呈现2阶段特征,累积入渗量先随着土壤初始含水率的增加而减少,之后随土壤初始含水率的增加而增加;3)Kostiakov入渗模型能很好地拟合累积入渗量随时间的变化过程,适用于存在优先流的土壤入渗模拟。该研究结果对土壤优先流水分模拟具有一定的指导意义。

Soil preferential flow causes reduction of soil fertility and contamination of deep soil or groundwater.In order to investigate the effect of initial soil water content on preferential flow,we conducted soil column infiltration experiments in laboratory with man-made macropores in two types of soil at different initial soil water contents.Results are shown as follows.1） When the initial soil water content is higher than the critical soil moisture of water repellency,the wetting front migration distance increases with rising initial soil water content for a given soil type,whereas the wetting front migration distance increases with the drop of initial soil water content.For different soil types,the wetting front migration distance deceases with increasing clay particles content.2） Cumulative infiltration which is affected by both water repellency and soil water storage differs from the change of wetting front migration.The cumulative infiltration of heilu soil in CK group and O-C-30 group （except for the 7.04％ moisture content） decreases with the increase of initial moisture content,whereas sand soil from Wei river in CK and O-C-30 group presents two-staged characteristics,i.e.,the cumulative infiltration firstly decreases and then increases with increasing initial water content.3） The Kostiakov model was used to simulate the cumulative infiltration change over time,and the results showed that the soil infiltration process of preferential flow can be fitted by the Kostiakov model.Our study would provide reference for preferential flow simulation.