黄土丘陵区多次降雨补充下草灌地土壤水分空间变化规律

Spatial variation of soil moisture on the grass and shrub land under multiple rainfall's supplement in Loess hilly area

利用黄土丘陵区燕沟流域42场模拟降雨下土壤水分观测数据,研究2种坡度的草地、灌木地在不同经营方式（原状地、刈割地、翻耕地）下的土壤水分对模拟降雨的响应。结果表明：（1）在5次降雨补充下,依据土壤水分的标准差和变异系数,0~100 cm土壤水分受土地经营方式影响表现为：原状草灌地土壤水分可划分为活跃层、次活跃层和相对稳定层;刈割地全剖面为相对稳定层,翻耕地可分为活跃层和相对稳定层。（2）单次降雨事件则随降雨量增加,各经营方式下的水分活跃层逐渐变薄或消失,次活跃层变厚,而相对稳定层变薄,整个土壤剖面水分变化趋于一致。（3）对于受高强度降雨补充后的土壤水分变异性分层,建议采用更加灵敏的土壤水分标准差和变异系数判别标准：活跃层,标准差大于1.4%,变异系数大于12%;次活跃层,标准差1.4%~0.9%,变异系数12%~8%;相对稳定层,标准差小于0.9%,变异系数小于8%。（4）坡度越小土壤水分含量越高,坡度对草灌木地、刈割地的影响较翻耕地显著,且对50~100 cm土层水分影响远大于对表层0~50cm的影响。总之,降雨后土壤水分0~100 cm土层不断增加,且剖面土壤水分逐渐一致,土地经营方式、坡度因素对土壤水分变化强度和在不同深度土层中的表现有显著影响。

Based on the observation data of soil moisture under 42 simulated rainfalls in Yangou watershed of the Loess hilly area,responses of soil moisture to the simulated rainfalls on grass land and shrub land under two slopes with different management methods（undisturbed,cutting,plowing） were studied.The results were as follows： Under five supplementary rainfalls,according to the standard deviation and variation coefficient of soil moisture,the effect of land management on soil moisture in the 0～100 cm soil layers showed that： the soil moisture in undisturbed grassbush land could be divided into active layer,relatively steady layer and sub-active layer;the whole soil profile of cutting land was a relatively steady layer;plowed land was divided into active layer and relatively steady layer.Under a single rainfall,the active and relatively steady layers would become thinner gradually or disappear with the increase of precipitation,while the sub-active layer increased,changes of the moisture content in the whole soil profile tended to be uniform.It was suggested that more sensitive descrimination sandards which were standard deviation and variation coefficient should be used to divide the soil layer according to moisture variability under high intensity supplementary rainfall： active layer,standard deviation1.4%,variation coefficient12%;sub-active layer,1.4%standard deviation0.9%,12%variation coefficient8%;relatively steady layer,standard deviation0.9%,variation coefficient8%.Soil moisture increased with the decreasing of slope.Slope had a more siganificant effect on soil moisture in undisturbed land and cutting land compared to plowed land,and the effect of slope on soil moisture in 50～100 cm soil layer was more siganificant than that in 0～50 cm soil layer.In conclusion,soil moisture in depth of 0～100 cm gradually increased after a single rainfall,and soil moisture of the profile became gradually stable.Land management as well as slope had siganificant effects on both the change intensity of soil moisture and changes of that in different soil depth.