洱海近岸菜地包气带土壤水分特征曲线参数变化及其影响因素

Water Retention Curve of Vegetative Soils in Erhai Lake Catchment and the Factors Affecting It

土壤水分特征曲线参数是研究土壤水分和溶质运移的重要参数。【目的】明确洱海近岸菜地土壤水分特征曲线参数空间变化及其影响因素。【方法】以洱海近岸菜地包气带土壤为研究对象,采用压力膜仪逐层测定了不同高程下土壤剖面各发生层的水分特征曲线,并用van Genuchten模型(VG模型)拟合土壤水分特征曲线。【结果】洱海近岸菜地包气带土壤含水率随着土壤吸力的增加呈先快速下降后变化平缓的趋势,VG模型能够较好地模拟各发生层土壤的水分特征曲线。土壤饱和含水率、残余含水率和参数n随着粉黏粒量、有机质和土壤孔隙度的增加而增加,随砂粒量和土壤体积质量的增加而减少,参数a呈相反的变化。土壤有机质、砂粒和黏粒量是影响土壤水分特征曲线参数空间变化的关键性因素,这些因素的差异把各发生层土壤划分为3类,即耕作层A为一类,犁底层P、母质层C和潴育层W为一类,潜育层G为一类。【结论】土层越深或越靠近洱海,土壤持水能力越差,土壤水分或溶质的迁移能力越强。潜育层、潴育层和母质层土壤水分特征曲线参数随高程呈较好的规律性变化,而长期耕种扰乱了耕作层和犁底层土壤水分特征曲线参数随高程的规律性变化。

【Objective】Water retention curve is one of the most important parameter to quantify movement and bioavailability of water in soil and in this paper we measured and compared the water release curve of vegetative soils in Erhai lake catchment as well as the factors affecting it.【Method】Soil samples at different locations and depths were taken based on soil genesis, and their water retention curves were measured using the pressure-membrane apparatus. For each measured curve, we fitted it to the van Genuchten model.【Result】Soil moisture content decreased as soil matric potential increased, and all measured water characteristic curves can be fairly well by the van Genuchten model. Saturated water content, the residual water content and the parameter n in the model increased with the silt and clay content, the organic matter and soil porosity, but decreased as the sand content and bulk density increased, as opposed to the parameter a in the model. Soil organic matter, sand and clay contents were the key factors that affected the shape of the soil water characteristic curve. Soil at different depths were divided into three categories based on the above factors. Category 1 consisted of the plough horizon, and Category 2 consisted of the pan horizon and parent-material horizon and the hydrogric horizon; the remaining was in Category 3.【Conclusion】The deep soil layer and the soil in proximity of the Erhai Lake shore have the lowest water holding capacity and are thus easy for water and solute to move through. The ability of the Gley horizon, the illuvium and parent maternal horizons to hold water increases with elevation, but the long-term cultivation alertes the ability in the plough layer and the pan horizon to hold water, rendering them independent of elevation.