宁南山区不同土地利用类型下土壤水分分布及其干燥化特征

为明确宁南山区不同土地利用类型下土壤干层垂直分布特征和影响因子，本试验运用干层起始深度（Forming depth of desiccated soil layer，DSLFD）、干层厚度（Thicknesses of desiccated soil layer，DSLT）、干燥化指数（Soil desiccation index， SDI）及土壤水分相对亏缺指数（Compared soil water deficit index，CSWDI）对0~600 cm土壤干层状况进行定量评价，同时采用典型相关性分析确定影响土壤干层的主控因素。结果表明：宁南山区林地、灌木地、草地、弃耕地和农地0~600 cm平均土壤水分（Soil moisture content， SMC）含量分别为11.46%，11.79%，14.97%，14.52%和14.66%。草地、弃耕地和农地未出现土壤干层，林地和灌木地分别呈现中等和轻度干燥化，DSLT均为440 cm，干层内土壤平均含水量（Desiccated soil layer-soil moisture content，DSL-SMC）分别为9.10%和9.93%，林地土壤强烈干燥层、严重干燥层、中等干燥层和轻度干燥层厚度分别为40，200，180和20 cm，灌木地土壤严重干燥层、中等干燥层和轻度干燥层厚度分别为80、240和120 cm。不同土地利用类型下60~600 cm土层CSWDI均值呈现出林地（0.58） > 灌木地（0.46） > 弃耕地（-0.03） > 草地（-0.08）。冗余分析（Redundancy analysis，RDA）分析表明土地利用类型、土壤、植被养分状况是影响土壤干燥化的主控因子。宁南山区不同土地利用类型下乔木和灌木存在土壤干层，应采取树体修剪、整地、控制种植密度等措施恢复土壤水分，以促进区域水土资源可持续利用和林草植被恢复。

Characteristics of Soil Desiccation and Soil Water Distribution in Different Land Types in Mountainous Area of Southern Ningxia

In order to clarify the vertical distribution characteristics and influence factors of soil dry layer under different land use types in the mountainous area of southern Ningxia,the dry layer initial depth (DSLFD),dry layer thickness (DSLT),desiccation index (SDI) and soil water relative deficit index (CSWDI) were used to quantitatively evaluate the condition of 0~600 cm soil dry layer,and the main affecting factors were determined by typical correlation analysis. The results showed that the average soil water content under forest land,shrub land,grassland,abandoned farmland and agricultural land were 11.46%,11.79%,14.97%,14.52% and 14.66%,respectively. There were no dry soil layers in grassland,abandoned farmland and agricultural land. The forest land and shrub land showed moderate and mild drying degree,respectively. DSLT on forest land and shrub land was 440 cm and DSL-SMC (Desiccated soil layer-soil moisture content,DSL-SMC) were 9.10% and 9.93%,respectively. The thickness of intense,severe,moderate and mild drying layer under forest land was 40,200,180 and 20 cm,respectively. The thickness of severe,moderate and mild drying layer under shrub land was 80,240 and 120 cm,respectively. The CSWDI of 60~600 cm soil layers under different land use types were forest land (0.58) > shrub land (0.46) > abandoned farmland (-0.03) > grassland (-0.08). The redundancy analysis showed that land use type,and different soil and vegetation nutrient condition were the main factors affecting the soil desiccation. The results indicated that different degrees of dry soil layers could be found under forest land and shrub land in the mountainous area of southern Ningxia. Some measures could be taken to promote the restoration of vegetation and the sustainable development of the soil and water environment,such as tree pruning,soil preparation and planting density.