Response of soil pore variation and infiltration to dry-wet changes at rock-soil and non-rock-soil interface in rocky desertification areas

Against the backdrop of global climate change, the frequent and intense fluctuations in soil moisture have a significant impact on the dry and wet states of surface soil layers, posing severe challenges to the fragile ecosystem and rocky desertification management in karst regions. The soil in karst environments is vulnerable to frequent alternations between dry and wet conditions, leading to continuous shrinkage and expansion, which in turn affects the internal pore structure and infiltration capacity of the soil. To investigate the significance of soil pore variation and infiltration response under dry-wet conditions on soil moisture replenishment and rainfall-runoff regulation in rocky desertification areas, an in-situ disk infiltration meter was used to conduct experiments under four pressure heads (−0.5,−3, −6, −15 cm). The shape of the rock face, pressure head, and dry-wet conditions were taken as driving factors, the soil at flat, convex, concave, and complex rock-soil interfaces (closely adhering to the rock surface) and non-rock-soil interfaces (horizontally 20 cm away from the rock-soil interface) was taken as the research object. The size, distribution, and infiltration capacity of soil pores were studied, and the response of soil pore structure variation and water infiltration to dry-wet changes were analyzed. The results indicated that: 1) Under drought conditions, the average non-capillary porosity of soil at rock-soil interfaces and non-rock-soil interfaces was greater than under wet conditions, and the average non-capillary porosity at non-rock-soil interfaces was greater than at rock-soil interfaces. The average change in soil porosity under dry-wet conditions, from highest to lowest, was non-capillary porosity, capillary porosity, air permeability, and total porosity. The number and volume ratio of soil pores under drought conditions were generally greater than under wet conditions. At rock-soil interfaces, the number and volume ratio of small pores (<0.2 mm) and medium pores (0.2-1.0 mm) were greater than at non-rock-soil interfaces, while the number and volume ratio of large pores (>1.0 mm) were smaller. The average change in the number and volume ratio of soil pores, from highest to lowest, were small pores, medium pores, and large pores. 2) Under drought conditions, both the stable infiltration rate and saturated hydraulic conductivity of the soil were greater than under wet conditions. Under both dry and wet conditions, the stable infiltration rate of soil at rock-soil interfaces and non-rock-soil interfaces decreased first and then increases with increasing head pressure, and exhibited a significant compound functional relationship. The soil hydraulic conductivity increased with increasing head pressure, and both the stable infiltration rate and saturated hydraulic conductivity were highest at a head pressure of −0.5 cm. 3) The soil infiltration capacity was related to the contribution of pores of different diameters to the soil infiltration flow. Under dry-wet changes, the contribution of various soil pores to soil infiltration decreased as the pore size decreases, with the contribution being highest for large pores, followed by medium pores I, medium pores II, and small pores. Non-capillary porosity and the number of large pores had the greatest impact on soil infiltration capacity. 4) The average changes in soil pore parameters and water infiltration at rock-soil interfaces under dry-wet conditions were greater than at non-rock-soil interfaces. The research results can provide scientific basis for understanding the changes of soil water recharge and rainfall and runoff regulation ability caused by soil pore variation under dry and wet changes, and the adaptive control of rocky desertification.