Response of soil water movement to rainfall under different land uses in karst regions

Abstract Soil water is a critical factor closely related to hydrological and ecological processes. Owing to the complex surface conditions with heterogeneous soil thickness and abundant underlying fissures, soil water in the karst region has been a complicated issue. In this study, the dynamic changes of soil water in the vertical profile of selected grassland, farmland and bare land on a karst yellow soil hillslope in southwest China were monitored at five depths including 20, 40, 60, 80 and 100 cm with an interval of 15 minutes. Results showed that (1) there were spatial differences in the response to rainfall of the soil water content at different depths. When the rainfall amount was similar, the soil water replenishment amount and migration depth under the three land uses decreased with the rainfall intensity. In the case of light rainfall, the soil water content at 20 cm was the most sensitive to rainfall, and the response of soil water to rainfall mainly occurred at 0–40 cm. In the case of moderate and heavy rainfall, soil water could migrate down to 100 cm on grassland but less than 100 cm on farmland and bare land under heavy intensity rainfall. (2) The variation in the soil water content had interlayer differences over time. The response of soil water to rainfall in different soil layers showed multipeak fluctuations. In general, when the rainfall intensity was the same, the soil water fluctuation on grassland and farmland at the same depth was larger than that on bare land; however, the peak value of soil water decreased with soil depth. (3) Land use and the antecedent soil water content had important effects on soil water loss during the dry period. Soil water loss was faster at the beginning and before slowing down. The soil water loss rate on grassland and farmland increased with the length of the dry period but decreased gradually on bare land. These results can support the utilization and protection of soil and water resources on karst yellow soil slopes and help to understand the temporal and spatial dynamics of soil water under natural rainfall.