Soil water response to rainfall in a dune-interdune landscape in Horqin Sand Land, northern China

Soil water dynamic is considered an important process for water resource and plantation management in Horqin Sand Land, northern China. In this study, soil water content simulated by the SWMS-2D model was used to systematically analyse soil water dynamics and explore the relationship between soil water and rainfall among micro-landforms (i.e., top, upslope, midslope, toeslope, and bottomland) and 0-200 cm soil depths during the growing season of 2013 and 2015. The results showed that soil water dynamics in 0-20 cm depths were closely linked to rainfall patterns, whereas soil water content in 20-80 cm depths illustrated a slight decline in addition to fluctuations caused by rainfall. At the top position, the soil water content in different ranges of depths (20-40 and 80-200 cm) was near the wilting point, and hence some branches, and even entire plants exhibited diebacks. At the upslope or midslope positions, the soil water content in 20-80 or 80-200 cm depths was higher than at the top position. Soil water content was higher at the toeslope and bottomland positions than at other micro-landforms, and deep caliche layers had a positive feedback effect on shrub establishment. Soil water recharge by rainfall was closely related to rainfall intensity and micro-landforms. Only rainfalls > 20 mm significantly increased water content in > 40 cm soil depths, but deeper water recharge occurred at the toeslope position. A linear equation was fitted to the relationship between soil water and antecedent rainfall, and the slopes and R2 of the equations were different among micro-landforms and soil depths. The linear equations generally fitted well in 0-20 and 20-40 cm depths at the top, upslope, midslope, and toeslope positions (R2 value of about 0.60), with soil water in 0-20 cm depths showing greater responses to rainfall (average slope of 0.189). In 20-40 cm depths, the response was larger at the toeslope position, with a slope of 0.137. In 40-80 cm depths, a good linear fit with a slope of 0.041 was only recorded at the toeslope position. This study provides a soil water basis for ecological restoration in similar regions.