The response of soil water and deep percolation under Caragana microphylla to rainfall in the Horqin Sand Land, northern China

In the semi-arid Horqin Sandy Land of northern China, Caragana microphylla, a leguminous shrub, is the dominant plant species widely used in re-vegetation efforts aimed at stabilization of mobile sandy lands. However, the effect of rainfall characteristics on soil water dynamics and deep percolation in C. microphylla shrublands are not well understood. The objective of this study was to examine the responses of volumetric water content (VWC) and deep percolation under the root zone of C. microphylla to different rainfall characteristics. An underground chamber with 23 concrete basins (200 × 200 × 230 cm3) was constructed to conduct this experiment during the growing seasons from 2010 to 2013. For this study, three of the basins were filled with sandy soil taken from the C. microphylla shrublands near to the station (about 200 m) and one C. microphylla shrub was transplanted into each basin in 2009. The corresponding hourly rainfall data were obtained from an automated meteorological station. VWC was recorded hourly using MiniTrase Soil Moisture Monitoring System at 0–20, 20–40, 40–60, 60–80, 80–100, 100–120, 120–140, and 140–160 cm soil depths. Deep percolating water was collected in the underground chamber and measured daily. Our results showed that rainfall amount, intensity, duration, and the duration of the dry interval were significantly correlated with VWC in different soil layers. The amount of deep percolation was significantly correlated with rainfall amounts and rainfall duration, but not with rainfall intensity and the duration of the dry interval. Average deep percolation in C. microphylla shrublands was 97.5, 114.3, 66.8, and 15.1 mm in 2010, 2011, 2012, and 2013, respectively, and accounted for 62.79%, 49.41%, 27.96%, and 7.36% of rainfall during the growing season. The coefficient of deep percolation was significantly negatively associated with annual mean shrub cover and canopy size, but not with annual mean height of C. microphylla. Our results suggested that re-vegetation with C. microphylla in this region is likely to result in a reduction in potential groundwater recharge and decrease of soil water content relations with an increase in age of the shrub.