Belowground soil water response in the afforestation-cropland interface under semi-arid conditions

Agroforestry is an effective measure to control soil erosion and maintain or increase productivity in semi-arid areas. However, the belowground soil water responses in the afforestation-cropland interface (ACI) is not well known. This study analyzed the variability of soil water storage (SWS) and deficit in three ACIs taking into account the distance between the forest and cropland. The variations of soil water content up to 4 m depth and at five distances from the interface (−5 m (in forest), 0 m (interface), 1 m, 3 m and 5 m (in cropland)) were estimated in three artificial forests (Salix matsudana, Sophora japonica, and Populus cathayana) and their adjacent croplands (maize). The results showed that soil water at the interfaces was significantly affected by forest. This effect was effective up to 160–170 cm of soil depth, and the ACI of S. matsudana had the greatest impact on the farmland soil water. There was no significant relative soil water deficit between 1 and 3 m length, and the ACI of P. cathayana showed the lowest changes in the lateral direction. The SWS of S. japonica in the ACI was clearly higher than the other two artificial forests (P < 0.05). Our findings indicated that S. japonica was the most suitable forest species for agriculture sustainability in the study area. The tree species and the distance between cropland and forest should be considered during the establishment of agroforestry systems. This study provided insights for water conservation and effective management of ACIs in semi-arid areas.