Effect of stand origin and slope position on infiltration pattern and preferential flow on a Loess hillslope

Preferential flow is expected to provide an important pathway to replenish soil water at deep soil layers in arid or semiarid areas; however, few studies have addressed this topic, especially in semiarid Loess hillslopes. This study aimed to quantify the effect of stand origin and slope position on the contribution of preferential flow to total infiltration and spatial variations in water flow. A blue dye tracer experiment was conducted to visualize water flow in Robinia pseudoacacia plantation (PL), natural forestland (NF), and natural grassland (NG) at the upslope, midslope, and downslope, and semivariance analysis was used to determine spatial variability at the centimeter scale. The results showed that role of macropore flow was dominant in upslope and midslope, and larger in NF than that in PL and NG, due to presence of abundant root systems in the upper soil of NF. Moreover, contribution of preferential flow at the upper slope in NF was larger than that in PL. At the downslope, the role of rock fragments coverage at the downslope was emphasized, leading lateral flow dominant at the downslope in PL and NG. In addition, contribution of preferential flow and vertical variability of infiltration at the downslope in PL was higher than that in NF. The findings demonstrate that compared with PL, NF has a more positive impact on increasing infiltration and preferential flow that can replenish deep soil water, and reducing surface runoff and soil erosion. The presence of rock fragments coverage can make lateral flow dominant at the downslope on the Loess hillslope, related to water movement along the slope toward streams and catchment outlets.