Characteristics of preferential flow during simulated rainfall events in an arid region of China

Little is known about preferential flow and its effects on vegetation under natural conditions in an arid oasis ecotone. In this study, we performed dye-tracer experiments using 5, 15, 35, and 55 mm water-sprinkling treatments at three sites: Grass (G), Haloxylon (H), and Populus (P). At each site, we determined soil texture and saturated hydraulic conductivity of the soil (K _s) and water flow parameters; we also defined characteristics of soil fracturing and measured plant biomass at site P. The tracer experiments revealed that the three sites displayed significant differences in the degree of preferential flow. Soil structure and surface characteristics were the primary controlling factors, however, they played a different role in different rainfall events. For small rainfall events, soil surface characteristics controlled the preferential flow pattern; for large or extreme rainfall events, soil structure was the critical factor. The effects of different rainfall events were complex and strongly varied among sites. Our results further indicated that preferential flow could impact the growth of annual plants. We conclude that preferential flow in an arid oasis ecotone is a common phenomenon affected by complex factors, and it may be important in soil water distribution and plant growth.