Mechanisms of grazing management impact on preferential water flow and infiltration patterns in a semi-arid grassland in northern China

Grazing management is widely used to control grassland degradation in Inner Mongolia. However, the correlation between the soil physical properties, root traits, and infiltration patterns of different types of grazing management has seldom been studied. To reveal the effect of grazing management on water infiltration and preferential flow behavior, we first investigated the soil and plant properties in a grazing exclusion (19 years, GE), cold-season grazing (19 years, CG), and free-grazing grassland (19 years, FG) in a semi-arid grassland in Inner Mongolia. Dye tracer infiltration was adopted to obtain the water infiltration patterns from different types of grazing management. Finally, root biomass and root morphological traits were measured in a field experiment. The results showed that the plant height, vegetation coverage, richness index, Shannon-Wiener index, soil water content, total porosity, and mean weight diameter were higher at the GE site than at the FG site, whereas soil bulk density and sand content were lower at the GE site than at the FG site (P < 0.05). In addition, the root mean diameter, specific root length, and root mass density were higher at the GE site than at the FG site. As a result, differences in these root traits and soil and vegetation properties affected the preferential water flow behavior in the three types of grassland. The preferential flow evaluation index (PFI) of the GE, CG, and FG sites was 0.89, 0.30, and 0.15, respectively, which indicated that more obvious preferential flow occurred at the GE site than at the CG and FG sites. These findings highlight that the long-term GE enhanced plant density and root biomass, which could potentially promote the natural restoration of soil pores and preferential water infiltration. Therefore, local governments and herders should implement GE rather than other grazing management practices to prevent grassland degradation.