Effects of herbaceous root development on soil water infiltration and hydraulic properties in loess

Root development alters soil pore structure and connectivity, thereby affecting un-saturated water movement; however, its growth-stage-dependent effects on infiltration and hydraulic properties in loess remain poorly quantified. In this study, one-dimensional soil column infiltration experiments were conducted on Festuca arundinacea root-soil composites under root distribution conditions corresponding to different growth stages (T = 0, 35, 52, 76, and 99d). The results showed that total infiltration duration decreased significantly with increasing growth stage, indicating enhanced water transport capacity in loess. Saturated hydraulic conductivity showed a strong linear relationship with root biomass ratio (RB), while the other hydraulic parameters varied systematically with increasing RB and were well described by exponential functions. Based on the temporal evolution of root distribution, quantitative relationships between hydraulic parameters and growth stage were established and incorporated into the Richards equation. HYDRUS simulations agreed well with the measured wet-ting-front advance and volumetric water content changes. These findings indicate that herbaceous root growth stage is an important biological factor regulating infiltration behavior and hydraulic properties in loess, providing parameter support for studies of vegetation-soil-water interactions and soil water infiltration modeling under vegetation restoration on the Loess Plateau.