Abstract: To understand the effects of root system on the infiltration capacity of grasslands in a purple soil watershed, we conducted a one-dimensional infiltration experiment with four common herbaceous plants (Torilis scabra, Youngia japonica, Lolium multiflorum, and Sinosenecio oldhamianus) in suburb Chongqing. The relationship between the characteristics of plant root structure and the infiltration capacity of root soil complex was examined, and the Kostiakov, Mezencev, Horton, and Phillip infiltration models were used to simulate the infiltration process. The results showed that the infiltration processes of root soil complex and rootless soil decreased sharply at first and then decreased slowly until stable. The stable infiltration rate of root soil complex increased by 1.35-2.96 times compared with that of rootless soil. The infiltration rate of fibrous root soil complex was higher than that of taproot soil complex. Sinosenecio oldhamianus performed better in improving the infiltration performance of purple soil. Root length density, root surface area density, and root volume fractal dimension were significantly positively correlated with the initial, stable, average, and cumulative infiltration rates of the root soil complex (P<0.01). However, there was no significant correlation (P>0.05) between root volume density and soil initial infiltration rate, root weight density and stable infiltration rate. The Mezencev model was the most suitable to characterize the infiltration of root soil complex of the four herbaceous species and rootless soil (R²=0.99), followed by Kostiakov model, Horton model, and Philip model. Moreover, the Kostiakov, Philip, and Horton models performed better in simulating the infiltration of taproot soil complex than that of fibrous root soil complex. The results can provide a scientific basis for slope vegetation construction and soil erosion prevention in  purple soil areas.

Key words: suburban Chongqing, purple soil, small watershed, grassland, loamy soil, soil infiltration