Fine roots determine soil infiltration potential than soil water content in semi-arid grassland soils

•Effects of root and soil water on infiltration rate were studied during different stages.•Root diameter became the main factor affecting soil infiltration along infiltration time.•The 0–2-mm-diameter root was positively correlated with infiltration rate.•The >4.5-mm-diameter root was negatively correlated with infiltration rate.•Fine roots more determine soil infiltration potential than soil water content. Soil water is the key limiting factor for achieving sustainable revegetation. Soil infiltration rate plays an important role in determining the inputs from precipitation, which is important for the plant growth and groundwater recharge in semi-arid regions. Soil infiltration rate is generally influenced by belowground biomass (BGB), soil water content (SWC) and other soil properties (total soil porosity, soil mean weight diameter and soil organic carbon). The aim of this study is to understand the effects of plant roots, SWC and other soil properties on soil infiltration rate, and to identify the main factor affecting soil infiltration rate. This study investigated the total soil porosity (TP), soil mean weight diameter (MWD), soil organic carbon (SOC), SWC and plant roots of five grasslands (Bromus inermis, Trifolium repens, Panicum virgatum, Medicago sativa and Miscanthus sinensis). An automatic measurement system of point source device was used to quantify the soil infiltration rate. Results showed that SWC significantly affected the initial infiltration rate (P 4.5 mm was negatively correlated with infiltration rate. Our results indicated that fine roots could increase soil organic matters and form soil pores, thus more determining the potential of soil infiltration than soil water content during the short-term vegetation restoration in semi-arid regions.