Preferential water flow: Influence of alfalfa (Medicago sativa L.) decayed root channels on soil water infiltration

Soil water infiltration is an important part of the land surface hydrological cycle, and plays an important role in the hydrological response of the soil, such as soil erosion. High infiltration rates favor an increase in the soil water storage capacity that allows maintaining vegetation restoration in arid and semi-arid regions. Alfalfa (Medicago sativa L.) is a quality perennial legume grassland, which is widely planted in semi-arid areas. In this study, the effects of the root channels formed by the decay of alfalfa on preferential flow were evaluated as a driving force to improve soil water infiltration and soil water supply. A double-ring infiltrometer (30-cm inner diameter and 60-cm outer diameter) was used to measure the infiltration process with the falling head method. Methylene blue was used to visualize the pathways followed by the infiltrated water. The results showed that the initial infiltration rate in the alfalfa grassland increased by 27.7%, compared with the control bare land, and the total cumulative infiltration was 1.13 times higher. The steady infiltration rate of the grassland increased by 31.8% compared to the bare land. The root channel diameters were measured with a Vernier caliper, and the average root channel area (RCA) was calculated through the average root channel diameter (ARCD). The values of ARCD and RCA were significantly and positively correlated with the infiltration rates, being the coefficients of determination 0.815 and 0.789, respectively. Our results indicated that root channels formed by the decayed roots of alfalfa played an important role in increasing soil water infiltration and soil water supply under semiarid conditions. Our research improves the understanding of the hydrological cycle processes at the plant-soil interface in semi-arid areas.