[Water repellency and its influencing factors in Manas River Basin, China]

Soil water repellency (SWR) impedes the processes of soil water infiltration and redistribution. Although water repellent soils exist extensively in the world, its causes were not very clear. In this research, three measurement methods including the water droplet penetration time (WDPT), the molarity of ethanol drop (MED) and the contact angle (denoted as θ below) methods, were applied to obtain different SWR indices for the tested soils collected in Manas River Basin, Xinjiang Uygur Autonomous Region, China. The height method and the mass method were conducted to measure θ values. WDPT values of different soil samples were compared to investigate whether WDPT values were affected after being oven-dried or by different bulk densities. The relationships among three SWR indices (WDPT, MED and θ) were compared, and the major soil physico-chemical properties which influenced SWR were analyzed to discuss the intrinsic mechanism that caused SWR. The results showed that WDPT values of higher bulk density were larger than those of lower bulk density, and WDPT values of oven-dried soils were larger than those of air-dried soils. There were correlations between the three SWR indices of WDPT, MED and θ, but MED was insignificantly related to θ, which showed the differences among various SWR indices, although they were related to each other. When measuring θ values of soil-water, θ values obtained using the height method were larger than those obtained using the mass method, and the differences of θ for the three replications with the height method were smaller than those with the mass method. When using octane as the reference liquid for measuring θ values of soil-water, the differences of the three replications were small, being lower than those using ethyl alcohol. Among the studied multi-physico-chemical properties, clay content affected WDPT and θ values more significantly than other soil physico-chemical properties. Concentrations of K⁺ and Na⁺ were both positively correlated to θ va-lues, while the content of montmorillonite was negatively correlated to WDPT and MED values. In summary, among the three SWR measurement methods, the WDPT method was quite simple in operation but was susceptible, the MED method shortened the infiltration time but was time-consuming in operation, and the contact angle method was complicated in operation but the results were relatively accurate. When using octane as the reference liquid for the height method, it was more reliable than using the other liquids. Because each index had its inherent nature, it was suggested to use multiple indices to characterize SWR comprehensively.