Soil water repellency and influencing factors of Nitraria tangutorun nebkhas at different succession stages

Soil water repellency(WR) is an important physical characteristic of soil surface. It is capable of largely influencing the hydrological and geomorphological processes of soil, as well as affecting the ecological processes of plants, such as growth and seed germination, and has thus been a hot topic in recent research around the world. In this paper, the capillary rise method was used to study the soil WR characteristics of Nitraria tangutorun nebkhas. Soil water repellencies at different succession stages of Nitraria tangutorun were investigated, and the relationships between soil WR and soil organic matter, total N, and total P, soil texture, pH, and concentrations of CO3 2-, HCO3-, Cl-, SO4 2-, Na+, K+, Ca2+and Mg2+were discussed. Soil WR may be demonstrated at the following nebkhas dune evolvement stages: extremely degraded>degraded>stabilized>well developed>newly developed>quick sand. Apart from some soil at the bottom, the WR of other soils(crest and slope of dune) was found to be largest at the topsoil, and decreased as the soil depth increased. The results showed that multiple factors affected soil WR characteristics, e.g. WR increased significantly as the contents of soil organic matter and total N increased, but did not change as the total P content increased. Soil texture was a key factor affecting soil WR; soil WR increased significantly as clay content increased, and decreased significantly as sand content increased. Low pH was shown to be more suitable for the occurrence of soil WR. Four cations(Ca2+, Mg2+, K+and Na+) and two anions(Cl-and SO4 2-) enhanced soil WR, while CO3 2-decreased it. HCO3-did not show any observable effect. Finally, we established a best-fit general linear model(GLM) between soil-air-water contact angle(CA) and influencing factors(CA=5.606 sand+6.496(clay and silt)–2.353 pH+470.089 CO3 2-+11.346 Na+–407.707 Cl-–14.245 SO4 2-+0.734 total N–519.521). It was concluded that all soils contain subcritical WR(0°<CA<90°). The development and succession of Nitraria tangutorun nebkhas may improve the formation of soil subcritical WR. There exist significant relationships between soils subcritical WR and soil physical or chemical properties.