Characteristics of surface soil salinity and impact factor analysis for the oasis in the upper reach of the Tarim River

Salinization of irrigated lands is a common phenomenon wherever irrigation is practiced under arid or semi-arid conditions. In arid land, salinization affects the sustainability of irrigation systems through causing significant degradation of soil resources. A case study was carried out in Alar irrigated area of Xinjiang Province to reveal the characteristics of total salt in the surface soil for different types of land uses (e. g., cropland, new cultivated cropland, abandoned land, plantation, natural forest, saline-alkali land and grassland). The path coefficient between total salt in the surface soil and their impact factors were also analyzed. The results showed that the total salt in the surface soil was higher than those in the subsoil and substratum soil, and this indicated a salt accumulation trend in the surface soil. The total salt content in the surface soil of saline-alkali land (52.93 g/kg) was highest between different types of land uses. The decreasing order of the total salt content in the surface soil was: saline-alkali land > natural forest > plantation > grassland > abandoned land > cropland > new cultivated cropland. Path analysis showed that the path coefficients between the total salt contents in the surface soil and other properties could be arranged as: S20-50(0.415), SAR(0.414), SDR(-0.344), Dg(-0.201), concentration ratio of Cl-and SO42-(0.200), concentration of HCO3-(0.162), pH(0.092), soil density(-0.086), S50-80(0.080) and SSP(0.071). In addition, the salt source distribution and chemical properties of ionic composition had the greatest contribution to salt accumulation in the surface soil. The direct path coefficients of total salt content in the subsoil and sodium adsorption ratio (SAR) were 0.415 and 0.414 respectively. The impact of ground water depth was less significant to the total salt content in the surface soil, and that of the soil physicochemical was the least significant. The total salt content in the surface soil and SAR showed that chemical properties of ionic composition were two primary factors of salt accumulation in surface soil.