Assessment of soil salinisation in the Ejina Oasis located in the lower reaches of Heihe River, Northwestern China

Recognition of the spatial-temporal distribution characteristics of soil salinity has become an important basis for the formulation of strategies required in the utilisation and sustainable development of soil resources in arid and semi-arid area. In this paper, based on vegetation cover dataset during 1998–2015 in Ejina region combined with the collected soil salinity data, geostatistical methods were used to explore the temporal and spatial dynamic characteristics of soil salinity and its impact on vegetation in the study area. The results showed significant differences in soil salinisation characteristics with a large variability in the soil salinity among the different soil depths, with a variation coefficient ranging from about 0.97–1.47. Soils are represented by a continuous variation, both in space and time. Soil salinity showed an obvious spatial autocorrelation, with a plaque type distribution. The areas of the salinised soil found for the years 2003, 2011 and 2015 were approximately 18,565, 23,206 and 17,721 km2, respectively. From the relationships deduced between the normalised difference vegetation index (NDVI) and soil moisture and salt content in different soil depths, the present study ascertains that the soil moisture content is the most important limiting factor of vegetation growth in Ejina Oasis.