Assessment of cultivated land transfer in and transfer out in the Ili River Basin from 1990 to 2020

In previous assessments of the quality changes associated with the transfer in and out of cultivated land, soil physical and chemical properties have rarely been considered. The Ili River Basin is an important agricultural and husbandry base in Xinjiang, which has undergone significant changes in its natural environment and socio-economic conditions over the past 30 years. This study used a 30-meter resolution dataset of China’s multi-year land cover to obtain the spatial distribution data of cultivated land in the Ili River Basin for the year of 1990 and 2020, exploring the changes in the quantity of cultivated land as well as the source and distribution of transferred-in cultivated land. Based on the DEM data and basic attribute dataset of China high resolution national soil information grid, we calculated the Cohen’s D values to compare the differences in elevation, slope, organic carbon content, total phosphorus content, total nitrogen content, sand content, and pH between transferred-in and transferred-out cultivated land, and compared these with the those from the seven major agricultural regions of China. Compared with 1990, the area of cultivated land in the Ili River Basin increased from 6,196.80 km² to 8,606.51 km² by 2020. The transferred-in cultivated land was mainly high-elevation grassland concentrated along the bank of the rivers, which is mainly related to improved irrigation and water diversion capacities in the Basin. From 1990 to 2020, transferred-in cultivated land increased greatly in elevation compared to transferred-out cultivated land, while the slope only showed a slight increase (Cohen’s D values of 0.851 and 0.276, respectively). Organic carbon content, total nitrogen content increased moderately and slightly, respectively, while the changes in total phosphorus content, sand content, and pH were very small (Cohen’s D values of 0.558, 0.308, −0.116, 0.081, and 0.001, respectively). This indicates that the soil quality of transferred-in cultivated land in the Ili River Basin is fairly good, which is different from those in Xinjiang and seven agricultural regions of China. There is still a large amount of arable grassland available for future cultivation in Ili. However, to ensure balanced development of agriculture and husbandry and to reduce ecological risks, future over-cultivation of grasslands should be limited, especially in ecologically vulnerable high-altitude areas (such as those above 2 000 m) and steep-slopes, which should receive special attention.