Spatial and Temporal Variation in Soil Salinity and Correlation with Groundwater Depth in the Karamay Irrigation District of China

The secondary salinization of irrigated areas poses a direct threat to both the sustainable development of oasis agriculture and ecological stability in arid regions. In this study, we conducted an experiment to examine alterations in groundwater levels and soil salinity within the plow layer, as well as their combined impact, in arid regions following extended reclamation in standard diversion irrigation areas. For this experiment, the Karamay irrigation district was selected. Four different years, namely, 1996, 2006, 2016, and 2021, were selected for soil sampling and groundwater monitoring data. Descriptive statistics, along with the use of GIS technology and Pearson’s correlation, were employed to analyze the data in order to discern the patterns of soil salinity and groundwater depth within the plow layer. Additionally, this approach helped establish the correlation between these factors over the last 25 years of reclamation in the Karamay irrigation district. The results showed that, (1) due to an increase in the reclamation duration, the groundwater depth in the irrigation area decreased year by year, and the salinity of the arable soil showed an overall decreasing trend, but it increased in local low-lying areas; (2) the influence of the groundwater depth on the salinity of the arable soil had a threshold value. It decreased from 3.1 m in 2016 to 2.4 m in 2021, and a significant negative correlation was observed between salinity and the depth of groundwater. When the groundwater depth was shallower than the threshold value, the soil salinity in the plow layer was negatively correlated with the groundwater depth. In the arid irrigation zone, inadequate drainage facilities resulted in a significant rise in the groundwater table due to the excessive amount of irrigation water. This created secondary salinization of the arable soil. It is thus concluded that implementing adequate drainage systems in arid irrigation regions will help prevent secondary salinization and promote the sustainable development of agriculture in these areas.