The role of wasteland in salt discharge and its impact on the distribution and transformation of arable land

Dry drainage systems enhance the leaching and migration of soil salinity in cultivated areas through evaporation in fallow zones (low-lying wastelands), improving soil quality in a cost-effective and environmentally friendly manner. However, the ongoing expansion of arable land reduces the extent of such wastelands, underscoring the need to optimize their management for maximal salt discharge. This study examines the contribution of wasteland to regional salt removal and its subsequent effects on arable land distribution, land-use conversion, and salinization dynamics. Taking the Hetao Irrigation District—a large irrigation area located in the upper reaches of the Yellow River and the largest designed irrigation area in China—as the research area, we conducted a salt inversion analysis based on Landsat remote sensing data and land use datasets to extract the distribution, location, and salinization levels of different land types. Our findings reveal substantial changes in both arable land and wasteland in the Hetao Irrigation District. From 2003 to 2023, arable land remained the dominant land-use type in the Hetao Irrigation District, characterized by widespread distribution and relatively large contiguous patches. In contrast, wasteland was primarily distributed in the western and northern regions in 2003, but after 2008, its area decreased significantly, exhibiting a trend toward smaller, more fragmented, and dispersed patches. Specifically, arable land expanded from about 7,800 km² to 8,600 km², accounting for 76.51% of the total area. Wasteland area declined annually from 2008 to 2018 but showed signs of recovery from 2018 to 2023. Although wasteland occupies a relatively small area, it acts as a major salinity sink, concentrating approximately 15.74%–35.09% of the total soil salts in the region. The spatial dispersion of wasteland fluctuated over the observation period. The distribution of wasteland showed the highest dispersion in 2003, followed by alternating phases of aggregation and re-dispersion, without forming a clear long-term trend and maintaining an overall dynamic equilibrium. This suggests that the spatial distribution of wasteland exhibits temporal elasticity, with its dispersion and aggregation significantly influenced by short-term factors, yet no systematic large-scale expansion or contraction occurred. Due to elevated salinization, some cultivated land became unsuitable for crops and transitioned primarily into wasteland or grassland. Spatially, wasteland shifted westward from 2003 to 2018, then returned eastward by 2023, with minimal north–south movement. The salinity dynamics in these discharge zones are influenced by climate, groundwater, and evaporation, which collectively alter salinization patterns and land suitability. Newly formed wastelands continue to absorb salts from surrounding soils, thereby modulating regional salinity levels and influencing land-use configurations. Overall, this study not only provides critical insights into the interactions between arable land and wasteland but also emphasizes the necessity of sustainable land management practices to address salinization challenges. Our findings can inform policymakers and land managers in developing strategies aimed at optimizing land use while preserving soil health and enhancing agricultural resilience in the face of increasing salinity pressures.