Characteristics and complexity of soil salinity distribution in agro-ecosystems of Hetao, upper Yellow River basin: insights from field, canal and regional scales

Soil salinization is one of the most common land degradation processes that impacts on agricultural production, environmental health, and economic welfare. In this study, the Hetao Irrigation District (Hetao) located in the upper Yellow River basin, with suffering long-term soil salinization problems, was selected as the case study area. The first task in managing soil salinity in Hetao is to understand the major factors controlling its spatial distribution, both over large regions and within individual fields. Therefore, field sampling experiments and investigations related to layered soil salt contents, groundwater, irrigation and ground elevation were carried out at three scales (field scale, canal scale and regional scale) covering both croplands and natural vegetation patches during 2016 and 2017. Spatial characteristics of soil salinity were analyzed for field, canal and regional scales. Results showed that, in the regional scale, the soil salinity distribution was dominated by topography and groundwater depth; in the canal scale, it was dominated by irrigation and cropping pattern; in the field scale, it was dominated by micro-topography and the uniformity of field irrigation. Therefore, soil salinity management strategies should be adaptable to its application scales. In the field scale, land leveling can be carried out to guarantee the uniformity of irrigation; in the canal scale, the cropping pattern and water allocation can be optimized to reduce salt accumulation; in the regional scale, the depth and density of drainage ditches can be increased to improve groundwater table control. This study can provide some new insights into soil salinity diagnosis, monitoring and management.