Land degradation decreased crop productivity by altering soil quality index generated by network analysis

Soil erosion is a principal mechanism of land degradation, and wind erosion is particularly marked in northeast China due to its ecological characteristics. However, most investigations on the implications of land degradation on soil quality and crop productivity have concentrated on water-erosion regions, and little focus has been placed on the wind-erosion region. Therefore, we examined the impacts of land degradation on soil quality and crop productivity in the degradation area of Horqin Sandy Land, the wind-eroded region of northeast China, which suffers from varying intensities of land degradation, that is, no degraded grassland, lightly, moderately, and severely degraded croplands. In our study, network analysis (NA) was applied as a novel approach to calculate the soil quality index (SQI), which covered 11 physical, 12 chemical, and 6 biological variables measured in the 0-20 cm soil layer as indicators of soil quality. Results showed that land degradation resulted in adverse effects on soil properties. SQI, crop yield, and above-ground biomass significantly decreased with land degradation increasing (P < 0.05). Specifically, the result of NA showed soil organic carbon, microbial biomass carbon, and bulk density (BD) were the most responsive factors impacting SQI under land degradation. Structural equation modeling showed that land degradation led to the reduction of crop productivity by altering soil properties and then changing SQI. Soil physical properties were the best mediator for the indirect effects of land degradation on SQI. In addition, the BD increased, but clay, soil total nitrogen, and organic matter content decreased from 1981 to 2022, which reveals land degradation in this area. Our investigation provides a theoretical foundation for preserving cropland in wind-eroded areas of northeast China.