Soil thinning dominates crop yield reduction among various degradation types in the typical black soil region of Northeast China

The degradation of black soil poses a substantial threat to the sustainability of agriculture in Northeast China. Although numerous studies have investigated the impact of soil degradation on crop yield, including soil thinning, nutrient depletion, and structural degradation, the primary form of degradation contributing to regional crop yield reduction remains unclear. We synthesized 488 paired observations from 32 studies to identify the predominant type of soil degradation in the typical black soil region of Northeast China. Subsequently, we examined the effects of environmental factors on crop yield occurring under the dominant degradation type. Our findings indicated that the yield reduction is the greater under soil thinning (effect size: −27 %), followed by nutrient depletion (effect size: −20 %) and soil structure degradation (effect size: −6 %). Focusing on the soil thinning, we identified 5 cm reduction in topsoil depth as the threshold, below which crop yields are not significantly affected. The impacts of soil thinning on yield followed a non-linear pattern, with severe yield losses for greater reduction in topsoil thickness, and a greater reduction in soybean yield compared to maize. The depth of topsoil removal was the primary factor causing crop yield reduction, followed by soil organic matter (SOM) and total soil nitrogen (STN). The structural equation model further indicated that topsoil removal depth, experimental duration, and fertilizer types not only directly affected the changes in crop yield, but also indirectly impacted yield by altering soil physical and chemical properties. Overall, our findings highlight the critical role of soil thinning in driving crop yield reductions in Northeast China, and emphasize that soil properties are key determinants in the recovery of crop yields in agricultural systems affected by soil thinning.