Regional disparity in the improvement of cultivated land quality in China since the 1980s.

Cultivated land is fundamental to global food security and sustainable development. However, quantifying changes in its long-term quality at a national scale remains a significant challenge. Here, we present a comprehensive assessment of the spatiotemporal evolution of cultivated land quality across China from the 1980s to the 2010s. By using a machine learning framework with over 190,000 soil samples and a suite of environmental variables, we found a significant nationwide improvement in the average cultivated land quality grade by 8.2% (0.44 grades) over the three decades. However, these changes differ across regions. The Huang-Huai-Hai Plain had the most substantial expansion of high-quality cultivated land, whereas low-quality cultivated land expanded in Northern and Western China, indicating ongoing land degradation in these ecologically vulnerable zones. The model interpretability analysis shows the relative contributions and complex interactions among soil properties, topography, climate and crop growth. Cultivated land quality sharply increased with increased soil organic matter and stabilized when soil organic matter approached approximately 40 g kg-1. The spatial heterogeneity in improved cultivated land quality in China underscores the critical need for targeted policies in ecologically sensitive regions to simultaneously ensure food security and environmental sustainability. Our findings provide valuable insights for designing effective land management strategies both in China and for other regions worldwide.