Spatiotemporal divergence of soil acidification in China’s cropland

Soil acidification in China's croplands, driven by intensive agriculture, threatens both agricultural sustainability and ecological security. However, its large-scale spatiotemporal dynamics and underlying drivers remain poorly understood. We developed a meta model coupling of process model and machine-learning, integrating national soil survey information from the Chinese Soil Series Records and the VSD+ model to simulate and map soil pH trajectories from 1980 to 2100. We found a pronounced national acidification trend from 1980 to 2020, with average cropland soil pH declining by 0.37 units (from 7.05 to 6.68). This trend varied regionally, with the most severe acidification in Northeast China (ΔpH = -0.67) and the slowest decline on the Qinghai-Tibet Plateau (ΔpH = -0.11). Projections show that even under a nitrogen fertilizer zero-growth scenario, soil pH will continue to decrease to 6.49 by 2100. Our model reveals that fertilizer management exerts a stronger influence on acidification than climate change, as evidenced by minor differences among climate scenarios. Mechanistically, nitrogen transformation was the dominant acidifying process in upland systems, while both HCO₃ leaching and nitrogen transformation were primary drivers in paddy systems. This study provides a quantitative basis for sustainable nutrient management and offers valuable insights for mitigating soil acidification in global agricultural systems.