For decades, China’s vital agricultural soils have been growing more acidic, a trend that threatens crop productivity and ecosystem health. This acidification has been driven by the massive use of chemical nitrogen fertilizers and industrial emissions required to feed its population and power its economy. Now, a groundbreaking study reveals a major turning point: this widespread acidification has, on the whole, ceased.

The research, led by Profs. YAO Yijun and LUO Yongming from the Institute of Soil Science of the Chinese Academy of Sciences, shows that the consistent acidification of China’s cropland soils that began in the 1980s stabilized around 2013. This change is strongly linked to agricultural policy reforms that altered patterns of nitrogen fertilizer application.

To uncover these trends, the researchers built the most extensive soil pH dataset for China to date, compiling information from 7,024 regional surveys conducted between 1985 and 2022. Using this data, they developed a sophisticated machine-learning model to project the spatiotemporal changes in topsoil pH across the country from 1985 to 2040. The results, published in Nature Geoscience, show a cumulative pH decline of approximately 0.25 units from 1985 to the turning point in 2013.

However, the study reveals the story is not uniform across all farmland. The team found a sharp divergence between different types of agricultural land. While paddy fields began to show signs of pH recovery after 2013, dryland soils have remained largely static, showing minimal rebound from their acidified state.

“For years, the narrative has been one of continuous decline in our soil health. Our work pinpoints a crucial halt in this trend and directly connects it to national agricultural strategies,” said Prof. Yao, a corresponding author on the study. “It’s a powerful testament to how targeted policies for sustainable fertilizer management can produce tangible, large-scale environmental results.”

Looking to the future, the model projects that even with continued reductions in nitrogen fertilizer use, a full recovery of soil pH to 1980s levels is unlikely by 2040, particularly in dryland areas. This suggests that simply cutting fertilizer use may not be enough to reverse decades of damage. The slow recovery highlights the soil's limited natural buffering capacity and the persistent effects of past acidification.

The findings underscore the urgent need for a more comprehensive approach to soil management. The researchers suggest that strategies must be tailored to specific regions and soil types. This could include promoting the use of organic fertilizers, adopting controlled-release fertilizers to improve nitrogen use efficiency, and developing other practices to restore soil health while maintaining high crop yields.

“This study provides more than just a historical assessment; it gives us a dynamic framework to monitor soil health in near real-time,” stated Prof. Yao. “This isn’t just about China; it’s a lesson for global agriculture. By integrating vast datasets with advanced models, we can better understand and manage our precious soil resources, paving the way for more sustainable farming practices worldwide.”