China's agricultural soils have become increasingly acidic over the last few decades, threatening crop productivity and ecosystem health. This acidification has been driven by the extensive use of chemical nitrogen fertilizers needed to feed the population, along with industrial emissions associated with economic development. Fortunately, a new study published in Nature Geoscience on Oct. 14 reveals that widespread acidification has ceased.

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

The researchers combined information from 7,024 regional surveys conducted between 1985 and 2022 to compile the most extensive soil pH dataset for China to date. Using this data, the researchers developed a sophisticated machine-learning model to identify spatiotemporal changes in topsoil pH across China from 1985 to 2040. Their analysis revealed a cumulative decline of approximately 0.25 pH units between 1985 and the stabilization point in 2013.

However, recovery has been uneven across different types of farmland. While paddy fields have shown signs of pH recovery since 2013, dryland soils have largely remained static, with 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, corresponding author of 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—especially in dryland areas. This suggests that reducing fertilizer use alone may not be sufficient to reverse decades of damage. The slow recovery process underscores the limited natural buffering capacity of soil and the enduring impact of past acidification.

The researchers emphasize the need for region-specific soil management strategies to accelerate restoration. These could include wider use of organic fertilizers, controlled-release nitrogen fertilizers, and other practices to restore soil health while maintaining high crop yields.

"This study provides more than just a historical assessment; it provides a dynamic framework to monitor soil health in near real-time," said 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."