Straw return exacerbates soil acidification in major Chinese croplands

Straw return has been widely recommended as a practice of climate-smart agriculture. It is generally conceived that straw return also alleviates soil acidification, though this assumption has not been tested over large geographical areas. Here, we assess its contributions to soil acidification based on three datasets across China. Unexpectedly, straw return was found to predominately aggravate soil acidification in 145 investigated field experiments. The magnitude of straw-induced soil pH change was negatively correlated with initial soil pH. The critical initial soil pH in dry and paddy lands, above which straw return caused further soil acidification, were 6.7 and 5.4, respectively. We estimated that straw return would exacerbate soil acidification in 77% and 80% of dry and paddy lands, respectively. Our analysis disclosed the first evidence of accelerated soil acidification by straw return at national scale, providing new insights into both sustainable straw utilization and soil acidification remediation.