The competitive effects of crop straw return and nitrogen fertilization on soil acidification

Soil acidification has become an increasingly severe issue in China, with the role of straw return practices in mitigating this challenge remaining widely debated. This study examines the combined effects of straw return and nitrogen (N) fertilization on soil pH, highlighting their competing influences on acidification. A metaanalysis of 44 field trials across China revealed that N fertilization alone reduced soil pH by an average of 3.72 %. However, straw return mitigated this pH decline, increasing soil pH by 0.02 and 0.10 units in acidic and neutral soils, respectively. Compared to N-only treatment, the interaction between N and straw return produced varying effects. High N inputs (>100 kg/ha) with low straw return further decreased soil pH, while high straw return with low N inputs moderately alleviated acidification. This phenomenon is attributed to the ability of straw return to counteract H+ ion production through several mechanisms such as replenishing cations removed during crop harvest, increasing soil organic carbon (SOC), and improving nitrogen use efficiency (NUE) by optimizing the soil carbon-to-nitrogen (C/N) ratio. These findings suggest that integrating balanced straw return practices with N fertilization can effectively mitigate acidification caused by N inputs. These strategies offer significant potential for promoting sustainable agricultural systems in China and beyond.