Diverse organic amendments mitigate soil acidification by improving soil organic matter in acid soil area over four decades

Organic amendments have shown profound performance to enhance soil carbon (C) sequestration and crop productivity.  However, the synergistic effects of various organic amendments on maintaining/improving pH buffering capacity (pHBC) remain unclear. Here, based on a 42-year ongoing field experiment, we explored the response of pHBC and crop productivity to synergistic incorporation of plant C input (green manure with or without straw) vs. diverse C input (livestock combined with plant C). Mineral fertilization caused pH decline by 0.12-0.39 units, compared with diverse C input. Plant C input showed no significant effect on pHBC, whereas diverse C input, e.g., synergistic incorporation of green and livestock manure, increased soil pHBC by 31-40% compared with control. This primarily attributed to the rise in Ex-Ca²⁺ and soil organic matter, particularly humic substance compositions. Furthermore, the protonation of organic anions produced from humic acid dissociation also enhanced pHBC. Critically, the mitigation of soil acidification establishes a critical foundation for improving crop yields, average outperforming control and plant C input by 32% and 12%, respectively. These findings highlight that the diverse C input based on soil amendments as agronomically optimal and sustainable strategy to mitigate soil acidification and sustain crop productivity in acid soil area.