Manure application mitigates the negative effects of acidification on soil quality, ecosystem multifunctionality, and crop productivity

Soil acidification imposes profound challenges on global food security and the functionality of agroecosystems. However, knowledge gaps remained concerning the interaction between varying soil pH and contrasting fertilization strategies on soil quality and crop productivity. Herein, a six-year field experiment was performed to investigate the effects of four acidity soils (no, low, medium, and high acid addition) and two fertilization types (synthetic fertilization vs. manure) on soil quality, ecosystem multifunctionality (EMF), and crop yields in the Huai River Basin. Soil acidification reduced maize and wheat yields by 6–45% and 14–47% after six years relative to non-acidic soil, respectively, while manure application maintained crop yields equivalent to that of synthetic fertilizer. Soil acidification increased the soil organic C (SOC) by increasing mineral-associated organic C due to the enhanced positive charge on mineral surfaces. Conversely, most of the soil properties and C, N-acquisition enzyme activities were reduced with soil acidification intensifying regardless of soil depth, resulting in considerable decreases of soil quality (36–56%) and EMF, as revealed by PLS-PM analysis. Manure application substantially increased the SOC, primarily attributing to its high organic matter content, regardless of soil depth and soil acidification levels. Finally, manure application increased soil quality by 13–17%, and enhanced the EMF due to stimulated C-acquisition enzyme activity. Additionally, the soil quality index exhibited a positive correlation with EMF across 0–20 cm and 20–40 cm soil depths. In conclusion, soil acidification compromises crop productivity and soil quality, yet manure serves as a compelling and sustainable alternative to synthetic fertilizer, effectively mitigating soil acidification, sustaining yields, and improving soil quality and ecosystem multifunctionality.