Paddy soil acidification: causes, harms, and mitigation measures

Paddy soil acidification is one of the most serious global land degradation processes, threatening the sustainable production of rice ( Oryza sativa L.). Its natural drivers include acid deposition, excessive fertilization, high-yield cultivar growth, and acids secreted by rice roots. The excessive fertilization breaks the nutrient balance in the soil, largely accelerating the soil acidification and degradation. The resultant soil acidification and degradation lead to direct agricultural losses (e.g., yield reduction, nutrient leaching, increased heavy metal uptake) and indirect ecological consequences (e.g., aggravated soil-borne diseases). A series of measures, such as application of alkaline amendments, biochar and microbial agents, have been employed to alleviate paddy soil acidification, and their underlying mechanisms are illustrated. Lime (CaCO 3 ) represents an efficient and economic-affordable reagent to remediate soil acidification. The dosage of lime usage depends on the acidification extent: “single-strength” buffer is recommended for soils with pH 5.0–6.4, while “double-strength” buffer is recommended for soils with pH < 5.0. This review provides a theoretical foundation and technical guidance for managing paddy soil acidification. Critical knowledge gaps persist in the synergistic effects of climate change, modern cropping systems, and intensive fertilization on the soil acidification. To realize sustainable management of acidified paddy soil, future efforts should integrate in situ monitoring, novel alleviation techniques, and fertilizer–water management optimization.