Soil acidification impacts on water dynamics and global paddy rice production challenges

Soil acidification in paddy rice systems is a growing global challenge that threatens rice production, water dynamics, and ecosystem health, with significant implications for food security. This review examines the causes, prevalence, and impacts of soil acidification in major rice-producing regions, including China, India, Vietnam, the United States and Tanzania. Natural processes, such as organic matter decomposition and soil weathering, and anthropogenic factors, including excessive nitrogen fertilizer use, acid rain, and intensive monoculture, drive pH declines below the optimal range of 5.5–6.5, particularly in acid sulfate soils. Acidification disrupts water dynamics by lowering floodwater pH to as low as 3.7–5.0, increasing the solubility of toxic metals like aluminum up to 20 mg/L and iron up to 50 mg/L, and altering soil physical properties, which reduce water retention by 5–15% and impair drainage (hydraulic conductivity reduced by up to 40%). These changes degrade irrigation water quality and contaminate runoff, threatening aquatic ecosystems by reducing microbial diversity, and fish populations. Region-specific variations highlight the need for tailored management strategies, such as liming, biochar amendment, balanced fertilization, and acid-tolerant rice varieties, to mitigate acidification. The review underscores the urgency of integrated approaches combining soil amendments, precision agriculture, and policy interventions to ensure sustainable rice production and environmental resilience.