Managing Soil Acidity and Fe–Al Toxicity in Submerged Paddy Soils: Biogeochemical Processes, Environmental Implications and Integrated Amelioration Strategies

Abstract

Submergence transforms acidic rice soils into a dynamic biogeochemical environment in which redox potential, pH, iron and aluminium speciation, nutrient availability and microbial activity change throughout the cropping period. These transformations can partly alleviate aluminium toxicity through pH-mediated hydrolysis, while simultaneously increasing soluble Fe(II) through microbial reduction of Fe(III) minerals. Consequently, acid-affected submerged rice soils may experience a shifting combination of acidity, aluminium toxicity, iron toxicity and nutrient imbalance rather than a single, static constraint. This review synthesises the mechanisms governing these changes and evaluates the roles of liming materials, phosphogypsum, dolomite, magnesium sulphate, calcium silicate, organic amendments and biological approaches. Particular attention is given to the complementary functions of amendments: acidity neutralisation, calcium and magnesium supply, aluminium detoxification, silicon-mediated stress tolerance and modification of the rhizosphere environment. The review also considers water management and the environmental implications of amendment use, including nutrient imbalance, amendment quality, sulphur cycling and the need to avoid excessive inputs. Evidence indicates that no single amendment can reliably resolve all constraints in strongly acid, Fe-rich submerged soils. A site-specific strategy that integrates soil diagnosis, temporal monitoring, complementary amendment functions and appropriate water management is therefore more defensible than blanket application. Future research should combine time-resolved soil chemistry with plant responses, amendment interactions, environmental risk assessment and field-scale validation to develop resilient and resource-efficient management strategies for acid-affected rice ecosystems.