Migration, Implications and Reduction of Sodium Ions in Soil: A Review

Sodium ions (Na+) are typically the dominant ions in soil salts, where their excessive accumulation forms sodic saline soils with degraded structure that harms crops and soil biota. However, the adverse effects of Na+ on soil functions and microorganisms have not yet been systematically investigated, and the application of conventional and emerging remediation methods with regard to Na+ dynamics remains unclear. This review synthesizes the current knowledge on natural and anthropogenic sources, distribution, and transport of soil Na+ and critically discusses its adverse impacts on soil function and crop performance. Long-used remediation techniques and recently developed emerging methods have been compared, and their mechanisms, reported effectiveness and practical applicability have been highlighted. Our study revealed that traditional reclamation methods through agronomic practices, ion exchange amendments (e.g., Ca- or K-rich conditioners), and plant–microbial interventions can effectively reduce soil Na+ and sodicity. Emerging saline–alkali soil amelioration methods (e.g., engineered/nano amendments, electrochemical stimulation, and salt-tolerant plant–microbe consortia), especially when combined in composite strategies, can more selectively and efficiently regulate Na+ and ion transport. Moreover, durable soil Na+ reduction is most consistently associated with integrated management strategies that couple optimized irrigation, water quality, and targeted amendments. Finally, we outline research needs for mechanistic, field-scale, long-term validation of the fate of Na+ and its transport for robust assessments of safety, durability, and cost to support scalable implementation.