Rethinking plant nutrients in practice: partial substitution of potassium by sodium in tropical agriculture

Abstract Background and Aims Potassium (K) is a key macronutrient that regulates diverse metabolic processes, yet K-deficiency is widespread in tropical crops because the underlying soils are inherently low in natural fertility. However, the high price of K-fertilizer constrains application rates, challenging efforts to sustain productivity within economically and environmentally sustainable systems. Increasing evidence indicate that K can be partially substituted by sodium (Na), which represents a cost-effective strategy to alleviate K deficiency while enhancing soil fertility and plant resilience. This review explores the physiological mechanisms, crop-specific potential, environmental implications, and agronomic feasibility of partially replacing K with Na, highlighting promising pathways toward more sustainable fertilization strategies in tropical agriculture. Outcomes Partial substitution of K with Na can provide physiological, environmental, and economic benefits, particularly in tropical systems. Sodium can partially sustain turgor, stomatal function, and enzyme activity in K-deficient plants, supporting photosynthesis and biomass accumulation, especially under drought. Economically, sodium chloride (NaCl) is more affordable than potassium chloride (KCl), while environmentally, its use can reduce reliance on non-renewable K sources and valorize industrial residues. Nonetheless, species-specific tolerance limits its broad application and risk of soil salinization is still uncertain under tropical conditions. Field experiments are therefore essential to establish safe, crop-specific guidelines, supporting sustainable and cost-effective fertilization strategies. Final Consideration Recognizing Na as a context-dependent co-nutrient allows for innovative, crop-specific fertilization strategies that improve agronomic efficiency, reduce costs, and promote environmental sustainability. However, the risks of soil salinization and variability in species tolerance underscore the need for long-term field studies to define safe application thresholds.