Revitalizing soil and crop nutrition: The agronomic potential of polyhalite as a sustainable multi-nutrient source

Modern agriculture’s historical reliance on mono-nutrient NPK fertilization has precipitated widespread soil degradation and the depletion of essential secondary macronutrients. This review evaluates the agronomic potential of Polyhalite (K2Ca2Mg(SO4)4.2H2O), a naturally occurring evaporite mineral emerging as a sustainable "4-in-1" fertilizer solution. Unlike synthetic blends, Polyhalite features a unique crystal structure providing Potassium, Calcium, Magnesium, and Sulfur in a chloride-free, semi-slow release matrix (27 g L-1 solubility) that effectively mitigates nutrient leaching. Polyhalite consistently transcends conventional yield ceilings. Significant productivity gains are documented in sulfur-responsive oilseeds (mustard yield +42%) and potassium-demanding cereals like rice (+16-67%). Beyond yield, it enhances critical quality parameters, including oil content in brassicas and starch levels in potatoes, driven by the synergistic physiological roles of Magnesium and Calcium. Environmentally, Polyhalite acts as a regenerative amendment; its low salt index (68.5) preserves the rhizosphere microbiome, stimulating beneficial bacterial phyla such as Proteobacteria. With a carbon footprint approximately 90% lower than chemically processed alternatives, it aligns with climate-smart agricultural mandates. However, widespread adoption faces specific challenges. The mineral's low solubility restricts its utility in precision fertigation systems due to emitter clogging risks. Furthermore, cation antagonism remains a concern in calcareous soils, where excess Calcium release may competitively inhibit Magnesium uptake. Conclusively, while Polyhalite is a robust tool for addressing global multi-nutrient "hidden hunger," its optimal use requires Site-Specific Nutrient Management (SSNM) and further investigation into long-term soil dynamics.