Agricultural Sciences: Techniques and Innovations Vol. 12

Polyhalite is a naturally occurring hydrated sulphate mineral that supplies potassium, sulphur, calcium and magnesium in a fixed stoichiometric association. Its increasing agronomic use has generated claims extending from balanced crop nutrition to improved soil health and lower environmental impact. This critical narrative review evaluates those claims by separating demonstrated nutrient-delivery effects from plausible but incompletely tested soil-health mechanisms. Literature published from 1 January 1991 to 5 June 2026 was identified through accessible scholarly indexes, bibliographic databases, journal platforms, institutional repositories and citation searching, with foundational mineralogical studies included where necessary. Evidence was appraised for comparator adequacy, nutrient-rate equivalence, duration, soil and crop representativeness, measured soil-health domains, independence of funding and consistency across studies. Polyhalite is an effective source of potassium and sulphate sulphur, while its calcium and magnesium can contribute to crop uptake and exchangeable pools under responsive conditions. Its slower dissolution than highly soluble potassium salts can moderate nutrient-release peaks, but release remains strongly dependent on particle form, moisture, soil texture and rainfall. Crop responses are generally positive relative to nutrient-omission controls, yet superiority over balanced conventional fertilisation is inconsistent. Direct evidence for durable improvement of soil structure, organic carbon, biodiversity or multifunctionality remains limited; most studies assess post-harvest nutrient concentrations, pH, electrical conductivity or short-term enzyme and microbial indicators. The product’s chloride-free composition is useful for chloride-sensitive crops and some salinity contexts, but does not establish universal agronomic or environmental superiority. A substantial share of the evidence base involves manufacturer funding or authorship, reinforcing the need for independent, long-term, nutrient-balanced trials. Polyhalite can support sustainable agriculture when selected through soil testing, crop demand, rainfall risk and whole-rotation nutrient budgets, preferably as part of blended and adaptive nutrient management rather than as a stand-alone soil-health intervention.