Evaluating urea‐polyhalite and ammonium nitrate‐polyhalite fertilizers for mitigating ammonia volatilization in contrasting soils

Abstract Ammonia (NH 3 ) volatilization from urea‐based fertilizers reduces nitrogen use efficiency and contributes to atmospheric NH 3 emissions and associated health risks. In a laboratory study, we compared NH 3 volatilization losses from urea (Urea) (with and without a urease inhibitor [UI]), ammonium nitrate (AN), ammonium sulfate (AS), polymer‐coated urea, co‐granulated urea‐polyhalite (Urea‐Poly) (with and without a UI), and co‐granulated AN‐polyhalite (AN‐Poly) in alkaline (pH 7.5) and acidic (pH 5.9) soils. Urea‐Poly and AN‐Poly are novel co‐granulated formulations whose multi‐nutrient profile can potentially modulate microenvironmental pH and reduce NH 3 loss. All treatments were applied at rates supplying equivalent quantities of nitrogen (N) but were not balanced for other nutrients contributed by polyhalite and AS. In alkaline soil, Urea lost up to 26% of applied N, which dropped to 13% with UI. Urea‐Poly + UI reduced NH 3 volatilization to 8.8%, outperforming both Urea + UI and Urea‐Poly alone. AN and AN‐Poly and AS performed similarly with a 2%–3.5% NH 3 losses. In acidic soil, NH 3 losses were inherently low (<6%), and UI further reduced losses to 0.6% for Urea and 0.2% for Urea‐Poly. Differences between Urea + UI and Urea‐Poly + UI were not significant in acidic conditions. AN, AN‐Poly, and AS performed similarly with less than 1% NH 3 losses. These results underscore the influence of soil pH and fertilizer formulation on NH 3 emissions. Urea‐Poly + UI offers a promising strategy for mitigating volatilization in alkaline soils while delivering a balanced nutrient profile for sustainable nutrient management.