Ammonia and methane mitigation from dairy manure using sulfur-based manure storage additives

Dairy manure storage is a major source of greenhouse gas emissions and other air pollutants, including methane (CH₄) and ammonia (NH₃). Easily deployable mitigation strategies, such as manure storage additives, can help reduce the environmental impact of dairy production. Sulfur-based manure storage additives, specifically gypsum (CaSO₄), have been proposed as low-cost manure amendments that may influence CH₄ emissions; however, their potential to mitigate NH₃ emissions and their effectiveness across sulfur dosages remain unclear. This study evaluated two gypsum additives at low and high levels (G1L: 4.23 mg L^-1; G1H: 21.15 mg L^-1; G2L: 5000 mg L^-1; G2H: 25,000 mg L^-1) to quantify their effects on NH₃ and CH₄ emissions from dairy manure over a 12-week period. Cumulative NH₃ and CH₄ emissions were measured using the closed-chamber manure emission system, which consisted of a closed chamber integrated with a multi-gas Fourier Transform Infrared analyzer, used to measure emissions from bucket-sized manure storages. Ammonia losses decreased by 27% and 33% in treatments G2L and G2H, respectively, while treatments G1L and G1H showed no significant effect. The effect on CH₄ emissions mitigation followed the same pattern, with reductions of 82% and 90% in treatments G2L and G2H, respectively. These results demonstrated a dose-response relationship, in which higher gypsum dosages yielded substantial reductions in NH₃ and CH₄ emissions. Overall, manure additive treatment using gypsum at sufficient rates offers a practical strategy to mitigate gaseous nitrogen and carbon losses from dairy manure, supporting more sustainable manure management and contributing to climate and air‑quality goals.