Acidification and nitrification inhibition of manure alters greenhouse gas emissions and nitrogen cycling in diverse agricultural soils

Manure amendments are widely used in agriculture to enhance crop productivity and maintain soil organic matter, but they also contribute to greenhouse gas emissions and reactive nitrogen (N) losses. Manure acidification and nitrification inhibitors (NIs) have been proposed as mitigation strategies, but their effectiveness likely varies with soil characteristics. To evaluate the influence of acidified and NI-treated manure on N cycling across different soil types, we conducted a 28-day laboratory incubation using soils collected from major agricultural regions in Wisconsin. We measured emissions of nitrous oxide (N₂O), nitric oxide (NO), carbon dioxide (CO₂), and methane (CH₄), along with soil ammonium (NH₄ ⁺) and nitrate (NO₃ ^-) dynamics. Acidified manure enhanced short-term NH₄ ⁺ retention in all soils but increased cumulative N₂O emissions in the sandy soil compared to untreated manure, likely due to pH-driven disruption of nitrification and incomplete denitrification. In contrast, the NI dicyandiamide (DCD) consistently suppressed nitrification early in the incubation, resulting in significantly lower N₂O and NO emissions, often approaching levels observed in the no-manure controls, particularly in the sandy soil. Manure amendments increased CO₂ fluxes relative to the no-manure controls, but acidified manure emitted less CO₂ than DCD-treated manure, likely due to temporary suppression of microbial respiration. CH₄ emissions were minimal and largely unaffected by treatments. NIs offer consistent benefits in reducing N₂O and NO losses, while acidification can increase these emissions in certain soil conditions, highlighting the importance of tailoring management practices to specific soil characteristics.