Topography, management, and extreme precipitation influence greenhouse gas emissions in a cool, humid corn silage...

Agricultural soils are sources of nitrous oxide (N₂O) and, under prolonged saturation, methane (CH₄)-two potent greenhouse gases (GHGs). Soil management, field topography, and climate all influence GHG emissions, yet their interactions are not well understood. Over 17 months, we evaluated how three distinct management systems-Conventional, a soil health system (Soil Health), and a flocculated manure solid amendment (Flocculated Solids)-interacted with topographically high and low areas to influence N₂O and CH₄ emissions in a 21 ha corn (Zea mays L.) silage field in western Vermont, during a period of abnormally high precipitation. At 18 plots (3 treatments × 2 topographic positions × 3 replicates), we measured GHG fluxes year-round alongside soil temperature, moisture, and inorganic nitrogen. Annual N₂O emissions were 4.4 times greater in Soil Health-Low plots (74.3 kg N₂O-N ha^-1 year^-1) than in Flocculated Solids plots, which had the lowest emissions (17.0 kg N₂O-N ha^-1 year^-1). Annual CH₄ emissions were greatest in low plots across all treatments, with low plots emitting 2.2 times more CH₄ than high plots. Boosted regression tree models identified soil moisture, ammonium, CO₂ flux, and nitrate as the strongest predictors of daily N₂O fluxes. For CH₄, inundation duration was the dominant driver, with emissions increasing sharply after >40 days of continuous saturation. Treatment and topography explained <5% of emissions in both models, indicating that their effects are primarily indirect, modifying soil moisture, nitrogen availability, and organic matter inputs that ultimately drive GHG emissions.