Legacy effects of inundation on greenhouse gas emissions and soil dynamics in forage systems

Soil inundation increases anaerobiosis, slows organic matter decomposition, and affects greenhouse gas production from soils. The objective of this study was to evaluate the effects of natural short-duration recurring inundation on CO₂, CH₄, and N₂O emissions, as well as on labile soil permanganate oxidizable carbon and autoclaved-citrate extractable (ACE) protein contents. We assessed two locations in Ohio separately: (1) in the Northwestern location, hayfields prone to high inundation (N-HIH), low inundation (N-LIH), and non-inundated (N-NIH), and (2) in the Southern location, pasture fields prone to inundation (S-IP) or non-inundated (S-NIP) and non-inundated hayfield (S-NIH). Inundation was not controlled or simulated; rather, we evaluated it as a long-term natural effect. We collected greenhouse gas (GHG) samples in spring, early and late summer, and fall of 2021 and 2022. At Northwestern location, N-LIH and N-HIH emitted less CO₂, likely because of lower organic matter oxidation under more intense inundation. This pattern was less evident in the Southern location, where S-NIP and S-IP generally showed similar CO₂ emissions. Both locations acted as CH₄ sinks, and emissions remained largely unaffected by inundation at either location, suggesting that inundation duration and/or intensity were insufficient to maintain anaerobic conditions. Inundation, however, clearly increased N₂O emissions in both locations, especially during the drying period in early and late summer, after the wetter spring seasons, characterizing a progressive response to inundation. We frequently observed the highest N₂O emissions alongside elevated soil ACE protein levels. Natural recurring short-term inundation increased GHG emissions from hayfields and pastures, mainly by increasing N₂O emissions during post-inundation periods.