Nitrous Oxide Fluxes As a Function of Diffusion and Profile Concentrations in the Upper Meter of an Agricultural Soil

Nitrous oxide (N₂O) production in arable soils is a major part of agricultural GHG emissions but not much is known about subsurface sources of N₂O. We examined N₂O production at different soil depths to 1 meter in order to quantify the total flux produced and the factors responsible for production at each depth. In rainfed and irrigated plots planted to corn at six fertilizer levels, we measured N₂O concentrations at 5 soil depths (10, 20, 30, 50, 75 cm) as well as surface fluxes to the atmosphere with an automated chamber. Soil environmental data (texture, water content, temperature and nitrate content) were simulated using the SALUS (System Approach to Land Use Sustainability) model. We measured diffusivity by injecting an inert tracer (SF₆) and high concentrations of nitrous oxide to different depths to validate a diffusivity model. We attributed specific portions of N₂O produced at different soil depths, with lower fluxes produced at depth despite surprisingly high N₂O concentrations to 1m. Major seasonal fluxes were produced in the top 25 cm.