Greenhouse Gas Emissions from Cover Crop Decomposition in an Organic Corn Field in Texas.

Organic production systems that use manure, organic amendments and plant residues rely on soil organic matter mineralization as the nutrient source. Throughout the mineralization process, greenhouse gasses (GHG) are emitted, and their production rate is regulated by soil temperature, moisture, residue exposure, C/N ratio, and soil disturbance. To better understand the factors regulating GHG emission during decomposition, we performed a 146-days soil incubation study with cover crop residues with a different composition. Residue treatments included a cover crop mixture of cereals and legume (Oats/wheat/barley/Austrian pea), a legume-only treatment (Austrian pea), and the control (no cover crop). The residues were added on the soil surface (to simulate no-tillage) and moisture was maintained at 60% water-filled pore space. Gas samples were collected periodically and analyzed by gas chromatography for carbon dioxide (CO₂) and nitrous oxide (N₂O) concentrations. Destructive soil samples were collected five times during the incubation period and analyzed for organic C and N, nitrate (NO₃^--N) and ammonium (NH₄⁺-N), and were correlated to GHG emissions. Cover crop inputs increased active C pool size (C_a), but did not affect active mineralization rates (k_a). Slow C pool size (C_s) was higher in legume/cereal mix compared to legume-only treatment due to a higher lignin fraction in the mixture. Legume-only additions increased potential mineralizable N and mineralization rates that were favored by a low C:N ratio and resulted in the production of mineral N. NO₃-N contributed the most to the inorganic N pool compared to NH₄-N. The legume-only showed the highest potential N₂O emissions of 1.01 µg N₂O-N g^-1 soil, followed by the cereal/legume mix in NT and CT with 0.42 and 0.34 µg N₂O-N g^-1 soil, and the control with 0.056 µg N₂O-N g^-1 soil.