Greenhouse gas emissions and C costs of N release associated with cover crop decomposition are plant specific and depend on soil moisture: A microcosm study

Abstract

Cover cropping is used to improve soil quality and increase N inputs in agricultural systems, but it also may enhance greenhouse gases (GHG) emissions. Here, a 47-d incubation study was conducted to track the decomposition process and evaluate GHG emissions and its drivers and to calculate the C costs of residue-derived N released following the addition of residues from cover crops (pigeon pea, cowpea, lablab bean, vetch, and black oat) and maize under two water-filled pore space (WFPS) levels (40 and 70%). For both WFPS levels, the increase in cumulative CO₂ fluxes in plots that received residues is mainly related with the increment of potentially mineralizable C. Crop residues increased the global warming potential (GWP) under both WFPS levels, with CO₂ emissions accounting for ≥98% of the GWP at 40% WFPS. At 70% WFPS, the GPW increment was driven by a notable increase in N₂ O emissions. The contribution of CH₄ in the GWP emissions was negligible for all the crop residues evaluated. Principal component analysis highlighted that the optimal conditions for production and release are specific for each GHG. The cleaner N source was cowpea at 40% WFPS, which produced only 17.7 kg CO₂ -eq kg^-1 N mineralized, compared with vetch residues, which produced 233 kg CO₂ -eq kg^-1 N mineralized. To integrate agronomic and climate change mitigation perspectives, we suggest considering the C costs of the residue-N released when choosing a cover crop.