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

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 N2O 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.

Automated summary

Cover cropping can improve soil quality and increase nitrogen inputs in agricultural systems, but it may also result in increased greenhouse gas emissions. This study examined the decomposition process of cover crop residues and evaluated the emissions of greenhouse gases, with a focus on carbon costs. The results showed that the addition of cover crop residues increased CO2 fluxes and global warming potential. The contribution of methane emissions to the global warming potential was negligible. The study suggests considering the carbon costs of residue-N released when choosing a cover crop.