Effect of organic mulches in vineyards: CH4 and N2O emissions and their contribution to the GWP and carbon balance

This study investigates the influence of different organic mulches—straw (Str), grape pruning debris (GPD), and spent mushroom compost (SMC)—on greenhouse gas (GHG) emissions and carbon balance in a Mediterranean vineyard over three growing seasons (2021–2023) in La Rioja, Spain. Weekly field measurements of CH 4 and N 2 O emissions were conducted using FTIR technology and static chamber methods, also evaluating their contributions to global warming potential (GWP). Results revealed that CH 4 fluxes varied significantly among treatments, with Str consistently showing net emissions (up to 13.7 mg m −2 day −1 ), while GPD acting as a methane sink, with mean fluxes reaching −3.62 mg m −2 day −1 . N 2 O emissions were highest in the SMC treatment due to its nitrogen-rich composition, reaching seasonal fluxes up to 93.7 g C vine −1 , while GPD and Str, with higher C:N ratios, exhibited lower emissions. Overall, organic mulching treatments—particularly GPD and Str—demonstrated a significant mitigation effect on GHG emissions compared to conventional controls (herbicide and tillage). Emission reductions were most pronounced in the third year, indicating a stabilising effect over time. Global warming potential (GWP) followed a decreasing trend over the study period, from 116.1 g CO 2 -eq m −2 day −1 in 2021 to 34.3 g CO 2 -eq m −2 day −1 in 2023, with SMC consistently showing higher values than Str and GPD. Weighted response ratios confirmed Str as the most effective treatment for GWP reduction. Carbon balance estimations for 2021 and 2022 incorporated net primary productivity (NPP), soil heterotrophic respiration, direct GHG emissions, and indirect inputs from vineyard operations. Str and GPD treatments provided the most favourable C balances due to higher carbon inputs (up to 2,745 g C per vine) and lower C losses, confirming their sequestration potential. Life cycle analysis(LCA) further demonstrated that mulch-based systems reduced environmental impacts by eliminating herbicide application and tillage operations, lowering the vineyard’s carbon footprint to 0.157 kg CO 2 -eq per kg grapes, compared to 0.202–0.208 kg CO 2 -eq for conventional treatments.