Long‑term responses of greenhouse gas emissions and soil organic carbon to maize cropping system and tillage intensity

Maize cropping systems contribute substantially to agricultural greenhouse gas (GHG) emissions, and long-term evidence is required to assess trade-offs between soil carbon (C) sequestration, gaseous losses, and crop productivity. Using a long-term experiment (LTE) established in 1994 in Central Italy, this study evaluated in 2022 and 2024 the effects of cropping system (continuous maize vs. a 3-year maize–winter wheat–faba bean rotation) and tillage intensity, comparing deep ploughing (DP), disk harrowing (DH) and ripper subsoiling (RS) on CO₂, N₂O and CH₄ fluxes, soil organic carbon (SOC) and nitrogen (N) pools, maize yield and microbial communities. Interannual variability strongly affected maize yield, N dynamics, and N₂O emissions. In 2024, higher soil water content and NH₄⁺ availability induced pronounced post‑fertilization N₂O peaks, increasing total GHG emissions by about 35%. Compared with monoculture, crop rotation consistently enhanced maize yield (by 88% with DP and 10% with DH), SOC (by 15% with DP, 45% with DH, and 40% with RS), and total N (by 26% with DH and 19% with RS). Tillage intensity was a key determinant of soil functioning and GHG emissions: with respect to DP, DH increased SOC (59% under monoculture and 101% under rotation), total bacterial abundance (by 108% under monoculture and 132% under rotation) and N-cycling functional gene abundances (by 47–176%), while reduced N₂O by 18% and cumulative GHG emissions by 42%, on average between monoculture and rotation. RS showed intermediate responses while maintaining high maize productivity. N₂O emissions were strongly driven by soil water content and NH₄⁺ availability and linked to shifts toward functionally dominant ammonia-oxidizing bacteria (AOB), particularly under deep ploughing via structural disturbance and increased mineral N. Overall, the combination of crop rotation and DH emerged as the most favorable long‑term strategy to enhance SOC, sustain maize yield, and mitigate climate impacts in rainfed Mediterranean maize systems.