Balancing the carbon budget in maize using hairy vetch and black oat cover crops

A two-year field experiment (2022-2024) was conducted in Ferrara (Italy) to evaluate the carbon (C) budget and agronomic performance of silage maize (Zea mays L.) cultivated following CCs under conservation agriculture. Three CCs [hairy vetch (HV), black oat (BO), and their 1:1 mixture (HV + BO)] were compared with a conventional maize (Conv). All CCs were terminated with a roller-crimper and maize was sown under no-till and unfertilized, while in Conv maize was sown in conventional tillage and received N fertilization. HV + BO mixture achieved the highest CC biomass (7.0 t DM m(-)2) and C input (2.80 t C ha(-)1), combining high biomass production with intermediate C:N ratio. Maize biomass was highest under Conv, followed by HV, HV + BO, while BO showed the lowest biomass values (18.1, 15.7, 14.4 and 10.8 t DM ha(-)1, respectively), mainly due to reduced soil N availability. Soil CO2 emissions peaked between 30 and 60 days after sowing and were influenced by soil temperature and moisture. HV and HV+BO exhibited higher cumulative CO2 fluxes than BO and Conv. The CO2 emission-to-yield ratio was low under Conv (0.82) similar to HV (0.91). The HV+BO mixture improved the input/output C ratio (0.297), suggesting a favorable balance between carbon inputs and outputs. CCs enhanced soil water retention and reduced soil compaction, particularly in HV plots. Integration of HV, either alone or in mixture with BO, under conservation agriculture emerged as a viable strategy to optimize C dynamics and enhance soil health for sustainable intensification of agroecosystems.