Trade-off between C sequestration and GHGs fluxes in a long-term maize crop under contrasting management options

Monitoring of long-term responses of crop systems to contrasting management options is of key importance to assess the capacity of agriculture to mitigate climate changes, by increasing carbon sequestration and reducing green-house gases emissions. To this aim, long-term trials are fundamental since allow the evaluation of the trade-off between processes occurring at different time frames, such as C storage and CO₂, CH₄ and N₂O emissions.

Within EJP SOIl – ∑OMMIT project a long-term trial established in 1994 was selected in a Mediterranean mountain area in Tuscany (Italy), comparing maize monoculture vs. rotation at contrasting tillage intensities (deep ploughing vs. disk harrowing).

Fluxes of CO₂, CH₄ and N₂O, have been measured in 2021 growing season together with climate factors, inorganic N availability and microbial communities’ composition, and compared with C accumulated in the last 20 years.

The objectives of the monitoring were to assess the impact of cropping systems at low and high tillage intensities on i) the trade-offs between long-term C accumulation and GHGs emissions, and ii) the microbial community composition and activity. Moreover, the work aimed at improving the understanding of the main abiotic and biotic drivers of GHGs exchanges considering the plant-soil-atmosphere integrated system.

The stage of crop rotation had the highest impact on both C storage and GHGs fluxes, showing larger C exchanges and lower N₂O emissions with leguminous than maize. Tillage intensities showed not significant changes in CO₂ emissions and a slight increase with deep ploughing with respect to disk harrowing, which also experienced a larger C accumulation. All cropping systems, independent of tillage and rotation phase, acted as sinks for CH₄.

The soil microbial communities resulted influenced by the different cropping systems. In particular, significant differences were highlighted in the abundance of microbial groups involved in denitrification and nitrification processes.