Evolution of soil organic carbon stocks and C:N ratios in arable soils

Summary

ln a climate change perspective, increasing soil organic carbon {SOC} stocks has been suggested to counterbalance excess atmospheric C. However, the effects of management practices call for long-term assessments. 1n the ACBB Estrées-Mons, a long-term experiment, we assessed the SOC stock evolutions in six-contrasted arable cropping systems, over the 2009-2021 period. Stocks were calculated at equivalent soil mass {ESM) up to 60 cm depth. The N surplus, i.e. the difference between total N inputs and exports, was also calculated on the same period. Carbon losses ranged from -0.12 t C ha·¹ yr·¹ in perennial cropping (RR-PER) to -0.48 t C ha·¹ yr·¹ in reduced nitrogen (RN) system for the topsoil (N0-35 cm) and even greater depletions were observed in the whole soil profile. We observed a slight general decrease of the C:N ratio over the study period without a significant  effect of the cropping system. N surplus proposed as a potential driver of the SOC stock, ranged from -5.5 in RN to +56.6 kg N ha·¹ yr·¹ in reduced tillage {RT}. Inclusion of leguminous crops in RN-LEG increased N surplus and reduced SOC stock depletion in comparison to RN (significantly only for the whole sample soil profile).

School: ISARA Lyon (France)