Surprising minimisation of CO2 emissions from a sandy loam soil over a rye growing period achieved by liming (CaCO3)

Liming is a common agricultural practice used to enhance soil productivity by correcting soil acidity and this change of soil chemical properties is often considered a potential strategy to mitigate nitrous oxide (N₂O) emissions from soils. However, its overall impact on greenhouse gas (GHG) dynamics remains uncertain due to the dual influence of liming product on carbon dioxide (CO₂) emissions: direct release from calcium carbonate (CaCO₃) and potential changes in soil organic carbon (SOC) dynamics. Existing studies, based on limited field data, report contrasting effects of liming on both inorganic and organic CO₂ emissions, raising concerns about whether reductions in N₂O emissions are counterbalanced by increased CO₂ fluxes.

This study investigated the impact of liming on soil GHG emissions by monitoring in situ N₂O and CO₂ fluxes following the application of two liming products: synthetic CaCO₃ (SC) and marine CaCO₃₃ (MC), in an acidic soil cultivated with winter rye. Using the static chamber method, we measured soil gas fluxes throughout the growing season alongside key variables, including soil pH, mineral nitrogen concentrations, moisture, and temperature. Biomass yield and SOC (stocks and composition) were also assessed at harvest.

Liming application increased soil pH from 5.7 to around 7.0 and enhanced kernel yield from 320 to over 400 g m^-2. Notably, both liming treatments reduced soil CO₂ emissions by about 40%, contrary to IPCC predictions of increased CO₂ from lime-derived carbon. While N₂O emissions rose slightly, they remained very low during the study period and did not impact the overall GHG budget of the crop. SOC stocks showed no significant change at harvest, though dissolved organic and inorganic carbon concentrations increased.

Our results suggest that current IPCC guidelines for estimating CO₂ emissions from liming may require revision, as liming could offer dual benefits for soil pH management and CO₂ emission mitigation under certain conditions. This session will be an excellent opportunity to discuss the hypothesis regarding pH influence on the CO₂ and N₂O emissions balance, to discuss underlying mechanisms of observed mitigation and explore potential pathways for optimising liming practices to enhance climate-smart soil management.