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

Abstract

Agricultural liming improves acidic soils productivity and is considered a lever for mitigating nitrous oxide (N₂O) emissions from soils. However, the benefit of liming in reducing soil greenhouse gas (GHG) emissions depends on the evolution of carbon from the calcium carbonate (CaCO₃), and on the evolution of soil organic carbon (SOC) after CaCO₃ application. The literature, based on limited field data, presents contrasting effects of liming on inorganic- and SOC-derived CO₂ emissions, raising concerns that the reduction in N₂O emissions could be offset by increased CO₂ emissions. Therefore, this study aimed to monitor N₂O and CO₂ emissions following the application of lime materials to an acidic soil. In situ, we monitored the effect of two liming products (SC = synthetic CaCO₃ and MC = marine CaCO₃) on soil CO₂ emissions and compared this with control plots, during the growing season of a winter rye, using the static chamber method. Soil pH, N₂O emissions, mineral nitrogen concentrations, soil moisture and temperature were measured during the experiment, as were plant biomass and SOC (stock and composition) on the day of harvest. Lime addition increased soil pH from 5.7 to around 7.0, kernel yield from 320 to >400 g m^-2 and resulted in a significant reduction in soil CO₂ emissions by approximately 40 % for both liming materials while it slightly increased N₂O emissions, that had nevertheless remained very low during the experiment. SOC at harvest was not significantly affected, while an increase in dissolved organic and inorganic carbon in the soil was observed. Further investigations is needed to clarify the mechanisms explaining these observations and to define conditions where liming application could act as a potential lever for carbon storage. Our results suggest that the IPCC principles, predicting increased CO₂ emissions from lime-derived C, may need to be re-examined in the future.