Measures and dynamics of soil organic carbon in calcareous soils

The 4‰ initiative aims to increase the soil organic carbon stocks by 4 per mille. Then comprehensive understanding of sinks and sources of soil carbon (C) became a highly studied research topic. However, in calcareous soils, dominant in arid areas, the soil C pool comprises two distinct components: soil organic carbon (SOC) and soil inorganic carbon (SIC). Because some methodological issues persist in measuring the contribution of SOC and SIC in total soil C or CO₂ fluxes from soils, these soils are poorly studied for the global C cycle. The communication will present recent methodological studies to show the need of further research to be able to understand SOC evolution in calcareous soils. Standard procedures to quantify SOC and SIC involving pretreatments to remove one of the C forms could lead to both analytical errors and measurement errors (Jakab et al. submitted). Thermal analysis (i.e. Rock-Eval®, RE) has been adapted to estimate SOC and SIC contents on a non-pretreated soil sample (Hazera et al., 2023, in press). Coupling RE to mass spectrometer is promising to also be able to estimate the ¹³C natural abundance of SOC and SIC without pretreatments (Hazera et al. 2025). When measuring soil respiration, SIC appeared to contribute to CO₂ emissions. The measuring method of soil respiration (trapping vs. accumulation) could affect these results as well as the apparent respiratory quotient (CO₂/O₂). All these results demonstrate interactions between SOC and SIC pools that needs to be better understood the C cycle in the calcareous soils.