Comparison of three methods to determine C decomposition of organic materials in soils under controlled conditions

SummaryThe carbon decomposition of crop residue and agro-industrial effluent was measured under controlled conditions in a highly calcareous and a loamy soil using three different methods: the dynamic cylinder method (DCM), the static cylinder method (SCM) and the static incubation method (SIM). For the latter two static methods, the CO2 trapped by NaOH was analyzed with continuous flow colorimetry, while the accumulated CO2 accumulated in the closed chamber of the dynamic method was measured directly with an infrared gas analyzer. CO2 emission fluxes obtained from the three methods were in good agreement and significantly correlated for both soils. Nevertheless, for fluxes ranging from 10 to 130 μg C-CO2 m−2 s−1, SCM overestimated CO2 emission fluxes by about 15% in comparison to DCM in highly calcareous soil. For fluxes ranging from 0.007 to 1.3 μg C-CO2 kg−1 s−1, SIM slightly underestimated CO2 fluxes from the decomposition of organic substrates. The calculated C mineralization rates of organic materials also confirmed that SIM underestimated C degradation of organic materials compared with SCM and DCM. This result was probably due to the poorer efficiency of the alkali trap. Finally, the static method appears to be inadequate for measuring CO2 emissions in highly calcareous soils since it leads to overestimating C decomposition rates of organic materials due to equilibrium interactions between soil carbonates and bicarbonates.