Three widely used methods for measuring total soil CO2 evolution are evaluated, including the dynamic CO2 absorption method, the static CO2 absorption method and the closed chamber method. The study covers laboratory experiments. numerical experiments with a simulation model and field measurements. The results are used to perform an error analysis. The aim of this error analysis is to indicate the impact of each method on the CO2 dynamics during the measurement, and to select the most suitable method for frequent field usage.
Laboratory experiments and simulation results show that the dynamic CO2 absorption method has the potential to absorb all CO2 evolving at the soil surface. The results also prove that the method has only a minor impact on the CO2 concentration-depth gradient and the CO2 efflux. The static CO2 absorption method underestimates the soil CO2 evolution, because the absorption velocity is too low, due to slow diffusion processes. Measurements with the closed-chamber method are based on an increasing concentration with time under a closed cover. However, the accumulation of gas alters the concentration gradient in the soil profile and thus causes a rapidly decreasing efflux during the measurement. A commonly used mathematical procedure, which corrects for the altered concentration gradient, does not yield the exact surface efflux, because the effect of increasing storage in the soil profile is not incorporated. Field measurements of CO2 evolution, using the closed-chamber method and the dynamic CO2 absorption method confirm the trends that have been predicted by the simulation model. The results of this study indicate that the dynamic CO2 absorption method is accurate. As it is cheap and simple, it is suitable for the study of temporal and spatial dynamics of CO2 evolution from the soil.