A comparison of field methods for measuring soil carbon dioxide evolution: Experiments and simulation

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.