DESCRIPTION OF A DYNAMIC CLOSED-CHAMBER FOR MEASURING SOIL RESPIRATION AND ITS COMPARISON WITH OTHER TECHNIQUES

Soil respiration is an important component of the net carbon dioxide e xchange between agricultural ecosystems and the atmosphere, and reliab le estimates of soil respiration are required in carbon balance studie s. Most of the field measurements of soil respiration reported in the literature have been made using alkali traps. The use of portable CO2 analysers in dynamic closed chamber systems is recent. The introductio n of this new technique requires its evaluation against existing metho ds in order to compare new information with older data. Nine intercomp arisons between dynamic systems and alkali traps were made. Measuremen ts of F-c,F-s obtained by both chambers showed a good agreement in all but two comparisons in which alkali trap measurements were lower than the dynamic chamber by about 22%. This first report of agreement betw een both techniques suggests that many measurements made in the past u sing alkali traps may be comparable to the measurements made more rece ntly using the dynamic chambers. Analysis of the soil temperature and CO2 concentration inside the alkali traps failed to explain why the al kali traps occasionally underestimated the fluxes. Soil respiration me asured with a dynamic closed chamber were closed compared to eddy-corr elation measurements. The results did not reveal any consistent bias b etween techniques but the scattering was large. This dispersion is lik ely the result of the difference between the areas measured by the two techniques.