Calibration of CO₂ Trapping in Alkaline Solutions during Soil Incubation at Varying Temperatures Using a Respicond VI

Abstract

Measurements of carbon dioxide (CO 2 )-evolution from soils are important in evaluating biomass and activity of soil microorganisms, as well as decomposition of soil organic matter. The Respicond VI is a fully computerized system allowing continuous measurement of CO 2 evolution in short- and long-term soil incubation experiments in up to 96 incubation vessels. The measurement of CO 2 evolution is based on the absorption of CO 2 by an electrolyte (KOH solution) producing a change in the cell conductance measured using two electrodes. In this study, the Respicond VI was recalibrated yielding 174.5 mg CO 2 as constant A expressing the theoretical maximum amount of CO 2 absorbed in 10 ml 0.5 M KOH. This value of A corresponds to 34.9 mg CO 2 ml -1 1 M KOH. The constant A does neither depend on the investigated incubation temperatures (5 ° C - 25 ° C) nor on the concentrations of the KOH solutions (0.5, 0.1, 0.05 M KOH). To eliminate any influence of changing incubation temperatures, either induced by uncertainties in temperature control or as a part of the experimental setup, on the conductance of KOH solution, a correction procedure was developed using a factor calculated from changing conductance of KOH solutions in incubation vessels without soil.