Examination of four methods for measuring soil respiration

We compared the accuracy of four methods for measuring soil respiration: the open-flow infra-red gas analyzer method (OF-method); the closed chamber method (CC-method); the dynamic closed chamber method (DC-method); and the alkali absorption method (AA-method), using artificial soil medium (vermiculite with glucose and mineral nutrients) inoculated with Trichoderma sp. as respiring microorganisms. The CO₂ emission rates from the medium were measured by the four methods once a day for 10 days. We compared the estimated amounts of glucose respired by Trichoderma sp. (EGR, an integration of measured CO₂ emission rates for 10 days) with the actual amounts of glucose respired (AGR, calculated from weight loss of the medium during the same period). In the AA-method, the EGR value was 1.3 times larger than the AGR value, while in the OF-, DC-and CC-methods EGR values were almost the same as the AGR (0.95, 0.95 and 0.94 times respectively). Higher CO₂ emission rates obtained by the AA-method were attributed to low CO₂ concentration (20-250 μl 1^-1) in the chamber, because at such low CO₂ levels the respiration rate of Trichoderma sp. was enhanced by 20-70%. These results indicate that the OF-, DC-and CC-methods are more suitable for soil respiration measurement than the conventional AA-method.