A field method for the measurement of substrate-induced soil respiration

A novel method for in situ measurements of microbial soil activity using th e CO2 efflux combined with kinetic analysis is proposed. The results are co mpared with two conventional, laboratory methods, (1) substrate-induced res piration using a 'Sapromat' and (2) dehydrogenase activity. Soil respiratio n was measured in situ after addition of aqueous solutions containing 0 to 6 g glucose kg(-1) soil. The respiration data were analysed using kinetic m odels to describe the nutritional status of the soil bacteria employing few representative parameters. The two-phase soil respiration response gave be st fit results with the Hanes' or nonparametric kinetic model with Michaeli s-Menten constants (K-m) of 0.05-0.1 g glucose kg(-1) soil. The maximum res piration rates (V-max) were obtained above Ig glucose. Substrate-induced re spiration rates of the novel in situ method were significantly correlated t o results of the 'Sapromat' measurements (r(2) = 0.81***). The in situ meth od combined with kinetic analysis was suitable for the characterisation of microbial activity in Boil; it showed respiration rates lower by 59% than m easured in the laboratory with disturbed samples.