Corrections for Effusion from Gas-Permeable Enclosures for the Determination of Low N2(C2H2) Fixation Rates in Situ
Soil Biology and Biochemistry
Use of plastic bag enclosures of potted soils and plants has been a common method for the determination of N2-fixation rates with the C2 H2-reduction method. It is recognized that this method may give considerable overestimates of the C2H4 production rates if the experimental period extends over a few hours and where these rates are comparatively very low. The overestimation is caused by the assay of gases of interest without a consideration of their continuous, varied and differential leakage from the enclosures. A method and an equation has been developed for the determination of low C2 H4 production rates applicable for assays of changes in gas concentrations in enclosures for periods extending to 10h. The correction factors for the following physical processes were included in the derivation of appreciable equations: continuous effusion of gases from the gas-permeable enclosure, differences in the effusion rates of the tracer gas and C2H2, changing ratios of the tracer gas to C2H4 during the assay and the presence of non-biogenic C2 H2 in the enclosed atmosphere at the beginning of the assay. A critical examination of the use of open-ended devices (cylinders) for the in situ determination of C2 H4 production rates showed that such devices are not suited for the determination of low N2-fixation rates.
Borjesson, I. and J. Skujins (1987). Corrections for effusion from gas-permeable enclosures for the determination of low N2(C2H2) fixation rates in situ. Soil Biol. Biochem. 20(1): 11-17.