FIELD TECHNIQUES USING THE ACETYLENE BLOCKAGE OF NITROUS OXIDE REDUCTION TO MEASURE DENITRIFICATION

Abstract

Four techniques for the measurement of denitrification rates in the field were compared. All involved the use of acetylene (C2H2) to block nitrous oxide (N2O reduction and subsequent measurement of accumulated N2O. Two extracted core techniques were compared with two in situ cylinder techniques. The single-wall cylinder technique involved partial insertion of a PVC tube into the soil, sealing the head-space, injection of C2H2 into the headspace and, after suitable time periods, assaying N2O concentration in the headspace. A double-wall cylinder technique was devised to allow more rapid C2H2 introduction into the soil core from an interwall space in situ. A comparison of the four techniques on a 1-m2 area in the field showed large spatial variability. Estimates of denitrification rates decreased in the order double-wall cylinder, single-wall cylinder, extracted encased core and extracted loose core. Variation among replicates varied between sampling occasions but, on aveage, decreased in the order single-wall cylinder, extracted encased core, extracted loose core and double-wall cylinder. Key words: Denitrification, field measurement techniques, acetylene blockage, spatial variability