Distinguishing between Nitrification and Denitrification as Sources of Gaseous Nitrogen Production in Soil

Abstract

The source of N 2 O produced in soil is often uncertain because denitrification and nitrification can occur simultaneously in the same soil aggregate. A technique which exploits the differential sensitivity of these processes to C 2 H 2 inhibition is proposed for distinguishing among gaseous N losses from soils. Denitrification N 2 O was estimated from 24-h laboratory incubations in which nitrification was inhibited by 10-Pa C 2 H 2 . Nitrification N 2 O was estimated from the difference between N 2 O production under no C 2 H 2 and that determined for denitrification. Denitrification N 2 was estimated from the difference between N 2 O production under 10-kPa C 2 H 2 and that under 10 Pa. Laboratory estimates of N 2 O production were significantly correlated with in situ N 2 O diffusion measurements made during a 10-month period in two forested watersheds. Nitrous oxide production from nitrification was most important on well-drained sites of a disturbed watershed where ambient NO 3 − was high. In contrast, denitrification N 2 O was most important on poorly drained sites near the stream of the same watershed. Distinction between N 2 O production from nitrification and denitrification was corroborated by correlations between denitrification N 2 O and water-filled pore space and between nitrification N 2 O and ambient NO 3 − . This technique permits qualitative study of environmental parameters that regulate gaseous N losses via denitrification and nitrification.