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

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.