An experimental determination of the scale length of N2O in the soil of a grassland

Abstract

Concentration profiles of N2O in a grassland soil and dynamic response curves to disturbance of the soil concentration (relaxation curves) were measured with a new membrane tube technique. Diffusive properties of the soil were derived from 222Rn measurements. The mathematical analysis of the relaxation curves yielded N2O uptake rates U, soil diffusivities Ds, scale lengths z*, and production rates P at different levels under the surface. The following ranges were found during 2 days of measurements: Ds = (0.4-5) × 10-7 m2 s-1, U = (1-20) × 10-4 s-1, z* = 0.7-2.8 cm, and P = 0.02-4.4 ppb s-1. These values were used to reproduce the measured N2O concentration profiles with a one-dimensional diffusive transport model of N2O in the soil air-filled pore space and to deduce flux profiles. Bidirectional fluxes occurred with small deposition fluxes up to a few ppt ms-1 during intensive growing phases of the grass. Uptake rates were high enough that N2O produced at greater depth did not reach the atmosphere. Copyright 2000 by the American Geophysical Union.