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

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 Rn-222 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 two days of measurements: Ds = (0.4-5) x 10 exp -7 sq m/s, U = (1-20) x 10 exp -4/s, z* = 0.7-2.8 cm, and P = 0.02-4.4 ppb/s. 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 during intensive growing phases of the grass. Uptake rates were high enough that N2O produced at greater depth did not reach the atmosphere. (Author)