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 curv es to disturbance of the soil concentration (relaxation curves) were measur ed with a new membrane tube technique. Diffusive properties of the soil wer e derived from Rn-222 measurements. The mathematical analysis of the relaxa tion curves yielded N2O uptake rates U, soil diffusivities D-s, scale lengt hs z*, and production rates P at different levels under the surface. The fo llowing ranges were found during 2 days of measurements: D-s = (0.4-5) x 10 (-7) m(2) s(-1), U = (1-20) x 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 concentr ation profiles with a one-dimensional diffusive transport model of N2O in t he soil air-filled pore space and to deduce flux profiles. Bidirectional fl uxes occurred with small deposition fluxes up to a few ppt ms(-1) during in tensive growing phases of the grass. Uptake rates were high enough that N2O produced at greater depth did not reach the atmosphere.