Spatial heterogeneity within the plough layer: high variability of N2O emission rates

The spatial heterogeneity and the temporal variability of N2O emission rate s were examined in an arable soil. The N2O emission rates were measured usi ng soil cover boxes. Rates were measured systematically at regular distance s (7 m) on a sampling grid (9 rows x 9 columns) across a field plot site (6 0 x 63 m). There were two sampling periods, one before (March, 4 flux rate measurements) and one after (May, 6 flux rate measurements) a field experim ent with three crops and three N-fertilization rates was laid out on an uni formly-managed area. The observed N2O emission rates were approximately log normally distributed. The spatial variability of the N2O flux rates was hig h (coefficients of variation > 150%), resulting from a few areas with extre mely high N2O emission rates (hot spots). Total N2O losses were not influen ced by the experimental treatments, but their spatial distribution within t he area changed with treatment. Differences in mineral soil N due to N-mine ralisation, N-fertilisation and plant uptake were responsible for these cha nges. The spatial pattern of the N2O flux rates persisted for only 1 d, ind icating a high temporal variability. (C) 1998 Elsevier Science Ltd. All rig hts reserved.