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

The spatial heterogeneity and the temporal variability of N2O emission rates were examined in an arable soil. The N2O emission rates were measured using soil cover boxes. Rates were measured systematically at regular distances (7 m) on a sampling grid (9 rows×9 columns) across a field plot site (60×63 m). There were two sampling periods, one before (March, 4 flux rate measurements) and one after (May, 6 flux rate measurements) a field experiment with three crops and three N-fertilization rates was laid out on an uniformly-managed area. The observed N2O emission rates were approximately log-normally distributed. The spatial variability of the N2O flux rates was high (coefficients of variation >150%), resulting from a few areas with extremely high N2O emission rates (hot spots). Total N2O losses were not influenced by the experimental treatments, but their spatial distribution within the area changed with treatment. Differences in mineral soil N due to N-mineralisation, N-fertilisation and plant uptake were responsible for these changes. The spatial pattern of the N2O flux rates persisted for only 1 d, indicating a high temporal variability.