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 x 9 columns) across a field plot site (60 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 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.