Short-range spatial variation of nitrous oxide fluxes in relation to compaction and straw residues

The spatial heterogeneity of N2O flux at short distances (0.1-2 m) was characterized in relation to various soil physical and chemical properties and the location of incorporated crop residues in arable soils. Plots were prepared with uniform compaction (either zero or compacted by a laden two-wheel-drive tractor) in two field experiments, one under winter barley (Hordeum vulgare), the other under oil-seed rape (Brassica napus). Flux measurements were made of N2O using small chambers (7.3 cm diameter) placed at intervals of approximately 10 cm along a transect (c. 2 m long) across the direction of application of the treatments of compaction and residue incorporation. The flux of N2O and many other measurements showed large variation over short distances, particularly when fluxes were small. The spatial variation of the flux was not closely related to the soil properties. Correlations showed that cone resistance, air permeability and closeness to incorporated residues were as important as soil NO3, NH4 and soluble C in determining flux of N2O from non-compacted soils. Most properties of compacted soils did not correlate with N2O flux. Correlation and multiple regression analysis failed to establish consistent relations between soil environmental variables and N2O flux, but principal component regression indicated that, overall, N2O flux increased with decreasing distance from straw residues and air permeability, and with increasing cone resistance and wet bulk density.