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 char acterized in relation to various soil physical and chemical properties and the location of incorporated crop residues in arable soils. Plots were prep ared 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 interval s of approximately 10 cm along a transect (c. 2 m long) across the directio n of application of the treatments of compaction and residue incorporation. The flux of N2O and many other measurements showed large variation over sh ort distances, particularly when fluxes were small. The spatial variation o f the flux was not closely related to the soil properties. Correlations sho wed that cone resistance, air permeability and closeness to incorporated re sidues 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 no t correlate with N2O flux. Correlation and multiple regression analysis fai led to establish consistent relations between soil environmental variables and N2O flux, but principal component regression indicated that, overall, N 2O flux increased with decreasing distance from straw residues and air perm eability, and with increasing cone resistance and wet bulk density.