Combining laboratory and field measurements to define the hydraulic properties of soil

In situ field measurements and laboratory determinations are presented of the saturated and unsaturated flow properties of two contrasting soils. Field measurements were obtained with ponded rings or disc permeameters of different radii. A pressure-transient outflow technique was used in the laboratory on undisturbed cores. The soil water diffusivity function from this, when integrated, provides a good rendition of the growth of the field-measured sorptivity as the surface potential, ψo, approaches zero. The undisturbed wetting hydraulic conductivity K(ψ) from the cores of both soils merged neatly with the near-saturated field results. One soil from within the herbicide strip of an apple orchard had a smoothly continuous K(ψ) befitting its texture. However, the K(ψ) of the other soil, from a dairy pasture, displayed a matrix-macropore dichotomy due to its high level of soil floral and faunal activity. Here, a mean pore size weighted for unsaturated flow, when ψo < −100 mm, was 17 ± 4 µm. For ponded infiltration, this changed abruptly to 2.2 ± 0.6 mm. Large and connected macropores caused K to change three orders of magnitude as ψo went from just −100 mm to zero