COMBINING LABORATORY AND FIELD-MEASUREMENTS TO DEFINE THE HYDRAULIC-PROPERTIES OF SOIL

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, ψ0 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 fauna activity. Here, a mean pore size weighted for unsaturated flow, when ψ0 < -100mm, was 17 ± 4 μm. For ponded infiltration, this changed abruptly to 2.2 ± 0.6mm. Large and connected macropores caused K to change three orders of magnitude a ψ0 went from just -100mm to zero. -from Authors