Most studies of empirical estimates of unsaturated hydraulic conductivity functions do not account for water which may be relatively immobile under the conditions in which field measurements of conductivity are made. To investigate this, unsaturated hydraulic conductivity data were obtained for three monolith lysimeters, 80 cm in diameter by 135 cm deep, using the instantaneous profile technique. The lysimeters contained well‐structured, freely draining loam soil and moisture measurements were made using a neutron probe. Conductivity estimates were also obtained from laboratory measurements of soil moisture characteristics using the modified Millington and Quirk computational method. Ratios of the calculated to measured conductivities at a matching point near saturation were so large as to suggest that only a minor proportion of the soil pore space was contributing to flow through the whole profile.
Volumetric water contents of 17 mineral and 3 peat soils were measured at 15 bar pressure using the ceramic plate and the pressure membrane apparatus. There was no overall significant difference between the results from the two types of apparatus and both ranked the soils in essentially the same order. Although soils of high clay or organic matter content retained up to 13.5% more water on the ceramic plate than on the pressure membrane, available water capacity (AWC) of a clay soil would be decreased by only 1-2%, and that of a peat soil by 3 4 % . Due to its greater reliability, the ceramic plate is an acceptable alternative to the pressure membrane when used to determine the 15 bar water content.
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