Comparison of Soil Hydraulic Property Measurement Methods

Unsaturated and saturated soil hydraulic properties were determined and compared for three sandy soils at adjacent field sites. Drying soil-water retention curves were measured on soil specimens using a pressure plate apparatus. Saturated hydraulic conductivities (Ks) were measured with a Guelph permeameter and falling head tests. Parameter optimization was used to simultaneously estimate the drying and wetting soil-water retention and hydraulic conductivity curves from cone permeameter and multistep inflow/outflow data. Ks values from all test methods were within an order of magnitude of each other at each site and, as expected, trended with bulk density. The Guelph permeameter generally yielded the highest Ks values. The soil-water retention curves were similar in shape, except for the cone permeameter curves, which had steeper slopes due to rapid flow of water into the soil. Relative hydraulic conductivity curves were similar in character to the soil-water retention curves. Each method provided important information about the soil hydraulic properties. No one method provided the entire range of information provided by all of the tests combined, and no one method was found to be superior to the others.