Ks is low in fine-textured clay soils Resistance to water movement in saturated soil is primarily a function of the arrangement and size distribution of pores. Soils with high clay content generally have lower hydraulic conductivities than sandy soils because the pore size distribution in sandy soil favors large pores. When the soil is saturated, it can flow wasily through pore spaces. However, when the soil dries, only a film of water remains coating each soil particle. The adhesive forces of the particles are so strong that Y w can become significantly negative because of the negative matric potential Y m.
Hydraulic conductivity is a highly variable soil property.
Measured values easily may vary by 10-fold or more for a particular soil. Values measured on soil samples taken within centimeters of one another may vary by 10-fold or more. In addition, measured hydraulic conductivity values for a soil may vary dramatically with the method used for measurement. Laboratory determined values rarely agree with field measurements, the differences often being on the order of 100-fold or more. Field methods generally are more reliable than laboratory methods.