Seasonal variation in field-saturated hydraulic conductivity in two swelling clay soils in Sweden

A simple method (the inversed auger hole method) for measuring field-saturated hydraulic conductivity (K_fs) was investigated. Measurements were carried out in the spring, summer and autumn at three depths in two Swedish clay soils (Ultuna and Limsta, with clay contents of 45–60%0 and 65–80%, under barley and grass/clover ley respectively). Seasonal fluctuations in K_fs at Limsta were more pronounced, and were observed deeper in the profile. This was attributed primarily to larger structural changes due to a higher capacity for swell/shrink (normal shrinkage over the available water range) and an earlier drying up of the soil under grass/clover ley. It was shown that the measured K_fs values were strongly correlated with the total inter aggregate (macro-) porosity (e_t), estimated from a simple model of soil shrinkage. Combining the data from both soils, a single power-law relation was adequate (r= 0.73) to describe the variations in K_fs with e_t