SEASONAL-VARIATION IN FIELD-SATURATED HYDRAULIC CONDUCTIVITY IN 2 SWELLING CLAY SOILS IN SWEDEN

A simple method (the inversed auger hole method) for measuring field‐saturated hydraulic conductivity (Kfs) 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 Kfs 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 Kfs values were strongly correlated with the total inter aggregate (macro‐) porosity (et), 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 Kfs with et Copyright © 1990, Wiley Blackwell. All rights reserved