THE DETERMINATION OF FIELD-SATURATED HYDRAULIC CONDUCTIVITY IN SOME SCOTTISH SOILS USING THE GUELPH PERMEAMETER

Soil hydraulic conductivities are frequently required for process-base d modelling of the soil water regime. Field-saturated hydraulic conduc tivity was measured with the Guelph permeameter in 10 soil series with a range of structures and textures. The permeameter offers a range of options for calculating conductivities depending on soil conditions, particularly homogeneity of pore distribution within each horizon. How ever, even horizons described as massive or apedal were not sufficient ly homogeneous to satisfy the boundary conditions entirely. Hydraulic conductivities were calculated by the one head, fixed alpha procedure ; alpha is an index of capillarity. No direct correlations were found between hydraulic conductivity ind land use. However, the average hyd raulic conductivity of coarse textured topsoils which were mainly unde r arable agriculture was less than that of the finer textured topsoils largely under grassland. Even limited structural development increase d the hydraulic conductivities of fine textured, compact subsurface ho rizons. It is important to match the adopted procedure to the soil con ditions both during the determination of flow rates in the field and i n the subsequent analyses.