The relationship between field-saturated hydraulic conductivity and soil structure: development of class pedotransfer functions

A method to predict field-saturated hydraulic conductivity (Kfs) from soil structure, as described in soil profile descriptions, was developed using 6 27 Kfs measurements. As the soil structure classes used are very similar to an international classification (FAO, 1990), the derived relationships (cl ass pedotransfer functions) could be widely applicable. A total of 49 uniqu e combinations of primary and secondary structures were identified but the relationship between these structures and Kfs was poor. However, this relat ionship became clearer when the structures were grouped according to both t he ped size and ped orientation. It improved further with the removal of da ta from horizons with significant amounts of vertically orientated angular stones or very coarse roots. Soils with vertically orientated peds larger t han 50 mm had a geometric mean conductivity of 0.33 cm day(-1) while those with fractures in both the horizontal and vertical planes had a geometric m ean conductivity of 4.1 cm day(-1). Soils with peds between 20 and 50 mm ha d a geometric mean conductivity of 17.9 cm day(-1) and those with peds < 20 mm had a geometric mean conductivity of 53.0 cm day(-1). Those soils with only horizontally orientated structures proved to be anomalous in that the conductivity increased as ped size increased.