Prediction of near-saturated hydraulic conductivity in three podzolic boreal forest soils

Steady-state infiltration fluxes into the soil were measured with a tension infiltrometer at supply potentials of -0.35, -0.70, and -1.10 kPa, and the near-saturated hydraulic conductivities (K) were calculated using an expon ential model. Measurements were conducted in four mineral soil horizons at three forest sites, representing contrasting textures. The analysis was con centrated on K at -0.35 kPa [K(- 0.35)] since this potential corresponds to the 1-min pore diam., which is often considered to be the limit between ma cropores and mesopores. The average K(-0.35) of the site varied in the pare nt soils of the three sites from 0.46 to 40.98 cm h(-1): while in the two u ppermost horizons the variability was smaller: 0.30 to 0.69 cm h(=1). Three multiple linear regression models of log[K(-0.35)] were constructed by ste pwise regression analysis. The retained water content at the seven potentia ls; textural fractions; dry bulk density; and Al, Fe, and C contents were s uggested as predictor variables. In addition, simple functions of these var iables were suggested. In Model 1, all horizons were included (n = 83); in Model 2, all horizons except the upper illuvial horizon were included (n = 61); and in Model 3, only the lowest horizon was included (n = 20). Adding predictor variables increased r(2) in all models. The water content at -100 kPa, which depends on pore-size distribution and C content (which produce a strong retarding effect on water now), were the most important predictors for K(-0.35). Similarly, by gradually excluding horizons where pedological and biological processes had changed the structure and pore-size distribut ion, r(2) increased from 0.86 (Model 1) to 0.99 (Model 3).