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 exponential model. Measurements were conducted in four mineral soil horizons at three forest sites, representing contrasting textures. The analysis was concentrated on K at −0.35 kPa [ K (−0.35)] since this potential corresponds to the 1‐mm pore diam., which is often considered to be the limit between macropores and mesopores. The average K (−0.35) of the site varied in the parent soils of the three sites from 0.46 to 40.98 cm h −1 , while in the two uppermost 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 stepwise regression analysis. The retained water content at the seven potentials; textural fractions; dry bulk density; and Al, Fe, and C contents were suggested as predictor variables. In addition, simple functions of these variables 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 flow), 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 distribution, r 2 increased from 0.86 (Model 1) to 0.99 (Model 3).