Prediction of Near-Saturated Hydraulic Conductivity in Three Podzolic Boreal Forest Soils
2000
Mecke, M. | Westman, C. J. | Ilvesniemi, H.
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).
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