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 step-wise 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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