Hydraulic Conductivity, Immobile Water Content, and Exchange Coefficient in Three Soil Profiles

We used tension disk infiltrometers to determine the hydraulic conductivity at the matric potential of −0.1 kPa ( K −0.1 ), the immobile water fraction (θ im /θ), and the mass exchange coefficient (α) in three soil profiles of an agricultural field cropped with winter wheat ( Triticum aestivum L.). A significant effect of soil horizonation was found for K −0.1 , θ im /θ, and α and could be related to soil structure as determined either by tillage for surface horizons or by pedogenetic factors for subsurface horizons. The seedbed had lower K −0.1 values (31 to 99 mm h −1 ) than the plowed layer under the seedbed (94–430 mm h −1 ). The θ im /θ was highly variable in the seedbed (0.213 to 0.882), while α had values ranging from 0.0006 to 0.0115 h −1 Values of θ im /θ and α in the plow layer under the seedbed were similar but less variable than those found in the seedbed. In the subsoil, clay‐enriched illuvial horizons had K −0.1 values similar to those found in the seedbed, but lower than those of the heavy clay horizon (average value of 260 mm h −1 ) and the limestone horizons (average value of 450 mm h −1 ). In the illuvial and heavy clay horizons, both θ im /θ and α parameters had a small variability. In the limestone, we found a high variability of both θ im /θ values (0.506–0.933) and α values (0.0006–0.0424 h −1 ) associated with high average values. The presence of subsoil horizons with large θ im /θ and low α values may have a significant impact on ground water contamination.