Bestimmung von hydraulischen Parametern für die Wasserhaushaltsuntersuchungen im natürlich gelagerten Boden. Ein Vergleich von Feld‐ und Laboratoriumsmethoden

Abstract

Determination of hydraulic parameters to estimate water movement and water storage in undisturbed soil. A comparison of field and laboratory methods.The soil moisture characteristics and the unsaturated conductivity were measured under field and laboratory conditions. In an undisturbed soil monolith in continous connection with the underlying loess‐soil‐layer 60 tensiometer and a neutronprobe‐accestube were used respectively to determine the matric potential and water content changes during a transient drainage experiment. Within the matric potential range of 0 to approximately −50 to −100 mbar the soil moisture characteristics determined in the laboratory and in the field are substantially different. When the matric potential is more negative than −100 mbar the slope of these curves and hence the specific moisture capacities are relatively well comparable.The field‐measured conductivity functions differ considerably from those values which were either measured under lab‐conditions or computed from the soil moisture characteristics data. The conductivities are expressed as a function of the matric potential which is possibly the major reason for these remarkable differences. However, the changes in water content in this dense silty clay loam are too small to express the unsaturated conductivity as a function of the absolute water content. The most serious problems in extrapolating the results of the less time consuming laborcalculation methods to field conditions arise in that range of matric potentials where water movement is significant.