Effective Soil Hydraulic Properties in Space and Time: Some Field Data Analysis and Modeling Concepts.

Soil hydraulic properties, which control surface fluxes and storage of water and chemicals in the soil profile, vary in space and time.  Spatial variability above the measurement scale (e.g., soil area of 0.07 m² or support volume of 14 L) must be upscaled appropriately to determine “effective” hydraulic properties at scales of interest (e.g., areas from 1 m² to 1 ha) for spatial elements in process simulation models.  In this presentation, field-saturated hydraulic conductivity from steady infiltration measurements at 150 “points” will be compared with vertically averaged hydraulic conductivity estimated from soil water contents in 0-0.1 and 0.1-0.2 m intervals measured two days after infiltration and at saturation. We apply a method developed previously using generated soil properties for computing hydraulic properties of spatially heterogeneous soils to preserve areal-averaged infiltration and vertical soil-water redistribution.  The resulting effective soil hydraulic properties will be analyzed over the field and at ten landscape positions with implications for spatial modeling. Individual soils and their upscaled properties will likely change temporally due to tillage, cropping, rainfall, and freeze-thaw events.  Soil dynamics associated with such events can be simulated numerically, but temporal measurements are limited, particularly over a range of spatial scales and landscape positions.   Ideas for integrating future measurement and modeling will be discussed in light of the data and upscaling analyses to date.