199-6 Revealing in-Situ Unsaturated Soil Hydraulic Conductivity at Fine Depth Scale.
Tuesday, October 24, 2017: 10:45 AM
Tampa Convention Center, Room 21
Unsaturated soil hydraulic conductivity (Ku) plays a significant role in processes important for ecological, agricultural, and hydrological applications. In general, Ku is measured in the laboratory, or more commonly, predicted using soil water characteristics and saturated hydraulic conductivity. In the field, Ku can be estimated through infiltration experiments. None of these approaches are capable of continuously tracking in-situ Ku dynamics under natural conditions. In this study, we investigated an approach to continuously estimate fine depth-scale Ku dynamics under field conditions. Heat pulse, time domain reflectometry, and water potential sensors were installed at multiple depths within the 0-16 cm layer of a loamy sand field soil to monitor evaporation rates, water contents, and water potential gradients, respectively, during several natural wetting-drying cycles. We estimated soil water flux at different depths from evaporation rate and water content data using a simple water balance. Then, Ku at 2, 4, 8, and 13 cm depths were derived using the Darcy equation from water fluxes and measured water potential gradients. The approach provided reasonable Ku estimates, which agreed well with those measured in the laboratory using a Hyprop technique and those predicted using the van Genuchten–Mualem model. The Ku varied with depth and time following changes in soil water content. At shallower depths, Ku varied over a larger range than at deeper depths because surface soil water content changed rapidly. At the same water content, Ku at 2 and 4 cm depths were greater than those at 8, and 13 cm, which is likely due to differences in soil bulk density. Fine-scale in situ Ku estimates have potential to reveal the influence of natural soil conditions on hydraulic properties as they change with depth and over time.