Comparing the Automated Dual-Head Analysis from a Single-Ring Infiltrometer with a Double-Ring Infiltrometer.

Understanding the effects of land use changes, landscape position, and soil morphology on soil physical properties, like field saturated hydraulic conductivity (K_fs), is crucial when modeling changes in hydrology. Traditional methods for determining K_fs are based on infiltration measurements, require numerous factors to correct for three-dimensional flow, are time consuming, and have large water requirements. Analysis for determining K_fs employs numerically determined shape factors for ring radius, depth of ring insertion, ponding depth, and soil hydraulic properties. The correction factors for soil hydraulic properties are typically taken from a table based on soil capillary length. Significant error can occur in the calculation of K_fs when the correction factor is large and infiltration is low. Using a dual-head infiltration measurement and methods proposed by Reynolds and Elrick (1990) for analysis of steady flow from a ponded infiltration in a single ring, we can reduce the error by eliminating the need to use soil capillary length as a correction factor in analysis. In this study the DualHead Infiltrometer (DHI) (Meter Group Inc., Pullman, WA, USA), an automated instrument that employs the dual-head analysis approach, was compared with the traditional double-ring infiltrometer approach. The measurements were conducted at the same time within the same 1 m² area and 7 different locations on a field. Overall, the two methods compare well, except in cases where there are large structural macropores that can be destroyed when subjected to the amount of force required to install the double-ring infiltrometer.