Comparing two methods of analysis of single-ring infiltrometer data for a sandy–loam soil

The single-ring pressure infiltrometer (PI) with the steady-state Two-Ponding-Depth (TPD) application method were developed to simultaneously determine the saturated soil hydraulic conductivity, Kfs, and the α⁎-parameter in the field. Methods of analysis of transient PI data are also available but they have received little testing so far. The transient WU method and the TPD method were compared for a sandy-loam soil. A linearization technique of the infiltration curve yielded more reliable Kfs and α⁎ results (i.e., falling within expected ranges) than a non-linear optimization technique. The WU method gave both positive and reasonable Kfs and α⁎ values for all infiltration tests. Using the mean soil water content for all tests instead of the locally measured ones did not affect substantially the calculations because the maximum absolute discrepancy between two estimates of a given variable (Kfs or α⁎) at a location was equal to 22%. In some cases, the TPD method yielded negative results or excessively low α⁎ values. The mean results of the TPD method and the WU method with the linearization technique were similar for both Kfs and α⁎ (Kfs: 175.1–214.1 mm h− 1; α⁎: 3.32–3.94 m− 1). The differences between these two methods were reduced, also in terms of relative variability of the data (coefficient of variation = 76.9–81.3% for Kfs and 126.1–149.4% for α⁎), when locations yielding both positive and reasonable results with the TPD method were considered. It was concluded that the WU method is a valid alternative to the TPD method. The transient method should be preferred especially when time available for the test is limited and flow rates can easily be monitored at short time intervals from the beginning of the test.