Validation of Soil Survey Estimates of Saturated Hydraulic Conductivity in Major Soils of Puerto Rico

Abstract

Ranges or “classes” of probable saturated hydraulic conductivity values (Ksat) are listed for all soil series in USDA-NRCS Soil Survey reports. Listed values are not measured, but rather estimated from other soil properties using a pedotransfer function (PTF). To validate the PTF, we compared estimated Ksat classes with measured values in various horizons of nine major soil series of Puerto Rico. For each horizon, a minimum of 9 and usually 16 Ksat measurements were made with Guelph permeameters near locations where soil pedons had been thoroughly described. In most horizons, Ksat was log-normally distributed. The ratios of Ksat values corresponding to one geometric standard deviation above and below the mean were usually less than 10, which is the ratio of upper and lower class boundaries in the Ksat classification system. For most horizons, measured Ksat values were distributed among the rated Ksat class and the next higher class, indicating that the PTF systematically underestimated the Ksat distributions, but by less than an order of magnitude. From the point of view of soil and water management decisions requiring conservative Ksat estimates, the PTF estimates appeared reasonably conservative without deviating from actual values so as to limit the usefulness of the estimates.