Factors affecting measurement of the near-saturated soil hydraulic conductivity

Different techniques and different technique application procedures are available to determine soil hydraulic conductivity (K). The objective of this study was to determine the dependence of the K values on the selected technique and application procedure. Soil hydraulic conductivity was determined on a sandy loam soil in the near-saturated zone by the pressure infiltrometer, the tension infiltrometer field techniques, and the inverse method applied to laboratory outflow multistep experiments. Other experiments included a study of ascending and descending pressure heads (h) On the K values measured by the tension infiltrometer technique, and the effect of contact material on ponded infiltration rates. Differences between ascending and descending K means and coefficients of variation were <20% for low pressure heads (h less than or equal to -120 mm). Three successive pending infiltration runs produced mean field-saturated hydraulic conductivities decreasing from 42.7 to 81.8 mm h(-1) to 12.9 to 20.6 mm h(-1) whether or not contact material was present on the infiltration surface. The mean values of K obtained by the selected three methods ranged between 47.1 to 71.9 mm h(-1) at saturation and 0.2 to 2.6 mm h(-1) at h = -120 mm. The K(h) relationships obtained by the pressure with tension infiltrometer and multistep techniques were essentially overlapping. The pressure infiltrometer produced K(h) relationships that were different from those determined by the two Other techniques. In conclusion, ponded infiltration measurements were not usable for estimating unsaturated soil hydraulic conductivity, but contact material and ascending vs. descending direction had no substantial effect on infiltration rate.