Manual packing and soil reuse effects on determination of saturated hydraulic conductivity of a loam soil

Performing laboratory measurement of saturated hydraulic conductivity, Ks, of sieved soil is important for many scientific purposes such as testing theories and methods to determine Ks. A given soil mass can be used only once or it can be reused after a previous use. Little is known on the dependence of the Ks measurements on both the applied packing method and the reuse of the same soil mass. This lack of knowledge makes comparisons among different investigations more or less uncertain. Four packing methods were tested on an initially dry loam soil by measuring Ks with the simplified falling head (SFH) technique. The four methods differed by the used compacting procedure (dropping from a given height, pestle imparting vertical and radial forces on the pressed soil surface) and the number of soil layers disposed at each step of the procedure. Changes in Ks due to the reuse of the same soil mass were also determined. Depending on the packing method and the number of times a given soil mass was used, the means of Ks varied from 51 to 110 mm h−1, with a ratio between these two extremes of 2.2, and the coefficients of variation, CVs, ranged between 10 and 36%, depending on the developed dataset (sample size, N = 15 for each dataset). Therefore, the packing method and the reuse of the same soil had a moderate effect on determination of Ks. For a given pre-treatment of the soil mass, the lowest variability of Ks was detected by using the pestle, probably because this simple device favored homogenization of the soil and enhanced the contact with the walls of the cylinder. With the pestle, reusing the soil once was enough to pass from a medium (CV = 23–27%) to a low (CV = 12%) variation of Ks. Taking into account that the best procedure yields the lowest variability of the individual Ks measurements, the conclusion was that the pestle and a previously wetted soil should be used. In the future, additional experiments should be carried out on other soils, in different antecedent soil water conditions and with other laboratory measurement methods of Ks. This study provided new information on soil sample preparation methods and it showed that simple procedures could be applied for preparing different samples with similar Ks values.