Soil reuse effects on determination of saturated hydraulic conductivity of different loamy soils

Laboratory measurement of saturated hydraulic conductivity, Ks, of sieved and packed soil is important for many scientific purposes. A given soil mass can be used once or several times. Little is known of the dependence of the Ks data on the reuse of the same soil mass. For three loamy soils, this investigation tested reuse effects of exactly the same soil mass on determination of Ks with the simplified falling head technique. For a given soil, the Ks values of 15 repacked soil samples were determined by using the same soil for a total of eight times. The means of Ks, initially equal to 45–159 mm/h, depending on the soil, decreased by nearly two or three times with the reuse of the same material, and they settled on values of 23–59 mm/h by the end of the experiment. Low, stable and little variable (coefficients of variation ≤15%) Ks values were obtained after the soil was used three to five times although there was some sign that stabilization of Ks could also require more reuses. The soil became finer with more reuses and the textural characteristics of the undispersed soil explained a large amount of the mean Ks results (coefficient of determination between means of Ks and the mean weight diameter = 0.65–0.76, depending on the soil). Taking into account that the best procedure for determination of Ks of sieved and packed soil samples yields the lowest variability of the individual Ks data, the conclusion was that a soil pre-treatment including several wetting and drying cycles should be realized to obtain a soil mass usable repeatedly. The history of the used soil mass should be reported in the investigations dealing with sieved and repacked soil samples.