# Due to the importance of Ks many direct

As a confirmation, Drew (1973) observed that measuring BD is avoided in many studies where it should nevertheless be included. The BD of the soil is defined as the ratio between the mass of the soil sample dried in the oven and the apparent volume of the sample in situ. Values of BD are required for calculating the porosity of the soil (Blake and Hartge, 1986). The porosity n may be calculated by Eq. (1) that relates BD and particle density ρs of the soil.equation(1)n=1−BDρs