Observations of the behaviour of large cores of soil during drainage, and the calculation of hydraulic conductivity

This paper reports observations on the behaviour of large cores of undisturbed clay-loam soil during the drainage of water under an imposed step in potential. Rates of outflow and the matric potential at various points in the core were recorded during drainage. The volumes of ‘macropore-channels’(large, continuous voids) were estimated to be 0.005 m³ m^?3 in a subsoil sample, and 0.026 m³ m^?3 in a topsoil sample from arable land. The calculated values of hydraulic conductivity were found to vary with the size of the step in potential imposed on the sample at the start of each drainage experiment. The available evidence suggested that the apparent K/Ψ_m relationship was influenced by the rate that air could enter the soil to replace water during drainage. The degree of restriction on air movement was affected by the initial drainage behaviour, and this varied with the imposed step in potential.