Vertical variation of near-saturated hydraulic conductivity in three soil profiles

Abstract

Hydraulic conductivity is an important parameter of water and solute transport in soils. Hydraulic conductivity is known to be highly variable in space, but its dependence on soil horizonation has seldom been explored. We measured the near-saturated hydraulic conductivity of three soils located in the Centre of France, a Néoluvisol, a Calcisol, and a Calcosol (according to the “Référentiel Pédologique”), using tension disc infiltrometry. The Reynolds and Elrick's multipotential technique has been applied to the steady state infiltration kinetics measured at potentials −1.5, −0.6, −0.3, −0.1 and −0.05 kPa to derive the hydraulic conductivity values. Each horizon of the three soil profiles has been characterised at least once at three locations 50-cm apart from each other on a flat surface prepared within the same access pit. Some horizons have been characterised on a second occasion in other access pits opened at nearly 10 m from the previous ones. On average, hydraulic conductivity values increased from 1.3×10 −7 m/s at −1.5 kPa to 2.5×10 −6 m/s at −0.3 kPa. Saturated hydraulic conductivity varied between 3.6×10 −6 m/s for the ploughed layer of the Calcosol and 4.9×10 −3 m/s for the Calcosol substrate (C horizon). The various horizons of the Néoluvisol had hydraulic conductivity values which were not significantly different from each other, except the ploughed layer which had lower hydraulic conductivity values than the underlying horizons. The tilled layers of the Calcisol and the Calcosol also had lower hydraulic conductivity values than their respective underlying cambic horizons. Further, the hydraulic conductivity of the tilled layer of the Calcosol was lower than that of the tilled layers of the Calcisol and the Néoluvisol. This difference was attributed to the effect of different tillage systems, the Calcosol being superficially tilled while the Calcisol and Néoluvisol were ploughed each year. The structural S cambic horizons of the Calcisol and Calcosol had similar hydraulic conductivities but lower than their respective substrate (limestone).