Surface Hydraulic Conductivity Measurements On Salinized Soils: Validation by Pore Image

Irrigation with saline water has become a widely diffused practice in the whole Mediterranean area, due to the increase of water demand and reduction in water quality. One major effect is the modification of the soil physical conditions and particularly the hydraulic properties. Most developed methods to determine hydraulic properties are not appropriate in presence of salt accumulation in the soil and their application produce weak estimations.Objective of this study was to investigate hydraulic conductivity changes at the surface of a clay-loam soil in Southern Italy resulting from saline watering.In situ near-saturated hydraulic conductivity has been measured using tension infiltrometer and the results compared with the pore size distribution, measured by means of image analysis techniques on the same soil volume involved in the hydraulic measurements; soil texture has also been determined. All the measurements have been performed both on plots irrigated with saline (ECw=15 dSm-1) and fresh water (ECw=1 dS m-1). Hydraulic conductivities (K) were obtained by Wooding's analytical solution for infiltration from a circular source, following a multiple heads (h) approach; K(h) curves were obtained using a piecewise exponential relationship; digital images of 8 vertical sections for each undisturbed specimen at a resolution of 18 ?m were used to perform the pore analysis based on the "opening" morphological algorithm; soil texture was obtained by the pipette method.The results coming from the three different techniques (functional, geometrical and indirect) have confirmed the influence of the salt in the soil quality worsening. The comparison between the hydraulic conductivities and the pore size distributions by image analysis has shown good agreement which allows to attribute greater reliability to the hydraulic measurements and has evidenced some limitation of the adopted K(h) model to infer the value at the saturation.