Field estimation of soil hydraulic and chemical transport properties

Al-Jabri, Salem
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Managing soil and groundwater resources requires characterization of the hydraulic and chemical transport properties. The determination of such properties on field scales requires conducting extensive numbers of measurements to well represent the spatial distribution and variability of field properties. However, extensive measurements of properties in the field is hampered by the long time-frame required by most of current field procedures.;This study introduces a setup and procedure by which the hydraulic and chemical transport properties can be rapidly estimated at multiple locations. The setup consists of a multiple dripper permeameter, where drippers serve as point sources. The hydraulic properties include saturated hydraulic conductivity (Ks) and macroscopic capillary length (lambda c). The hydraulic properties were estimated by measuring a sequence of steady-state water flux densities on the soil surface. The chemical transport properties include immobile water content (thetaim), mass exchange coefficient (alpha) and dispersion coefficient in the mobile domain ( Dm). These chemical transport properties were determined by applying a sequence of conservative tracers into the soil (ST method).;The setup and the procedure were evaluated on six sites on a greenhouse soil pit and tested under actual field conditions with a total of 50 sites. The hydraulic and chemical transport properties were found to be representative when compared with previously reported results for nearby locations and similar soils. A field procedure for determining the chemical transport properties, based on using time domain reflectometry (TDR), was also presented. Breakthrough curves of 38 field locations were obtained from real-time TDR-measurements of soil bulk electrical conductivity. The transport parameters (theta im, alpha, Dm) from the BTCs were found to be comparable with the parameters produced by the ST-method conducted on the same field location.;The overall results of this study show that the setup and procedure presented here facilitate rapid measurements of surface hydraulic and chemical transport properties at multiple field locations. Such procedures are ideal for management studies that require conducting extensive measurements to better characterize transport processes through the vadose zone.

Agriculture, Soil Science, Agronomy, Water resources