Reliable parameterizations of water uptake under osmotic stresses depend on the appropriate description of the interacting effects of root distribution and activity over the root zone. These effects should be evaluated under transient salinity conditions. To show that, a crop was irrigated with three salinity inputs using a randomized block design. Root‐zone water storage and pressure heads measured at the bottom of the root zone allowed to calculate the evapotranspiration under the different salinity levels imposed. Root densities were measured by direct sampling twice during the growth season. Transpiration was distributed along the root zone according to a Feddes‐type sink term and a reduction function accounting for osmotic stress. These data allowed evaluating the effects on the reduction function of (1) the actual salinity and root distributions under different osmotic stress and (2) discontinuous osmotic stress conditions occurring locally in the root zone because of salt leaching. When considering the space–time salinity distribution and the specific root distribution, a unique reduction curve was found, independently of the salinity level of the irrigation water. The effect of discontinuous stress was modelled by introducing (1) a hysteretic behaviour in the salinity reduction function, to be applied only to root compartments actually experiencing discontinuous stress and (2) a scaling factor acting on the whole root zone, based on the ratio of the actual (induced by salinity) to the potential root density. Results suggested that the reduction of transpiration under salinity may be partly caused by irreversible physiological adaption of the roots to saline stress and partly by reduced root density. Copyright © 2014 John Wiley & Sons, Ltd.

Cadmium is a toxic non-essential metal for almost all living systems. It is one of the biggest challenges for farmlands and the food chain because of its toxic effect on human health. This research aims to determine the Cd content in soils, litter and cacao beans, following the Cd fluxes within each cacao system using the two-dimensional electrical resistivity tomography technique. The study was carried out in four farms located in the Magdalena basin in Antioquia, Colombia. The farms showed a heterogeneity in relation to cacao cultivars, altitude, topography and geology. The soil cation electrical capacity, pH and soil organic matter levels, as well as the Al, Al 3+ H + , Ca, K, Mg and P contents were measured at different depths. Moreover, the Cd content was correlated to the resistivity values of samples taken in situ using ERT. Soil Al 3+ H + and the altitude of the farms fitted as the best predictors of the beans' Cd content. Furthermore, the Cd content in soils from the assessed farms ranged between 1.22 and 2.03 mg kg −1 . The Cd content in cocoa beans ranged from 0.07 to 1.44 mg kg −1 , with a value of 0.40 mg kg −1 on average. The resistivity values obtained in field showed a high correlation with the soil Cd content determined (R 2 = 0.82). The predictive tomography plots highlighted topsoil Cd dynamics between litter, amendments and fertilizers. Therefore, these results underlie the utility of the combined geophysical techniques and soil chemical properties including the analysis of fertilizer amendments to improve the understanding of Cd dynamic.

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Contamination of soils with non-aqueous phase liquids (NAPL) constitutes a serious geo-environmental problem, given the toxicity level and high mobility of these organic compounds. To develop effective decontamination methods, characterisation and identification of contaminated soils are needed. The objective of this work is to explore the potential of dielectric permittivity measurements to detect the presence of NAPLs in soils. The dielectric permittivity was measured by Time Domain Reflectometry method (TDR) in soil samples with either different volumetric content of water ( w) and NAPL ( NAPL) or at different stages during immiscible displacement test carried out with two different flushing solutions. A mixing model proposed by Francisca and Montoro, was calibrated to estimate the volume fraction of contaminant present in soil. Obtained results, showed that soil contamination with NAPL and the monitoring of immiscible fluid displacement, during soil remediation processes, can be clearly identified from dielectric measurements. IntroductionSubsurface contamination of soil and groundwater with organic compounds from waste disposal sites, industrial spills, gasoline stations, mine tailings and industrial processes constitutes a serious geoenvironmental problem. The detrimental effects are limited not only to deterioration of chemical, physical and mechanical properties of soils, but also constitute a real risk to human health and the well-being of other living species.Non-aqueous phase liquids (NAPLs), are organic compounds immiscible with water. They have low solubility that may still be several orders of magnitude higher than that of acceptable drinking water standards. NAPLs can be further subdivided into those that are denser than water (DNAPLs) and those that are lighter than water (LNAPLs). Chlorinated solvents such as trichloroethylene (TCE) and tetrachloroethylene (PCE) and polychlorinated biphenyl oils (PCBs) are common examples of DNAPLs. Hydrocarbon fuels such as gasoline, kerosene and jet fuels are common LNAPL contaminants which pollute the environment extensively (Illangasekare, 1998;Jury and Horton, 2004).Following a near-surface release, NAPLs penetrate the subsurface as an immiscible oil phase that migrates in response to gravity and capillary forces. This results in substantial sensitivity to the local distribution of soil and aquifer properties (e.g. permeability and porosity) beneath the source (Gerhard et al., 2007). As a result, the NAPL body (e.g. the source zone) is often expected to exhibit a complex heterogeneous distribution of both mobile pools (i.e. connected-phase accumulations) and immobile residuals (i.e. disconnected blobs and ganglia (Mercer and Cohen, 1990).The remediation of contaminated soil sites requires knowledge of the contaminant distribution in the soil profile and groundwater. Methods commonly used to characterize contaminated sites are coring, soil sampling and the installation of monitoring wells for the collection of groundwater samples (Mercer and Cohen, 1...