Field determined hydraulic and chemical transport properties can be useful for the protection of groundwater resources from land-applied chemicals. Most field methods to determine flow and transport parameters are either time or energy consuming and/or they provide a single measurement for a given time period. In this study, we present a dripper-TDR field method that allows measurement of hydraulic conductivity and chemical transport parameters at multiple field locations within a short time period. Specifically, the dripper-TDR determines saturated hydraulic conductivity (Ks), macroscopic capillary length (λc), immobile water fraction (θim/θ), mass exchange coefficient (α) and dispersion coefficient (Dm). Multiple dripper lines were positioned over five crop rows in a field. Background and step solutions were applied through drippers to determine surface hydraulic conductivity parameters at 44 locations and surface transport properties at 38 locations. The hydraulic conductivity parameters (Ks, λc) were determined by application of three discharge rates from the drippers and measurements of the resultant steady-state flux densities at the soil surface beneath each dripper. Time domain reflectometry (TDR) was used to measure the bulk electrical conductivity of the soil during steady infiltration of a salt solution. Breakthrough curves (BTCs) for all sites were determined from the TDR measurements. The Ks and λcvalues were found to be lognormally distributed with average values of 31.4 cm h−1 and 6.0 cm, respectively. BTC analysis produced chemical properties, θim/θ, α, and Dm with average values of 0.23, 0.0036 h−1, and 1220 cm2 h−1, respectively. The estimated values of the flow and transport parameters were found to be within the ranges of values reported by previous studies conducted at nearby field locations. The dripper TDR method is a rapid and useful technique for in situ measurements of hydraulic conductivity and solute transport properties. The measurements reported in this study give clear evidence to the occurrence of non-equilibrium water and chemical movement in surface soil. The method allows for quantification of non-equilibrium model parameters and preferential flow. Quantifying the parameters is a necessary step toward determining the influences of surface properties on infiltration, runoff, and vadose zone transport. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. AbstractField determined hydraulic and chemical transport properties can be useful for the protection of groundwater resources from land-applied chemicals. Most field methods to determine flow and transport parameters are either time or energy consuming and/or they provide a single measurement for a given time period. In this study, we present a dripper-TDR field method that allows measurement of hydraulic conductivity and chemical transport parameters at multiple field locations within a short time ...

Hydraulic and chemical transport properties are needed for accurate prediction of water and chemical movement through the vadose zone. Field methods used to estimate such properties are often hampered by extensive labor and time constraints. One of the objectives of this study was to develop an experimental setup and a procedure for a point-source method that facilitates rapid and simultaneous measurements of soil hydraulic and chemical transport properties at multiple locations. Another objective was to evaluate the pointsource method by comparing the parameters with those produced by ponded and tension infiltrometers. The experimental setup consisted of three dripper lines equipped with pressure-compensating drippers. The setup was evaluated on a greenhouse soil pit. Determined hydraulic properties were the saturated hydraulic conductivity (K s ) and the macroscopic capillary length (λ c ). Hydraulic properties (from the point-source method) were determined by applying four consecutive discharge rates on the soil surface and measuring their corresponding steady-state saturated areas. Determined chemical transport parameters were the immobile water fraction (θ im /θ) and the mass exchange coefficient (α). They were determined by applying a sequence of conservative fluorobenzoate tracers. The point-source method gave consistent and reliable estimates for both sets of properties. Except for α, there was no significant difference between the two procedures (point source vs. infiltrometers) in determining both sets of properties. The study showed that the point-source setup could be utilized for rapid and simultaneous estimation of soil hydraulic and chemical transport properties at multiple locations with minimum labor requirements. and Collins, 1971; van Genuchten and Wierenga, 1976;Clothier et al., 1992; Jaynes et al., 1995), there have been Hydraulic and chemical transport properties are needed for accu- ABSTRACT

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Chemicals that leach through soil pose threats to surface and groundwater quality. It is difficult and expensive to measure subsurface chemical transport and the transport properties required for extrapolating predictions beyond limited observations. The objective of our study was to evaluate whether solute transport properties measured at the soil surface could be used to predict subsurface chemical movement. The study was conducted in a greenhouse soil pit. The solute transport properties of the surface 2-cm soil layer were determined by using time domain reflectometry (TDR) to measure the bulk electrical conductivity during a step application of CaCl 2 solution. The movement of chemicals in the subsurface was measured within the top 30 cm of soil following a pulse input of CaCl 2 solution. A comparison of the measured chemical transport properties in the surface and subsurface zones of the soil showed that the parameters were similar. Furthermore, the estimated parameters determined by the surface TDR method were used to predict the chemical concentration distributions within the 30-cm soil layer, and it was found that the centers of mass of predicted chemical distributions were not significantly different from the measured ones. Therefore, the surface TDR measurements could be used to successfully predict subsurface chemical transport within the upper 30 cm of the soil. This surface measurement technique is a promising tool for vadose zone chemical transport studies. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted.

The most limiting factor for the agricultural sector in the Sultanate of Oman is a lack of water, and security of supply in terms of both quantity and quality. Salinization of both soils and groundwater systems along the coastal strip of Al-Batinah has placed a substantial burden on farmers regarding crop selection and, therefore, farm profitability. Desalination of brackish and seawaters might be an attractive option to sustain salt-affected lands in the Sultanate, particularly given that recent advances in desalination technologies have reduced energy and running cost requirements. This review is a summary of the international experience on desalination for irrigation water; the opportunities and challenges of the use of this technology for sustaining agriculture in arid environments; and the outcome of a survey that explores the extent of the use of desalination for providing irrigation water on the Al-Batinah coast, Oman. The main challenges for adopting this technology for agriculture are the initial cost of desalination units and the cost of environmentally sustainable disposal of reject water. However, there is a need for more applied research efforts to minimize the detrimental impact of disposal of reject water on the environment, long-term impact of desalinated water on agricultural soils as well as cost and benefit analysis of the technology.