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A beta-test version of TETrans (acronym for Trace Element Transport) is presented which models the movement of inorganic solutes through the vadose zone under transient-state conditions. TETrans is a complete software package consisting... more
A beta-test version of TETrans (acronym for Trace Element Transport) is presented which models the movement of inorganic solutes through the vadose zone under transient-state conditions. TETrans is a complete software package consisting of an interactive tutorial, user's guide and applications software. Both IBM-compatible and Macintosh versions are available to users. TETrans is specifically designed to be intuitive in its operation and require only readily available input parameters in order to enhance its utility as a real-world applications tool for transport modeling. The transport model utilizes a mass-balance approach to determine solute concentration distributions over time and solute-loading to the groundwater. Several modeling options are available for simulating such transport-influencing factors as plant-water uptake, hydraulic bypass and adsorption. In the Macintosh version, TETrans makes full use of the Macintosh interface to enhance the user-friendliness of the model. All functions are available from pull-down menus, and simulation results are displayed in text and graphic windows. Test data are shown which include a comparison of simulated and measured results for the movement of chloride through a soil lysimeter column over a 900-day study period. Excellent agreement is found when a single parameter for bypass is used. TETrans is distinguished from other transport models in the straightforward manner in which it handles the exacerbating problem of hydraulic bypass. The hydraulic bypass parameter, termed the mobility coefficient, is determined from simple chemical analysis of chloride in the soil solution through the soil profile following the application of a plug of chloride in the irrigation water. The mobility coefficient reflects the volume of soil water which is not subject to piston displacement
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The ability to measure and map volumetric soil water (θ) quickly and accurately is important in irrigated agriculture. However, the traditional approach of using thermogravimetric moisture (w) and converting this to θ using measurements... more
The ability to measure and map volumetric soil water (θ) quickly and accurately is important in irrigated agriculture. However, the traditional approach of using thermogravimetric moisture (w) and converting this to θ using measurements of bulk density (ρ—cm3/cm3) is laborious and time consuming. To speed up the process electromagnetic (EM) instruments have been used to assist in mapping average θ along a transect or across a field. This is because the apparent soil electrical conductivity (ECa) measured by EM instruments has been shown to be a function of θ, when other soil properties are uniform. However, mapping depth-specific soil θ has been little explored. One possible approach is to invert the ECa data to calculate estimates of true electrical conductivity (σ) at specific depths (i.e., 0.15, 0.45, 0.75, 1.05 and 1.35m) and couple this to measured θ. This research explores this possibility by using a single frequency multi-coil DUALEM-421 across a centre-pivot irrigated Lucerne field (Medicago sativa L.) in San Jacinto, CA, USA. The first aim is to determine an optimal set of inversion parameters (i.e., forward modelling, inversion algorithm and damping factor—λ) which are appropriate to establish a calibration between σ and θ. In this regard the largest coefficient of determination (R2=0.56) is achieved when we used the FS model, S2 algorithm and a λ=0.3. The second aim is to see if all the coil arrays of the DUALEM-421 are necessary. We conclude that while the DUALEM-1 produces a larger R2 (0.59), the use of the DUALEM-421 data is better (R2=0.56), because the total model misfit (4.70mSm−1) is smaller and because it better accounts for the spatial variation of θ in the subsoil. In terms of predicting θ, the calibration equation (θ=2.751+0.190×σ) was examined using a leave-one-out cross validation. The Lin’s concordance (0.73) between measured and predicted θ was good. The resulting 2-d depth slices and cross-sections gave insights into the spatial distribution of θ which allowed the inference of depth of saturated soil and location of the wetting front and identified areas where deep drainage may be problematic. The approach has applications for water use and management given it can identify inefficiencies in water application rates and use.
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Reliable simulation models are an essential prerequisite to accurate assessment of present and future consequences of human activities on ecosystem health and functioning. In particular, for non-point source pollution assessments in the... more
Reliable simulation models are an essential prerequisite to accurate assessment of present and future consequences of human activities on ecosystem health and functioning. In particular, for non-point source pollution assessments in the vadose zone, chemical fate and transport models are required at field and watershed scales. However, developing such models that characterize adequately the processes occurring during an arbitrary period of time within an arbitrary spatial region in unsaturated soil is a challenging task due in part to the complexity of the processes and heterogeneity of the properties involved. This task requires developing, calibrating, and evaluating an appropriate process description for the region of interest from relatively sparse spatial and temporal information. Here we discuss and point to some of the relevant literature addressing the various "hurdles" that need to be overcome in order to develop non-point source pollution transport models. Of central concern are spatial heterogeneities of physical properties over a range of scales, how these can be inferred from spatial data, how heterogeneities are effectively represented by macroscale parameters and how (or if) processes can (or should) be related over a range of effective scales. Upscaling from observed microscale processes could yield useful results.
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Research Interests: Environmental Science, Geology, Biological Sciences, Environmental Sciences, Chemical Analysis, and 15 moreCoefficient of Variation, Arid Zone, San Joaquin Valley, Analysis of Variance, Chemical Properties, Soil Properties, Forage yield, Dry Matter, Electric Conductivity, Physicochemical Properties, Sodic Soil, Bermuda Grass, GEODERMA, Saturated hydraulic conductivity, and Field Measurement
In California, perennial crops increasingly are planted on better, more uniform soils, but the most responsive locations to site specific management likely will be fields with more marginal soils and greater variation, where lower valued... more
In California, perennial crops increasingly are planted on better, more uniform soils, but the most responsive locations to site specific management likely will be fields with more marginal soils and greater variation, where lower valued field crops like sugarbeets are produced. Soil texture, salinity, or other limitations can influence crop yields in these fields. In general, crop responses in poor quality soils are less understood than on b~tter soils, and can be erratic in response to management inputs. Precision management techniques might be of use to farmers, but their successful adoption is dependent on poorly characterized crop response. An assessment of field scale variation and the characterization of crop response associated with this variation are first steps in evaluating the potential for variable rate technologies and other aspects of precision agriculture. As an initial attempt at site characterization, the response of sugarbeets to salinity and residual nitrogen was studied at sites in the Imperial and San Joaquin Valleys.