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| Web URL(s): | http://archive.lib.msu.edu/tic/rpr/1999/72330,%20U%20Maryland, Carroll.PDF
Last checked: 04/05/2013
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| Publication Type:
| Report |
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| Material Type: | Manuscript |
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| Monographic Author(s): | Carroll, Mark; Hill, Robert L. |
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| Author Affiliation: | Principal Investigator, University of Maryland, Department of Natural Resource Sciences & Landscape Architecture |
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| Monograph Title: | Development of a Layered Model to Predict Pesticide Transport in Turfgrass Thatch: 1999 Annual Report, 1999. |
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| Publishing Information: | [College Park, Maryland]: University of Maryland, Department of Natural Resource Sciences & Landscape Architecture |
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| # of Pages: | 3 |
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| Collation: | [3] pp. |
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| Abstract/Contents: | "Objectives: 1. To develop a two phase layered pesticide transport model which considers equilibrium or non-equilibrium transport within each layer and the use of appropriate pesticide adsorption coefficients for each layer. 2. To evaluate the use of the model for two of the pesticides used in the previously funded USGA study. 3. To evaluate the effectiveness of the model to predict pesticide transport in comparison to commonly used pesticide transport models such as PRZM2 or GLEAMS. Mathematical models are often used to estimate potential pesticide transport before management strategies are implemented. Most agricultural pesticide transport models used to predict the transport of pesticides applied to turf either neglect the existence of thatch or average the carbon content of the thatch layer into the organic carbon content of the soil. Because of the high organic matter content of thatch this media has the potential to retain surface applied pesticides prior to their release to the less absorptive soil layer. In highly porous media such as thatch, however, pesticide equilibrium is rarely achieved. Most regulatory agencies and environmental consulting firms use pesticide transport models based on linear equilibrium assumptions. Previous column studies conducted in our laboratory have shown that thatch has a significant effect on pesticide transport and that use of a two-site non-equilibrium model provides superior predictions of pesticide transport. Development of a model that considers non-equilibrium transport within thatch and soil should result in improved predictions of pesticide transport within turf. A problem with creating such a model is how to address pesticide transport in field situations where it is difficult to estimate transport parameters. We are currently in the early stages of developing a two phase model which considers equilibrium or non-equilibrium transport within a soil containing a surface layer of thatch. An extensive examination of existing pesticide transport models has been conducted to review the various numerical techniques used to estimate pesticide transport and to determine which techniques are best suited for adoption in predicting pesticide transport for turfgrass. Although models such as the Pesticide Root Zone Model (PRZM2), the Groundwater Loading Effects of Agricultural Management Systems (GLEAMS) model, and the Chemical Movement in Layered Soils (CMLS) models are commonly used by agencies such as the Environmental Protection Agency and the USDA Agricultural Research Service, these models do not consider non-equilibrium pesticide transport. Two presently available models which consider non-equilibrium transport are the Root Zone Water Quality Model (RZWQM) and the HYDRUS model. Although these two models result in pesticide transport for non- equilibrium conditions, the numerical methods used for describing solute transport differ. While each numerical approach that one does not need to estimate the non-equilibrium field transport parameters. A disadvantage of this approach is that all soil layer thickness must be an integer number and the first horizon must be equal or greater than 2 cm in thickness. Thatch layer thickness is frequently less than 2 cm. We are presently evaluating methods by which we might modify the partial-displacement and mixing numerical techniques to more accurately address the retentive contributions of a thin thatch layer. The HYDRUS model is a finite element model for stimulating the multi-dimensional movement of water, heat, and multiple solutes in variety-saturated media. The model implements a Marquardt-Levenberg (i.e., least sum of squares) type parameter estimation procedure for inverse estimation of selected soil hydraulic and/or transport data. The procedure permits several unknown field parameters to be estimated from observed water contents, pressure heads, concentrations, and/or instantaneous or cumulative boundary fluxes (e.g., infiltration or outflow data). Although the numerical techniques appear attractive, the formulation of mesh grids is felt to generally be beyond the computation capabilities of most end users of the proposed model. We are studying the difficulties of porting similar numerical techniques in a one-dimensional finite difference approach." |
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| Language: | English |
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| References: | 0 |
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| See Also: | See also related summary article, "Development of a layered model to predict pesticide transport in turfgrass thatch", 1999 Turfgrass and Environmental Research Summary [USGA], 1999, p. 43-44, R=72330. R=72330 |
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| Note: | "1999 Annual Report" |
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