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| Web URL(s): | http://archive.lib.msu.edu/tic/rpr/2000/72155,%20U%20Maryland,%20Carroll.PDF
Last checked: 02/08/2013
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| Publication Type:
| Report |
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| Material Type: | Manuscript |
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| Monographic Author(s): | Carroll, Mark J.; Hill, Robert L. |
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| Author Affiliation: | Principal Investigator |
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| Monograph Title: | Development of a Layered Model to Predict Pesticide Transport in Turfgrass Thatch: 2000 Annual Report, 2000. |
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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: | 7 |
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| Collation: | [7] 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 teh use of appropriate pesticide absorption coefficients for each layer.; 2. To evaluate the use of the model for two of the pesticides used in the previously funded GUSGA 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. Modeling non-equlibrium pesticide transport requires at least two additional transport parameters beyond that needed to estimate pesticide transport using a linear-equilibrium approach. These parameters are usually obtained from curve fitting procedures involving field tracer and pesticide leachate data or from sorption studies specifically designed to investigate non-equilibrium adsorption. When transport parameters are obtained from field data, a least sum-of-squares optimization procedure is generally used to estimate the required transport parameters. From a programming perspective, incorporating sub-routines that estimate non-equilibrium field transport parameters from least sum-of-squares square optimization procedures is complex. In addition, formulating a model that uses this approach inevitably elevates the complexity of model to a level where the end user of the model needs to have considerable expertise in porous media solute transport processes. The programming complexity and data input requirements of a solute transport model can be simplified by reducing the number of rate-based parameters used in the model. At the most fundamental level, water in porous media moves in response to a hydraulic gradient and at a rate dependent upon the hydraulic conductivity of the soil. The latter is a rate parameter used in mechanistic transport models to calculate instantaneous water movement in soil. A popular approach used to simplify water movement in many models is to predict water movement based on differences in the water content of soil layers. In these models downward water movement in a layer of soil may be specified to occur only when the water content of a soil layer exceeds a specified value such as field capacity. Models that use capacity factors to simplify water and solute transport are called functional models. A primary advantage of these models is that the models require less data input and computer expertise to perform transport simulations than models that use rate-based equations. We are in the process of constructing a functional transport model that considers non-equilibrium sorption of pesticides to thatch and soil. The model partitions thatch and soil water into mobile and immobile phases and considers time-dependent pesticide sorption using two-site sorption kinetics. A "tipping bucket" methodology will be used to simulate pesticide transport in the thatch and soil layers of the model. A secondary objective of this project is to compare the predictive transport of pesticides obtained using the PRZM2 and GLEAM's models with predictions obtained from the two-phase model which is being developed. While direct comparison of the three models in not yet possible; a preliminary comparison of the predicitive capabilities of PRZM2 and GLEAMS was completed this year. Carbaryl and 2,4-D leachate data collected from previously conducted laboratory column studies were used to evaluate the pesticide transport predictive capabilities of the two models. The columns were 12 to 15 cm in length and contained soil only or soil plus a 2 to 3 cm surface layer of thatch. PRZM2 and GLEAMS model simulations were conducted by evaluating pesticide leaching through a bare-layered soil devoid of a turfgrass canopy. Input parameters for both models were based on actual experimental conditions and on a series of laboratory determinations performed on columns collected from the same location as the columns used in the pesticide leachate study. The columns containing a surface layer of thatch were characterized by model simulations by using the actual measured thatch layer values as the input parameters for the column surface layer. The GLEAMS model underestimated observed pesticide leachate losses in the columns containing a surface layer of thatch by 82% (^D+- 13, n=4). This difference was slightly higher, but not statistically different, from the amount observed in the soil columns devoid of the thatch layer (69% ^D+- 17, n=4). PRZM2 always overestimated pesticide leaching in the soil columns devoid of the thatch layer. The presence of thatch had no consistent effect on PRZM2 model performance. The performance of PRMZ2 and GLEAMS will be compared with functional two-phase model currently under development. It is anticipated that development the two-phase model will be completed in the latter half of 2001." |
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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", 2000 Turfgrass and Environmental Research Summary [USGA], 2000, p. 54, R=72155. R=72155 |
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| Note: | Tables
"2000 Annual Report"
Also appears as pp. 245-251 in the USGA Turfgrass Research Committee Reporting Binders for 2000. |
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| ASA/CSSA/SSSA Citation (Crop Science-Like - may be incomplete):
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