1. General Model Information

Name: CALF- Leaching Model

Acronym: VARLEACH


Main medium: terrestrial
Main subject: ecotoxicology, biogeochemistry, hydrology
Organization level: ecosystem
Type of model: not specified
Main application:
Keywords: pesticides, leaching, pesticide degradation rates, residue concentrations, soil layers

Contact:

Original CALF model from Peter Nicholls
VARLEACH model available from Allan Walker

Support Groups:
Dr. A. Walker
Horticulture Research International
Wellesbourne
Warwick CV35 9EF
United Kingdom
Tele: **44 789 470382
Fax: **44 789 470552

Mr. P.H. Nicholls
Rothamsted Experimental Station
Harpenden
Herts AL5 2JQ
Tele: **44 582 763133
Fax: VariCAD bin nsmail rchange.log startrem 44 582 760981

Author(s):

Dr. A. Walker
Horticulture Research International
Mr. P.H. Nicholls
Rothamsted Experimental Station

Abstract:

Purpose:
VARLEACH is a simple leaching model that incorporates sub-routines to allow for the effects of temperature and soil moisture on degradation rates in soil.

Model Algorithms:
Input parameters:
Minimum data requirements include weather data file containing daily records of maximum and minimum air temperatures, rainfall and potential evaporation; if evaporation data are not available, the model will calculate them; measurement (or estimate) of soil moisture content at applied pressures of 5 kPa (field capacity), and 200kPa; half-life for the pesticide at a known temperature and soil moisture content, or preferable a range of half-lives at different temperatures and moisture contents; and adsorption distribution coefficient. Soil parameters can be varied with depth in the profile.

Output Parameters:
The model output gives moisture content with depth, residue concentrations with depth, water-phase concentration with depth, total flow across the lowest boundary, total leaching loss, and average "leachate" concentration over the whole simulation period, and average leachate concentrations over successive (user-specified) time periods.

Output Flexibility: The output from the model is printed at user-specified intervals. All calculation in the model are carried out in successive 1-cm layers, but the user specifies the depth increments for output (eg 0-5, 5-10, 10-15 cm etc). Output Format is standard tabular information of residue concentrations and soil water concentrations with depth.

Critical Assessment:
Strengths of Model: Few input parameters; rapid run time; detailed simulation of temperature and moisture effects on degradation.

Weaknesses of Model:
No allowance for volatilization; no sub-routines for crop growth; "tipping bucket" type water flow routines.

Known Bugs: None at present. The model has been very widely distributed and used with no report-back of problems to the authors.

Internal Diagnostics: None

Current Version No.: 1.0

Format: IBM MS-DOS

source of abstarct: American Crop Protection Association (ACPA) model database (04/1998)


II. Technical Information

II.1 Executables:

Operating System(s): IBM compatible 80286 Graphic Capability: Output provides summary data format suitable for direct input to FREELANCE graphics package.

II.2 Source-code:

Programming Language(s): Availability of Source Code: Distributed on diskette Version Control: There is currently no strict version control of the original CALF model. The most recent version has been named VARLEACH 1.0 and any updates will be given new version numbers as appropriate.

II.3 Manuals:

Documentation: Explanatory notes are available as README file with diskette; full annotation included in source code; no users manual available.

II.4 Data:



III. Mathematical Information


III.1 Mathematics


III.2 Quantities


III.2.1 Input

Input parameters:
Minimum data requirements include weather data file containing daily records of maximum and minimum air temperatures, rainfall and potential evaporation; if evaporation data are not available, the model will calculate them; measurement (or estimate) of soil moisture content at applied pressures of 5 kPa (field capacity), and 200kPa; half-life for the pesticide at a known temperature and soil moisture content, or preferable a range of half-lives at different temperatures and moisture contents; and adsorption distribution coefficient. Soil parameters can be varied with depth in the profile.

III.2.2 Output

Output Parameters:
The model output gives moisture content with depth, residue concentrations with depth, water-phase concentration with depth, total flow across the lowest boundary, total leaching loss, and average "leachate" concentration over the whole simulation period, and average leachate concentrations over successive (user-specified) time periods.

Output Flexibility: The output from the model is printed at user-specified intervals. All calculation in the model are carried out in successive 1-cm layers, but the user specifies the depth increments for output (eg 0-5, 5-10, 10-15 cm etc). Output Format is standard tabular information of residue concentrations and soil water concentrations with depth.

Output provides summary data format suitable for direct input to FREELANCE graphics package.


IV. References

Vischetti-C; Perucci-P; Scarponi-L; Wagener-A; 1997. Rimsulfuron in soil: effect of persistence on growth and activity of microbial biomass at varying environmental conditions. Special Issue.XII International Symposium on Environmental Biogeochemistry. 1997, 39: 2, 165-176; 21 ref.
Cheah-UanBoh; Kirkwood-RC; Lum-KengYeang; Cheah-UB; Lum-KY; 1997. Adsorption, desorption and mobility of four commonly used pesticides in Malaysian agricultural soils. Pesticide-Science.1997, 50: 1, 53-63; based on a communication presented at the COST ACTION 66 6th international workshop 'Pesticides in the soil and the environment', Stratford on Avon, UK, 13-15 May 1996; 48 ref.
Baer-U; Calvet-R; 1996. Simulation of the persistence of atrazine and sulcotrione in two cultivated soils.(original title :Simulation de la persistance de l'atrazine et de la sulcotrione dans deux sols cultives.) Seizieme conference du COLUMA.Journees internationales sur la lutte contre les mauvaises herbes, Reims, France, 6-8 decembre 1995. Tome 1. 1996, 83-90; 11 ref. Publisher information: Association Nationale pour la Protection des Plantes (ANPP); Paris; France
Giupponi-C; Bonaiuti-G; Capri-E; Errera-G; Trevisan-M; Re-AAM-del (ed.); Capri-E (ed.); Evans-SP (ed.); Trevisan-M; 1996. Effects of alternative soil tillage systems on the degradation and sorption of herbicides. The environmental fate of xenobiotics.Proceedings of the 10th Symposium Pesticide Chemistry, 30 September-2 October, 1996, Castelnuovo Fogliani, Piacenza, Italy. 1996, 151-161; 19 ref. Publisher information: Facolta/grave/ di Agraria, Universita/grave/ Cattolica del Sacro Cuore; Milan; Italy
Brown-CD; Baer-U; Gunther-P; Trevisan-M; Walker-A; 1996. Ring test with the models LEACHP, PRZM-2 and VARLEACH: variability between model users in prediction of pesticide leaching using a standard data set. Pesticide-Science.1996, 47: 3, 249-258; 11 ref.
Walker-A; Welch-SJ; Melacini-A; Moon-YH; 1996. Evaluation of three pesticide leaching models with experimental data for alachlor, atrazine and metribuzin. Weed-Research-Oxford.1996, 36: 1, 37-47; 25 ref.
Gottesburen-B; Mittelstaedt-W; Fuhr-F; Walker-A (ed.); Allen-R (ed.); Bailey-SW (ed.); Blair-AM (ed.); Brown-CD (ed.); Gunther-P (ed.); Leake-CR (ed.); Nicholls-PH; 1995. Comparison of different models to simulate the leaching behaviour of quinmerac predictively. Pesticide movement to water. Proceedings of a symposium held at the University of Warwick, Coventry, UK, on 3-5 April 1995. 1995, 155-160; BCPC Monograph No. 62; 13 ref..Publisher information: British Crop Protection Council (BCPC); Farnham; UK
Borchers-U; Peters-B; Overath-H; Walker-A (ed.); Allen-R (ed.); Bailey-SW (ed.); Blair-AM (ed.); Brown-CD (ed.); Gunther-P (ed.); Leake-CR (ed.); Nicholls-PH; 1995. Limits and possibilities of using computer models to predict fate and behaviour of pesticides in soil. Pesticide movement to water.Proceedings of a symposium held at the University of Warwick, Coventry, UK, on 3-5 April 1995. 1995,281-286; BCPC Monograph No. 62; 7 ref..Publisher information: British Crop Protection Council (BCPC); Farnham; UK
Pestemer-W; Gunther-P; Walker-A (ed.); Allen-R (ed.); Bailey-SW (ed.); Blair-AM (ed.); Brown-CD (ed.); Gunther-P (ed.); Leake-CR (ed.); Nicholls-PH; 1995. Use of a pesticide monitoring system (PEMOSYS) for the risk assessment of pesticide leaching potential - concept for post registration activities. Pesticide movement to water.Proceedings of a symposium held at the University of Warwick, Coventry, UK, on 3-5 April 1995. 1995,351-356; BCPC Monograph No. 62; 14 ref.. Publisher information: British Crop Protection Council (BCPC); Farnham; UK
Trevisan-M; Capri-E; Re-AAM-del; Vischetti-C; Marini-M; Businelli-M; Donnarumma-L; Conte-E; Imbroglini-G; Walker-A (ed.); Allen-R (ed.); Bailey-SW (ed.); Blair-AM (ed.); Brown-CD (ed.); Gunther-P (ed.); Leake-CR (ed.); Nicholls-PH; 1995. Evaluation of pesticide leaching models using three Italian data-sets. Pesticide movement to water. (models:VARLEACH, PRZM-2, LEACHP and PESTLA) Proceedings of a symposium held at the University of Warwick, Coventry, UK, on 3-5 April 1995. 1995, 269-274; BCPC Monograph No. 62; 12 ref..Publisher information: British Crop Protection Council (BCPC); Farnham; UK
Bunte-D; Pestemer-W; Gottesburen-B; 1992 Application of a simulation model (VARLECH) for calculation of herbicide distribution in the soil under field conditions. Part 1: influences of spatial variability of soil properties. (original German title: Anwendung eines Simultionsmodells (VARLEACH) zur Berrechnung der Herbizidverlagerung im Boden unter Freilandbedingungen. Teil 1: Einfluss der raeumlichen Variabilitat von Bodeneigenschaften.) 16th German conference on weed biology and control, held at Stuttgart-Hohenheim, Germany, on 10-12 March 1992. Zeitschrift-fuer-Pflanzenkrankheiten-und-Pflanzenschutz-Z. 1992, Sonderheft 13, 317-325; 17 ref..
Gottesburen-B; Pestemer-W; Bunte-D; Wang-K; Wischnewsky-MB; Zhao-J; 1992 Application of a simulation model (VARLEACH) for calculation of herbicide distribution in the soil under field conditions. Part 2: integration into the expert system HERBASYS. (original German title: Anwendung eines Simulationmodells (VARLEACH) zur Berechnung der Herbizidverlagerung im Boden unter Freilandbedingungen. Teil 2: Einbindung in das Expertensystems HERBASYS.) 16th German conference on weed biology and control, held at Stuttgart-Hohenheim, Germany, on 10-12 March 1992. Zeitschrift-fuer-Pflanzenkrankheiten-und-Pflanzenschutz-Z. 1992, Sonderheft 13, 327-336; 24 ref..



V. Further information in the World-Wide-Web



VI. Additional remarks

Validations Reported:
Comparisons of model prediction with observed soil distribution profiles have been reported for chlorsulfuron, metsulfuron-methyl, triasulfuron, alachlor in field and outdoor column experiments. Further validation exercises are currently in progress.

Last review of this document by: Juergen Bierwirth Tue Oct 13, 11:33:10 MET 1998
Status of the document:
last modified by Tobias Gabele Wed Aug 21 21:44:51 CEST 2002

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