1. General Model Information

Name: Leaching Estimation and Chemistry Model

Acronym: LEACHM

Main medium: terrestrial
Main subject: biogeochemistry, hydrology
Organization level: ecosystem
Type of model: partial differential equations (finite differences,1D), ordinary differential equations
Main application: research, decision support / expert system
Keywords: soil, water transport, unsaturated zone, nitrogen dynamics, micro-organisms, pesticide, salinity, tracer, chemical movement, root zone, leaching, plant uptake, GIS, richards equation, convection-dispersion equation, sink terms


Dr. J.L. Hutson

School of Earth Sciences
The Flinders University of South Australia
GPO Box 2100, Adelaide SA 5001

Phone: (08) 8201 2616
Fax: (08) 8201 2676
email: john.hutson@es.flinders.edu.au
Homepage: http://fiams.es.flinders.edu.au/People/jhutson.htm


Hutson, J.L., Wagenet, R.J.


LEACHM (Leaching Estimation and Chemistry Model) refers to a suite of simulation models describing the water and chemical regime in the soil root zone.
LEACHM was developed by John Hutson and Jeff Wagenet, in the Department of Soil, Crop and Atmospheric Sciences at Cornell University, Ithaca, New York. It has undergone numerous extensions and revisions since 1984, many of these in response to the requirements and experience of users around the world.
The LEACHM suite consists of four simulation models and several utilities. The simulation models utilize similar numerical solution schemes to simulate vertical water and chemical movement. They differ in their description of chemical equilibrium, transformation and degradation pathways.
LEACHW describes the water regime only. The other simulations describe pesticides (LEACHP), nitrogen and phosphorus (LEACHN), and salinity in calcareous soils (LEACHC).
The models simulate chemical fate and transport in transient-flow field situations as well as in laboratory columns subject to steady-state or interrupted flow.
Water flow and solute transport is described by the Richards and convective-dispersion equations, or by a modified Addiscott mobile/immobile capacity (tipping-bucket) concept. (Source of abstract: http://fiams.es.flinders.edu.au/LeachmDownload/LEACHWEB.HTM)

LEACHM requires several soil parameters as input (physical properties, bulk density, particle size distribution, water retention characteristic). It also requires the amount of nitrogen and phosphate, daily maximum and minimum temperature, precipitation and evapotranspiration estimates. The model predicts amount of chemical leaching below the root zone and amount taken up by the plants. The model uses a daily time step and is executed for one growing season or over a several year period.

Jabro et al. (1995). tested the abilities of the Richards and convection-dispersion equations approach (LEACHNR) and the capacity model approach ( LEACHNA) of the nitrogen version (LEACHN) of the LEACHM model to simulate nitrate leaching were evaluated using field data from a 5-year nitrate leaching experiment conducted in central Pennsylvania on Hagerstown silt loam soil (fine, mixed, mesic, Typic Hapludalf). Nitrate leaching losses below the 1.2-m depth from N-fertilized and manured corn were measured with zero-tension pan lysimeters. Three N-fertilized and manured treatments for 1988-1989, 1989-1990, and 1990-1991 and two N-fertilized treatments for 1991-1992 and 1992-1993 were used from the leaching experiment to evaluate both approaches of LEACHN. The individual monthly simulations of nitrate leaching were compared with the mean of pan efficiency corrected-measured data for these five years. Both approaches of the model were calibrated to the site conditions using the data of 1989-1990 and then were evaluated using 1988-1989, 1990-1991, 1991-1992 and 1992-1993 nitrate leaching data. Simulated results for the calibration year for both models were reasonably accurate (31of 36 months simulated within the experimental 95% confidence limits). The statistical analysis used in this study indicated that both LEACHNA and LEACHNR adequately (91 of 120 months within the 95% confidence limits) predicted nitrate leaching below the 1.2-m depth for treatments in the refinement years. Much of the simulation error in some treatments in the refinement years seemed to be related to the sub-routine controlling soil nitrogen transformation processes and their rate constants in the model. The large deviations in NO3-N leached in some winter months may be related, in part, to problems with simulated water flow associated with the frozen soil conditions and snow accumulation. The addition of a dual-pore water flow option (LEACHNA) to the nitrogen version of LEACHM did not improve prediction of nitrate leaching beyond the rooting zone of corn under Pennsylvania conditions.

Abstract Reference:
Jabro, J.D., J.D. Toth, Z. Dou, R.H. Fox, and D.D. Fritton. 1995. Evaluation of nitrogen version of LEACHM for predicting nitrate leaching. Soil Sci. 160:209-217.

II. Technical Information

II.1 Executables:

Operating System(s): DOS

II.2 Source-code:

Programming Language(s): FORTRAN 77

II.3 Manuals:

II.4 Data:

III. Mathematical Information

III.1 Mathematics

III.2 Quantities

III.2.1 Input

Soil parameters (physical properties, bulk density, particle sizedistribution, water retention); amount of N, P; weather data (max / min temperature, precipitation,evapotranspiration); soil N transformation, management information, some information acquiredfrom literature.

Soil conductivity is a highly variable parameter and this affectsmodel performance. Model needs to be calibrated for each situation.

III.2.2 Output

Water in soil, drainage, hydraulic conductivity, residue N in soil, amount leachedbelow root zone, amount of uptake by plants.

Temporal Scale: Growing season or many years. It depends on data input. Time step most oftenis daily, but can use monthly.

Spatial Scale: Point model.

IV. References

Hutson, J.L., Cass, A., 1987A retentivity function for use in soil-water simulation models. Journal Soil Science, 38, 105-113.
Hutson, J.L., Wagenet, R.J., 1991Simulating nitrogen dynamics in soils using a deterministic model. Soil Use and Management, 7, 74-78.
Hutson, J.L., Wagenet, R.J., 1992LEACHM: Leaching estimation and chemistry model: Aprocess-based model of water and solute movement, transformations, plant uptake and chemical reactions in the unsaturated zone. Version 3.0.
Department of soil, crop and atmospheric sciences, Research Series No. 93-3, Cornell University, Ithaca, New York.
Simulationsmodelle zur Stickstoffdynamik. Eds.: Engel, T., Kloeking, B., Priesack, E., Schaff, T., 1993. Agrarinformatik, Bd. 25. Eugen Ulmer Verlag, Stuttgart. ISBN 3-8001-8643-8.
Wagenet, R.J., Hutson, J.L., Biggar, J.W., 1989Simulating the fate of a volatile pesticide in unsaturated soil: A case study with DBCP. Journal Environmental Quality, 18, 78-84.
Khakural B.R., Robert P.C. 1993: Soil nitrate leaching potential indices: using a simulation model as a screeening system. J. of Env. Quality, 22,4, 839-845
Clemente, R.S., R. de Jong, H.N. Hayhoe, W.D. Reynolds and M. Hares 1994: Testing and comparison of three unsaturated soil water flow models. Agricultural Water Management, 25,135-152
Hutson, J.L. R.J. Wagenet and M.E. Niederhofer. 1997.Leaching estimation and chemistry model: a process based model of water and solute movement, transformations, plant uptake and chemical reactions in the unsaturated zone. Versions LEACHF and LEACHG (for simulating nitrogen and phosphorus transformations, cycling and transport). Research report R97-1, Department of Soil, Crop and Atmospheric Sciences, Cornell University, Ithaca, New York, 138pp.

V. Further information in the World-Wide-Web

VI. Additional remarks

LEACHM can be for studying various chemical leaching rates and how theymight be affected by atmospheric and management changes. It is used widelywithin the ARS and contains many standard leaching state equations. Someresearchers (e.g. Steve DeGloria at Cornell University) have linked LEACHM to aGIS. LEACHM has been used to examine leaching of atrazine, cyanazine and pendimethalin in corn crops and soil and water quality impacts of wasteapplication.

Source : CIESIN Report

Last review of this document by: T. Gabele: 17. 07. 1997 -
Status of the document:
last modified by Joachim Benz Wed Mar 7 08:17:07 CET 2007

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