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ExtractChem Model
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The program can be downloaded from
the software download area.

Year: 2007
Version: 2.0


This program is developed to predict the major ion, B composition, electrical conductivity (EC) and osmotic pressure (OP) of a soil solution at a desired water content based on the known ion composition at another water content.

The major uses of the model are envisioned as:
  1. Obtaining a predicted saturation extract composition, EC and OP based on analysis of a 1:1, 1:2 or 1:5 soil water extract.
  2. Correction of the soil water extract data for gypsiferous soils when calibrating field electromagnetic or electrical resistivity surveys for salinity.
  3. Calculating UNSATCHEM or other chemical transport model input soil water concentrations at a specific pressure head (and thus water content) based on analyses of soil extracts.
Basis of the model

The program is based on the chemical routines used in the UNSATCHEM model (Suarez and Simunek, 1996, 1997). It considers major ions, boron, and the chemical processes of cation exchange, precipitation-dissolution of calcite and gypsum, and boron adsorption using the constant capacitance model.

The model can be run in batch mode or in individual cases with display to the screen.


D.L. Suarez and J. Simunek, 1997. UNSATCHEM: Unsaturated water and solute transport model with equilibrium and kinetic chemistry. Soil Sci. Soc. Am. J. 61:1633-1646.

Suarez, D.L., and J. Simunek. 1996. UNSATCHEM code for simulating one-dimensional variably saturated water flow, heat transport, carbon dioxide production and transport, and multicomponent solute transport with major ion equilibrium and kinetic chemistry. U.S. Salinity Laboratory Tech. Report No. 129.


Donald Suarez
USDA-ARS U.S. Salinity Laboratory
450 W Big Springs Road
Riverside, CA 92507-4617

Tel: 951-369-4815
Fax: 951-342-4960