The majority of the computer models available for water and solute transport in the soil (e.g. Swatre,[1] DrainMod [2] ) are based on Richard's differential equation for the movement of water in unsaturated soil in combination with a differential salinity dispersion equation.

The models use short time steps and need at least a daily data base of hydrological phenomena.

Altogether this makes model application to a fairly large project the job of a team of specialists with ample facilities.

Literature references (chronological) to case studies after 2000:[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Older examples of application can be found in: There is a need for a computer program that is easier to operate and that requires a simpler data structure than most currently available models.

Therefore, the SaltModod program was designed keeping in mind a relative simplicity of operation to facilitate the use by field technicians, engineers and project planners instead of specialized geo-hydrologists.

It aims at using input data that are generally available, or that can be estimated with reasonable accuracy, or that can be measured with relative ease.

Although the calculations are done numerically and have to be repeated many times, the final results can be checked by hand using the formulas in the manual.

The computation method Saltmod is based on seasonal water balances of agricultural lands.

The other water balance components (like downward percolation, upward capillary rise, subsurface drainage) are given as output.

The input data on irrigation, evaporation, and surface runoff are to be specified per season for three kinds of agricultural practices, which can be chosen at the discretion of the user: The groups, expressed in fractions of the total area, may consist of combinations of crops or just of a single kind of crop.

Creative combinations of area fractions, rotation indexes, irrigation quantities and annual input changes can accommodate many types of agricultural practices.

Variation of the area fractions and/or the rotational schedule gives the opportunity to simulate the effect of different agricultural practices on the water and salt balance.

(In a future version of Saltmod, the upper soil reservoir may be divided into two equal parts to detect the trend in the vertical salinity distribution.)

It takes a number of repeated calculations (iterations) to find the correct equilibrium of the water balance, which would be a tedious job if done by hand.

When no drainage system is present, installing drains with zero capacity offers the opportunity to obtain separate water and salt balances for an upper and lower part of the transition zone.

In Saltmod, the salt concentration is expressed as the EC of the soil moisture when saturated under field conditions.

The dissolution of solid soil minerals or the chemical precipitation of poorly soluble salts is not included in the computation method, but to some extent it can be accounted for through the input data, e.g. by increasing or decreasing the salt concentration of the irrigation water or of the incoming water in the aquifer.

The method can gradually decrease: Response (1) is different for ponded (submerged) rice (paddy) and "dry foot" crops.

The user can also introduce farmers' responses by manually changing the relevant input data.

The user can also introduce farmers' responses by manually changing the relevant input data.

The program offers the possibility to develop a multitude of relations between varied input data, resulting outputs and time.

However, as it is not possible to foresee all different uses that may be made, the program offers only a limited number of standard graphics.