The Solute module is an APSIM plug-in-pull-out module that keeps a solute balance of up to five different solutes.
The Solute module itself does not change the state of the solutes, but lets other modules change the solute information according to their own processes.
For example, a solute may have its state changed by a soil water balance module as a result of its leaching calculations.

Things to note when using the Solute module

The Solute module can keep track of Nitrate and Ammonium, but must do so independent of any other soil balance module ( e.g. SoilN2).
The Solute module is designed primarily to trace solutes such as Bromide and Chloride through soil layers.

Solute module outputs

The outputs for this module flow on from the input parameters.
The module will provide the amount of solute in kg/ha on a layered basis for each of the specified solutes.

For the sample illustrated above, the possible outputs would be “br” or “cl”.
Additional outputs are:

  1. ‘max_xxxx’ (the maximum amount of solute xxxx in any layer (kg/ha)),
  2. ‘maxppm_xxxx’ (the maximum amount of solute xxxx in any layer (ppm)), and
  3. ‘maxlayer_xxxx’ (the soil layer number corresponding to the maximum solute load for solute xxxx’).

For Chlorine in the above example, these outputs would be

  1. max_cl,
  2. maxppm_cl, and
  3. maxlayer_cl.


Solute Diffusion

Whilst the mass flow or advection of solutes is provided by the equations within the soil water modules, solute diffusion can be calculated within the solute module by supplying a diffusivity coefficient for an individual solute as follows.


solute_names = cl


cl =   0 0 0 0 0 0 0 0 (kg/ha) ! Initial Cl profile


d0_cl = 108

The solute flux is calculated as

Flux = D0 * θ*τ*dc/dx

Where D0 is the diffusivity in free water, θ is water content, τ is the soil water pore space tortuosity (=θ2/ θs2) and dc/dx is the concentration gradient within the soil water solution.