I have done geochemical analysis for groundwater samples and obtained results of major cations and anions. In order to evaluate the suitability of groundwater quality for various crops, I am desired to use spatial models that incorporate the major quality parameters in an integrated manner (e.g. USSL diagram, but it is based on SAR and EC alone).
Most of papers (researchers) used arbitrary weightes/rankings for different parameters and finally they have applied weighted overlay analysis for demarcation of quality zones.