I used percolation columns to reclamation saline-sodic clay soils .
And my question is, What is the difference between soluble ions and exchangeable cations?
Dear Dr Ebrahim --- please have a look at the following useful links:
https://andrewsforest.oregonstate.edu/sites/default/files/lter/pubs/pdf/pub2709.pdf
You may refer to the following book.
Richards LA (ed) (1954) Diagnosis and improvement of saline and alkali soils. USDA Agriculture Handbook 60. USDA, Washington, DC, USA
Dear Ebrahim,
I used the article recommended to you by Dr. Durrani and added a few notes to the original text https://andrewsforest.oregonstate.edu/sites/default/files/lter/pubs/pdf/pub2709.pdf
..."those ions only in the solution phase" = by this is meant in most cases a "pool" (share) of ions, very weakly (if at all) bound to the adsorption centers of the soil sorption complex. Hence, this "pool" of water-soluble ("soluble"?) is easy displaced into soil solution even by the weakest "leachate" – by water. The more correct term than "soluble" or "solubility" should therefore be "water soluble", ever better "water extractable".
...."opossed to total exchangeable nutrients, that have both solution and surface adsorbed phases" very briefly described "exchangeable" nutrients form. There are predominantly electrostatically bound to soil surface and released into solution from these surfaces by ionic extragents having varying extent of extraction efficiency (KCl>NH4OAc>NH4NO3>CaCl2, e.g.). To quantify "exchangeable" soil forms there is in W. Europe, US, etc. just 1M ammonium acetate (NH4OAc) with pH = 7.0 used. For a longer time , however, the "in" universal extragent is Mehlich-3.
(See, please, some works of Jiri Zbiral on Researchgate). So with some simplification, "soluble" (i.e. water-extractable) forms of ions in the soil can be considered to be their weaknest bound "exchangeable" forms.
Unfortunately, methods for the extraction of dissolved-only nutrients are not provided in this Chapter (6), but in Chapter 9.
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