Total dissolved solids and major ions

It is the total dissolved solids (TDS) — Refers to the total amount of soluble salts in a soil-saturated paste extract expressed in parts per million or milligrams per liter (ppm or mg/L)) that contributes to salinity problems. The dissolved salts release cations (positive charge) and anions (negative charge) to water. The major cations contributing to soil salinity include

Ca²⁺, Mg²⁺, Na⁺, K⁺

and the major anions contributing to soil salinity are:

SO₄^2-, Cl^-, HCO₃^-, CO₃^2-, NO₃^-

If your laboratory reports are in ppm (mg/L), you can convert ppm to mmol. or mmolc (meq.) by dividing the numbers in the above table.