Bicarbonate | HCO3- |
Sulfate | SO4-- |
Chloride | Cl- |
Nitrate | NO3- |
Ca2+, Mg2+, Na+, K+, Fe2+ | |
Silica | Si(OH)4 |
With regard to landscape irrigation, the most important water quality parameters are as follows:
The total dissolved solids (TDS) can be measured directly; however, the procedure is time-consuming. It is common nowadays instead to estimate TDS from the water's electrical conductivity (EC). TDS, EC, and the equation relating the two are described elsewhere in this tutorial.
Usually, the main cations in irrigation water are sodium (Na+), calcium (Ca2+), and magnesium (Mg2+). The main anions typically are chloride (Cl-), sulfate (SO42-), and bicarbonate (HCO3-).
Potassium (K+) may be present, but its concentration typically is kept low by interactions with soil particles, especially clay minerals. Likewise, carbonate (CO32-) generally is not a major constituent, except under unusual circumstances. It can become a major element only when a water's pH exceeds 8.0 — a situation that is relatively uncommon for fresh waters. Boron (B) is present in most irrigation waters. Typically, in surface waters it occurs only at low concentration, whereas in groundwater, its concentration can range quite a bit higher.
Several other parameters pertain to the biological constituents of water or the effects thereof:
These parameters are useful for studies related to health effects or environmental concerns, but are not particularly relevant for studies of salinity or the suitability of water for irrigation. Consequently, they will not be considered further here.
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