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Carbonate (CO3) – Since calcium (Ca) and magnesium (Mg) carbonates are relatively insoluble, high carbonate water means that the cations associated with them are likely to be either potassium or sodium. Most of the time, they are always sodium. Upon drying in the soil, the carbonate ion will remove Mg and Ca from the clay similar to bicarbonate, and an alkali soil will develop. Carbonate content of water will normally be less than 10–15 ppm.
Bicarbonate (HCO3) - Large amounts of bicarb ions in irrigation water will, upon drying in the soil, precipitate Ca, thereby removing it completely. This then leaves sodium (Na) in place of the Ca. In this way, a Ca dominant soil becomes a known Na dominant soil by use of a high bicarbonate irrigation water. See table 2.
Calcium (Ca) - Ca is an essential plant nutrient that is typically found in soils like gypsum (calcium sulfate), limestone (calcium carbonate), and in various forms of calcium phosphates. A soil that contains appreciable quantities of Ca is easily worked and friable, and it permits water to infiltrate into the soil. Excess Mg and Ca is hazardous due to the effects of soil pH.
Magnesium (Mg) - Another essential plant nutrient is Mg. It has a similar reaction to Ca and it is generally found in large abundances in soil. A common source of Mg is dolomitic limestone.
Sulfate (SO4) - Sulfate can be found in nature and is typically found in the form of gypsum, also known as calcium sulfate. Sulfate is an essential plant nutrient and is readily available to plants.
Sodium (Na) - Na is not typically referred to as an essential nutrient for plants. All the common salts of Na are water-soluble. Na is considered the most troublesome of the major constituents in irrigation water. If the soil has a high level of Na, the soil runs together or disperses and becomes very tight. Water will not be able to easily penetrate the soil. Problems of Na in irrigation water are reflected in Table 3.
Sodium Adsorption Rate (SAR) adj - The SAR indicates the activity of the Na ions as they react with the clay. Adjusted (adj) SAR includes the added effects of the precipitation of Ca related to carbonates and bicarbonates. The potential of problems associated with SAR levels is shown in Table 4.
Learn more about irrigation water and the problems that may arise.
Different minerals and nutrients can be present in your water. Do you know which ones are there?
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Testing for Irrigation Suitability
Your water report can be divided up into two different parts, quality and nutrient availability.
The alkalinity or acidity of water is expressed with the pH. A pH reading of anything less than 7 is considered acidic and anything above 7 is considered to be alkaline. Most water ranges from 7 to 8.5 on the pH scale. Some streams of water may be acidic and read 6.5. Electrical Conductivity (EC) reflects the total amount of salt content present in water. Chemically pure water does not conduct electricity, but water that has salts dissolved in it will.
EC can detect two distinct possible water-soil conditions:
1) Salt or salinity condition. This is one of the hazards of irrigation and is the accumulation of soluble salts in the root zone when irrigated with waters with a high EC.
2) Permeability problems or poor water intake caused by a condition in which the sodium portion attached to the clay increases and the salt then tends to disperse or run together, bringing about reduced rates of water penetration. See table 1.
Is your irrigation water acidic or alkaline?