Irrigation Water for Greenhouses
Water Hardness
The term hardness refers to the combined concentration of calcium and magnesium in the water and is generally expressed as the total amount of calcium carbonate (CaCO3) in mg/L or ppm. Other cations such as iron, manganese, aluminum and zinc can also contribute to hardness. Hardness in water for greenhouse and nursery use should not exceed 150 mg/L (CaCO3). High concentrations (hard water) of calcium and magnesium in the water will generally be accompanied by similarly high levels of bicarbonate and carbonates. Temporary hardness is a type of water hardness caused by the presence of dissolved carbonate minerals (calcium carbonate and magnesium carbonate).
Estimating Water Hardness
Hardness can be calculated from individual concentrations of calcium and magnesium using following equation.
Lime Deposition Potential
Lime deposition potential (LDP) is an indicator used to evaluate whether lime deposition could happen through precipitation of calcium or magnesium carbonates (lime) out of the irrigation water, which leaves white residues or deposits. Factors affecting lime deposition are higher temperatures, higher pH, loss of carbon dioxide in the water, and evaporation.
Estimating Lime Deposition Potential
To calculate lime deposition potential of irrigation water, use a similar equation as SAR. However, bicarbonate + carbonate are compared to calcium + magnesium; the number that is the least is the LDP. LDP is reported in meq/L where 1 meq/L = 50 ppm CaCO3 equivalents. LDP is the lower number between the following two calculations:
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