Chapter 11

Irrigation Water for Greenhouses

(draft book excerpts)

A dependable supply of high quality irrigation water is a vital component of any greenhouse growing operation. Characteristics of irrigation water that define its quality vary with the source of the water. There are regional differences in water characteristics, based mainly on geology and climate. There may also be great differences in the quality of water available on a local level depending on whether the source is from above ground (rivers and ponds) or from groundwater aquifers with varying geology, and whether the water has been chemically treated. There are a number of factors, which determine water quality. Among the most important are alkalinity, pH and soluble salts. But there are several other factors to consider, such as whether hard water salts such as calcium and magnesium or heavy metals that can clog irrigation systems or individual toxic ions are present. Poor quality water can be responsible for slow growth, poor aesthetic quality of the crop and, in some cases, can result in the gradual death of the plants. Water quality factors outside the acceptable range do not necessarily mean that the water source cannot be used. There are several water treatment options available to greenhouse operations that can correct many water quality problems. However, water treatment systems differ in installation costs, operating costs, mode of action, space requirements, water volume treated, and worker safety. No single system is best for all greenhouses. A combination of both chemical and physical treatment methods is often needed. Before investing in any treatment system, however, it may be advisable to investigate the possibility of switching to an alternate water source, or mixing water sources, if it is an economical alternative for solving a water quality problem. Water usage is affected by many variables. Most important of these is the level of solar radiation within the greenhouse. The main sources for irrigation water are groundwater from wells, surface water, drainage ponds, rain, and municipal water.

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