Irrigation Water for Greenhouses
Irrigation Water Testing and Analysis
Greenhouse growers utilize a variety of sources of water for irrigation. Water quality is most important for crops grown in small amounts of growth media (e.g., plugs, small pots) or hydroponically. Greenhouse environments also increase the importance of water quality because irrigation is the only source of water. Crops grown outside are less affected by irrigation water sources if they experience dilution from natural rainfall. In any case, water testing should be the first step when considering the use of irrigation water to ensure that maximum crop yield will be realized and that disastrous plant toxicity issues will not develop. All irrigation water sources should be tested for pH, alkalinity, conductivity, hardness, chloride, and sodium at a minimum since these are common issues in water supplies. A more thorough test is ideal and should also include total dissolved solids, boron, calcium, magnesium, sodium adsorption ratio (SAR), nitrate-nitrogen, ammonium-nitrogen, phosphorus, potassium, sulfur, iron, manganese, copper, molybdenum, and zinc.
Water Quality Target Parameters
Water quality target parameters include physical, chemical, and microbial properties. Physical properties include suspended solids, such as soil particles. Suspended solids such as soil particles are potential problems since these particulates can clog irrigation nozzles and cause abrasion of irrigation equipment. Chemical properties are typically given the most focus when dealing with irrigation water. From the grower’s standpoint, the most critical chemical water quality parameters are soluble salts, hardness, sodium and chloride concentration, and pH. In a few cases, elements such as iron, boron, and fluoride are also considered critical parameters
Analysis Units
Laboratories will report values in different units depending on their protocol. Thus, it is often necessary to convert from one unit of measurement to another. Parts per million (PPM), milligrams per liter (mg/L), and milligrams per kilogram (mg/kg) are numerically equivalent and interchangeable. If necessary, use Appendix B, Water Quality Conversion Table, to convert to other units of measure. Another unit that is often reported, milliequivalent weight (mg/meq), is a unit used to compare concentrations of ions with different atomic weights and charges.
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