SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.
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FieldScience | By Dr. Peter Landschoot Irrigation water quality guidelines for sports turf I RRIGATION WATER QUALITY is becoming more important for managers of sports turf and grounds. With the demand for potable water increasing, users of irrigation water are considering alternatives sources, such as recycled or effluent water. Because water quality can influence soil quality and turfgrass performance, it's advisable to test irrigation water periodically. Recently, Penn State's Agricultural Analytical Services Lab began an irrigation and drinking water testing program, with a special program just for turfgrass irrigation water. Below are guidelines used in our test program; these can be followed when interpreting results of irrigation water analyses. pH The pH of irrigation water should be determined in a laboratory and listed in your test report. Water with a pH in the range of 6.0 to 7.0 is most desirable for use on turfgrasses. Water with a pH value outside of this range may not directly influence turfgrass performance, but indicates a need to evaluate other chemical components of the water. RESIDUAL SODIUM CARBONATE (RSC) The sodium permeability hazard for irrigation water is usually assessed when bicarbonate and carbonate levels are >120 and 15 ppm, respectively. Residual sodium carbonate (RSC) is a common means of assessing the sodium permeability hazard, and takes into account the bicarbonate/carbonate "and" calcium/magnesium concentrations in irrigation water. RSC is important because it's not the absolute bicarbonate and carbonate concentrations that are important, but instead, the relative concentrations of bicarbonate and carbonate compared to concentrations of calcium, magnesium, and sodium. RSC is calculated as follows: RSC (meq/L) = (HCO3- + CO3-2) - (Ca + Mg) Note that for this equation, all concentrations are expressed in meq/L. Typically, water with a RSC value of 1.25 meq/L or lower is safe for irrigating turf. RSC values between 1.25 and 2.5 meq/L is marginal, and above 2.5 meq/L is considered excessive. ELECTRICAL CONDUCTIVITY (EC) AND TOTAL DISSOLVED SOLIDS (TDS) EC is a measure of the degree in which water conducts electricity. It is determined by passing an electrical current through a water sample and recording the resistance in mmhos/cm or dS/m. EC is used to estimate the concentration of TDS in water, using the following equation: TDS (ppm or mg/L) = EC (mmhos/cm or dS/m) × 640 TDS is occasionally referred to as total dissolved salts (also abbreviated TDS), or total soluble salts (TSS), and both are determined using the same equation. Acceptable TDS concentrations for turfgrass irrigation range from 200 to 500 ppm (EC = 0.31 to 0.78 mmhos/cm). TDS concentrations higher than 2,000 mg/L (EC = 3.1 mmhos/cm) can damage turfgrasses. If using irrigation water with a TDS concentration higher than 500 mg/L, attention should focus on irrigation duration and frequency, drainage, and turfgrass species selection. SODIUM Sodium exists in nearly all irrigation water and is not necessarily a cause for concern unless high concentrations are present. High concentrations (> 70 ppm) can be BICARBONATES AND CARBONATES Bicarbonate (HCO3-) and carbonate (CO3-2) are common constituents of irrigation water, and can influence soil properties and turfgrass performance. If bicarbonate and/or carbonate levels are high (>120 and 15 ppm, respectively), these ions can react with calcium and magnesium in the soil to form insoluble calcium carbonate and magnesium carbonate (lime). This reaction reduces the amount of free calcium and magnesium in soil, allowing sodium to compete for and occupy negatively-charged sites on clay particles. Excess sodium in clay results in destruction of soil structure and reduced water percolation though the soil profile. This effect is referred to as the sodium permeability hazard. 18 SportsTurf | October 2013 www.sportsturfonline.com