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.
Issue link: https://read.dmtmag.com/i/484138
www.stma.org April 2015 | SportsTurf 39 with excess sodium and low calcium and magnesium is applied frequently to clay soils, the sodium will tend to dominate negatively-charged sites on clay particles, resulting in breakdown of structure and reduced perme- ability. Sodium absorption ratio (SAR) provides a useful indicator of the potential damaging effects of sodium on soil structure and permeability. It is calculated by the laboratory using a formula that takes into account the chemical weight and charge of sodium, calcium, and magnesium. Because this number is a ratio, no units are listed on the report. Although some labs report percent- ages of sodium, calcium, and magnesium; reliance on percentages alone as a meaningful quality indicator is misleading because they do not take into account charge differences among the ions, which impacts how they act in the soil. Typically a SAR value below 3.0 is considered very safe for turfgrasses. In Pennsylvania, we usually see SAR values between 0.02 and 2.0. Three recent reports from the Penn State lab indicated SAR values between 3.0 and 4.0, and all three involved recycled water. In west- ern states, water with a SAR of 9.0 or above sometimes occurs and can cause significant structural damage to clay soils. Sandy soils are not as susceptible to structure and permeability problems, and can tolerate higher SAR values (up to 10 or 12 in most cases). The soil damaging effects of sodium also depend on EC of your water. As EC increases, soils are less likely to be damaged by water with intermediate SAR. If your water has a SAR higher than 3, you will want to have an adjusted sodium hazard (adj RNa) value on your report to take into account the bicar- bonate concentration in your water. High bicarbonate levels can accentuate soil permeability problems if your SAR is high. More information on SAR and adj RNa can be found in the publications listed below. If your water is consistently within acceptable guide- lines for the quality factors on your water test report, you don't have much to worry about. Even if one or two factors are a bit outside the normal ranges for irrigation water, this does not necessarily mean you will run into turf and soil problems. In the Northeast, where natural precipitation is around 40 inches per year, and irrigation is usually applied over relatively short periods of summer drought, it's a good idea to rely on soil tests for factors such as pH, calcium, and salts. ■ ST By Pete Landschoot, PhD, is professor of turfgrass sci- ence, Department of Plant Science, The Pennsylvania State University.