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/338693
20 SportsTurf | July 2014 www.sportsturfonline.com W e have discussed in past issues ofSportsTurf understanding salinity measurements and causes of salinity. This final article recaps what salinity and specifically sodium (Na) does to plants and soils, and discusses how to beat back the a-SALT with general management. Low levels of salts, including Na, are not dangerous to most turfgrasses. If salt levels accumulate in the rootzone to high enough concentrations, it is difficult for turfgrasses to uptake water. This is because solutes (salts dissolved in water) like water, and want to hold on to it. Think of the result as a tug-of-war game, where water is the rope: on one end are the turfgrass roots, on the other end are solutes. The more solutes present, the more muscle at the salt end of the water rope. Furthermore, like many organisms, turfgrasses try to achieve a balance between the salt levels inside and outside their cells. Thus, a turfgrass grown in salt affected soil or irrigated with saline water must exert more energy to extract water from the soil. This results in a type of water/drought stress. Turfgrasses spend more energy trying to simply survive, instead of using the water for routine metabolic processes. Certain solutes [especially sodium (Na), chloride (Cl), bicarbonates (HCO 3 ) and boron (B)] that are passively taken up with water can concentrate within the turfgrass and result in ion toxicity. Ion toxicities are most evident in roots and leaves since they are the main points of entry for water to enter the plant. Certain turfgrasses are more tolerant than others. For example, in general, warm-season grasses such as bermudagrass and seashore paspalum are more tolerant than cool-season grasses like bentgrass. How? Many warm-season grasses have salt glands that secrete salts from leaves (pretty cool, right?). When Na is the specific salt in either water or soil, plant uptake of Na increases and Na can begin to block uptake of and displace calcium (Ca), magnesium (Mg), ammonium (NH 4 + ) and potassium (K) within plant cells. When salinity (definition in next section) levels in water are very low, supplemental Ca, Mg, and K may be needed for plant nutrition. SaltS and SoilS Structure Salinity is when acid-base pairs form from K, Ca, Mg, sulfate (SO 4 ), HCO 3 , Cl and Na. Fine soil particles (silt and clay) and organic matter flocculate (bind together) into aggregates in the presence of Ca and Mg ions from these pairs. Calcium and Mg dominated salinity improves soil porosity, increases soil stability, and creates an opti- mum environment for root penetration and growth. This trend holds true with high salinity too. Thus, simply because salinity is high does mean a negative change in soil structure. However, if Na is the dominant ion contributing to the water salinity, it will displace Ca and Mg in soils (those primarily clay based, or with organic matter). Due to its single charge, Na does not "bridge" soil particles together. In fact, it has the quite opposite effect. The large ionic swarm and its appetite for water result in dispersion or spreading of soils. This results in individual soil particles plugging pore spaces and a reduction in total soil porosity. Sodium affected soils compact easily when dry too. The Countera-SALT: successfully managing salinity Field Science | By Dara M. Park and Sarah A. White