Regenerant wastewater irrigation and ion uptake in five turfgrass species

Abstract

The effects of wastewater and high concentrations of chloride (Cl), magnesium (Mg²⁺), calcium (Ca²⁺), and potassium (K⁺) on ion uptake and growth of turfgrass species were studied. Simulated water softener regenerated wastewater was prepared based on 1.8 kg KC1 regeneration rate to attain ion concentrations of 30 mM of K⁺, 100 mM of Ca²⁺, 100 mM of Mg²⁺, and 420 mM of Cl^‐. It was diluted to 1/5, 1/10, and 1/20 concentrations with tap water for the irrigation studies. Wastewater irrigation did not affect the growth rates of the turfgrass. No significant increase of Ca²⁺, K⁺, and Mg²⁺ uptake was detected under the wastewater irrigation treatment. However, the Cl^‐uptake was significantly different between irrigation treatments. It was found that in the spring, in the turf plots irrigated by 1/20 concentration wastewater, an amount equivalent to 60% of the applied Cl^‐ was taken up and removed in the Kentucky bluegrass and perennial ryegrass clippings, and more than 80% was taken up by tall fescue, bermudagrass, and zoysiagrass. A lower percentage of the applied Cl^‐ was removed by the clippings when the turf was irrigated with higher wastewater concentrations. Soil exchangeable Mg²⁺ and Cl^‐ concentrations were slightly, but significantly, higher under the wastewater irrigation treatments. Soil salinity measured by electrical conductivity (EC) was not significantly affected by the 1/20 wastewater irrigation. The soil EC values of the turf plots irrigated with 1/10 and 1/5 wastewater were highest in the summer (10 and 14 dS m^‐1) and lowest in the winter (2 to 4 dS‐m^‐1). This study suggests that the turfgrass species are relatively tolerant to high Cl^‐ concentrations, and under appropriate management, regenerant wastewater can be used for turfgrass irrigation with minimal environmental impact.