Irrigating Kentucky bluegrass with recycled water

Researchers compared sites irrigated with effluent water to those irrigated with surface water, analyzing soil, shoots and turf quality.

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Editor’s note: This research was funded in part by the United States Golf Association.

Golf courses in the western United States are increasingly being irrigated with effluent water. Limited research information is available regarding the degree of accumulation of different minerals or salts in turfgrass shoots when effluent water is used for irrigation. More research is needed to determine the relationships among soil salinity parameters, turf quality and shoot mineral concentrations.

Research was conducted on eight golf courses in the semi-arid front range of Colorado, including three courses with effluent water irrigation for 10 years, three courses with effluent water irrigation for 18 to 26 years, and two courses with surface water for irrigation for 15 and 18 years. Turf quality of Kentucky bluegrass (Poa pratensis), the most widely used turfgrass species in the United States, was evaluated on 25 roughs from the above-mentioned golf courses.

Concurrently, Kentucky bluegrass shoot samples and soil samples were collected from these sites. Shoots of Kentucky bluegrass were analyzed for mineral concentrations of sodium (Na), calcium (Ca), magnesium (Mg), potassium (K), chloride/chlorine (Cl), boron (B), sulfur (S), phosphorus (P), manganese (Mn), iron (Fe) and zinc (Zn). Electrical conductivity (EC) and sodium absorption ratio (SAR) of saturated soil-paste were determined.

Kentucky bluegrass at the surface-water irrigation sites and the 10-year effluent water irrigation sites had similar turf quality ratings. The average turf quality of Kentucky bluegrass irrigated with effluent water for 18 to 26 years was lower than that of the surface-water irrigation group and of the 10-year effluent water irrigation group (Table 1).

Sodium accumulation in the shoots was found in all courses irrigated with effluent water. Mean sodium ion (Na+) concentration in Kentucky bluegrass shoots in milligrams/kilogram was 329 for the surface-water irrigation group; 1,427 for the 10-year effluent water irrigation group; and 3,256 for the 18+-year effluent water irrigation group. Effluent water irrigation increased clipping sodium by 4.3 times in the 10-year group and by 9.9 times in the 18+-year group; it increased chloride by 1.5 times in the 10-year group and by 1.3 times in the 18+-year group.

Kentucky bluegrass shoots irrigated with effluent water for 18-plus years had 3.5 times the boron concentration and 16% lower potassium concentration than Kentucky bluegrass shoots irrigated with surface water.

There was a negative linear relationship between turf quality and sodium concentration in the shoots (Figure 1). Soil SAR at a depth of 0 to 8 inches (0 to 20 centimeters) was highly associated with Kentucky bluegrass shoot sodium (Figure 2). Sodium accumulation in the shoots was the leading plant variable causing the decline of turf quality under effluent water irrigation. Therefore, it is reasonable to believe that water treatment and management practices that can reduce soil SAR and sodium concentration in Kentucky bluegrass shoots would improve turf quality and plant health.

Acknowledgments

This research was previously published as “Mineral composition of Kentucky bluegrass under recycled water irrigation on golf courses” in HortScience, 54(2):357-361 (2019). https://doi.org/10.21273/HORTSCI13650-18


Yaling Qian is a professor in the Department of Horticulture and Landscape Architecture at Colorado State University, Fort Collins, Colo. Yuhung Lin was a graduate student at the university when this research took place.

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