Tailored reclaimed water irrigation effects on turfgrass visual quality, rootzone salinity, nitrogen species, and denitrifying microorganisms in the vadose zone

Abstract

Water is essential for any functioning society, but drinking water supplies are becoming increasingly insufficient for current and future demands. To alleviate stress on diminishing potable water resources, reclaimed water can be a viable option for replacement in many different schemes, like turfgrass irrigation. Irrigating turfgrass with reclaimed water can reduce demand on potable water supplies and provide essential nutrients for turfgrass health and aesthetic appeal, but can also be associated with nitrate leaching to groundwater and salt accumulation in the rootzone. The purpose of this study was to address concerns surrounding the use of tailored reclaimed water for turfgrass irrigation by measuring turfgrass visual quality, rootzone salinity, nitrogen leaching, and the abundance of denitrifying microorganisms in the vadose zone during irrigation with reclaimed water. In this study, tailored reclaimed water from the Mines Park sequencing batch membrane bioreactor was utilized in a semi-arid environment to irrigate 67% of a turfgrass area, consisting of buffalograss and Kentucky bluegrass, while the remaining 33% was fertilized with granular fertilizer and irrigated with potable water from the City of Golden drinking water treatment plant. For the second study year, all turfgrass plots receiving reclaimed water were tailored with calcium nitrate-nitrogen to achieve 15 mg L-1 of nitrate (NO3--N), while for the third year 50% of the reclaimed water plots were dosed with calcium nitrate to achieve 8 mg L-1 of NO3--N (a more representative concentration in the reclaimed water industry) and the remaining were dosed at 15 mg L-1 NO3--N. The turfgrass plant health was monitored on a weekly basis, with both a qualitative visual assessment and quantitative digital imaging analysis. The accumulation of salts and the fate and transport of NO3- throughout the vadose zone were monitored both from monthly soil pore water samples and soil samples taken before, during, and after the growing season. The abundance of denitrifying microbial communities was also analyzed from soil samples. Throughout this study, 198 x 103 L of potable water and 27 kg of 20-10-5 granular fertilizer were saved by irrigating turfgrass with tailored reclaimed water rather than irrigating with potable water supplemented with granular fertilizer. This study also found no aesthetic differences between using tailored reclaimed water or potable water for turfgrass irrigation, though sodium adsorption ratio values were higher in plots irrigated with reclaimed water (particularly Kentucky bluegrass plots). Nitrate concentrations for both irrigation water types in the soil pore water and soil were higher throughout the spring and fall months, nirK denitrifying genes for both irrigation water types (potable and reclaimed) were seasonally lower in the spring and fall months, and nirK genes were more abundant than nirS genes; nosZ denitrifying genes were not detected.