Nitrogen from recycled wastewater can benefit turf-grass growth, study finds

According to a new study conducted by the American Society for Horticultural Science, recycled wastewater can be beneficial for turf-grass growth because it contains valuable nutrients -- such as nitrogen and phosphorous -- that are essential to plant health.

GAINESVILLE, FL, Jan. 5, 2015 -- As competition for freshwater increases and fertilizer prices rise, the horticulture industry is looking to reclaimed wastewater as a valuable resource for supplying irrigation and necessary nutrients for urban landscapes. According to a new study conducted by the American Society for Horticultural Science (ASHS), recycled wastewater can be beneficial for turf-grass growth because it contains valuable nutrients -- such as nitrogen and phosphorous -- that are essential to plant health.

Reclaimed water (RW) is defined as wastewater that has gone through at least secondary treatment. "The main difference between RW that has received secondary treatment versus advanced treatment is the reduced level of nutrients and other chemicals remaining in water subjected to advanced treatment," said Jinghua Fan and George Hochmuth, corresponding authors of the study. "Water receiving advanced treatment typically has 25 percent of the nitrogen and phosphorus and less soluble salts than contained in secondary treatments. Increasingly, the reclaimed water used for irrigation is from advanced wastewater treatment facilities."

As production and testing of RW increases, there is more interest in using the resource to irrigate residential lawns and urban landscapes. One benefit to using this water containing nitrogen is that it may allow for reductions in the amount of other sources of nitrogen fertilizers. "It is important to determine the optimum combinations of water and nutrient applications to support turf-grass production without impairing groundwater through losses of nutrients from the landscape," Fan and Hochmuth said. They noted that few studies focused on the degree to which residential turf-grass can use the nitrogen from RW following advanced treatment.

The state of Florida, for example, is a large user of recycled water, with more than 50 percent of the state's RW being used for irrigation of recreational areas such as golf courses, parks and residential landscapes. A University of Florida research team designed greenhouse experiments using 'Floratam' st. augustine grass (Stenotaphrum secundatum) and 'Empire' zoysiagrass (Zoysia japonica.). Treatments included irrigation with tap water (control), irrigation with RW from a university wastewater treatment facility, irrigation with RW with additional nitrogen supplied from ammonium nitrate (to achieve 5, 9, and 13 mg·L-1 N solutions), and a dry-prilled fertilizer treatment.

Results showed that turf-grass growth responded positively to nitrogen concentration in the irrigation water. The concentration of nitrogen in the unamended wastewater was not sufficient for optimal turf-grass growth. Measurements showed no difference in turf-grass growth with the base level nitrogen in the delivered RW compared with tap water. The data showed that as more nitrogen was added to the base recycled water, turf-grass growth increased.

"The nitrogen concentrations in reclaimed water from advanced wastewater treatment facilities in the study were too low to benefit turf-grass and achieve acceptable quality," the scientists said. Grass quality and turf-grass clipping yields maximized when the total nitrogen concentration in the irrigation water was at least 5 mg·L-1. Turf-grass receiving dry synthetic nitrogen fertilizer resulted in greater growth and two-fold greater nitrogen leaching than with the remaining treatments for both turf types, though leaching of nitrogen was determined to be negligible with all treatments.

The authors said that their greenhouse studies show that nitrogen from recycled water can be beneficial for turf-grass growth and health, but the concentration of nitrogen in recycled water with advanced treatment needs to be at least 5 mg·L-1. They recommended outdoor field-scale experiments to validate the results of the greenhouse studies.

See also:

"WERF awards UC Berkeley, Stanford University contract to study nutrient removal from urban runoff"

"Rare collaboration aims to reduce nutrient pollution in Mississippi River Basin"


About ASHS

The American Society for Horticultural Science is the world's premier professional society for horticultural science. Founded in 1903, the mission of ASHS is to promote and encourage national and international interest in scientific research and education in horticulture in all its branches. The more than 2500 ASHS members in all 50 states and 60 countries around the world fulfill this mission by sharing the results of their research, teaching, and extension activities with their colleagues and humankind the world over. For more information, visit www.ashs.org.

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