Recycled wastewater contains nutrients that are essential to plant health, such as nitrogen and phosphorous. Should it be used more widely to irrigate turfgrass in urban environments?

A new study published in HortScience suggests that reclaimed water can be beneficial for turfgrass growth and health, but only if the concentration of nitrogen is high enough.

Reclaimed water is defined as wastewater that has gone through at least secondary treatment. Water that goes through further, advanced treatment typically has 25 percent less nitrogen and phosphorus, yet the reclaimed water used for irrigation increasingly comes from advanced wastewater treatment facilities.

Researchers at the University of Florida compared how well turfgrass grew when it was irrigated with tap water (control), reclaimed water from a university wastewater treatment facility, or with reclaimed water containing additional nitrogen supplied from ammonium nitrate (to achieve 5, 9, and 13 mg∑L-1 N solutions). They also treated samples with a dry synthetic nitrogen fertilizer treatment.

Results from the greenhouse experiments showed that turfgrass growth responded positively to nitrogen concentration in the irrigation water. As more nitrogen was added to the base recycled water, turfgrass growth increased.

However, the concentration of nitrogen in the unamended wastewater was not sufficient for optimal turfgrass growth and in fact there was no difference in turfgrass growth with the base level nitrogen in the reclaimed water compared with tap water.

Grass quality and turfgrass clippings yield maximized when the total nitrogen concentration in the irrigation water was at least 5 mg∑L-1. Treatment with the dry synthetic fertilizer resulted in greater growth and two-fold greater nitrogen leaching than with the other treatments, although overall the leaching of nitrogen was determined to be negligible with all treatments.

One benefit to using reclaimed water containing nitrogen to irrigate residential lawns and urban landscapes is that it may allow for reductions in the amount of other sources of nitrogen fertilizers.

The authors said their study shows that nitrogen from recycled water can be beneficial for turfgrass 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 that outdoor field-scale experiments be conducted to validate the results.