MAKING THE SWITCH TO WASTEWATER IRRIGATION

Superintendents considering the switch from fresh irrigation water to water from wastewater treatment plants will need to study all the adjustments required to accommodate the switch. A study in southern Nevada, by University of Nevada researchers, looked at changes in electric conductivity, pH, nitrate, phosphate, temperature, algae and fecal colliform levels, among other items. Their study was performed over a four-year period and compared freshwater-irrigated courses, courses making the transition from freshwater to reuse irrigation water and courses that were long-time users of reuse water. Note that the wastewater treatment plants were able to provide 100 percent of irrigation water during only the winter months. Spring, summer and fall, irrigation water for transition and long-term courses was a blend of wastewater and Colorado River water.

The research results were a mix of good news and bad. On average, changing to reuse irrigation resulted in the following: temperature increased 25 percent, electric conductivity (EC) increased 53 percent, algae increased by 436 percent, clarity decreased by 46 percent and nitrate (N) and phosphate (P) concentrations increased by more than 1,000 percent. You might guess that some of these changes were beneficial. More nitrate applied with irrigation water, for example, would lead to lower need for nitrogen and phosphorus fertilizer. On the other hand, the increased algae population (measured as algal chlorophyll) would decrease the aesthetic value of the pond. The increase in EC indicates higher amounts of soluble salts in the water. Bermudagrass is fairly tolerant of salts, however, if the irrigation water oversprays the turf and hits the landscaped areas, sensitive plants could be damaged.

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The researchers recommend studying the capacity for your local wastewater treatment plants to supply your irrigation water needs. Some courses involved in reuse systems have then been asked to restrict all irrigation during extended droughts. The result can be a significant buildup of soil profile salinization and possible irrigation with water too saline for the greens. They also recommend that courses maintain adequate field-based leaching fractions.

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