Using Wastewater For Vineyard Irrigation
April 15, 2016 The winemaking process requires water – barrels, bottles, and equipment all need to be washed – and that wastewater has to go somewhere.
Why not in the vineyard?
That’s the question University of California, Davis researchers set out to answer in a new study in which they looked at winery wastewater samples each month over the course of two years to determine if the treated water could be reused to irrigate vineyards.
The general consensus? Yes. But, there are some things to consider first.
Researcher and lead author of the paper Maya Buelow says wastewater salinity is one of the biggest concerns. While it might seem that issues from nitrate or phosphate concentrations in the water would be more troubling, she points out there are systems in place for effectively removing those constituents.
Salt, on the other hand, is much harder to remove.
“It’s sort of like a quiet demon, because there’s really no energy-efficient way to get it out,” Buelow says.
She adds that it’s not necessarily the salt itself that creates issues. “Salinity in itself can cause aggregation, so it can actually help soil structure,” she says. “But if you have a high ratio of sodium or potassium to the other types of salts in your water, those salts can actually lead to the reverse effect, which would be to disperse your soil.”
Over time, this can lead to an accumulation of more sodium or potassium, which can cause issues such as crusting and water ponding.
In addition, some of those dispersive effects are non-reversible. “Once you have done that to your soil, it’s really a pretty grave problem,” Buelow says.
But that doesn’t mean growers should shy away from reusing wastewater for irrigation. In fact, salt levels at the wineries in the study were generally below thresholds that could create problems for the vines.
Growers just need to pay attention to the sodium absorption ratio (SAR = Na+ / ((Ca2+ + Mg2+)/2)^1/2) and potassium absorption ratio (PAR = K+ / ((Ca2+ + Mg2+)/2)^1/2).
Most vineyards, Buelow adds, already have wastewater testing capabilities, and they’re generally aware of the mineralogy of their soil. The goal is to make sure the soil and wastewater will play nicely together.
She recommends trying wastewater irrigation on a small test block to start with. Even if there are issues, sometimes simply adding gypsum can mitigate the negative effects of excess sodium and potassium.
In the meantime, the researchers are working to develop some best management guidelines. Overall, though, it appears wastewater irrigation could prove to be very beneficial to vineyards, particularly considering the water shortage California is still facing.
“There’s growing interest all the time,” Buelow says of wastewater irrigation. “It’s a very good, promising water source to reuse.”
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