My recent USGA Course Consulting Service visits to the mountainous states of Utah, Colorado, Wyoming, Montana and Idaho have all had something in common. Where sprinklers consistently hit tree trunks, the bark is stained white. What is happening here? If irrigation water turns the trees white, does that mean it could be problematic for the turf?
To uncover what is causing the white tree trunks we first need to look at the chemistry of the irrigation water.
- Carbon is ubiquitous in our world, including in our water. Carbon dioxide, carbonic acid, bicarbonates and carbonates can all be present in our water.
- Calcium and magnesium are also very common ionic components in water that we drink or irrigate with. Water hardness is essentially the amount of dissolved calcium and magnesium in water, although some other dissolved minerals may also contribute. The more dissolved calcium and magnesium, the harder the water is.
- When water has a total hardness over 120 ppm (milligrams per liter), bicarbonate or carbonate levels of 150 ppm or above, and a pH higher than 7.5, there is a good chance that calcium and magnesium will be attracted to bicarbonates and form calcium carbonate (lime) or magnesium carbonate (dolomitic lime). Both are salts derived from the reaction of an acid and a base.
As the water containing calcium or magnesium carbonate evaporates from the tree bark, the salt is left behind and eventually builds up to a point where it becomes visibly white. This doesn’t only happen on trees. Rocks, buildings or other hardscapes can have the same look and carbonates can also clog drip irrigation emitters. So, does this mean the water is bad for our turf? If lime scaling is so evident on tree trunks, it surely must be bad for the grass and soil, right?
Water that is high in bicarbonates is believed to contribute to soil pore clogging and reduced infiltration rates through the rootzone. If rootzone performance is compromised, turf health will follow. But tree trunks, hardscapes or even drip irrigation emitters are not turfgrass systems. These surfaces dry out completely after watering, which is what allows the carbonate residue to form. I have never encountered a golf course that grows high-quality turf by letting the soil dry out completely in between irrigation events. This is what would need to happen for carbonates to form crusts within the soil profile that restrict water movement. With continuous moisture in turfgrass rootzone systems and aeration multiple times per year, I have yet to see any evidence that lime scaling is compromising turf health. Research has shown this as well.
Two excellent articles were published in 2016 on the topic of putting green rootzones and high-bicarbonate irrigation sources. Drs. Glen Obear, Doug Soldat and Phillip Barak reported their findings on the relationship between climate, irrigation water quality, and soil properties, as well as on how water chemistry and nitrogen source affect accumulation of carbonates in the soil. To quote them, “These findings do not support the claim that irrigating turfgrass with water containing elevated levels of bicarbonate will negatively impact soil physical properties.”
I would encourage you to read these articles. They may help assuage long-held concerns about high-bicarbonate irrigation water.
West Region Agronomists:
Brian Whitlark, regional director – bwhitlark@usga.org
Cory Isom, agronomist – cisom@usga.org