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Hard water can hinder chemical efficacy

Agriculture.com Staff 02/27/2007 @ 12:30pm

It may leave your dishes spotted and your showerheads clogged, but hard water can have more costly effects when it comes to your field chemical applications.

The idea of applying crop herbicides mixed with soft water recently had farmers chatting at the Crop Talk section of the Agriculture Online. Discussion group poster Jim B. in Iowa says he's watched his neighbors make the switch and wonders whether it's worthwhile considering his circumstances.

"My household softener went to heck. I need a new one, as we have very hard water with quite a bit of iron," he writes. "For more money I can get a big enough softener to be able to fill my semi tanks at night with soft water. It's only a matter of a couple thousand dollars more and I would think, if it helps chemicals work better, it might be money well-spent."

Poster downwardspiral says Jim B. in Iowa is on the right track. Like Jim says, downwardspiral agrees that chemicals like Roundup aren't "tied up" as much with soft water, thereby improving efficacy. He says "chemical action" results have been better with soft water in the eight to nine years he's been using it on his farm.

Research shows that indeed Jim B. in Iowa's judgment is correct. According to Michigan State University Extension Integrated Pest Management (IPM) specialist Gary Thornton, hard water containing high concentrations of salt, calcium and magnesium can lead to "hard water antagonism," a condition in which chemical absorption becomes blocked by compounds created when the water is mixed with a chemical. It's especially poignant with glyphosate, Thornton and MSU entomologist emeritus Jim Johnson write.

"The glyphosate, which is negatively charged, will combine with [soluble salts, calcium and magnesium] to form glyphosate-magnesium and glyphosate-calcium compounds," write Thornton and Johnson. "These compounds are not as easily absorbed by the plant and the result is poor uptake and poor weed control."

Glyphosate is not the only herbicide inversely affected by hard water. According to Montana State University IPM specialist Reeves Petroff, chemical ingredients sethoxydim, imazethapyr and glufosinate can also create compounds that can block efficacy.

Tank-mixing with soft water is just one way to offset the damage hard-water minerals can cause. If soft water is not available, surfactants and chemical additives like ammonium sulfate (AMS) and urea-ammonium nitrate (28% liquid nitrogen) can be added to the mix to lessen the formation of compounds that can cut chemical efficacy.

But, softened water is not always ideal, according to Kansas State University Extension weed specialist Dallas Peterson. Much the same as with magnesium and calcium in hard water, the sodium that's typically used in water softeners can also bond with glyphosate to form compounds that can block spray efficacy.

"I'm not sure soft water takes care of the problem," Peterson says. "It will add sodium, and if the concentrations are high enough, it can cause the same problem, only creating different compounds." He adds inserting AMS into the tank mix may be the most effective protection against such compounds.

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