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Ammonium Thiosulfate (ATS) as an Ammonium Sulfate (AMS) Replacement (06/01/17)

Question: I received a call who was talking to a neighbor about an idea of substituting ammonium thiosulfate rather than using AMS with glyphosate. He normally uses 8.5 lbs. AMS per 100 gallons of water as a water conditioner. Presently he is considering inducting liquid AMS versus handling the dry product this year for their post work which is a fair amount of work currently with the dry bags.

Ammonium Thiosulfate (ATS) as an Ammonium Sulfate (AMS) Replacement

Question: I received a call who was talking to a neighbor about an idea of substituting ammonium thiosulfate rather than using AMS with glyphosate. He normally uses 8.5 lbs. AMS per 100 gallons of water as a water conditioner. Presently he is considering inducting liquid AMS versus handling the dry product this year for their post work which is a fair amount of work currently with the dry bags.

They are also considering using liquid ammonium thiosulfate as a substitute because it is cheaper but want to know if weed control would be better than AMS? Both methods apply some sulfur to the crop but on a crop removal basis would only be a small percentage of what is being removed.

Answer: Weed scientists at Kansas State University compared AMS to ATS and found ATS was less effective as AMS at conditioning water and enhancing glyphosate. Since the comparison of AMS and ATS had been shown with glyphosate I continued this comparison with Liberty last year in 2016 applied at comparable sulfate rates as shown below:

zollinger

Summary: The data validates KSU data that ATS is less effective in overcoming hard water cations and enhancing weed control from weak-acid herbicides like Liberty than AMS. The question has been asked: “Why are they not the same?” or even, “Why is not ATS better than AMS since it contains more sulfate?”

The answer: With some explanation from Dr. Dave Franzen, NDSU Soils Specialist and some research, it appears that despite the name – ammonium thiosulfate, ATS does NOT contain sulfate!

Sulfate = SO4(2−) = 1 sulfur and 4 oxygen
Thiosulfate = S2O3(2-) = 2 sulfur and 3 oxygen
The prefix ”thio” indicates that the thiosulfate ion is a type of sulfate ion with one oxygen replaced by sulfur. In this form it does not act as the pure sulfate ion. This is an example of where small difference (a substitution of 1 oxygen with 1 sulfur) makes a significant difference in activity. This may add some insight of “why”.

 

Rich Zollinger

Extension Weed Specialist

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