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Toxic gick in straw field

 
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Honest question here.

I can’t remember the name of the persistent ‘cide that is applied to pastures/fields to control broadleaf, but I was wondering how long it persists in soil.  More specifically, if I am trying to buy organic straw, how long does a field need to be free of said gick in order for the straw to be considered organic.  5 years?  10?  20?  Does one application permanently render the soil non-organic?  I am just wondering how far back I need to go to get to organic straw again.

Thanks in advance,

Eric  
 
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I'm guessing you're talking about aminopyralids. As for how long they persist, i am not sure. You raise a great point that with persistent herbicides like that, straw being organic might not be enough and more research into the place it was grown might be necessary. From my understanding, even very tiny amounts of that kind of herbicide can cause issues.
 
Eric Hanson
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Thanks Heather.  Yes, those were the ‘cides I was thinking about.  

I assume (hope?) that they do have a lifespan, even if a long one.  I would certainly hope that one application would not ruin the soil for all time.  I guess the reason for a little bit of optimism is that even these persistent ’cides “need” reapplication in a chemical-ag environment for them to work.  If my line of thinking is clear, this means that those nasties, persistent though they are, are not actually permanent.

Even better would be if they can be broken down by something like fungi.  I don’t know if that is possible but I would love to think it is.

Maybe I am being too optimistic though.  I would love to hear feedback about whether I am at least on the right track or not.

Eric
 
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I consulted the oracle of Google, and the EPA has a data sheet for Aminopyralid here.

Ctrl+F for "half-life" yields a bunch of different times, ranging from 31.5 to 533.2 days.  EPA risk assessment standard is 103.5 days.

The EPA datasheet at the above link wrote:Under aerobic conditions, degradation of aminopyralid in five different soils resulted in
the production of CO2 and non-extractable residues. Half-lives ranged from 31.5 to
533.2 days in 5 soils. For risk assessment purposes, EPA used a half-life of 103.5
days.
Aminopyralid photolyzed moderately slowly on a soil surface. The half-life was 72 days
and CO2, non-extractable residues and small amounts of acidic volatiles were the
degradates.



So from there, just use a Half-Life Calculator.  

Start with the half-life (t 1/2) corresponding to your personal scientific risk beliefs; or just trust the government and use EPA standard of 103.5 days.  Recall that a longer half-life assumes a more conservative risk, while a shorter half-life means less risk aversion, believing the material will degrade sooner.
Using an initial quantity of 100 N0, choose a desired quantity remaining based off your risk tolerance.  For instance, 95% gone would mean 5% toxic gick remaining, (Nt = 5).  The remaining 4th field will give you the time to get to that amount (in this instance, in days).  Make sense?

Another converter calculator can then help put the days into better perspective.  
In this example, you would want to wait 1 Year, 2 Months and 3 Weeks for 5% of the toxic gick to remain using EPA standards.  
A super risk-adverse person using a half life of 533 days, and only 1% remaining, on the other hand, would end up waiting  9 Years, 8 Months, 1 Week, and 5 Days.

But let's put math aside and just go with the politics of the word.  If you are referring to "organic" in the US government-owned official marketing meaning of the work, follow their National Organic Program standards.  In that case, the answer you're looking for is likely 3 years.
 
Eric Hanson
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Thanks George!  That’s the kind of answer I was looking for.

Eric
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