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Re: Purity Of Organic Foods/Compost



Luckily, when you take leaves contaminated with who-knows-what pesticide and compost them, letting the microorganisms do their thing, the microbes chew up the pesticides, turning them into carbon dioxide, water, more microbial biomass and some waste materials that are then used by other microbes. 

The important thing is to make sure you maximize the DIVERSITY of microbes in your compost, so you are most likely to have the microbes needed to chew up the pesticides.   You also need a diversity of food resources, that is, kinds of organic matter, so you have the diversity of foods that the diverse set of microbes need to do their jobs. 

The more diverse, the more likely you will get decomposition of toxic chemicals.  We're talking diversity of BOTH plant material and microbes here.  And a couple more things are needed....

Typically you need some temperature in your compost pile so the microbes have the energy to decompose the difficult chemical structures of pesticides.  All those chlorines and bromines and benzene rings in most pesticides require production of seriously high-energy-requiring enzymes to allow break-down of the pesticide.  

But that's the right amount of heat - not too much, not too little.  If you see "compost" that has turned black, the composter fried the most important critters, and the pesticides are probably still present.  Compost is supposed to be dark brown, not black.  Nor do the pesticides generally decompose if the compost turns anaerobic.  So, stinky, smelly compost is not compost.  If it smells bad, it means something is not right.  Don't put it around your plants.  Learn what is a bad odor, versus a soil smell.   You may need a course in composting from someone who knows something about these smells and what they mean.

So, you have to have water and air correct in your pile.  More "not-too-much, not-too-little" factors.  We need air and water just right - the Goldilocks principle.  Compost is not a simple linear system, multiple factors have to be correct all at the same time.  Water influences the amount of air present.  Too wet, and you go anaerobic.  Too dry, and the microbes are sound asleep. Must get it just right. 
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Heavy metals may be sequestered, or tied up in organic forms in compost, in forms that all but the most destructive chemical analysis will not detect.  Heavy metals stay plant-not-available if you maintain the organic matter level in your soil.  You lose organic matter in your soil most rapidly when you plow or physically disturb soil.  Minimize tillage, and you minimize organic matter loss.  Maintain organic matter, and heavy metals remain immobile and not-plant-available.

Does that mean you should never till?  I said, minimize tillage.  Till to the least extent possible.  Vern Cole and Bobby Brock have both shown this to be the case, along with quite a number of researchers that followed on their leads.  Minimize tillage. 

Residues left in your field in the fall should be decomposed by the microbes, not sliced and diced and plowed into the soil.  If your residues do not "disappear", there's something wrong with the set of microbes in your soil, and you need to fix them and get them working for you again.  If you till residues into the soil, they may just produce plant-toxic compounds if they decompose without enough air in compacted soil. 

But back to pesticides in compost.  We have a recent addition to the herbicide world that apparently does not decompose during the composting process.  Chlopyralid is a serious problem, and this chemical should be banned from ever being put on another ecosystem.  Nothing decomposes it, and once you put it on your lawn, you will not be able to convert that lawn into a vegetable garden or into broad leaf plant production.  I'm rooting for the little critters, however, and hoping that somewhere, someone will find the microbe that will decompose chlopyralid.  For more information on the topic, please look at the City of Seattle's website, and the writings of David McDonald from Seattle.  I recall that Steve Diver from ATTRA has put together a good reference list on this topic as well.  Check www.ATTRA.org

To summarize then, to get the decomposition of toxic chemicals in your compost, you have to have the right microbes, good food for them, correct air/water mix and additional energy, such as heat, or passage through an earthworm.  Then, you can feel pretty safe about the "purity" of your compost.

One last point - In Europe, we almost invariably have to add the right set of microbes to compost piles, because in most places, the plant material no longer has the desired set of microbes on the plant material.  In the US, in the major cities, the same problem occurs quite often.  The plant material does not contain the necessary set of organisms that decompose pesticides.  An inoculum of beneficial microbes is needed.  Commercial composters find that adding back a little of the last pile, or adding a commercially available inoculum of microbes, is necessary.  Add organisms to make sure the minimum diversity is present.   This says something that should be of concern to everyone about the wide-spread presence, use and impact of pollutants in the world.   

At Soil Foodweb Inc, we will be offering assays to allow people to determine whether they have the beneficial organisms in their soil, compost or compost tea.  The ability to determine presence of beneficial organisms is not available elsewhere.  Check our website for more information.

Elaine Ingham
President, Soil Foodweb Inc.
www.soilfoodweb.com