Results rolling in from the first batch of samples, and it's not too impressive. I'll be posting more detail later, but I'm sure you're all dying to know, so, the 5 inexpensive retail products looked like this:
Organic matter (loss on ignition) 3.2 to 15.7%, average 8.4%
Water 28 to 52%, average 38%
Everything else (?????), by subtraction, average 54%.
Now, really good garden soil is about 10% OM. I would have thought compost would be much higher than that, although the mineral fraction will be higher than in uncomposted vegetation after being concentrated in the compost.
I found results online for our city landfill compost. It's 15-19% OM, which still seems low. They do use drywall scrap, so there is going to be significant mineral content there, but the gypsum is actually beneficial for the clay soil here, so they don't get dinged for high mineral content. At least you know what it is, and it's a waste reduction approach.
I am sending another batch of samples including some high dollar products - I got a bag of cotton burr compost that seems very fluffy, and some more expensive mushroom and cow manure from nurseries (egad, 10 bucks a bag! Still pays to make your own). And, my own backyard stuff from last winter's batch. This way there will be something to compare the low quality products with.
Thinking about a 1-pg fact sheet to put out at our city compost demo trailer at the Earth Day celebration.
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Last edited by toxcrusadr on Fri Apr 01, 2011 2:40 pm, edited 1 time in total.
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Just got the comprehensive analysis on 12 samples this morning - not only moisture and OM but also NPK, Ca/Mg/Fe etc., and CN ratio. I'll post some stuff when I have digested it.
swickstrum: the 'other material' category is all mineral matter or 'ash' content, including all minerals incorporated in the original vegetation and any soil or other mineral matter mixed into the ingredients or the compost. They say manure is 'salty' which I assume means that salts are concentrated in cattle poo. Of course urine is salty and that is probably mixed with the manure. Our city landfill mixes shredded scrap drywall into their ingredients, which boosts up the mineral content considerably. But they disclose that information freely, and the other guys do not.
I was surprised at the mineral content of my own compost, since I don't add any soil. But it was lower than all the commercial products.
More coming soon!
swickstrum: the 'other material' category is all mineral matter or 'ash' content, including all minerals incorporated in the original vegetation and any soil or other mineral matter mixed into the ingredients or the compost. They say manure is 'salty' which I assume means that salts are concentrated in cattle poo. Of course urine is salty and that is probably mixed with the manure. Our city landfill mixes shredded scrap drywall into their ingredients, which boosts up the mineral content considerably. But they disclose that information freely, and the other guys do not.
I was surprised at the mineral content of my own compost, since I don't add any soil. But it was lower than all the commercial products.
More coming soon!