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High carbon materials for humanure composting

Humanure pathogensNext week, I'll continue our humanure lunchtime series by delving into several different types of composting systems.  However, before you get too excited, I want to take a step back and consider the biggest issue with humanure composting.

No, I'm not talking about disease.  Joseph Jenkins does an admirable job of explaining how a well-managed humanure recycling system is perfectly safe.  (Check out The Humanure Handbook if you don't believe me.)  I'm more concerned with an issue that's already problematic on our farm --- a paucity of high carbon materials.

Deep beddingWe've been experimenting with deep bedding in our chicken coop for the last couple of years, which is a bit like a humanure composting system for chickens.  Theoretically, the idea has merit, and it does work pretty well in practice, but I'm always scrambling in search of quality bedding.

In a pinch, I can use straw, but I don't like buying carbon for my chickens to poop on, and the optimal bedding is higher in carbon and smaller in size so chickens can scratch through and mix the bedding regularly.  When we run out of autumn leaves, either raked from the woods or collected by my kind mother during city trash pickup days, manure piles up, smells turn foul, and flies start to plague our porch dinners.  The conclusion is: we don't have enough high carbon materials for essential uses right now without diverting some to a humanure composting system.

Jenkins recommends hunting down 20 cubic feet of sawmill sawdust per hundred pounds of human body weight in the household per year, which (rounding up to include guests and to give us a bit of wiggle room) would equate to 80 cubic feet (600 gallons) for us.  That's 120 five gallon buckets or 7 of our 95 gallon wheelie bins full --- a pretty hefty helping of sawdust for which we've yet to find a source.  In addition, he recommends having about ten bales of straw or hay on hand for covering the outdoor pile.  (I'll explain more about the uses of the two types of high carbon material in a later post.)

Humanure compostingJenkins does offer sawdust alternatives, including peat moss, leaf mould, rice hulls, or grass clippings (although I'm not so sure grass clippings would work well --- they're pretty high in nitrogen).  However, all of those sources would either have to be bought or would require considerable effort to gather, making their use equally problematic.

Mark isn't a fan of humanure composting, so he was very relieved when I told him I couldn't even consider a system until we stock up on enough high carbon bedding for the chickens plus a year's supply for a humanure system.  Looks like we'll be scouring the countryside in search of a sawmill....

If humanure composting seems too intense, you'll enjoy easier projects outlined in The Weekend Homesteader.

This post is part of our The Humanure Handbook lunchtime series.  Read all of the entries:

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I had the same struggle.

First, I found planar shavings. There are lots of woodworkers around here, and they were glad to have help getting rid of it. However, this doesn't work as well as sawdust, taking a very long time to break down.

I looked everywhere for something better, and finally broke down and bought a truckload of sawdust from a sawmill. 40-45 yards. It's huge. It will last years. Most of the price was the cost of trucking it to me.

Recently a neighbor had some trees cut and milled. He asked me to help him get rid of the sawdust, so we headed over with snowshovels and filled the truck. (Remember to put a tarp down first, and close the back window!)

Comment by Jay Bazuzi Mon Sep 3 22:28:31 2012
You have to let the grass dry out. It's just like harvesting hay or straw... Also, instead of lumber mills: Do you have local arborists (or county or city arbor service)? Whether they're trimming for power line interference or for homeowner requests, they have to get rid of what they cut down. If you let them dump it at your place for free it's cheaper than a landfill.
Comment by Nolan Mon Sep 3 22:41:52 2012
Also, if you just need the carbon and not the nutrients, paper is an excellent high-carbon material. There are many sensitive document shredding companies, perhaps you could obtain shredded paper from them.
Comment by Nolan Mon Sep 3 22:43:55 2012

Jay --- The Humanure Handbook does make a firm distinction between sawdust from a woodworking shop and the wetter sawdust from a mill. Like you, I'd be thrilled to buy a truckload of sawdust from a mill, but haven't found a place that would deliver it. I guess I should look into that....

Nolan --- The trouble with grass isn't the wetness, but the nitrogen. You want to add high carbon materials to counteract the high nitrogen humanure so that the mixture is close to the 30:1 C:N recommended for making compost. That's why sawdust works so well --- it has a C:N of about 200:1 to 500:1 (depending on type of tree and whether it's partially rotted). Grass clippings have a C:N of 15:1, which means that they'll off-gas nitrogen when composted by themselves and won't counteract any other high nitrogen materials.

We do get wood chips, which we rot down and use for mulch around trees and berries. But the author of The Humanure Handbook notes that wood chips don't work well with humanure because of their consistency, which is very different from sawdust.

I like your shredded paper idea best, although we live way out in the country and don't have sources nearby.

Comment by anna Fri Sep 7 14:18:34 2012

If you live in a rice growing area like Louisiana, Missouri, or Gulf Coast TX (if my 8th grade geography lessons served me well there...) you can probably get some rice hulls cheap. That is what we use. Downside is possible pesticides on them. But usually they are not sprayed after they flower.

A chainsaw probably spits a fair amount of quality sawdust as well. Not 20 cubic feet per person, and harder to gather, but it is a bit.

I have a friend in Equador who uses soil. It comes out very improved by the end of the composting.

And finally, fall leaves are excellent as well.

Comment by Eric in Japan Fri Sep 7 18:34:34 2012
Put a tarp down when cutting firewood with your chainsaw in order to catch the saw dust. It may not be enough, but you an collect several cubic feet of carbon material this way that you would otherwise be unable to utilize when and where you want.
Comment by Darryl Fri Sep 7 21:16:30 2012

Eric --- We've been collecting sawdust when we cut bought firewood down to our smaller stove size with the miter saw. It doesn't add up to all that much, but is handy. Wish we were closer to the rice-growing region....

I'm not sure about the method of using soil. I suspect what it does is cut down on smell, but that you end up losing a lot of nitrogen (which is generally the problem if you don't mix manure or urine with a high C:N additive).

Darryl --- If we were cutting firewood on a lawn or driveway, a tarp might work well. But just trying to lay down a tarp in our woods would end up trampling all the undergrowth and almost definitely ripping the tarp a few times!

I wish they made some kind of attachment that bagged sawdust as it was made. I sometimes gather up little piles of it by hand after Mark cuts wood, but it's hard to get much....

Comment by anna Sat Sep 8 12:16:35 2012
Maybe I'm missing something here, but, if your problem with a humanure pile is out-gassing and loss of N, then any barrier, like dirt, would suffice. If the problem is a final material that is too high in N, then you could dilute it a priori with wood shavings, etc, or post priori by just spreading it more thinly on its target soil. Carbon itself is not an issue. Plants take in almost all of their carbon from the amosphere, not the soil. Carbonaceous materials in the soil give it a less dense, more "airy," more beneficial texture.
Comment by doc Sun Sep 9 08:03:05 2012

Chapters 4 and 5 of the humanure handbook didn't contain much useful information, IMO.

Chapter 6 was an interesting overview of low temperature systems. And chapter 7 deals with disease-causing agents in urine and excrement. What I don't get is why the author dwells on those, when the point has already been made in earlier chapters that you'd need relatively high temperatures to get safe compost?

Chapter 8 seems the most interesting chapter of the book so far; a working high-temperature composting system. Since the author has done measurements of his compost piles' temperatures as well as had his compost tested for nutrients and disease vectors, it seems to me the most valuable chapter of the book.

Comment by Roland_Smith Sun Sep 9 08:09:22 2012

Doc --- In my understanding and experience, composting is a bit like baking a cake. If you don't get the proportions right, something goes wrong. Putting dirt over top would be like slapping a lot of frosting on a slumped cake --- it might look okay until you bit into it.... :-) (And now you know what kind of cook I can be... :-) )

When you don't add much carbon to a compost pile, microorganisms break down the nitrogen into a gas and much of it is lost to the air. So a barrier like dirt would hold that gas in place in the pile, but wouldn't prevent its production in the first place. Presumably, when you cut into the pile with a shovel, you'd get off-gassing.

With the right proportions of carbon and nitrogen in the compost pile, there is no outgassing, so the finished product is actually higher in nitrogen. In addition, the carbon gets converted into humus, which is what separates the effects of compost from the effects of short term chemical fertilizers. Sure, plants take in carbon dioxide out of the air, but humus holds water, provides a home for handy soil microorganisms, and slowly releases nitrogen over time --- it's essential for good organic gardening.

Roland --- Yep, those are other parts of what I mean by it being a self-published book --- repetitive, has trouble getting to the point... :-) I think some people are afraid that if the book doesn't look long enough, no one will buy it. Too bad because I vastly prefer to read a short, to-the-point book!

Comment by anna Sun Sep 9 08:54:10 2012

Would e.g. the dead branches on your property make enough sawdust when processed with a sawdust maker?

Comment by Roland_Smith Mon Sep 10 16:40:52 2012
Roland --- Usually sawdust is a waste product, so I'd rather take it out of the waste stream than produce it, if possible. The machines I saw online all seem big (and presumably expensive) too. I clearly need to put in more phone time to find a local mill option!
Comment by anna Mon Sep 10 18:14:53 2012