Carbon-Nitrogen ratio

The International Compost Sanitation Forum and Message Board: Humanure Composting Around the World: Carbon-Nitrogen ratio
Author: Louis Nicholas
Saturday, June 16, 2001 - 10:52 am
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I've read in several books on composting that the carbon to nitrogen ratio should be between 20:1 and 30:1 to encourage the growth of thermophilic bacteria. In practical terms what does that mean?

Does that mean 20 to 30 pounds of carbon materials (leaves, saw dust, peat moss, straws, etc) to 1 pound of humanure? The reason I ask is that humanure is not pure nitrogen. So is 20 to 30 pounds of carbon materials to one pound of humanure too high a carbon/nitrogen ratio?

Author: Joe Jenkins
Saturday, June 16, 2001 - 3:14 pm
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Humanure is not pure nitrogen and "carbon materials" are not pure carbon. You will have to experiment with the materials you have in order to determine what ratios work best. Try covering the nitrogenous deposits with enough carbon material to prevent odor and see if that gives you the correct ratio.

Author: Rob Canning
Sunday, September 02, 2001 - 11:24 pm
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My brother asked me a question about snow the other day, to which I had no answer. The question was about oxygen in water and snow. Would thermophilic bacteria thrive on highly oxygenated water, or is it air that they need, not just oxygen? Snow is supposed to have a high oxygen content, though I guess its low temperature would naturally discourage thermophilic bacteria.

Anyway, can snow insulate a compost pile to the point that thermophilic bacteria would still be active?
And, if so, would they be able to take advantage of the oxygen content in the snow?

Author: Joe
Wednesday, September 05, 2001 - 5:15 pm
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I doubt that thermophilic bacteria would benefit from the oxygen in snow. As you say, if they are in contact with the snow, the coldness will inactivate them.

Author: BT Benjaminson
Tuesday, February 05, 2002 - 9:03 am
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Speaking of composting in cold climates--I am wondering whether or not to plan an on-farm humanure composting system so that the body warmth of farm animals can help prevent the compost from freezing (and stopping its processes) in the winter. In practical terms, this would amount to building the compost bins/piles in a shed adjacent to or coming off of a large barn that could be enclosed in the barn during winter and opened to the outside during warm weather. Obviously, fly control would have to be a part of it. Has anyone tried this? Alternatively, has anyone just added humanure to the animal manure composting system they already have in place? The large volume of animal manure is less likely to freeze during the winter.
I would like to find ways of preventing freezing because the soil on the farm is fairly poor and it needs a lot of admendments asap in order to become productive.

Author: admin
Tuesday, February 05, 2002 - 1:42 pm
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For what it's worth, my humanure compost was 110 degrees F a couple days ago, February, in north western PA. This is unusual. Global warming? It hasn't frozen in any of the past 4 years while it used to freeze every year since 1979.

Author: BT Benjaminson
Tuesday, February 05, 2002 - 7:40 pm
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I'm also noticing the global warming in New York City. No steam from the piles here--the weather is way too warm! Gotta get out of this coastal area before we are flooded!!

The farm in question will be in Massachusetts though, probably somewhat colder than PA.

Author: lynne rosner
Thursday, May 19, 2005 - 1:49 pm
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Do you know if there has ever been a comparison of the carbon nitrogen ratio of humanure of a vegan to a meat/dairy eating person?

Author: admin
Thursday, May 19, 2005 - 7:48 pm
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I know of no research along those lines - sorry.

Joe Jenkins

Author: Larry
Thursday, May 19, 2005 - 9:43 pm
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Lynne asks an interesting question. I recall that feces contain relatively little nitrogen, consisting mostly of carbon. Urine contains most of the nitrogen excreted by a human, and undoubtedly varies in concentration according to various factors such as diet, fluid intake, exercise, age, etc. I would like to learn more about this.

Author: admin
Monday, May 23, 2005 - 4:57 pm
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I doubt that a vegan or vegetarian diet makes much difference. It depends on what you eat as a vegan or vegetarian. I was vegan for about 5 years and vegetarian for about 15, but have now adapted my diet to the place where I live (western PA, which now includes venison, dairy, etc.). I know vegetarians who have not eaten meat for decades, but are considerably overweight. I think vegans and vegetarians both can consume lots of protein if they want to. I found it interesting that some cultures that have high fiber diets (African, for example) had considerably larger average stools. Anyway, this is from the Humanure Handbook, 2nd ed., page 57:

Table 3.3
Composition of Humanure

Fecal Material:
0.3-0.6 pounds per person per day
(135-270 grams), wet weight.

Organic Matter (dry weight) 88-97%
Moisture Content 66-80%
Nitrogen 5-7%
Phosphorous 3-5.4%
Potassium 1-2.5%
Carbon 40-55%
Calcium 4-5%
C/N Ratio 5-10

Urine:
1.75-2.25 pints per person per day (1.0-1.3 liters)
Moisture 93-96%
Nitrogen 15-19%
Phosphorous 2.5-5%
Potassium 3 -4.5%
Carbon 11-17%
Calcium 4.5-6%


Source: Gotaas, Composting, (1956), p. 35

Author: lynne rosner
Monday, May 23, 2005 - 9:15 pm
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It was just my curiosity because i noticed that cows and horses had a much more ideal c/n ratio to their stool and look at what they eat! i know it sounded out there. That study in Africa could not have been looking at large populations of Africa where i think people are starving and dying due to aids, lack of proper nutrition and sanitation. Your book should become a part of every governments agenda for a sustainable world.

Author: Anonymous
Tuesday, May 24, 2005 - 10:46 am
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I'll second the thing on governments.

Author: admin
Wednesday, May 25, 2005 - 2:27 pm
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Most cow manure is mixed with straw or other bedding and that's why it composts so well.

Author: Vaughn Christens
Monday, June 06, 2005 - 5:26 pm
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It *does* matter whether or not you are a vegetarian. A vegetarian is less likely to consume more protein than he or she needs, ergo will excrete urine that is lower in nitrogen. That's why the nutrient value of excreta varies so widely around the world. The Gotaas figures were likely just an average of samples from some typical Americans. You'd find different ratios in Viet Nam, India, etc.

However, for the purposes of this system, it's probably not a major issue.

Be a systems thinker!

Author: lynne rosner
Wednesday, June 08, 2005 - 12:06 pm
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What system are you talking about? I noticed that in the list on page 56 in the book animal residues (blood, meat scraps, etc) contained more nitrogen. Maybe the less in your poop the less you have to balance your poop. that's just my personal system that i was thinking about.

Author: sean hill
Wednesday, June 22, 2005 - 1:29 pm
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Composting- As "Sludge Manager" for a UK utility, we recycle some 260,000t 'biosolids' to farm. For C:N ratio we look for 14:1 (that would be chemical analysis) but for simplicity, we add some 5% straw to a typical raw material, and 50-70 degrees C are achieved with 3 days. You could add anything from 3-15% and get the same effect. The main aim for us is to add carbon ( cardboard may also do) and to allow air into the mixture. I have been reliably told that addition of lime (CaCO3) would keep the pH up, and prevent the process becoming too acid, and therefore possibly pickling the poo rather than decomposing it!--I could go on for hours....... Poo..... its my life! :-)

Author: Max
Wednesday, December 14, 2005 - 2:42 pm
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does anyone know what the C/N ratio of molasses is? i started a new thread on this but it was deleted for some reason.

molasses is basically sugar (with many extras), so it is a simple carbohydrate with high carbon bioavailability. i am currently using it and find that it reduces the need for the large volume of cover material normally used. i dissolve the molasses in warm water and mix it with the cover material and allow it to dry.
it is also known to reduce odours, so this allows one to use much less cover material than usually needed to supress odours.

so if molasses has 76.5g carbohydrate per 100g, and considering its high carbon bioavailability, how many parts of sawdust are equal to 1 part molasses?

Author: Max
Wednesday, December 21, 2005 - 11:03 am
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ok, the answer is about 50:1

Author: TCLynx
Tuesday, January 03, 2006 - 7:14 pm
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the use of molasses or sugar just helps combat amonia smell by binding with some of the nitrogen in the urine.

Author: Max
Wednesday, January 04, 2006 - 6:26 am
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no, not really. it's all about the thermophillic bacteria.

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