eXtension

Changing Carbon to Nitrogen ratios of materials as they age (breakdown?).

Asked May 18, 2020, 10:01 AM EDT

I'm looking the Carbon/Nitrogen ratios of materials to help me manage my hot, turn composting. I usually see listings on tables, such as: Leaves 60:1 Grass Clippings 20:1 Wood Chips, Wood, Saw Dust, Branches w/ranges from 100:1 to 750:1 What I have deduced, is that: When leaves are listed, it is assumed they are the dry Autumn leaves that have fallen on their own. When grass clippings are listed, it is assumed they are dumped right from the bagger when mowing. All wood products seem to be "as lumber". I assume leaves and grass clippings would be similar when comparing fresh to fresh or dry to dry, other than leaves having a bit more fiber = less nitrogen. In my many searches I did find articles on OSUext which mentioned that green prunings and shrubbery were in the correct C:N range for compost. Finally, my question(s) / what I would like to know: The ratios of any of things listed above (in what state). A timeline vs ratio graph of fresh cut wood as it dries, (and beyond, I will often find a piece of lumber/wood to add to the compost pile that is spongy to falling apart rotten). Some explanation of the process. Is the nitrogen released into the atmosphere? Is there bacterial component? Climate Change implications? Obviously I'm not expecting you to create content, just pointed toward info would be great, my hours of searching have yielded little.

Clackamas County Oregon

1 Response

Good Morning! I've copied and pasted what you would like to know into this frame and will try to address your questions.
The ratios of any of things listed above (in what state).
It seems to me you've done extensive research on the web and in our websites, so I think you have those ratios covered. If you're looking for exact numbers, I'm afraid you'll only find ranges - because as you indicate, time from cutting as well as storage conditions, whether and extent to which things have been ground, etc etc all impact C:N.
A timeline vs ratio graph of fresh cut wood as it dries,
I've never seen anything like this. I would assume that as wood dries, the N content drops and thus the C:N as a ratio assumes a larger value. I think spongy
lumber/wood has been broken down by fungi, which are specialists in "earning a living" in environments with fewer resources - ie, high C:N, low water, low macro/micro nutrients.
Is the nitrogen released into the atmosphere?
No, generally it's the carbon that's released to the atmosphere, as carbon dioxide (CO2), or in oxygen-limited environments as methane CH3. The microbes doing the decomposition - whether bacteria or fungi - are scavenging every scrap of nitrogen available for their life processes. Now, if I stacked up a HUGE fresh green grass clippings, I could probably get an ammonia gas (NH3) release.
Is there bacterial component?
When air, water and nitrogen are abundant, the work in compost piles is largely done by bacteria. When those are limited, the work is done largely by fungi.
Climate Change implications?
Well, sure, we all release carbon dioxide and methane gas all the time. Just by being alive we have a carbon footprint. I have the interest and knowledge to manage much of my domestic-scale organic waste on my own property. If I lacked interest, ability or knowledge, and sent those things off in the yard debris cart it would come with an added cost of the fuel invested in getting them to a central facility and the processing. The quality of life in cities requires organized organic waste is management.

I think you must be composting and I think you may wish some coaching on your process. If so, write back and tell me how you're composting and what the change is you'd wish to see.