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Q: composting ( Answered 5 out of 5 stars,   2 Comments )
Subject: composting
Category: Science > Chemistry
Asked by: grooviogrl-ga
List Price: $10.00
Posted: 19 Aug 2004 07:02 PDT
Expires: 18 Sep 2004 07:02 PDT
Question ID: 389901
What materials decompose the fastest?  Those high in carbon or those
high in nitrogen?
Subject: Re: composting
Answered By: hummer-ga on 19 Aug 2004 08:20 PDT
Rated:5 out of 5 stars
Hi grooviogrl,

The short answer to your question is those materials high in nitrogen
will decay more quickly, however, you need both carbon and nitrogen at
the proper ratio to have success with your compost pile.

"Grass, weeds and kitchen waste [high in nitrogen] may be used in
great quantity, as they decay very rapidly. Leaves, hay, sawdust,
cornstalks and straw [high in carbon] are slower and require a longer
decomposition period."

"If your compost mix is too low in nitrogen, it will not heat up. If
the nitrogen proportion is too high, the compost may become too hot,
killing the compost microorganisms, or it may go anaerobic, resulting
in a foul-smelling mess. "

A Characteristics of Raw Materials:

Carbon to Nitrogen Ratios:

Grass Clippings               19:1
Sewage Sludge (digested)      16:1
Food Wastes                   15:1
Cow Manure                    20:1
Horse Manure                  25:1

Leaves and Foliage         40-80:1
Bark                     100-130:1
Paper                        170:1
Wood and Sawdust         300-700:1

Feeding the Soil - Carbon/Nitrogen Ratio:
What is the carbon/nitrogen ratio anyway?
"The carbon/nitrogen ratio (C/N) is the amount of carbon in a residue
in relation to the amount of nitrogen. The rate of organic matter
decomposition and timing of nutrient availability are influenced by
the C/N ratio. Everything organic has a ratio of carbon to nitrogen in
its tissues."
"Crop residues will decompose faster when the C/N ratio is low or have
a high N content."
Role of C/N Ratio and N Content on Organic Matter Decomposition and Soil Fertility
"In general, organic materials (crop residues or animal wastes) added
to soils with C/N ratios greater than 30/1 or with 1.5% or less N
(e.g., corn residues) will usually result in an initial nitrogen
immobilization or "tie-up". This means, that inorganic nitrogen such
as ammonium (NH4+), and nitrate (NO3-) from the soil solution will be
"borrowed" by the soil microorganisms to decompose the added material
(microorganisms need nitrogen for cell growth and function).
Eventually the nitrogen will be returned to the soil as the
microorganisms die and decompose. The amount of available N in the
soil solution will depend upon crop uptake, volatilization,
denitrification, immobilization, and leaching. On the other hand,
organic materials added to the soil with C/N ratio of less than 20 or
with 2% or more N(e.g., alfalfa hay) will result in an initial N
mineralization. This means that organic N will be transformed to
inorganic N and be released to the soil solution, making it readily
available for crop uptake. Keep in mind that these are
generalizations, and many factors such as soil pH, soil temperature,
moisture, etc., influence the decomposition rate of organic materials
and the release or tie-up of nitrogen. For instance, crop residues
decompose very slowly in cold dry soils. These generalizations will
also apply if you are composting organic materials."

Building a Compost Pile:
"The subtlety of carbon-nitrogen ratios is important only if you're
producing compost quickly and want as much nitrogen as possible in the
finished product. The difference in the nitrogen content of a compost
that decomposed slowly over a year or longer and a compost made
carefully but quickly is relatively small. Slow compost protected from
the weather may contain between 1/2 and 1 percent nitrogen; quick
compost made with attention to the carbon-nitrogen ratio may contain 2
percent nitrogen."


Step-By-Step Instructions to Build a Compost Pile:

Composting basics including: uses, siting, materials and trouble shooting:

I hope this helps. Please let me know if you have any questions by
posting a clarification request before closing/rating my answer and
I'll be happy to reply.

Thank you,

Google Search Terms Used:

"high nitrogen content" compost
materials high in nitrogen
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compost "rate of decomposition" nitrogen carbon
how to make a compost pile
grooviogrl-ga rated this answer:5 out of 5 stars
answered my question and gave me more information for further research!

Subject: Re: composting
From: hummer-ga on 19 Aug 2004 11:02 PDT
Thank you, grooviogrl, I'm happy you are happy. Sincerely, hummer
Subject: Re: composting
From: neilzero-ga on 19 Aug 2004 11:49 PDT
Fast composting increases the probability that the process will
approach cost effective, so several percent nitrogen is needed.
Generally it is thought that about one meter by one meter by one meter
is the optimum dimenions, somewhat larger in winter. Moist air at
temperatures up to 140 degrees for one day is desireable to start the
process. If hot spots over 140 degrees f develop in the pile, cool
water, cool air and stiring are good remidies. The pile needs fresh
air thoughout the pile which needs to stay warm, damp, but not wet.
See mushroom growing for details on fast composting. Some lime rock is
often added to prevent too low a ph in the pile. Neil

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