An Introduction to the CCQC Maturity Index

H O W D O I K N O W T H A T
C O M P O S T I S M A T U R E ?
An Introduction to
the CCQC Maturity Index
California Compost Quality Council
19375 Lake City Road, Nevada City, CA 95959
www.ccqc.org

WHAT IS MATURE COMPOST?
Maturity is the degree or level of completeness of composting. This means that raw
starting materials (feedstocks) have been sufficiently decomposed under controlled
moisture and aeration conditions that results in a stable organic amendment product.
WHY IS COMPOST MATURITY IMPORTANT?
Most uses of compost require a stable product that will prevent nutrient tie up and
maintain or enhance oxygen availability in soil or growth media. Continued active
decomposition when immature materials are added to soil or growth media may have
negative impacts on plant growth due to reduced oxygen, water infiltration and/or
available nitrogen.
Most uses of compost require a mature product free of potentially plant toxic
components. An immature compost may contain or produce high amounts of free
ammonia, certain organic acids, or other water-soluble compounds which can limit
seed germination and root development.
IF IT LOOKS GOOD, IS IT MATURE?
Use your eyes, but a brown color or the look of coffee grounds is not foolproof.
IF IT SMELLS GOOD, IS IT MATURE?
Does the compost smell like household cleaner or good rich soil? But be aware that it
is too old it could be more like soil than organic matter.
HOW CAN I TELL IF COMPOST IS MATURE?
Maturity is not described by a single property and therefore measuring two or more
chemical/biological properties of the composted product best assesses maturity.
California Compost Quality Council (CCQC) registered compost producers provide
their most recent laboratory analysis of the chemical and physical properties of their
materials. A numerical Maturity Index has been developed which uses standard lab
test methods to rate compost maturity.
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California Compost Quality Council www.ccqc.org

CCQC MATURITY INDEX
The CCQC Maturity Index uses the organic carbon to nitrogen ratio and at least one
test from Group A and at least one test from the Group B list (see below). Tests from
Group A measure whether adequate decomposition has occurred by measuring carbon
dioxide release or oxygen use. Tests from Group B measure directly potentially toxic
compounds like ammonia or indirectly by measuring seed germination and/or plant
growth.
Carbon to Nitrogen (C:N) Ratio
Compost must first have a C:N ratio less than or equal to 25 in order to be rated as
acceptable prior to additional maturity rating from results of tests in Group A and B.
Group A
These tests indirectly measure the degree of organic matter decomposition. Lower
values from these tests generally indicate more mature products. Some measure
carbon dioxide release or oxygen consumption by microbes, while the heating test
measures heat generated by a sample. Both tests are done for a fixed time period.
Carbon Dioxide Release or Respiration
Oxygen Demand
Dewar Self Heating Test
Group B
These tests measure directly or indirectly chemical characteristics of the product,
some of which can be toxic to plants. Ammonia and organic acids have a maximum
allowable value, while plant tests measure germination rate and root/plant growth in
the product and compare it to a standard control.
Ammonium:Nitrate Ratio
Ammonia concentration
Volatile Organic Acids concentration
Plant test
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California Compost Quality Council www.ccqc.org

I N T E R P R E T A T I O N
The three rating categories of the index: Very Mature, Mature, and Immature relate
to the following compost characteristics:
V E R Y M A T U R E M A T U R E I M M A T U R E
Well cured compost Cured compost Uncured compost
No continued decomposition Odor production not likely Odors likely
No odors Limited toxicity potential High toxicity potential
No potential toxicity Minimal impacts on soil N Significant impact on soil N
S E L E C T E D MA T U R I T Y IN D E X RA T I N G VA L U E S FO R C O M P O S T E D PR O D U C T S *
Method Units Rating
Very Mature Mature Immature
CO2 Test C / unit VS / day < 2 2 - 8 > 8
Ammonia : Nitrate Ratio No units < 0.5 0.5 - 3 > 3
Total Ammonia ppm, dry basis < 100 100 – 500 > 500
Seed Germination % of control > 90 80 - 90 < 80
Plant Trials % of control > 90 80 - 90 < 80
*The CCQC Maturity Index requires three different types of tests to confirm the
maturity of a composted product. Many of these tests are standard laboratory tests
compost producers will normally conduct. Additional technical details on these tests
are available from the California Compost Quality Council.
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California Compost Quality Council www.ccqc.org

Select Definitions
MATURITY. The degree or level of completeness of composting. Maturity is not
described by a single property and therefore, maturity is best assessed by measuring
two or more parameters of compost in part, affected by the relative stability of the
material but also describes the impact of other compost chemical properties on plant
development.
MATURITY INDEX. An evaluation procedure to describe the degree of
decomposition and completeness of a compost process. The maturity Index relies on
any two or more test methods performed concurrently on the same sample. Test
methods that are applicable are those which have demonstrable relevance to stability
and maturity. For a Maturity Index, tests should include at least one parameter each
from the A list and the B list (see Maturity Index Test Methods).
PHYTOTOXIC to maturity, phytotoxicity is not a single property of compost.
Factors such as salt, volatile organic acids, or ammonia all play a role in determining
phytotoxicity. ITY. A condition or quality of compost that negatively influences
plant growth. Similar
STABILITY. A specific stage or state of organic matter decomposition during
composting, which is related to the type of organic compounds remaining and the
resultant biological activity in the material. The stability of a given compost is
important in determining the potential impact of the material on nitrogen availability
in soil or growth media and maintaining consistent volume and porosity in container
growth media.
What is the CCQC?
The California Compost Quality Council (CCQC) represents an unprecedented
alliance of farmers, compost producers, soil scientists, landscape contractors,
agricultural advisors, environmentalists, soil testing laboratories, and others
interested in increasing the production and appropriate use of compost in California.
CCQC serves as a forum to stimulate dialog between compost producers and users,
develop compost quality criteria, standardize analytical methodology, ensure
compliance through a voluntary monitoring program, and verify claims of products
that meet the criteria developed by the CCQC.
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California Compost Quality Council www.ccqc.org

Additional Resources on Compost Maturity
1. "The CCQC Maturity Index" (Final Report). Available from CCQC
(www.ccqc.org)
2. "The CCQC Guide to Compost Maturity". Available from CCQC
(www.ccqc.org)
3. "Compost: Matching Performance Needs with Product Characteristics”, Available
from the CIWMB, 916-341-6620
4. "How Agricultural End Users Can Access Compost Quality, Jean Vandergheynst,
UC Davis, Available from the CIWMB (916) 341-6620
5. Compost – A Guide for Evaluating and Using Compost Materials as Soil
Amendment. William Darlington, Soil and Plant Laboratories, Inc. Available
from the CIWMB at 916-341-6620.
LIMITATIONS
Compost producers and users should realize that the presently accepted methods to
evaluate stability and maturity may not completely or precisely address the most
important concern, ‘Is it appropriate for the particular end-use?’. All of the test
procedures described in this document and the complete CCQC Maturity Index
Report provide indirect interpretations for the potential impact on plant growth. In
most cases these tests and determinations are performed on samples comprised of 100
percent compost. However, compost is used as an additive that may range from 30
percent to less than 1 percent of the total media or soil volume. In the absence of even
more specific tests that evaluate the material based on a particular use, it is very
important for the producer of compost to become more aware of the requirements for
different end-use markets.
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