Testing and judging condition of compost
Composters want to ensure the compost they
make is adequate for their purposes.
There are many tests and checks by which
various aspects of the composting process
and the condition of compost may be judged.
From the point of view of the overall operation
and the final product there are three groups
of tests:
- test of the sanitary quality of the operation
and of the finish product, i.e., pathogen
and parasite destruction and absence of flies
and odors;
- test of fertilizer or agricultural or horticultural
value, i.e., the amount of nitrogen, phosphorus,
potash, and other nutrients, nutrient conservation,
the C:N ratio, and compost value ;
- assessment of the biological activity of
the compost, how many and what types of soil
dwelling animals and microorganisms it contains;
and
- economic test, i.e., whether the total cost
of producing the compost is less than its
value as fertilizer plus the cost of disposal
by other means, such as incineration or land
fill.
Health organizations and laboratories can
make tests for organisms of public health
significance when necessary. Chemical tests
for nitrogen in its different forms, phosphorus,
potash and the organic character of the material
can be made by standard techniques and are
useful in analyzing the finished product
and to determine the effect of different
composting procedures. For routine day-to-day
operations, temperature, appearance of material,
odors, and the presence of flies are important
tests. Cleanliness and the absence of flies
at the site, as well as the absence of large
numbers of larvae in the piles, are criteria
of sanitary quality of the compost operation.
Temperature is the best single indicator
of the progress of aerobic composting and
also the basis for determining whether pathogen,
parasites, and weed seeds are being destroyed.
Laboratory analyses for nitrogen, phosphorus,
and potash are more precise and require more
elaborate equipment, but are relatively simple
chemical determinations to make. If compost
is modified by adding ammonium sulfate, phosphates,
or other nutrients for special fertilizer
purposes, percentages of these nutrients
on a dry basis must be determined, so that
users can compare them with other fertilizers.
Determining the C:N ratio, which is so important in regard to
nitrogen conservation and for estimating
the quality of the finished compost, is more
of a problem, because the quantitative analyses
of carbon is difficult, time consuming, and
expensive.
There are laboratories that specialize in
“counting” living organisms in compost (fungi,
bacteria, protozoa…). While it is difficult
to get precise measurements, trends can be
discovered, such as determining whether there
is fungal or bacterial dominance in the finished
compost.
The gardener, small farmer and other small
compost operator usually will not be concerned
with detailed tests other than those to confirm
that the material is safe from a health standpoint.
This will be judged from its temperature,
and its satisfactory appearance as a soil
additive.
The temperature of compost can be checked
by:
- digging in the pile and feeling the temperature
of the material;
- feeling the temperature of a rod after insertion
into the material; or
- using a thermometer.
Digging into the pile will give an approximate
idea of the temperature. The material should
feel very hot to the hand and be too high
to permit holding the hand in the pile for
very long. Steam should emerge from the pile
when opened. A metal or wooden rod inserted
2 feet into the pile for a period of 5-10
minutes for metal and 10-15 minutes for wood
should be quite hot to the touch, in fact,
too hot to hold. These temperature-testing
techniques are satisfactory for the smaller
compost operations. Long stem metal thermometers
are available for temperature testing.
Compost may be considered finished when it
can be stored in large piles indefinitely
without becoming anaerobic or generating
appreciable heat. It can be safely spread
because of its low C:N ratio or the poor availability of its carbon.
The material, however, is still slowly active
and will "ripen" somewhat in the
large stacks. At this time it should be grayish-black
or brownish-black in color, depending on
what color of materials were used. However,
color alone is not a good criterion of finished
compost because the appearance of rich soil
humus develops in a good compost long before
the temperature decline signals the decrease
in microbial activity.
Characteristic changes in odor during the
period of composting help define stable compost.
The material should be odorless, or have
a slightly earthy odor or the musty odor
of molds and fungi, similar to the forest
floor. Also, look for compost critters, redworms,
centipedes, sowbugs, fungi—these can identify
compost as healthy and living. They are indicators
of an abundance of organisms, some of which
can keep disease and pests in check.
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