and judging condition of compost
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,
conservation, the C:N ratio, and compost value ;
- assessment of the biological activity of the compost, how many
types of soil dwelling animals and microorganisms
- economic test, i.e., whether the total cost of producing the
compost is less than its value as fertilizer plus
the cost of disposal
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
temperature of compost can be checked by:
digging in the pile and feeling the temperature of the material;
the temperature of a rod after insertion into the material; or
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
operations. Long stem metal thermometers are available for temperature
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.
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,
can identify compost as healthy and living. They are indicators of
an abundance of organisms, some of which can keep disease and pests
These approximate physical tests are adequate for most small compost