Compost Fundamentals

Compost Benefits & Uses

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:

  1. 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;
  2. 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 ;
  3. assessment of the biological activity of the compost, how many and what types of soil dwelling animals and microorganisms it contains; and
  4. 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:

  1. digging in the pile and feeling the temperature of the material;
  2. feeling the temperature of a rod after insertion into the material; or
  3. 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.

These approximate physical tests are adequate for most small compost operations.

economic aspects

testing and judging condition of compost

quality of composts

benefits of compost

use of compost

Why Compost | Biology & Chemistry | Compost Needs
Composter's Needs | Benefits & Uses | Conclusion

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