As the moisture content decreases below 50 percent, the rate of decomposition decreases rapidly. As a rule of thumb, a mixture of organic wastes that contains 50 percent moisture feels damp to the touch but is not soggy. The temperature increase that occurs during composting results from the breakdown of organic material by bacteria, actinomycetes, fungi and protozoa. The temperature can range from near freezing to 160 degrees F. Starting at ambient temperature when the components are mixed, the compost can reach 150 degrees F in less than two days. Applying heat to compost from an external source serves no purpose unless ambient temperatures are far below freezing.
Heat is generated from within the compost medium.
In composting, as in the decomposition of any complex substance, the breakdown is a dynamic process accomplished by a succession of microorganisms with each group reaching its peak population when conditions have become optimum for its activity. One group of microorganisms dies and another group thrives until the next incremental change in nutrition and temperature occurs, etc. Composting rate is generally measured by rate of carbon dioxide production. At these temperatures the rate of organic matter decomposition is maximum, and weed seeds and most microbes of pathogenic significance cannot survive. It is important that piles are turned frequently to ensure that all parts are exposed to high temperatures.