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Home Composting Slide Show, Part II

Thomas Richard, Robert Kozlowski, Nancy Dickson and Roger Kline
July 1989

II. Manageable Components of the Composting Process

While the natural process of decomposition will occur without any assistance from us, several factors can be managed to accelerate the compost process. (Substitution - original slide not available in electronic form).
Organisms utilize carbon as a source of energy and nitrogen to grow and reproduce. Without enough nitrogen, there will be few microorganisms, and decomposition will be slow. If there is too much nitrogen in the compost, some of it will turn to ammonia that will volatilize, creating an odor.
The optimum C:N ratio is about 30 to 1. This ratio will make fast, hot compost. Grass, animal manures and fresh green plants are high in nitrogen.
Leaves, brush, sawdust and wood chips are all good sources of carbon. Blending these carbon sources with nitrogenous materials can provide a satisfactory C:N ratio.
Surface area is another key factor to consider. Since decomposition is a microbiological process, it occurs in thin films on the surface of particles. A large particle has less total surface area than the same particle chopped into small pieces. Therefore if particles are too big, the process will take longer. A one-inch wood chip will decompose much slower than grains of sawdust. An easy way to shred fallen leaves is to mow them before raking.
Decomposer organisms need water also. The decomposition process will slow down with either too much or too little water. The optimum moisture content for compost is about 40 to 60 percent, damp enough so that a handful feels moist to the touch, but dry enough that a hard squeeze produces no more than a drop or two of water.
Most microorganisms active in composting require oxytgen to live. Their "aerobic" activity forms carbon dioxide and heat as by-products. If too little oxygen gets into the compost, the process can become "anaerobic." This condition results in foul odors. The by-products of anaerobic decomposition include methane and hydrogen sulfide gas. Hydrogen sulfide smells like rotten eggs.
Oxygen will move into the pile if it is loose and there is plenty of space between particles, as when straw is mixed in the pile. Finer material may need to be aerated by physically turning the pile with a pitch fork or a compost turning tool. With the rapid decomposition that occurs with high nitrogen materials, turning the pile becomes necessary to prevent anaerobic conditions from developing.
Heat will be given off as organisms feed on wastes and break them down into less complex molecules. Ideal temperatures for composting are between 90 and 150 degrees Fahrenheit. High temperatures can help kill weed seeds and disease organisms, but temperatures above 150 degrees Fahrenheit will also kill the decomposers and slow the process.
Compost piles should be a minimum of one cubic yard in size. Smaller piles may not have enough mass to hold the heat of decomposition.
Bacteria reproduce very quickly and are naturally present in air and soil, so there is usually no need to add them to the compost pile. Of the many inoculants, or compost starters available, the best is a handful of freshly made compost.

Continue on with slideshow: Part III. Materials that can be Composted

Back to Composting Slideshow Part I: Organisms Involved in the Compost Process


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