What is Compost?

Compost is created from the decomposition and recombining of various forms of plant and animal life, such as leaves, grass, wood, garbage, natural fiber clothes, hair and bones. These materials are organic matter. Organic matter is only a small fraction of the total material that makes up the soil-between 1% and 8%. Yet it is absolutely essential to the sustenance of soil life and fertility. Organic matter refers to dead plant and animal residues of all kinds and in all stages of breakdown or decay. Inseparable from these decaying dead residues are the living microorganisms that decompose, or digest, them.

Microscopic life forms (bacteria and fungi) in the soil produce the recombining process. The result is humus. Heat energy is liberated during the process and this is the warmth felt in the compost pile. Most of the decomposition involves the formation of carbon dioxide and water as the organic material is broken down. As the available energy is consumed, the microbial activities slow down and their numbers diminish-the pile cools. Most of the remaining organic matter is in the form of humus compounds. As humus is formed, nitrogen becomes part of its structure. This stabilizes nitrogen in the soil, because the humus compounds are resistant to decomposition. They are worked on slowly by soil organisms, but the nitrogen and other essential nutrients are protected from rapid salability and dissipation.

Humus also acts as a site of nutrient absorption and exchange for plants in the soil The surfaces of humus particles carry a negative electrical charge. Many of the plant nutrients, such as calcium, sodium, magnesium, potassium, and most trace minerals carry a positive electrical charge in the soil solution and are thereby attracted and adhere to the surface of humus. Some of the plant nutrients are not positively charged, such as phosphorus, sulfur, and the form of nitrogen that is available to plants. Fortunately, a good supply of these nutrients becomes available to the plants through biological transformations in the compost pile and soil.

As plant roots grow through the soil in search of nutrients, they feed off the humus. Each plant root is surrounded by a "halo" of hydrogen ions which are a by-product of the roots' respiration. These hydrogen ions also carry a positive electrical charge. The root actually "bargains" with the humus, exchanging some of its positively charged hydrogen ions for positively charged nutrient ions stuck on to the surface of the humus. An active exchange is set up between humus and roots. The plants "choose" which nutrients they need to balance their own inner chemistry.