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Compost

Compost refers to a biological process that uses any one of several methods to speed up the decomposition of raw organic matter, usually by piling, aerating, and moistening. It is also the crumbly, nutrient-rich product of this process.

Composting is an important means of recycling organic wastes to return their nutrients to the soil, where they become available to plants. Composting reduces or eliminates problems with odors and water pollution from raw waste products such as livestock manure and slaughterhouse and food-processing wastes. Many cities compost yard wastes in order to conserve scarce landfill space. High-temperature composting methods also kill weed seeds and pathogens, turning a potentially expensive health hazard into a valuable resource. The resulting product contains balanced soil and plant nutrients, including trace minerals, and is rich in beneficial microbes that further improve the soil's ability to nourish plants. Composed primarily of humus, compost also conditions the soil, making it easier to work and improving its drainage, aeration, and nutrient holding capacity.

Almost anything that was once alive or is a waste product of a living organism can be composted. Dry, bulky materials, including wood products such as sawdust and newspaper, as well as straw, cornstalks, and leaves, contain a high proportion of carbon relative to nitrogen. Materials that are wet, heavy, and smelly, such as manure, grass clippings, and fish wastes, are usually high in nitrogen relative to carbon. Both types of materials should be combined in a ratio of about thirty parts carbon to one part nitrogen to promote thorough decomposition. Mineral powders such as rock phosphate can be added to compost as a source of trace elements, which can also be supplied by organic materials such as seaweed and bonemeal. Microbial cultures and worms are sometimes used to improve compost activity. Large quantities of fats or oils, as well as toxic or synthetic materials, should not be added to compost.

Compost requires enough air and moisture to provide optimum conditions for microbial activity. Turning compost to incorporate more air will speed decomposition, generating higher temperatures. Compost can be finished in anywhere from two weeks to a year, depending on climate, what kinds of materials are used, and how often it is turned. Finished compost has a spongy texture and earthy fragrance, and its original ingredients are no longer identifiable.

Compost can be used as a fertilizer and soil conditioner on any scale, from houseplants to large farms. It contains a good balance of essential plant nutrients in a stable form that will not leach away in the rain, and can be applied at any time of year without danger of burning plants. Compost can be included in potting soil, spread on lawns, worked into garden beds, side-dressed around trees and perennials, and added to transplant holes. Compost is often used to stimulate growth of new vegetation on land that has been strip-mined or badly eroded. Compost tea can give growing plants a quick boost, and is known to suppress certain plant diseases because of its beneficial microorganisms. Organic farmers rely on compost to build soil fertility and recycle nutrients.