Composting is a way for gardeners and farmers to enrich and otherwise improve the soil while reducing the flow of household waste to landfills. Essentially the slow, natural decay of dead plants and animals, composting is a natural form of recycling in which living organisms decompose organic matter.
The decay of dead plants and animals starts when microorganisms in soil feed on dead matter, breaking it down into smaller compounds usable by plants.
Collectively, the breakdown product is called humus, a crumbly, dark brown, spongy substance. Adding humus to soil increases its fertility. Compost and composting derive from the Old French composter, “to manure” or “to dung.”
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History
The origins of human composting activities are buried in prehistory. Early farmers discovered the benefits of compost, probably from animal manure deposited on or mixed with soil.
In North America, American Indians and then Europeans used compost in their gardens. Public accounts of the use of stable manure in composting date back to the eighteenth century. Many New England farmers also found it economical to use fish in their compost heaps.
While living in India from 1905 to 1934, British agronomist Sir Albert Howard developed today’s home composting methods. Howard found that the best compost pile consists of three parts plant matter to one part manure.
He devised the Indore method of composting, alternating layers of plant debris, manure, and soil to create a pile. Later, during the composting process, he turned the pile or mixed in earthworms.
How Composting Works
By manipulating the composition and environment of a compost pile, gardeners and farmers can reduce composting time to three to four months. Important factors to consider are the makeup of the pile, the surface area, the volume, the moisture, the aeration, and the temperature of the compost pile.
Yard waste, such as fallen leaves, grass clippings, some weeds, and the remains of garden plants, make excellent compost material. Other good additions to a home compost pile include sawdust, wood ash, and kitchen scraps, including vegetable peelings, egg shells, and coffee grounds.
Microorganisms digest organic matter faster when they have more surface area on which to work, so gardeners can speed the composting process by chopping kitchen or garden waste with a shovel or running it through a shredding machine or lawn mower.
The volume of the compost pile is important because a large compost pile insulates itself, holding in the heat of microbial activity, which in turn accelerates decomposition.
A properly made heap will reach temperatures of about 140 degrees Fahrenheit in four or five days. Then the pile will settle, a sign that the process is working properly.
Piles 3 feet cubed (27 cubic feet) or smaller cannot hold enough heat, while piles 5 feet cubed (125 cubic feet) or larger do not allow enough air to reach the microbes in the center of the pile. These portions are important only if the goal is fast compost. Slower composting requires no exact proportions.
Moisture and air are essential for life. Microbes function best when the compost heap has many air passages and is about as moist as a wrung-out sponge.
Microorganisms living in the compost pile use the carbon and nitrogen contained in dead matter for food and energy. While breaking down the carbon and nitrogen molecules in dead plants and animals, they also release nutrients that higher organisms, such as plants, can use.
The ratio of carbon to nitrogen found in kitchen and garden waste varies from 15 to 1 in food waste to 700 to 1 in wood. A carbon-to-nitrogen ratio of 30 to 1 is optimal for microbial decomposers.
This balance can be achieved by mixing two parts grass clippings (carbon to nitrogen ratio 19:1) and one part fallen leaves (carbon to nitrogen ratio 60:1). This combination is the backbone of most home composting systems.
Uses and Practice
Composting household waste reduces the volume of municipal solid waste and provides a nutrient-rich soil additive. Compost or organic matter added to soil improves soil structure, texture, aeration, and water retention. It improves plant growth by loosening heavy clay soils, allowing better root penetration.
It improves the water-holding and nutrient-holding capacity of sandy soils and increases the essential nutrients of all soils. Mixing compost with soil also contributes to erosion control and proper soil pH balance, the amount of acidity or alkalinity present.
Some municipalities collect and compost leaves and other garden waste and then make it available to city residents for little or no charge. Some cities also compost sewage sludge, or human waste, which is high in nitrogen and makes a rich fertilizer. Properly composted sewage sludge that reaches an internal temperature of 140 degrees Fahrenheit contains no dangerous disease-causing organisms.
One possible hazard, however, is that it may contain high levels of toxic heavy metals, including zinc, copper, nickel, or cadmium.
The basic principles of composting used by home gardeners also are used by municipalities composting sewage sludge and garbage, by farmers composting animal and plant waste, and by some industries composting organic waste. Food and fiber industries, for example, compost waste products from canning, meat processing, and dairy and paper processing.
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