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Composting: The Art and Science
of Converting Organic Waste to a Valuable Soil Resource
Leslie R. Cooperband, Ph.D,
Department of Soil Science, University of Wisconsin-Madison.
Behold this compost!
behold it well!....
Out of its hill rises the yellow maize-stalk,
the lilacs bloom in the dooryards,
The summer growth is innocent and disdainful above all those strata
of our sour dead."
(from Walt Whitman The Compost)
Composting is manipulation
of decomposition, a natural breakdown process that occurs whenever
organic residues come in contact with soil. In composting, raw
organic materials like manure, leaves, grass clippings, food wastes
and municipal biosolids are converted to stable soil-like humic
substances. This final product, the finished compost, is a valuable
soil resource for agricultural, horticultural and silvicultural
purposes.
Composting is an ancient
technology undertaken at a variety of scales from home to industrial.
As landfills reach their capacities and ban acceptance of organic
wastes, composting has become an increasingly important treatment
of organic waste.
History of composting
Composting is an
ancient technology. There are Roman and biblical references to
composting as well as numerous accounts of farmer composting practices
in subsequent millennia (Rynk, 1992). George Washington, the nation's
first president, was also the nation's first recognized composter
(Arner, 1995). He was acutely aware of the degradative effects
of farming on the soil resource, and he built a "dung repository"
to make compost from animal manure so he could replenish the soil's
organic matter (Figure 1).
Sir Albert Howard was probably
the first agricultural scientist to bring a scientific approach
to composting almost 75 years ago in India (Howard, 1943). His
Indore process involved stacking alternate layers of animal manure,
sewage sludge, garbage, straw and leaves. Stacked material was
turned occasionally over a six month period or longer. Leachate
from the decomposing residues was recycled to maintain adequate
moisture in the piles. Current day composting practices essentially
use the same principles that Howard promulgated.
As Post World War II agriculture
became increasingly mechanized, the use of synthetic fertilizers
replaced the practice of applying manure or composts to soils
to maintain soil fertility. As such, composting fell out of fashion.
In recent years, there has been a resurgence in composting initiatives
at various scales as urban and rural inhabitants are faced with
increasing landfill costs and decreasing landfill space.
Current composting trends in
the U.S.
In a recently released study of composting trends in the U.S.,
"Organic Materials Management Strategies" (U.S. EPA,
1998), 85% of the nation's municipal waste stream was identified
as organic in nature (Sparks, 1998).
This translates to approximately
177 million tons of organic waste per year, mostly as food scraps,
yard trimmings and paper. It does not include organic wastes generated
from agricultural and industrial sectors including food processing,
paper production, biotechnology, forest products processing and
livestock production. If all of these materials were composted,
estimates of potential market demand for finished compost would
greatly exceed the amount of compost produced from these sources.
Markets included agriculture, silviculture,
residential retail, nursery sod and ornamentals production and
landscaping totaling a demand of approximately 1.27 billion tons
of finished compost annually. Depending on the type of waste and
the method of composting, average national savings from composting
municipal organic by-products over conventional landfill disposal
range from $9 to $38/ton.
Questions? Comments?
Please contact Dr.
Leslie Cooperband,
Department of Soil Science,
University of Wisconsin-Madison
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