Compost is organic material that can be used as a soil amendment or as a medium to grow plants. Mature compost is a stable material with a content called humus that is dark brown or black and has a soil-like, earthy smell. It is created by: combining organic wastes (e.g., yard trimmings, food wastes, manures) in proper ratios into piles, rows, or vessels; adding bulking agents (e.g., wood chips) as necessary to accelerate the breakdown of organic materials; and allowing the finished material to fully stabilize and mature through a curing process.
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Compost use can produce a variety of environmental benefits. The following are a few of the most important ones:
Compost enriches soils
Compost has the ability to help regenerate poor soils. The composting process encourages the production of beneficial micro-organisms (mainly bacteria and fungi) which in turn break down organic matter to create humus. Humus - a rich nutrient-filled material - increases the nutrient content in soils and helps soils retain moisture. Compost has also been shown to suppress plant diseases and pests, reduce or eliminate the need for chemical fertilizers, and promote higher yields of agricultural crops.
Compost helps cleanup (remediate) contaminated soil
The composting process has been shown to absorb odors and treat semivolatile and volatile organic compounds (VOCs), including heating fuels, polyaromatic hydrocarbons (PAHs), and explosives. It has also been shown to bind heavy metals and prevent them from migrating to water resources or being absorbed by plants. The compost process degrades and, in some cases, completely eliminates wood preservatives, pesticides, and both chlorinated and nonchlorinated hydrocarbons in contaminated soils.
Compost helps prevent pollution
Composting organic materials that have been diverted from landfills ultimately avoids the production of methane and leachate formulation in landfills. Compost can prevent pollutants in stormwater runoff from reaching surface water resources. Compost has also been shown to prevent erosion and silting on embankments parallel to creeks, lakes, and rivers, and prevents erosion and turf loss on roadsides, hillsides, playing fields, and golf courses.
Using compost offers economic benefits
Using compost can reduce the need for water, fertilizers, and pesticides. It is a low-cost alternative to artificial soil amendments. Composting also extends municipal landfill life by diverting organic materials from landfills and provides a less costly alternative to conventional methods of remediating (cleaning) contaminated soil.
Yard trimmings and food residuals together constitute 23 percent of the U.S. waste stream, as documented by EPA. An estimated 56.9 percent of yard trimmings were recovered for composting or grasscycling (mowing that leaves grass clippings on a lawn) in 2000, a dramatic increase from the 12 percent recovery rate in 1990. Accompanying this surge in yard waste recovery is a composting industry that has grown from less than 1,000 facilities in 1988 to nearly 3,800 in 2000. Once dominated by public sector operations, the composting industry is increasingly entrepreneurial and private-sector driven, led by firms that add value to compost products through processing and marketing. Compost prices have been as high as $26 per ton for landscape mulch to more than $100 per ton for high-grade compost, which is bagged and sold at the retail level.
While yard trimmings recovery typically involves leaf compost and mulch, yard trimmings can also be combined with other organic waste, such as food residuals, animal manure, and biosolids to produce a variety of products with slightly different chemical and physical characteristics. In contrast to yard trimmings recovery, only 2.6 percent of food waste was composted in 2000. The cost-prohibitive nature of residential food waste separation and collection is the primary deterrent to expanding food waste recovery efforts. Yet in many communities, edible food residuals are donated to the needy, while inedible food residuals are blended into compost or reprocessed into animal feed. In some areas, composting operations are working with high-volume commercial and institutional food producers to recover their food byproducts, saving these firms significant disposal costs.
What to Compost - The IN List
- Animal manure
- Cardboard rolls
- Clean paper
- Coffee grounds and filters
- Cotton rags
- Dryer and vacuum cleaner lint
- Fireplace ashes
- Fruits and vegetables
- Grass clippings
- Hair and fur
- Hay and straw
- Nut shells
- Shredded newspaper
- Tea bags
- Wood chips
- Wool rags
- Yard trimmings
What Not to Compost - The OUT List
- Black walnut tree leaves or twigs - Releases substances that might be harmful to plants
- Coal or charcoal ash - Might contain substances harmful to plants
- Dairy products (e.g., butter, egg yolks, milk, sour cream, yogurt) - Will create odor problems and attract pests such as rodents and flies
- Diseased or insect-ridden plants - Diseases or insects might survive and be transferred back to other plants
- Fats, grease, lard, or oils - Will create odor problems and attract pests such as rodents and flies
- Meat or fish bones and scraps - Will create odor problems and attract pests such as rodents and flies
- Pet wastes (e.g., dog or cat feces, soiled cat litter) - Might contain parasites, bacteria, pathogens, and viruses harmful to humans
- Yard trimmings treated with chemical pesticides - Might kill beneficial composting organisms
NOTE: Finished compost can be applied to lawns and gardens to help condition the soil and replenish nutrients. Compost, however, should not be used as potting soil for houseplants because of the presence of weed and grass seeds.
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