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Source: EPA
Wikipedia: Composting is the controlled decomposition of organic matter. Rather than allowing nature to take its slow course, a composter provides an optimal environment in which decomposers can thrive. To encourage the most active microbes, the compost pile needs the proper mix of the following ingredients:
Decomposition happens even in the absence of some of these ingredients, but not nearly as quickly and not nearly as pleasantly (for example, the plastic bag of vegetables in your refrigerator is decomposed by microbes, but the absence of air encourages the growth of anaerobic microbes that produce disagreeable odors).
Compost ingredients
The goal in a compost pile is to provide a healthy environment--and nutrition--for the rapid decomposers, the bacteria.
The most rapid composting occurs with the ideal ratio--by dry chemical weight--of carbon to nitrogen, from 25-to-1 to 30-to-1. In other words, the ingredients placed in the pile should contain 30 times as much carbon as nitrogen. For example, grass clippings average about 19-to-1 and dry autumn leaves average about 55-to-1. Mixing equal parts by volume approximates the ideal range. Commercial-grade composting operations pay strict attention to this ratio. For backyard composters, however, the charts of carbon and nitrogen ratios in various ingredients and the calculations required to get the ideal mixture can be intimidating, so many rules of thumb exist to guide composters in approximating this mixture.
High-carbon sources provide the cellulose needed by the composting bacteria for conversion to sugars and heat.
High-nitrogen sources provide the most concentrated protein, which allow the compost bacteria to thrive.
Some ingredients with higher carbon content:
Some ingredients with higher nitrogen content:
Poultry manure provides lots of nitrogen but little carbon. Horse manure provides both. Sheep and cattle manure don't drive the compost heap to as high a temperature as poultry or horse manure, so the heap takes longer to produce the finished product.
In an attempt to judge the proper mix of materials, different rules of thumb are available. Some prefer to add one basket full of nitrogen source followed by one basket of carbon source. Mixing the materials as they are added increases the rate of decomposition, but some people prefer to place the materials in alternating layers, approximately 15 cm (6 in) thick, to help estimate the quantities. Keeping carbon and nitrogen sources separated in the pile can slow down the process, but decomposition will occur in any event.
Greasy food waste and wastes from meat, dairy products, and eggs should not be used in compost because they tend to attract unwanted insects and other animals. Eggshells, however, are a good source of nutrients for the compost pile and the soil although they typically take more than one year to decompose.
Composting techniques
There are two primary methods of aerobic composting:
Home composters use a range of techniques varying from extremely passive composting (throw everything in a pile in a corner and leave it alone for a year or two) to extremely active (monitoring the temperature, turning the pile regularly, and adjusting the ingredients over time) and combinations of both.
Some composters use mineral powders to absorb smells, although a well-maintained pile seldom has bad odors.
Source: wikipedia
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