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Compost

Compost is the decomposed remnants of organic materials (those with plant and animal origins). Compost is used in gardening and agriculture, mixed in with the soil. It improves soil structure, increases the amount of organic matter, and provides nutrients.

Compost is a common name for humus, which is the result of the decomposition of organic matter. Decomposition is performed primarily by microbes, although larger creatures such as worms and ants contribute to the process. Decomposition occurs naturally in all but the most hostile environments, such as buried in landfills or in extremely arid deserts, which prevent the microbes and other decomposers from thriving.

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:

• Carbon
• Nitrogen
• Oxygen (air)
• Water

Table of contents

1 Decomposers 2 Compost ingredients 3 Composting techniques 4 Microbes and heating the pile 5 Other ingredients 6 Composting systems 7 External links

Decomposers

The most effective decomposers are bacteria and other microorganisms. Also important are fungi, molds, protozoa, and actinomycetes--which is something between a fungus and a mold and is often seen as white filaments in decomposing organic matter. At a macroscopic level, earthworms, ants, snails, slugs, millipedes, sow bugs, springtails, and others work on consuming and breaking down the organic matter. Centipedes and other predators feed upon these decomposers.

Compost ingredients

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:

• Dry, straw-type material, such as cereal straws
• Autumn leaves
• Sawdust and wood chips
• Some paper and cardboard (such as corrugated cardboard or newsprint with soy-based inks)

• Wilted green material (usually crop residues, or plants mowed for the purpose)
• Animal manures (vegetarians, not meat-eaters)
• Grass clippings
• Fruit and vegetable trimmings, skins, and waste

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 inches) 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.

Composting techniques

Microbes and heating the pile

The heap should be about 1 m (3 ft) wide, 1 m (3 ft) tall, and as long as is practicable – the advantage to making the heap at least 1 m³ (1 yd³) is that it provides suitable insulating mass to allow a good heat build-up as the material decays. The ideal temperature range hovers around 60 °C (140 °F), which kills most pathogens and weed seeds and also provides a suitable environment for thermophilic (heat-loving) bacteria, which are the fastest acting decomposers. The centre of the heap should get quite warm, possibly hot enough to burn a bare hand. If this fails to happen, common reasons include the following:

• The heap is too wet, thus excluding the oxygen required by the compost bacteria
• The heap is too dry, so that the bacteria do not have the moisture needed to survive and reproduce
• There is insufficient protein (nitrogen rich material)

Depending on how quickly the compost is required, the heap can be turned one or more times to bring the outer layers to the inside of the heap and vice versa, as well as to aerate the mixture. Adding water at this time keeps the pile as damp as a wrung-out sponge. One guideline is to turn the pile when the high temperature has begun to drop, indicating that the food source for the fastest-acting bacteria (in the center of the pile) has been largely consumed. After the temperature stops rising after the pile has been turned, there is no further advantage in turning the pile. When all the material has become barely recognisable from the original ingredients, turning into dark brown or nearly black crumbly matter, it's ready to use. Some practitioners like to leave the compost to mature further for up to a year as this seems to make the benefits of compost last longer.

Other ingredients

The animal manure part of compost source materials can be collected by composting toilets (in this case, human feces). However, such compost is usually not used as a fertilizer for plants that are directly edible (e.g., salad crops) but should instead be used on trees, bush fruits or else on the ornamental garden.

Composting systems

• Container composting
• German mound
• Leaf mold
• High fibre composting
• Worm compost
• Spent mushroom compost
• Sheet composting
• Windrow composting

• Compost Guide
• Home Composting
• Master Composter
• Cornell Composting--Science and Engineering

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