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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 to improve its structure (by increasing its organic content) and fertilizing quality.
Compost is a common name for humus, which is the result of the composting process. The most rapid composting occurs with a starting mix of equal parts, by dry weight, of nitrogen and carbon. For most composters, figuring out the dry weight of single chemical ingredients is impractical, so many rules of thumb exist to guide composters in approximating this mixture.
Composting is performed primarily by microbes, although larger creatures such as worms and ants contribute to the process. 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 microbes that produce disagreeable odors).One possible recipe for compost consists of roughly one third by volume of materials from the following three groups:
In an attempt to judge the proper mix of materials, again different rules of thumb are available. Some people prefer to place the materials in alternating layers, approximately 15 cm (6 inches) thick. Some prefer to add one bushel basket of nitrogen source followed by one basket of carbon source. Research has shown that mixing the materials, rather than leaving them in layers, increases the speed of the composting, although, as stated earlier, compost happens in any event.
As the heap is built, it is wetted to the consistency of a well wrung-out sponge. 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 cu m (1 cu yd) is that it provides suitable insulating mass to allow a good heat build-up as the material decays. The ideal temperature range hovers around 140 degrees F, which kills most pathogens and weed seeds and also provides a suitable environment for thermophilic (heat-loving) bacteria, which accelerate the decomposition process. 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:
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 all the material has become barely recognisable from the original ingredients, 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.
Some like to put special materials and activators into their compost. A light dusting of agricultural lime (not on the animal manure layers) can curb excessive acidity that can slow down the fermentation. Seaweed meal can provide a ready source of trace elements. Finely pulverised rock dust can also provide needed minerals, but watch out for rock dust that consists mostly of clay.
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.