Manure is organic matter used as organic fertilizer in agriculture. Manures contribute to the fertility of the soil by adding organic matter and nutrients, such as nitrogen that is trapped by bacteria in the soil. Higher organisms then feed on the fungi and bacteria in a chain of life that comprises the soil food web.
The term "manure" was used for inorganic fertilizers in the past, but this usage is now very rare.
Most animal manure is feces — excrement of plant-eating mammals (herbivores) and poultry — or plant material (often straw) which has been used as bedding for animals and thus is heavily contaminated with their feces and urine. Manure from different animals may have different qualities and require different dosage, common forms of animal manure includes horse manure, cow manure, pig manure, sheep manure, chicken and turkey manures, rabbit manure, seabird and bat Guano.
Green manures are crops grown for the express purpose of plowing them under. In so doing, fertility is increased through the nutrients and organic matter that are returned to the soil. Leguminous crops, such as clover, also "fix" nitrogen through rhizobia bacteria in specialized nodes in the root structure.
Manure has been used for centuries as a fertilizer for farming, as it is rich in nitrogen and other nutrients which facilitate the growth of plants. Liquid manure from pig/hog operations is usually knifed (injected) directly into the soil to reduce the unpleasant odors. Manure from hogs and cattle is spread on fields using a Manure spreader. Due to the relatively lower level of proteins in grasses, which herbivores eat, cattle manure has a milder smell than the dung of carnivores — for example, elephant dung is practically odorless. However, due to the quantity of manure applied to fields, odor can be a problem in some agricultural regions. Poultry droppings are harmful to plants when fresh but after a period of composting are valuable fertilizers.
The dried manure of animals has been used as fuel throughout history. Dried manure (usually known as dung) of cow was, and still is, an important fuel source in countries such as India, while camel dung may be used in treeless regions such as deserts. On the Oregon Trail, pioneering families collected large quantities of "buffalo chips" in lieu of scarce firewood. It has been used for many purposes, in cooking fires and to combat the cold desert nights.
Another use of manure is to make paper, this has been done with dung from elephants where it is a small industry in Africa and Asia, and also horses, llamas, and kangaroos. Other than the llama, these animals are not ruminants and thus tend to pass plant fibres undigested in their dung.
In 2008, chemists at the National Institute of Standards and Technology (NIST) developed the first detailed chemical analysis revealing what processing is needed to transform pig manure derived 'crude oil' into fuel for vehicles or heating. Mass production of this type of biofuel could help consume a waste product overflowing at U.S. farms, but it will require a lot of refining. Their analysis is described in the 2008 issue of Fuel.
There is also a risk of insects carrying feces to food and water supplies, making them unsuitable for human consumption.