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 are 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.
There are three main classes of manures used in soil management:
Most animal manure is feces. Common forms of animal manure include farmyard manure (FYM) or farm slurry (liquid manure). FYM also contains plant material (often straw), which has been used as bedding for animals and has absorbed the feces and urine. Agricultural manure in liquid form, known as slurry, is produced by more intensive livestock rearing systems where concrete or slats are used, instead of straw bedding. Manure from different animals may have different qualities and require different application rates, such as manure from farm animals such as horses, cattle, pigs or sheep, chicken and turkey manures, rabbit manure, human sewage and guano from seabirds and bats.. For instance, sheep manure is high in nitrogen and potash, and pig manure is relatively low in both. Horse manure also contains lots of weed seeds, as horses do not digest seeds the way that cattle do. Chicken manure, even when well rotted, is very concentrated and should be used sparingly.
Animal manures may also include other animal products, such as wool shoddy (and other hair), feathers, blood and bone.
Compost is the decomposed remnants of organic materials – usually of plant origin, but often including some animal dung or bedding.
Green manures are crops grown for the express purpose of plowing them in, thus increasing fertility through the incorporation of nutrients and organic matter into the soil. Leguminous plants such as clover are often used for this, as they fix nitrogen using Rhizobia bacteria in specialized nodes in the root structure.
Other types of plant matter used as manure include the contents of the rumens of slaughtered ruminants, spent hops (left over from brewing beer) and seaweed.
Uses of manure
Animal dung has been used for centuries as a fertilizer for farming, as it improves the soil structure (aggregation), so that it holds more nutrients and water, and becomes more fertile. Animal manure also encourages soil microbial activity which promotes the soil's trace mineral supply, improving plant nutrition. It also contains some nitrogen and other nutrients itself which assist the growth of plants.
Manures with a particularly unpleasant odor (such as human sewage or slurry from intensive pig farming) is usually knifed (injected) directly into the soil to reduce release of the odor. Manure from pigs and cattle is usually spread on fields using a manure spreader. Due to the relatively lower level of proteins in vegetable matter, herbivore manure has a milder smell than the dung of carnivores or omnivores – for example, elephant dung is practically odorless. However, herbivore slurry which has undergone anaerobic fermentation may develop more unpleasant odors, and this 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.
Manure is also commercially composted and bagged and sold retail as a soil amendment. Sometimes even human sewage sludge is used, as is the case for Dillo Dirt, a product which has been sold by the city of Austin, Texas municipal wastewater department since 1989.
Manure generates heat as it decomposes, and it is possible for manure to ignite spontaneously should it be stored in a massive pile. Once such a large pile of manure is burning, it will foul the air over a very large area and require considerable effort to extinguish. Large feedlots must therefore take care to ensure that piles of fresh manure (faeces) do not get excessively large. There is no serious risk of spontaneous combustion in smaller operations.
There is also a risk of insects carrying feces to food and water supplies, making them unsuitable for human consumption.
Livestock antibiotics and hormones
In 2007, a University of Minnesota study indicated that foods such as corn, lettuce and potatoes have been found to accumulate antibiotics from soils spread with animal manure that contains these drugs.
Organic foods are much less likely to contain antibiotics as veterinary drugs are not routinely used in organic farming systems. Most organic arable farmers either have their own supply of manure (which would therefore not normally contain drug residues) or else rely on green manure crops for the extra fertility (if any nonorganic manure is used by organic farmers, then it usually has to be rotted or composted to degrade any residues of drugs and eliminate any pathogenic bacteria - Standard 4.7.38, Soil Association organic farming standards).
- Anaerobic digestion
- Coprophilous fungi
- Cow dung
- Ecological sanitation
- Winterhalder, B., R. Larsen, and R. B. Thomas. (1974.). "Dung as an essential resource in a highland Peruvian community". Human Ecology 2: 89–104. doi:10.1007/BF01558115.
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- Antibiotics and Hormones in Animal Manure (Webcast): A two part webcast series about the science available on potential risks and best management practices related to antibiotics and hormones from animal manure
- Livestock and Poultry Environmental Learning Center, an eXtension community of practice about animal manure management