Dung is a colloquial term for manure, or animal excrement. The word cow, female bovine, used in the plural, cows, is sometimes used colloquially to mean cattle. Nitrogen and other plant nutrients in cow manure make it useful as a fertilizer. Cow dung also gives off methane gas, which pollutes the ozone layer of the atmosphere, the thinning of which may contribute to global warming. Researchers are finding ways of collecting methane from cow manure as a power source.
Cow Manure Fertilizer
Cow manure is rich in humus, the bulky, fibrous material that comes from undigested plant matter. Humus makes plants easier to cultivate, and it helps the soil store moisture during dry spells. It also helps drain wet soils. Humus also stores nitrogen and encourages microbes in the soil, which provide plants with trace minerals. Cow manure contains only 5 percent each of nitrogen, phosphorus and potassium; it is most useful as a fertilizer when it is allowed to mature in a compost pile.
Cow Manure Compost
Commercial cow manure has already been composted. Cow manure is composted by putting it into a bin or pile and letting it sit.
Fresh cow manure contains lots of ammonia, a source of nitrogen. Adding fresh manure to compost speeds the rate of decay. Fresh manure contains more weed seeds, which might grow into plants if the manure is put directly onto plants; composting suppresses the ability of these seeds to germinate.
Fresh manure is added slowly to a compost pile for days or weeks, but not for two months preceding its use as a fertilizer. Temperatures in manure composts reach 140 to 180 degrees F; the compost is finished when it ceases to produce heat and loses most of its smell.
Compost piles that are too small will not decompose properly and produce no heat; the inner layers of piles that are too large do not get air and will not rot while the outer layers decompose. Manure compost needs fresh air that can be delivered by tossing it with manure forks or adding straw, leaves or other plant matter to it.
Cow Manure Slurry
Liquid manure, called slurry, is produced by anaerobic fermentation, producing strong odors of methane, ammonia and sulfur. Slurries are ordinarily produced from the manure of cattle raised in concrete enclosures.
Manure slurries are sometimes produced in ponds called lagoons. A layer of chopped straw, sawdust or peat moss is sometimes allowed to float on top of a slurry to absorb the smell. Slurries are also produced in enclosed cement containers that are vented to carry away the odor.
Cow Manure Methane
Methane gas, produced by decomposition, is yielded by swamps and by the flatulence of all animals; however, the manure of ruminants, including cows, yields far more methane than that of other animals.
Ruminants have multiple stomachs. The first stomach softens grass or other plant matter. Cows regurgitate this into a cud that they chew again. When the fiber in a cud is sufficiently broken down, the cow sends it to yet another stomach. The digestive process of ruminants yields large quantities of methane gas.
Uses of Cow Manure Methane
Gobar (the Hindi word for cow dung), an Indian research company, says that 1 lb. of cow manure can yield enough methane to cook the meals of four to six people for one day. In one year the manure from a single cow can produce enough methane to equal 50 gallons of gasoline.
The New York Times reports a Chinese plan to build a power plant using methane produced from a 250,000-head dairy operation in northeast China.
The village of Redage, Luxembourg, converts the methane produced by the manure from 28 local dairy herds to heat its local school, sports center and swimming pool.