Manure is any substance produced by animals or plants that is used as fertilizer. Most manure consists of animal waste mixed with straw or hay from barnyards, though it may be pure animal waste. This waste is collected and spread onto fields. When it decays, it releases important nutrients that enrich the soil and aid plant growth. Manure also loosens the soil and improves its ability to absorb water. A special kind of manure called green manure is obtained from plants that are plowed into the soil and allowed to decay.
The content of animal manure varies widely, depending on the kind of manure and whether it is fresh, dried, or partly decayed. Most animal manure in the United States is from the wastes of cattle and chickens. Horses, hogs, and sheep also provide manure. Animal manure is an excellent source of organic matter (substances containing carbon) for the soil. But it is low in such important nutrients as nitrogen, phosphorus, and potassium. In general, it takes about 2,000 pounds (907 kilograms) of manure to supply as much of these three substances as 100 pounds (45 kilograms) of a commercial fertilizer.
The most common green manure plants are grasses and legumes. Legumes belong to the pea family. They include alfalfa, beans, clover, and peas. Grasses and legumes provide the soil with organic matter. Legumes provide large amounts of nitrogen.
