Manure is material—usually some kind of farm waste material, often consisting the feces of animals—used as agricultural fertilizer. It must be used with care to prevent the spread of bacterial infection.
Human manure, known as "night soil," was a traditional form of fertilizer in China and Japan. Human manure was also used in Europe until about the middle of the 19th century. At that point it was usually replaced by cheap and effective Guano imported from Peru. In the United States, heavily treated products derived from municipal sewage are sold for use as fertilizer, one example being Milorganite.
Green manure consists of crops which are deliberately planted for the purpose of being plowed under later in order to improve the soil.
During the First World War, the Germans were successful in fixating nitrogen from the athmosphere, thus heavily reducing the need for 'natural' manure.
Notes and references
G.J. Leigh: The worlds greatest fix: A history of nitrogen and agriculture. Oxford University Press 2004.