Glossary

Fertilizer
Fertilizer, natural or synthetic chemical substance or mixture used to enrich soil so as to promote plant growth.

Humus
Humus, decaying organic matter found in soil and derived from dead animal and plant material. During early decomposition, some of the carbon, hydrogen, oxygen, and nitrogen are quickly dissipated as water, carbon dioxide, methane, and ammonia, but the other constituents decompose slowly and remain as humus. The chemical composition of humus varies, because it depends on the action of living soil organisms, such as bacteria, protozoa, fungi, and certain kinds of beetles, but usually it contains varying amounts of proteins and certain uronic acids combined with lignins and their derivatives. Humus is a homogeneous, amorphous, dark-colored, and practically odorless material. The end products of the decomposition of humus are mineral salts, carbon dioxide, and ammonia.

Manure
Manure, plant or animal wastes used as fertilizer. Rich in humus (decaying organic matter), manure releases many important nutrients into the soil. However, manure is deficient in three important nutrients: nitrogen, phosphorus, and potassium. A commercial fertilizer has about 20 times as much nitrogen, phosphorus, and potassium as an equally massive amount of manure. For this reason, manure is often used in conjunction with other fertilizers. Manure also helps to loosen soil and retain water.


source: wikipedia, encarta