Agricultural practices produce a variety of waste products or byproducts, such as animal faeces, material eroded from land, excess fertilizer, inorganic salts and minerals resulting from irrigation, herbicides and pesticides; to these may be added various infectious agents contained in wastes. Under simple agricultural systems, wastes from one harvest or form of animal husbandry could be used as a resource for another. With increasing specialization in primary production, however, there is less economic opportunity to use animal manure for fertilizer, for example.
Vegetable material from agriculture has been used as mulch or compost for the soil, as an alternative source of fuel, for drying fruit, cocoa and coffee beans, or for sale in the form of briquetted charcoal to other users of wood fuel, cellulose for paper and fibreboard production, and livestock bedding and cattle ration. An example of special uses, is cocoa sweatings as ingredients in wine, alcohol, vinegar and jelly production; substandard cocoa beans can be included in livestock feed.
The total quantity of such wastes is large. In the USA, for instance, the production of animal wastes exceeds that of human wastes by a factor of at least five on a biochemical oxygen demand (BOD) basis, seven on a total nitrogen basis, and ten on a total solids basis. Most developing countries have economies based predominantly on agriculture. With agro-industrialization increasing during the past three decades, many countries find themselves with a growing surplus of agricultural wastes such as rice hull, jute stalk, groundnut shell, bagasse and coconut husk and pith. These materials are available in large quantities and are presenting serious problems of disposal.