1. American Society of Agronomy. 1976.Multiple Cropping., ASA Special Publication No. 27 378Wisconsin.: Madison.
2. Barbarika, A., Colacicco, D. and Bellows, W. J. 1980.The value and use of organic wastes, Maryland Agri-Economics, May 1980 5College Park, Maryland: Cooperative Extension Service, University of Maryland.
3. F.A.O. 1975.Organic materials as fertilizers. Soils Bulletin No. 27. Food and Agriculture394Rome.: Organisation, United Nations.