Verwysings
- Anoniem . 1979 . Kortbegrip vir Landboustatistiek , Pretoria : Staatsdrukker .
- Caldwell . 1975 . “ Primary production of grazing lands ” . In Photosynthesisand production in different environments , Edited by: Cooper , J.P. Cambridge : Cambridge University Press .
- Jewell , W.J. , ed. Energy, agriculture and waste managemant . Proceedings of the 1975 Cornell Agricultural Waste Management Conference . Ithaca, New York.
- Ward , G.M. , Knox , P. , Hobson , B. and Yorks , T.P. 1977 . “ Energy requirements of Alternative Beef Production Systems in Colorado ” . In Agricultural and Energy , Edited by: Lockeretz , W. New York : Academic Press .