1. Awad F, Khalil K W and Maksoud M A 1993 Comparative effects of some organic manures and bentonite as soil amendments. Agrochimica (In press).
2. Balba A M 1988 Factors affecting the efficiency of soil conditioners. Int. Symp. on the use of soil conditioners for reclamation and farming of desert land. 11–13 Oct. 1988, Cairo, Egypt, pp 21–30.
3. Berrow J L and Webber J 1972 Trace elements in sewage sludge. J. Sci. Food Agric. 23, 93–100.
4. Bloomfield C and Pruden G 1975 The effects of aerobic and anaerobic incubation on the extractabilities of heavy metals in digested sewage sludge. Environ. Pollut. 8, 217–232.
5. Chaney R L 1973 Crop and food chain effects of toxic elements in sludges and effluents. In Proc. Joint, Conf. on Recycling Municipal Sludge and Effluents on Land, pp 129–142. Nat. Assoc. Stats Univ. and Land Grant. Coll. Washington DC.