1. Department of Environmental Chemistry; Soil And Water Inst., A.R.O., Volcani Center; P.O. Box 6 Bet Dagan 50250 Israel
2. Department of Agronomy; Univ. of Kentucky; Lexington KY 40546-0091
3. Department of Land Resource Sci.; Univ. of Guelph; Guelph Ontario N1G 2W1 Canada