1. Field Service, Extension Service, Ministry of Agriculture; P.O. Box 7054 Tel-Aviv 61070 Israel
2. Dep. of Soil and Water Sciences, Faculty of Agricultural, Food and Environmental Quality Science; The Hebrew Univ. of Jerusalem; Rehovot 76100 Israel
3. Institute of Soils and Water, ARO; The Volcani Center; P.O. Box 6 Bet Dagan 50250 Israel