1. Institute of Soil, Water and Environmental Sciences; Volcani Center, Agricultural Research Organization; HaMaccabim Road 68, P.O. Box 15159 Rishon Le Zion 7505101 Israel
2. Dep. of Soil and Water Sciences, Robert H. Smith Faculty of Agriculture, Food and Environment; Hebrew Univ. of Jerusalem; P.O. Box 12 Rehovot 76100 Israel