1. UMR Environnement et Grandes Cultures, INA P-G/INRA; 78850 Thiverval-Grignon France
2. CSIRO Land and Water; Pye Laboratory; GPO Box 1666 Canberra ACT 2601 Australia
3. The Institute of Soil, Water and Environmental Sciences; Volcani Center, A.R.O.; P.O.B. 6 Bet-Dagan 50250 Israel