1. Dep. of Earth and Environmental Science, Division of Soil and Water Management; KU Leuven, Kasteelpark Arenberg 20 B-3001 Heverlee Belgium
2. Fertilizer Technology Research Centre; School of Agriculture, Food & Wine, Univ. of Adelaide; Waite Campus, PMB1 Glen Osmond SA 5064 Australia
3. CSIRO Land and Water; Locked Bag 2 Glen Osmond SA 5064 Australia