1. Soil and Earth Sciences, Institute of Natural Resources, Massey University, Palmerston North, New Zealand;
2. Present address: R. Castro Alves, 654, B. Aclimação, Ed. Alabastro, AP. 101, São Paulo, SP, Brazil, CEP 01532‐900
3. The Horticultural and Food Research Institute of New Zealand. Palmerston North, New Zealand;
4. The Centre for Environmental Research in Minerals, Metals and Materials, University of British Columbia, 6350 Stores Road., Vancouver BC V6T 1Z4, BC, Canada;