1. Univ. of São Paulo; CP 9 13418-900 Piracicaba SP Brazil
2. Institute of Plant Nutrition and Soil Science; Federal Agricultural Research Center (FAL); Bundesallee, 50 D38116 Braunschweig Germany
3. Institute of Ecological Chemistry and Waste Analysis, Technical Univ. Braunschweig; Hagering, 30 D-38106 Braunschweig Germany
4. LUFA-ITL; Gutenbergstrasse, 75 D-24116 Kiel Germany