1. Instituto Superior de Agronomia, UIQA, TU Lisbon; Tapada da Ajuda 1349-017 Lisboa Portugal
2. Chemistry Centre, Dep. of Soil Science; Universidade de Trás-os-Montes e Alto Douro; Apartado 1013 5001-801 Vila Real Portugal
3. North Wyke Research; Okehampton EX20 2SB UK
4. Centre for the Research and Technology of Agro-Environment and Biological Sciences, Dep. of Plant Science and Agricultural Engineering; Universidade de Trás-os-Montes e Alto Douro; Apartado 1013 5001-801 Vila Real Portugal