1. Division of Soil and Water Management; Catholic Univ. of Leuven; Kasteelpark Arenberg 20 B-3001 Leuven Belgium
2. Instituto de Recursos Naturales y Agrobiología de Sevilla, CSIC; Avenida Reina Mercedes 10, Apartado 1052 E-41080 Seville Spain
3. Bacteriology and Immunology; Veterinary and Agrochemical Research Centre (VAR); Groeselenberg 99 B-1180 Brussels Belgium
4. Environmental and Process Technology; Flemish Institute for Technological Research (VITO); Boeretang 200 B-2400 Mol Belgium