1. DLO–Inst. for Agrobiology and Soil Fertility P.O. Box 14 6700 AA Wageningen The Netherlands
2. Escuela de Agric. de la Región Tropical Húmeda (EARTH) Las Mercédes Costa Rica
3. Dep. of Computer Science Univ. of Minnesota 4‐192 EE/CSci Building, 200 Union St. SE Minneapolis MN 55455
4. USDA‐ARS, Univ. of Minnesota 439 Borlaug Hall, 1991 Upper Buford Circle St. Paul MN 55108