1. Instituto de Recursos Naturales y Agrobiología de Sevilla, CSIC; P.O. Box 1052 41080 Sevilla Spain
2. Dep. Soil, Water & Climate; Univ. Minnesota; St. Paul MN 55108
3. USDA-ARS; Soil and Water Management Research Unit; 1991 Upper Buford Cir. Rm 439 St. Paul MN 55108