1. USDA-ARS; National Soil Tilth Lab.; 2150 Pammel Drive Ames IA 50011
2. USDA-ARS; Southwest Watershed Research Center; 2000 E. Allen Road Tucson AZ 85719-1596
3. Dep. of Plant and Soil Sciences; Mississippi State Univ.; P.O. Box 9555 Mississippi State MS 39762