1. USDA-ARS; National Soil Tilth Lab.; 2110 University Blvd. Ames IA 50011-3120
2. Dep. of Crop and Soil Sciences; Washington State University; PO Box 646420 Pullman WA 99164-6420
3. USDA-ARS; New England Plant, Soil, and Water Lab.; Orono ME 04469-5753