1. USDA‐ARS National Soil Tilth Lab. 2110 University Blvd. Ames IA 50011
2. CALMIT, School of Natural Resources Univ. of Nebraska Lincoln NE 68583
3. USDA‐ARS Soil and Water Conservation Unit, 120 Keim Hall, Univ. of Nebraska Lincoln NE 68583
4. USDA‐ARS National Program Staff 5601 Sunnyside Ave. Beltsville MD 20705