1. USDA-ARS; Wheat, Sorghum, and Forage Res. Unit; 344 Keim Hall, Univ. of Nebraska Lincoln NE 68583 USA
2. USDA-ARS; National Soil Tilth Lab; 2150 Pammel Drive Ames IA 50011 USA
3. USDA-ARS; 215 Johnson Hall, Washington State Univ. Pullman WA 99164-6421 USA
4. Dep. Soil, Water, and Climate; 1991 Buford Circle, Univ. Minn. St. Paul MN 55108 USA