1. Dep. of Crop and Soil Sciences; North Carolina State Univ.; Raleigh NC 27695
2. USDA-ARS, Soybean Nitrogen Fixation Unit; 3127 Ligon St. Raleigh NC 27607
3. USDA-ARS, Plant Science Research Unit; North Carolina State Univ.; Raleigh NC 27695
4. Dep. of Crop and Soil Environmental Sciences, Virginia Tech; Blacksburg VA 24060