1. USDA-ARS; P.O. Box 5367 Mississippi State MS 39762
2. USDA-ARS; Florence SC 29501
3. Agronomy, Horticulture, and Plant Science Dep.; South Dakota State Univ.; Brookings SD 57007
4. Dep. of Soil and Crop Sciences; Texas A&M Univ.; College Station TX 77843-2474