1. School of Plant and Environmental Sciences Virginia Polytechnic Institute and State Univ. 675 Old Glade Road, Virginia Tech Box 0330 Blacksburg VA 24061‐0330 USA
2. Dep. of Crop, Soil, and Environmental Sciences, 201 Funchess Hall Auburn Univ. Auburn AL 36849 USA
3. Crop and Soil Sciences Dep. Univ. of Georgia Griffin GA 302223 USA
4. Dep. of Crop and Soil Sciences North Carolina State Univ. Raleigh NC 27695 USA
5. Dep. of Plant and Environmental Sciences Clemson Univ. Clemson SC 29634 USA