1. USDA‐ARS‐ERRC, Plant and Soil Biophysics Res. Unit600 E. Mermaid LanePhiladelphiaPA19118
2. USDA‐ARS, Tobacco and Forage Res. Unit. Agric. Sci. Center‐North
3. Agronomy Dep., Agic. Sci. Center‐NorthUniv. of KentuckyLexingtonKY40456‐0091
4. Agronomy Dep., Univ. of KentuckyLexingtonKY40456‐0091