1. Dep. of ChemistryMiddle East Technical Univ.Ankara06531Turkey
2. USDA‐ARS‐FCR, Dep. of AgronomyIowa State Univ.AmesIA50011
3. Dep. of AgronomyUniv. NebraskaLincolnNE68583
4. Agronomy Dept.Univ. of MarylandCollege ParkMD27042
5. USDA‐ARS, Soybean and Alfalfa Research Lab.BeltsvilleMD20705