1. a Texas Agricultural Experiment Station , Texas A&M University , Route 2, Box 2E, Munday , TX , 76371
2. b Agriculture and Agri‐Food Canada , Brandon Research Centre , P. O. Box 1000 A, R. R. # 3, Brandon , Manitoba , R7A 5Y3 , Canada
3. c Department of Agronomy , University of Illinois at Urbana‐Champaign , 1102 South Goodwin Ave., Urbana , IL , 61801