1. Research Associate, Southwest Research and Extension Center, Kansas State Univ., Garden City, KS 67846.
2. Assistant Professor, Southwest Research and Extension Center, Kansas State Univ., Garden City, KS 67846 (corresponding author).
3. Professor, Dept. of Agronomy, Kansas State Univ., 1712 Claflin Rd., Manhattan, KS 66506.
4. Research Leader, USDA-ARS Grazinglands Research Laboratory, 7207 West Cheyenne St., El Reno, OK 73036.