1. USDA-ARS; Northern Great Plains Research Lab.; P.O. Box 459 Mandan ND 58554 USA
2. USDA-ARS; Northwest Irrigation and Soils Research Laboratory; 3793 N, 3600 E. Kimberly ID 83341 USA
3. USDA-ARS; Forage and Range Research Lab., Utah State Univ.; Logan UT 84322 USA
4. Agriculture and Agri-Food Canada; Semiarid Prairie Agricultural Research Centre; P.O. Box 1030, Swift Current Saskatchewan Canada S9H 3X2