1. USDA‐ARS, Central Great Plains Res. Unit P.O. Box 400 Akron CO 80720
2. USDA‐ARS, Soil‐Plant‐Nutrient Res. Unit 301 S. Howes Ft. Collins CO 80522
3. USDA‐ARS, Water Management Res. Unit, Agric. Eng. Res. Ctr., Colorado State Univ. Ft. Collins CO 80523
4. Great Plains Systems Research Unit, USDA‐ARS 301 S. Howes Ft. Collins CO 80522