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- Charles F. Curtiss Distinguished Professor in Agriculture and Life Sciences, 2011-present.
- Pioneer Hi-Bred Professor of Agronomy, 2017-present.
- Professor of Agronomy, Iowa State University, 1993-present.
- Senior Research Fellow, AgResearch Grasslands, New Zealand, 1998.
- Research Agronomist, USDA-ARS, 1989-93.
- Adjunct Professor of Agronomy, University of Nebraska, 1993-95.
- Adjunct Associate Professor of Agronomy, University of Nebraska, 1989-93.
- Associate Professor of Agronomy and Horticulture, New Mexico State University, 1988-89.
- Assistant Professor of Agronomy and Horticulture, New Mexico State University, 1987-88.
- Assistant Professor of Agronomy, University of Illinois, 1983-87 .