Kenneth G. Cassman,^* Achim Dobermann,^** Daniel T. Walters<sup>***


*</sup>Kenneth G. Cassman is professor of agronomy at the University of Nebraska. He is a systems agronomist who has conducted research on processes governing nutrient cycling and opportunities to improve nutrient management in the major cereal production systems of Asia, North and South America, and North Africa. His address: Department of Agronomy and Horticulture, University of Nebraska, Lincoln, NE 68583-0915, USA. kcassman1@unl.edu
^**Achim Dobermann is associate professor of soil science at the University of Nebraska. He is a soil fertility and nutrient management specialist who has conducted research on soil variability, processes governing nutrient cycling and site-specific nutrient management in the major cereal production systems of Asia and North America. His address: Department of Agronomy and Horticulture, University of Nebraska, Lincoln, NE 68583-0915, USA. adobermann2@unl.edu
^***Daniel T. Waters is professor of soil science at the University of Nebraska. His research emphasis has been the study of nitrogen carbon cycling in intensively managed agroecosystems. He has conducted research in the major cereal systems of north and Central America and Southern Africa. His address: Department of Agronomy and Horticulture, University of Nebraska, Lincoln, NE 68583-0915, USA. dwalters@uninotes.unl.edu