Contributors to this special 100th volume of Advances in Agronomy were carefully selected by the editor for their perspectives on not only the current state of their topic but also where their fields are going and what future opportunities exist to advance scientific frontiers. Originating in 1949, Advances in Agronomy is a venerable serial featuring state-of-the-art reviews on crop and soil sciences over the years, and is highly regarded around the world. Volume 100 continues this long tradition of excellence, with cutting-edge and visionary reviews from distinguished scientists at the top of their respective fields.