Contributors to this special 100th volume were carefully selected by the editor for their perspectives on not only the current state-of-the-art of their topic but also where their fields are going and what future opportunities exist to advance scientific frontiers. Volume 100 continues a long tradition of excellence, with cutting-edge and visionary reviews from distinguished scientists at the top of their respective fields. It includes: contributions from leading scientists in crop and soil sciences and allied fields including geochemistry, environmental microbiology, and microbiology; dynamic illustrations; an extensive literature review; and, grand research challenges and opportunities.