Mike Castellano is a professor of soil science at Iowa State University. His research focuses on biogeochemical cycling and transport within the soil as it extends to the atmosphere and subsoil. Our ultimate objective is to maximize sustainable productivity of agricultural systems. We have particular interest in nitrogen because nitrogen frequently limits production and is easily lost from agricultural systems to the surrounding environment, where it represents an economic loss to farmers that can diminish air and water quality. Minimizing nitrogen limitation on crop production while maximizing nitrogen retention within agricultural systems is among the most important global research priorities of the 21st century. To reach these goals we use agronomic, ecological, and biogeochemical principles to advance our basic understanding of element cycling and improve ecosystem management.