Dan Olk is a soil biochemist with the U.S. Department of Agriculture-Agricultural Research Service and works at the National Laboratory for Agriculture and the Environment in Ames, Iowa. He is a Ph.D. graduate (1993) of the University of California, Davis and worked for eight years at the International Rice Research Institute in the Philippines before his employment with the USDA-ARS (2001-present). Since 2009 Dr. Olk has conducted field evaluations of humic products in corn─soybean rotations of the U.S. Midwest, studying the efficacy of humic products for improving crop growth as influenced by environmental variables, including annual weather patterns and soil type. Field research has also addressed responses by corn structural biochemistry and root growth to humic products, and more recently has studied long-term benefits to soil physical properties. His laboratory research has used an integrated extraction for physical and chemical fractions of soil organic matter to link seasonal changes in their masses and biochemical natures to crop production and soil nutrient cycling in field conditions.