Liwang Ma is a soil scientist with the USDA-ARS, Agricultural Systems Research Unit in Fort Collins, Colorado. Dr. Ma received his B.S. and M.S. in agricultural biophysics from Beijing Agricultural University (now China Agricultural University) in 1984 and 1987, respectively, and his Ph.D. in soil science from Louisiana State University in 1993. He has authored and coauthored 70 journal papers and 50 other published works (books, book chapters, and proceedings). His research interests center on agricultural systems modeling and include pesticide fates, plant growth, soil carbon/nitrogen dynamics, plant water and nitrogen uptake, and soil water and nutrient movement. He is the principal scientist responsible for developing, enhancing, and maintaining the USDA-ARS Root Zone Water Quality Model (RZWQM2). He is a Fellow of the American Society of Agronomy and has served as an associate editor of the Journal of the Soil Science Society of America (2001-2007). He is now serving as associate editor of the Agronomy Journal and the Journal of Environmental Quality. Lajpat (Laj) R. Ahuja is a supervisory soil scientist and research leader of the USDAARS, Agricultural Systems Research Unit in Fort Collins, Colorado. He has made original and pioneering research contributions in several areas of agricultural systems, including infiltration and water flow in soils, estimation and scaling of hydraulic properties, transport of agrochemicals to runoff and to groundwater through soil matrix and macropores, quantification of the effects of tillage and other management practices on relevant properties and processes, and modeling of entire agricultural systems and application of system models in field research and technology transfer. Dr. Ahuja has authored or coauthored 270 publications and served as associate editor (1987-1992) and technical editor (1994-1996) of the Journal of the Soil Science Society of America. He is a Fellow of the Soil Science Society of America (SSSA), the Ameri
