This issue's cover: Dr. Jorge A. Delgado and Mr. Andrew Newhart working on collection of potato (Solanum tuberosum L.) samples with the assistance of a Differential Global Position System (DGPS) at the Kunugi Farms in south-central Colorado, where N management studies to increase N fertilizer use efficiency and protect water quality are being conducted. Photo by Anita Kear USDA-ARS-NPA-Soil Plant Nutrient Research Unit. See "Simulation of Nitrate-Nitrogen Dynamics for Cropping Systems with Different Rooting Depths" by J.A. Delgado, R.F. Follett, and M.J. Shaffer, p. 1050-1054.