Environmental nitrogen (N) losses (e.g., nitrate leaching, denitrification, and ammonia volatilization) frequently occur in maize (Zea mays L.) agroecosystems. Decision support systems, designed to optimize the application of N fertilizer in these systems, have been developed using physically based models such as the Precision Nitrogen Management (PNM) model of soil and crop processes, which is an integral component of Adapt-N, a decision support tool providing N fertilizer recommendations for maize production. Such models can also be used to estimate N losses associated with particular management practices and over a range of current climates and future climate projections. The objectives of this study were to update the PNM model to include an option for simulating soil-water processes in artificially drained soils, and to calibrate the revised PNM model and test it against multiyear field studies in New York and Minnesota with different soils and management practices. Minimal calibration was required for the model. Denitrification rate constants were calibrated by minimizing the error between simulated and observed nitrate leaching for each study site. The normalized root mean squared error of cumulative daily drainage for the validation sets ranged from 10 to 23%. For cumulative daily nitrate leaching, the normalized root mean squared error ranged from 11 to 28% for the validation sets. The minimal calibration required and relatively simple data inputs make the PNM model a broadly applicable tool for simulating water and N flows in maize systems. , 1997;Cassman et al., 2002Cassman et al., , 2003van Es et al., 2002). To increase the sustainability of maize production and maintain important ecosystem services under a changing climate, we need to better understand how climate and management affect the multiple N-loss pathways at the field, landscape, and regional scales. Such understanding is crucial for improved decision support systems for N management in maize agroecosystems.The interaction of climate, management practices, and soil physical and biological properties significantly affects both the magni- ). These interactions are complex, nonlinear, and dynamic; therefore, estimating the fate of N under different climate and management scenarios in cropping systems is a formidable challenge (Smil, 1999;Jayasundara et al., 2007). Well-calibrated and tested dynamic simulation models of soil and crop processes have potential for estimating the fate of N, including the environmental impact of N practices in crop production across a broad range of environments and production systems (Shaffer and Ma, 2001;Laurent and Ruelland, 2011;Grizzetti et al., 2015). We have developed the Precision Nitrogen Management (PNM) dynamic simulation model to estimate N-leaching losses from the rootzone, total N losses, aboveground biomass production, and crop N uptake in maize production systems (Melkonian et al., 2007).The PNM model is a daily time-step, process-based model that was built on two model components: LEACHN (...