Students apply the Law of Conservation of Mass to understand nitrogen (N) budgets for a Corn-belt agricultural system at the plot level. A 45-minute, in-class introduction enables students to complete an outside-of-class activity using a process-based simulation model in ‘lab mode’ address ‘What-If’ questions about effects of various management practices on N cycling. Then, during one 75-minute class, teams use the model in a game-like mode to compete in attaining four different goals: 1) Maximize income; 2) Increase soil carbon; 3) Reduce nitrate flow to streams; and 4) Optimize yield and soil organic N while reducing N in streams.