It has been known that crops are able to use only 50-70% of the applied N fertilizer.  Residual soil N after crop harvest is lost through volatilization, leaching, denitrification, or greenhouse gas (N2O) emissions. Opportunities exist to improve crop N-use efficiency and reduce the environmental impact of N fertilization.  This symposium will elucidate our current state of knowledge on N dynamics in agroecosystems. An increase in soil N storage can reduce N losses through leaching, volatilization, denitrification, surface runoff, erosion, and N2O emissions. Since N can also be mineralized from crop residue and soil, information on N storage and mineralization is needed to optimize N availability for crops , increase N-use efficiency, sustain crop yields and quality, and reduce N fertilization rate and the potential for N loss. Management practices are needed to conserve soil N and reduce N losses through soil processes. At the same time, a balance between N conservation and mineralization is also needed to optimize soil N availability that can sustain crop yields and quality and reduce the cost and rates of N fertilization. The objectives of this symposium are to: (1) discuss soil N conservation, N mineralization, and N balance, (2 reduce N fertilizer rates and improve N use efficiency, and (3) identify management practices that conserve soil N and reduce N losses.