The overall goal of this research project is to describe the impacts of cropping system diversity, management and soil type on the cycling, storage, and losses of soil C and N at a long-term research trial in Lamberton, MN. For a number of management systems, including conventional reduced input, conventional high input, organic input (with and without cover crop), and a two vs. four year rotation, our specific objective was to use 13C and 15N labeled inputs to measure the storage and turnover of C and N in active and resistant organic matter pools.  A year after labeling, the greatest proportion of root-derived C was found in soils from the organic plus cover crop and the 4 year reduced input systems.  The same treatments had the greatest proportion of root-derived N, suggesting that decomposition of root-derived C and N is coupled.  Amounts of shoot-derived C in soils were much more variable and unrelated to amounts of shoot-derived N. Separation and analysis of free and occluded light fraction (LF) in soil samples from labeled microplots showed that labeled shoot residue occurred primarily in the free LF, while labeled roots were more prominent in the occluded LF, at least initially. Movement from the occluded to free fraction occurred over time with the shift occurring earlier in the high input than in the organic management system.