Technical Abstract: Sustainable soil fertility management depends on long-term integrated strategies that build and maintain soil organic matter and mineralizable soil N levels. These strategies increase the portion of crop N needs met by soil N cycling and reduce dependence on external N inputs required for crop production. To better understand the impact of management on soil N dynamics, we conducted field and laboratory research on five diverse management systems at a long-term study in Maryland, the USDA-ARS Beltsville Farming Systems Project (FSP). The FSP is comprised of a conventional no till corn–soybean–wheat/ soybean rotation (NT), a conventional chisel-till corn–soybean–wheat/soybean rotation (CT), a 2-yr organic corn–soybean rotation (Org2), a 3-yr organic corn–soybean–wheat rotation (Org3), and a 6-yr organic corn–soybean–wheat–alfalfa rotation (Org6). We found that particulate organic matter (POM) C and N , chemically-labile organic matter (CLOM), potentially mineralizable soil N, and corn yield and N uptake from unamended plots were greater in organic than conventional cropping systems. All measures of N availability were generally similar between NT and CT. Among the three organic systems, all measures of N availability tended to increase with increasing frequency of manure application and crop rotation length (Org2 < Org3 = Org6). Our results demonstrate that organic management practices increase soil N availability by increasing labile soil organic matter compared to conventional systems. Relatively high levels of mineralizable soil N must be considered when developing soil fertility management plans for these systems.