Nitrogen management and cropping system history (tillage and crop rotation) have direct impacts on soil organic nitrogen (N) and carbon (C) pools, and the tie between soil organic N and C. Specific organic-N pools in soil can be an important source of plant-available N. Nitrogen availability in the soil environment also plays a significant role in determining soil C status. The objectives of this project are to demonstrate corn N fertilization needs and the short- and long-term N–C relationships across diverse soils, productivity, and crop management systems; and to evaluate and demonstrate the potential of a new soil N test (the Illinois N Soil Test, which is based on a readily mineralized organic-N fraction – amino sugar-N) in Iowa.