Abstract
Nitrogen mineralized from the active organic N fraction of soil organic matter sustained the requirements of cultivated crops for approximately 70 years after breaking the prairie grassland. However, in the past decade, the application of fertilizer N has become a common practice for ensuring optimum yields due largely to the major decrease in surface soil organic matter that has occurred with cultivation. Various management practices such as minimal tillage, elimination of cultivated fallow and inclusions of rotation containing legumes have been shown to significantly increase the quality of soil organic matter over a relatively short period.