Technical Abstract: Several long-term N fertility studies conducted in the northern and central Great Plains were examined to determine the influence of N fertilization on soil organic carbon sequestration in the form of soil organic matter (SOM). Three studies were examined that utilized several different cropping and tillage systems. Two were dryland studies and one an irrigated study. Nitrogen fertilization increased the quantity of crop residue returned to the soil in all studies. Nitrogen fertilization increased the quantity of SOM present when compared to plots with no N application after 9- to 30-yea cropping. In all cases, SOM increased with increasing N rate. Examination of dryland farming systems in western Nebraska showed that a no-till continuous cropping system after 27 years had a greater level of SOM and total soil nitrogen (TSN) than an adjacent field that had been conventionally tilled and maintained in a predominantly crop-fallow rotation. The no-till system had SOM levels approaching that of an adjacent native sod area. The research projects examined in this report indicated that a good N fertility program to optimize crop yields will also have positive effects on SOM levels.