Previous field research in Indiana found soil N supply was the most important factor determining fertilizer N rate needed to optimize corn yield. However, current soil testing methods do not predict soil N supplying capacity, which limits our ability to develop more accurate N fertilizer recommendations. The objectives of this study were to (1) determine the mineralizable N in major soil types of Indiana that differed substantially in organic matter, texture, and previous crop; (2) compare laboratory and greenhouse N mineralization estimates to field measurements of N supplying capacity. We assessed N mineralization in the soils with two incubation procedures - leaching tube incubation and static cup incubation. Total N uptake by wheat grown in the greenhouse was also measured to determine soil N supplying capacity under greenhouse conditions. The results showed soil N mineralization rates varied among different soils but were not correlated to soil organic matter content (p=0.18). Additionally, although the mineralized N in the laboratory incubation was consistent with greenhouse mineralization, it did not predict the field N supplying capacity.