The Ontario Soil Nitrogen Test (SNT) is a tool that Ontario corn growers can use to obtain nitrogen fertilizer recommendations for corn. This thesis investigated the temporal variability of the Ontario SNT as influenced by sampling time and organic amendments as well as soil temperature and moisture conditions. The Ontario SNT showed significant variability due to sampling time when samples were taken in early spring (late April - early May). The SNT could partially detect and compensate for added N from some organic amendments including spring-applied liquid hog manure and fall-killed red clover. The effects of soil temperature and moisture were modelled with a Cumulative Relative Microbial Activity Index (CRMAI) and correlated with plant available nitrogen (PAN) to develop an SNT adjustment. A Soil N database was employed to evaluate the effectiveness of the SNT adjustment and, for a Guelph regional dataset, it was found to significantly improve the accuracy of SNT recommendations.