One of the important strategies for improving nitrogen (N) fertilizer management in corn production is to engage growers and agronomists in active on-farm evaluations. This poster will describe a case study focused on continuous evaluations and refinement of N management practices by a group of about 30 growers in Greene Co, in central Iowa, during the last 10 yr. The growers use digital aerial imagery of the corn canopy, the late-season corn stalk nitrate test (CSNT), and replicated strip trial methodology. The strip trials include two N fertilizer treatments with a normal N rate (for both commercial N fertilizer and animal manure) and a rate that is one-third less or more than the normal. Yield differences between the two treatments are calculated at the field and sub-field levels and compared between different categories based on form and timing of fertilizer application, soil and terrain properties, or amount of rainfall in each location. About 50 corn fields, having uniform management and representing major N management practices in the studied area, are sampled annually for the CSNT using late-season imagery of the corn canopy and GPS technology. The evaluation results show how N status of corn changes over time and how rainfall and management practices (forms, timing, and placement) interact by affecting the risk of N losses and the likelihood of economic yield response to N.