Active crop canopy reflectance sensors have shown to be an efficient method for assessing spatially-variable crop nitrogen (N) need and controlling remedial in-season N applications in wheat. Recently, these sensors have been studied for N application in corn. This study will be conducted during the summer of 2007 to determine the optimal spatial scale of one sensor to give a proper assessment of the spatial patterns of N need within a cornfield. Research will be conducted on three irrigated producer fields in central Nebraska. Sensor readings will be collected at two corn growth stages from every row in a specified study area within each field. Geospatial statistics will be used to assess the variability of sensor readings within and between cornrows. Research results will help to determine the optimal number of sensors to use for in-season variable-rate N application in corn.