Very few studies have attempted to understand the bio-physical basis for the use of aerial color infrared (CIR) photography to quantify in-season corn (Zea mays L.) nitrogen (N) requirements. The objectives of this research were to: i) examine the response of corn agronomic parameters (biomass, plant N concentration, and total N uptake) and spectral parameters (near-infrared [NIR], red [R] and green [G]) from CIR measured at the V7 and VT growth stages to changing environments (year), irrigation, and N applications at planting (N_PL); and ii) determine the relationships between corn agronomic parameters and spectral parameters that influence the prediction of optimum N rates at growth stages V7 and VT. Research was conducted during the 2000-2003 corn growing seasons in North Carolina under irrigated and non-irrigated conditions with different N_PL rates as the main plot factor. Corn agronomic parameters were measured and aerial CIR photographs were obtained at each site at V7 or at VT. Results indicate that N_PL significantly influenced corn agronomic parameters measured at V7 and VT. Corn spectral parameters measured at V7 and VT varied with year and N_PL. Green and NIR were significantly correlated with biomass and total N uptake. Relative indices using G and NIR were related to plant N concentration. Among the different indices, relative green difference vegetation index (RGDVI) was the best predictor of corn N status (plant N concentration) at V7 and VT. RGDVI showed consistently significant relationships with corn agronomic parameters measured at VT when analyzed across irrigated and non-irrigated experiments.