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The nondestructive determination of plant biomass is not possible; however, crop-canopy sensors that determine the normalized difference vegetation index have the potential to estimate living biomass, which is indicative of plant vigor and stress. Pot experiments using sand culture were conducted in 2002 and 2003 under greenhouse conditions to evaluate the effect of nitrogen (N) deficiency on corn biomass and reflectance. Stress was imposed by implementing six to eight levels of N in Hoagland’s nutrient solution. Canopy reflectance measurements made at three growth stages with a variety of handheld spectral sensors (active and passive) were closely correlated with dry weight and chlorophyll meter readings of corn at flowering, as well as at the two earlier growth stages. Results indicate that selected ground-based sensors and related reflectance indexes can provide a nondestructive, real-time assessment of apparent plant N status and thus be used for in-season N-management decisions.