Detecting N-deficiency early in a plant’s development before visual symptoms becomes pronounced, and irreparable damage done is crucial to maintaining optimum grain yield and biomass production. Chlorophyll fluorescence technology (CFT) is a quick, non-invasive, non-destructive, and informative technique that is used to study the physiological status of plants at any given stage of development. The objective of the study was to determine the photosynthetic and growth responses of N-deficient maize seedling. Two N treatments, 10 t/ha N and 50 t/ha N were evaluated in a greenhouse in a completely randomized design with 12 replications. Results showed a significantly (p<0.05) higher CO₂ assimilation rate, maximum quantum yield of PSII photochemistry, effective quantum yield of PSII photochemistry, and chlorophyll concentration in plants that received 50 t/ha N compared to plants on 10 t/ha N at 3 and 4 weeks after fertilizer application (WAFA). In contrast, plants on 10 t/ha showed higher level of non-photochemical stress due to up regulation of nitric oxide production in PSII [Y(NO)] than plants on 50 t/ha. Non-photochemical quenching due to down regulation of nitric oxide production in PSII [Y(NPQ)] was comparable (P>0.05) in both treatments. There was no significant difference in plant height, although wider stem girth was recorded in plants on 50 t/ha. The significantly higher levels of Y(NO) in plants on 10 t/ha N suggests an alteration in nitrogen metabolism, and increased production of reactive nitrogen species which may potentially cause cellular damage if not diagnosed early and managed adequately.