Winter barley (Hordeum vulgare L.) production in the mid-Atlantic region occupies a substantial amount of arable land. Variable levels of winter and spring precipitation can result in N loss. The objectives of this study were to determine the optimum rate and timing of N fertilization and develop predictors of optimum N rates. An uptake study was conducted to determine N uptake of winter barley with respect to growth stage. Various N rate combinations at growth stages (GS) 25 and GS 30 were evaluated over twenty locations and three cropping seasons, to determine the application regime required to optimize grain yields at each site. Predictor variables at GS 25 and GS 30 were evaluated to predict optimum N rates. The N uptake study indicated an increased N uptake at GS 25 and GS 30. Yields from plots receiving no spring N varied from 1400 to 7530 kg ha⁻¹, at various sites, indicating a yield response of barley to residual N. Optimum N rates over locations varied from 0 to 136 kg N ha⁻¹, suggesting a need to diagnose site-specific N requirements. Plant tissue tests at GS 30 were the best predictor of GS 30 optimum N rates with a critical level of 3.5% N in plant tissue above which no economic response to applied N would be expected. GS 25 tiller density was the best predictor of optimum GS 25 N rates in 1994-1995. This season was climatically atypical thus this method must be evaluated further. / Master of Science