Perennial bioenergy crops are touted as a sustainable feedstock for energy production that can replace fossil sources and improve water quality. Such potential benefits, however, may be offset if excessive N fertilization during biofeedstock crop production substantially increases carbon costs due to the Haber-Bosch process used to produce fertilizer. Excess fertilizer application lead to soil nutrient losses, nutrient runoff, eutrophication of downstream water bodies, and increased soil greenhouse gas emissions. Furthermore, as yields respond to local changes in climate, nutrient requirements will change. Guidance is surely needed regarding the minimal N inputs necessary to ensure sustainable bioenergy crop yields for current and future climate scenarios. Here, in comparison with traditional regression-based approach, a pairwise meta-analysis was conducted to investigate the effects of N input (amounts and duration) and climate regime on the above-ground biomass yields of two advanced bioenergy crops, i.e., miscanthus (Miscanthus x giganteus) and switchgrass (Panicum virgatum L.). Both regression models and meta-analyses showed that switchgrass growth was more responsive to N fertilization than was miscanthus growth, although both showed significantly positive N effects. Compared to regression models, our meta-analysis further showed that the positive growth response of miscanthus production to N application increased with increasing N rates from 40 to 250 kg N ha-1, but the magnitude of the response decreased continually with continuation of fertilization up to 14 years. In addition, stimulating N effects on switchgrass biomass increased and peaked at N rates of 120-160 kg N ha-1 and 5-6 years of N inputs, but started to diminish for rates exceeding 300 kg N ha-1 and continual fertilization beyond 7 years. Our meta-analysis further revealed an interaction of N effects with climate that influences of N on switchgrass growth increased with both annual mean temperature and precipitation. On the contrary, miscanthus yields were less responsive to climate conditions than switchgrass yields. This global meta-analysis helps fill a gap in estimation of biofeedstock yields based on N fertilization that has primarily used model-based approaches. This could help better estimate the N requirement and soil management strategies for miscanthus and switchgrass cultivation with varying climatic conditions, thereby improving energy use efficiency in bioenergy cropping systems.