With increased cost of nitrogen fertilization and narrowing profit margins, cattle and hay producers cannot afford to expend resources to fertilize their pasture unnecessarily.  However, they also cannot afford to lose yield as a result of inadequate fertilization.  Understanding regrowth and assimilation responses to N fertilization will provide information to improve grower fertilization decisions on pasture and hay production.  A field study was conducted at the University of Florida Beef Research Unit at Gainesville, FL on established Tifton-85 Bermudagrass pasture during 2006.  Responses of Tifton 85 Bermudagrass (Cynodon spp.) to varying N rates were observed for two 28-day cutting cycles.  Residual leaf area index, subsequent regrowth, new tiller initiation, rhizome and root mass were measured immediately after harvest and at weekly intervals during each cutting-cycle.  Canopy carbon exchange measurements were also taken weekly.  Nitrogen fertilization caused an increase in biomass, leaf area index, canopy assimilation, and tiller initiation with time after each cutting.  Compared to unfertilized, fertilization with 135 kg N ha^-1 raised seasonal four-cut yield from 3070 to 10,760 kg ha^-1 and increased canopy assimilation rates from 27 to 48 μmol CO₂ m^-2 s^-1 at the end of each regrowth cycle.  However, there were almost no significant differences between the 90 kg N ha^-1 and 135 kg N ha^-1 treatments for any measured variables.  There were no observed treatment effects on root or rhizome mass which averaged 2,850 and 4,900 kg ha^-1, respectively.  In addition seasonal effects on growth and canopy photosynthesis were observed.  These data indicate no advantage to applying N in excess of 90 kg ha^-1 per cutting cycle.