Perennial ryegrass (PRG, Lolium perenne L.) is one of the most widely used turfgrass species for sports turf. There is no agreement among turfgrass managers as to the optimum N-K fertilization program for wear tolerance. The objective of this research is to identify specific mechanisms (plant factors) associated with wear tolerance of PRG in response to five rate levels of N (49, 147, 245, 343, and 441 kg/ha/yr) and three rate levels of K (49, 245, and 441 kg/ha/yr). Urea (45-0-0) was used as the source of N and potassium sulfate (0-0-41.5) was the source for K. Wear was applied in the field on Bright Star SLT PRG using a differential slip wear (DSW) and grooming brush wear (GBW) applied by a walk behind greens mower. Plots were mown at 3.125 cm and irrigated to prevent stress. Significant wear injury was imposed on all plots using both the DSW and GBW. A visual rating scale was used to assess wear injury (1 to 9, 9=no injury). Twelve morphological and anatomical characteristics were measured in the field at the time DSW was applied in June 2006. Greater wear injury with either K or N was associated with greater leaf growth rates. Leaf growth rate accounted for as much as 95% of the total variation in wear tolerance according to GBW and 88% of the total variation in DSW tolerance. Wear tolerance increased with greater leaf tensile strength and total cell wall content. Conversely, wear tolerance decreased with greater shoot moisture and relative leaf turgidity (leaf moisture relative to maximum). Shoot moisture and relative leaf turgidity accounted for 60% of the total variation in wear tolerance followed by leaf tensile strength and shoot density at 50% and total cell wall content at 40% of the total variation in wear tolerance.