The optimum plant population for maximum grain yield in maize (Zea mays L.) has increased steadily over the past 70 years as a result of the improved high plant density tolerance of modern hybrids.  Yet higher plant densities result in greater intraspecific competition among individual plants for limited resources, leading to increased plant-to-plant variability for grain yield and other morpho-physiological traits and the establishment of plant hierarchies (i.e., “dominated” versus “dominating” plants).  Results from a limited number of studies on per-plant variability in maize suggest that plant-to-plant uniformity is essential for high productivity.  To improve per-plant uniformity at high plant populations, fertility limitations must be minimized.  This study analyzed the effects of 3 nitrogen rates (0, 170, and 340 kg ha^-1) and 3 plant populations (54,000, 79,000, and 104,000 plants ha^-1) on the per-plant variability of multiple morpho-physiological parameters for 3 modern genotypes (hybrids Pioneer 31N28 (2006), 31G68 (2005, 2006), and 33N09 (2005)).  In 2005 and 2006, the growth and development of individual plants was measured from seedling emergence to physiological maturity using numerous morpho-physiological parameters.  These parameters included, but were not limited to, plant height, stalk diameter, leaf area index (2006), anthesis (2006) and silking date, grain yield, total kernel number, and kernel weight.  As anticipated, higher plant populations and lower nitrogen rates increased per-plant variability for grain yield and other morpho-physiological parameters, and, through intensive asymmetric intraspecific competition, facilitated the development of plant hierarchies.  In this presentation, we will further discuss the effects of nitrogen rate and plant density on (a) the establishment and seasonal dynamics of per-plant variability for a number of morpho-physiological traits and (b) the morpho-physiological characteristics of “dominated” versus “dominating” plants.