A greenhouse experiment was conducted comparing biomass of Indian grass (Sorgastrum nutans), a native warm-season grass, and spotted knapweed (Centaurea stoebe), an invasive forb, with different amendments used to alter the initial nitrogen levels of the soil. This experiment used a multifactorial design, with three levels of initial nitrogen (low, normal, and high) and three levels of plantings (Indian grass only, spotted knapweed only, and both spotted knapweed and Indian grass). The nine treatment combinations were repeated in five randomized complete blocks. The aboveground biomass of the two species and the final available soil nitrogen concentrations were compared using correspondence analysis, a multivariate statistical technique. The ordination of the correspondence analysis showed a trend that suggests high soil nitrogen favors spotted knapweed biomass and lower nitrogen favoring Indian grass. This trend implies reducing soil nitrogen as a restoration effort in spotted knapweed infested areas should promote native grass dominance.