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The effects of pH and phosphate concentration on the growth of Paspalum plicatulum Michx. (brownseed paspalum) and Schizachyrium scoparium (Michx.) Nash (little bluestem), two co-occurring C-4 grasses, was assessed in two factorial greenhouse experiments. Schizachyrium scoparium above- and belowground biomass showed significant increased growth with increased phosphate, The optimum pH range of biomass production for P. plicatulum and S. scoparium was 5.44-6.07. Although the two species did not differ in their response to soil pH, S. scoparium total biomass was approximately 1.7X greater and relative growth rates were 33% higher than P. plicatulum in the optimum pH range. Root:shoot ratios of both species also showed a significant pH effect. Highest root:shoot ratios for both species were at pH 3.98, with S. scoparium having the highest values when phosphate was increased. Increased S. scoparium biomass accumulation and growth in the optimum pH range and its response to phosphate additions may help explain the dominance of S. scoparium in the field.