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Abstract: Botanical composition and forage productivity of mixed cool- and warm-season perennial pastures are important determinants of agricultural sustainability. Effects of three sources of nutrient (inorganic only, organic+inorganic combination, and organic only) and four utilization regimes (unharvested, low and high grazing pressure, and hayed) were evaluated on botanical composition, residual forage mass, and forage production during seven years of management on tall fescue (Lolium arundinaceum, a cool-season C3 grass) overseeded into existing bermudagrass (Cynodon dactylon, a warm-season C4 grass) sod in Georgia. Nutrient source had few major impacts on responses, except for greater hay yield with organic fertilization (broiler litter) than with organic+inorganic and inorganic only fertilization. Botanical composition of grazed pastures shifted with time from initial dominance with bermudagrass (∼50% basal area) to mixed composition of tall fescue (60%)/bermudagrass (36%) under low grazing pressure and tall fescue (45%)/bermudagrass (48%) under high grazing pressure. To maintain optimum botanical composition and productivity for year-round sustainable grazing, forage mass needs to be balanced within a maximum threshold to avoid deterioration of forage quality and a minimum threshold to avoid environmental degradation. [Copyright &y& Elsevier]