A ladino clover and tall fescue pasture was established in September 1983 to determine the impact of ozone and available soil moisture on plants grown in open-top field chambers and exposed for 12 h daily to ozone (O3) from April through October in 1984 and 1985. Samples were removed periodically to measure above- and below-ground biomass and energy reserves of the clover and fescue. At the final harvest, clover was the dominant species in below-ambient O3 while fescue was the dominant species at ambient and above-ambient O3 concentrations. Ladino clover shoot and root biomass was reduced by O3 for all harvest when compared to clover grown in the charcoal-filtered-air. Statistically-significant O3 effects were observed on clover shoots prior to roots. For most harvests, the energy reserves of ladino clover roots were suppressed by increasing O3 concentrations. Clover shoot starch levels were not greatly affected by O3 or moisture.