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A detailed soil-plant-animal model was constructed and used to assess pasture and animal production at three superphosphate rates over three 15-year periods, (i) 1927–41, (ii) 1949–63, and (iii) 1972–86. At superphosphate rates of 125 and 250 kg super ha −1 yr −1 , wool production averaged 13% higher and liveweight gain 22% higher during periods (ii) and (iii) than (i). Relative fertilizer responsiveness was similar in all three periods. Climatic conditions were much harsher during the 1980's than during earlier years of period (iii). It is concluded that the period 1950–1979 was atypically wet, and that in parts of Australia where this feature applies, models should also be applied to the earlier years to obtain a more realistic understanding of climatic potential.