A long-term study of superphosphate and stocking rate on sheep production and plant and soil characteristics in central west New South Wales

The effect of 4 rates of superphosphate application (250 kg/ha.year, 125 kg/ha.year, 125 kg/ha every 2 years or 125 kg/ha every 4 years) and a low and high stocking rate (3.6 and 5.4 ewes/ha, 1980-86; and 4.0 and 7.0 ewes/ha, 1986-89) on sheep liveweight, fleece weight, lamb weaning weight, pasture production and botanical composition, soil pH, soil phosphorus, manganese and aluminium concentrations were measured on a Phalaris aquatica-subterranean clover pasture at Stuart Town, New South Wales. Only when 250 kg/ha of superphosphate had been applied annually was there a higher level of soil phosphorus than with the other 3 systems. None of the treatments affected soil pH, soil manganese or aluminium. There were large year effects and individual plot effects on pasture and sheep production but neither the superphosphate rates nor stocking rate significantly affected pasture or animal production. It was concluded that over a 9-year period the application of 125 kg/ha in alternate years can maintain adequate soil phosphorus levels, and satisfactory pasture and animal production on the central tablelands of New South Wales.