The impact of superphosphate and surface-applied lime on the profitability and sustainability of wool production on the tablelands of NSW

Soil acidification is one of the major forms of soil degradation in higher rainfall areas of the tablelands of NSW. A grazing experiment was conducted near Sutton, NSW, to assess the effect of various rates of superphosphate, lime, sewage ash and stocking rates on wool production and sustainability between 1999 and 2008. The results from the discounted cash flow analysis show that the net present value of the treatment without lime, the lower rate of superphosphate and the lowest stocking rate returned the highest net present value of $266.30/ha. Raising the application of superphosphate from 125kg/ha every two to three years to 250kg/ha every year on un-limed and limed soil reduced the net present value by $278.70/ha and $249.30/ha, respectively. The addition of lime at the rate of 4t/ha on un-limed soil at the low superphosphate level reduced the net present value by about $234.60/ha. The net present value fell by $205.24/ha when the level of superphosphate rate increased to 250kg/ha every year. The net present value decreased as the level of stocking rate increased. We conclude that wool producers will be unlikely to use lime to ameliorate acid soil, even though production will not be sustainable, unless there are more favourable input and commodity prices in the market and government intervention.