5.3.4. Fertilisers

Predictions from 2009 suggested that phosphorus might reach peak supply in 25 to 30 years. This has since been revised: it is now thought that P reserves might be four times larger than previously thought. Even with “peak P” postponed, the present rate of superphosphate application is certainly unsustainable. Indications of an approaching shortage can be seen the price of superphosphate, which has doubled in the last 10 years.

A survey of 700 landholders in the Murrumbidgee region (Davis, n.d.) found that 54% regularly top-dressed their paddocks, and more than 80% of these used some form of superphosphate. Two thirds of all respondents top-dressed their paddocks every year (34%) or every two years (roughly 33%). A further 20% top-dressed every three years. Though rates of application varied considerably, this still represents a significant consumption of a finite resource.

According to CSIRO, phosphorus available for recycling amounts to only 5-10% of the current demand. It will be necessary, if this is the case, to increase P-use efficiency in agriculture, which is presently considered to be relatively poor. This may require the use of plants with roots better able to access P in the soil. 

References and Resources
• CSIRO. 2011. Sustainable phosphorus use for the future.

• Davis, V (Murrumbidgee CMA). Undated. Dryland Farming Systems Survey: Final Report.