Soil nutrient management

On average, farm soils (i.e. pasture and arable) are over fertilised. They contain 1.3 – 1.6x as much phosphorus as is required for optimal production. Reducing the amount of phosphorus to optimal levels could lead to economic benefits (reduced fertiliser costs or redirection of fertiliser costs to removing other constraints), and reducing the off-site impacts of agriculture (reduced leaching and runoff of phosphorus).

Nutrients are required for productive agriculture. Too little of any nutrient can lead to poor biological growth and agricultural production and a poor economic outcome. Equally, too much of a nutrient can be an economic disadvantage if it is still being applied, and can lead to losses that result in off-site impacts. For example, algal blooms can occur if nitrogen and P are lost from agriculture through run-off and leaching to waterways.

Western Australia’s soils have long been renowned for their infertility. At the end of the 19th century, large increases in plant growth were obtained with the application of guano from the Abrolhos Islands, and later, imported superphosphate, the first inorganic fertiliser used in WA. Since then many farmers have adopted a traditional approach to P fertiliser management of ‘a bag of super to the acre each year. Given the traditional approach to P fertiliser management (Weaver and Wong 2011) nutrient applications, especially of P, need to be carefully managed to maximise farm profitability and reduce offsite impacts. Fertiliser represents the single largest farm input cost and fertile agricultural landscapes have a major impact on water quality.

Reducing phosphorous could lead to economic benefits

On average, farm soils (i.e. pasture and arable) are over fertilised. They contain 1.3 – 1.6x as much phosphorus as is required for optimal production. Reducing the amount of phosphorus to optimal levels could lead to economic benefits (reduced fertiliser costs or redirection of fertiliser costs to removing other constraints), and reducing the off-site impacts of agriculture (reduced leaching and runoff of phosphorus).

  • On average, pasture soils and arable soils contain 1.3 – 1.6x as much P as is required for optimal production (this has been recognised in e.g. the Leschenault Water Quality Improvement Plan (WQIP) as an issue, but specific estimates were not provided)
  • The direct cost of excess P application in the agricultural areas of the south-west of WA is estimated to be about $400 million per year
  • Reducing the amount of P to optimal levels could lead to economic benefits and reduce the off-site impacts of agriculture (reduced leaching and runoff of P).

Case Studies

Data Source:

  • Department of Agriculture and Food, 2013.  Report card on sustainable natural resource use in agriculture: Status and trends in the agricultural areas of the south west of Western Australia. Department of Agriculture and Food, Western Australia. 188 pages.