Farm gate nutrient balances in south west Western Australia – An overview

Farm-gate nutrient budgets can be used to identify the efficiency of nutrient use within and between individual enterprises and catchments, and may be used to represent a component of the risk that particular landuses represent to water quality. Over the past 5 years, more than 400 farm-gate nutrient balance audits have been conducted across a range of catchments and landuses in southwest Western Australia (WA). Values for nutrient use efficiency and surpluses across landuses and catchments are reported. Patterns of nitrogen and phosphorus signatures closely reflect one another across landuses, though nitrogen input, output and surplus values are consistently higher than those for phosphorus. High intensity landuses with high levels of input per hectare, such as annual horticulture and dairy systems, also show higher outputs than extensive landuses such as broadacre grazing and cropping systems. However, surpluses per hectare are also higher than for other landuses. Cropping systems were found to be less variable and more efficient in nutrient use than other animal based landuses. Annual horticulture displayed interesting disparity with other data by having relatively high N efficiency concurrent with low P efficiency, defying the trend of N and P signatures reflecting one another closely. The general surpluses and efficiencies for different landuses were also reflected in catchment nutrient use efficiencies, based on the landuse makeup in those catchments. Catchments dominated by animal based landuses such dairy and other grazing systems tended to have higher nutrient surplus and lower efficiency than catchments dominated by plant based cropping systems