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phosphorus, soil test, trend, nutrient management, nutrient status, phosphorus status, response curve, soil constraints, fertiliser advice


Condition and trend Nutrients, such as phosphorus (P), are essential for profitable agriculture in the south-west of WA; however, excess P – more than is required for optimal production – is stored in many agricultural soils. On average, pasture soils and arable soils contain 1.3 times and 1.6 times respectively, as much P as is required for optimal production. Production in P-enriched soils is more likely to be constrained by soil acidity (50–60% of pasture and arable soils), potassium (K) (50% of pasture soils and less than 10% of arable soils), and sulphur (S) (30% of pasture soils). Management implications 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 (reduced fertiliser costs or redirection of fertiliser costs to removing other constraints), and reducing the off-site impacts of agriculture (reduced leaching and run-off of P). Removing other nutrient and soil constraints (acid soils, K, S) is likely to increase productivity and profit of agriculture. Regular monitoring of soil nutrients at a paddock scale will provide the information to optimise fertiliser application and profitable yields, and minimise off-site impacts. Industry bodies, especially those providing fertiliser advice, need to be aware of this nutrient status assessment and should provide fit-for-purpose, element-specific fertiliser recommendations to derive optimal economic outcomes for producers and to minimise off-site impacts.