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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.

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