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WATCH: Is it time to re-think P critical levels in WA?

Applying phosphorus (P) to soils with seemingly adequate P stocks can boost yield. Trials in WA are showing crop response to P above critical levels. Critical levels indicate if a crop will respond to more of a certain nutrient. Above the critical level, there’s less than a 10% chance of a yield response to more fertiliser. 

Many soils in the WA wheatbelt are thought to have adequate P. From 2010 – 2017, Summit Fertilizers added P to soils with Colwell P values above the critical level. In most of the trials, wheat yield increased. Six to eight kgP/ha applied at seeding gave the best economic response. 

These trials highlight how important starter P is. Young plants can struggle to scavenge P from the soil, even if background levels are good. Impaired growth from P deficiency cannot be recovered later on in the season. Test strips with extra P will show if the next crop should have more starter P. 

More

How critical is the critical level?

Report card on sustainable natural resource use in agriculture

What is the DGT Phosphorus test and when should you use it?

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