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.