Wheat School: Predicting a response to added phosphorus and potassium

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Often when looking at soil samples, our eyes tend to flick straight to the nitrogen section. Where are N levels? What do we need to apply?

Nitrogen is very important in wheat production, but as Jeremy Boychyn, agronomy research extension manager with the Alberta Wheat and Barley Commissions explains, we still need to be keeping an eye on phosphorus and potassium levels — especially if we want to reach the highest possible yield potential.

We do know that depending on the amount of phosphorus and potassium is in the soil, says Boychyn, our yield response of that wheat crop is going to change. Also, it’s going to play a role in how we are managing our long term phosphorus and potassium plan.

“Phosphorus and potassium takes a little bit more time to manage,” he explains. “Typically, we want to look at a longer timescale more specifically at phosphorus.”

With a medium-to-low range of phosphorus soil test reading there is a 60 to 100 per cent chance of seeing a yield response to added P. For Alberta and Western Canada many soils are in the medium-to-low range. However, even if soil levels are on the higher side of the phosphorus equation, it’s important to know what the expected removal is that year, since phosphorus planning happens over multiple years’ time.

Currently most of the research that has been done with potassium is focused on barley, but as Boychyn says, we can expect a similar response on wheat.

“If we are 100 pounds or less — so 50 ppm or lower — we have about a 75 per cent chance of response to an application of potassium with that seed,” he says. “If we’re in that 100 to 200 range, we’re more likely in that 66-24 per cent chance of a yield response. And then if we are 250 pounds or more with potassium, the per cent chance of a response is around three per cent.”

But again, paying attention to removal will be key, as the potassium levels can’t be brought back in a single season.

Check out the full conversation between Boychyn and RealAgriculture’s Kara Oosterhuis, below:

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