The Agronomists, Ep 111: P & K for soybeans with Horst Bohner, Megan Bourns, and Don Flaten

Soybeans showing K deficiency (Photo credit: M. Bourns)

When it comes to soybean fertility, there are many different pieces of the puzzle we could look at.

Tonight’s episode of The Agronomists focuses particularly on P and K management. Do starter and pop-up fertilizers make a significant impact on soybean performance compared to just broadcasting the crops’ nutrient needs? When do we soil test ahead of beans, and will soybeans respond?

Host Lyndsey Smith is joined by Horst Bohner of the Ontario Ministry of Food and Rural Affairs (OMAFRA), Don Flaten, retiree from the University of Manitoba, and Megan Bourns of Kansas State University.

This episode of The Agronomists is brought to you by ADAMA Canada, The Sharp Edge, and the Soybean School!



  • Don is recently retired, but still so happy to talk about research. Still fairly active on research boards
  • It’s wet in Ontario, but the forecast going forward looks good — so we’re rearing to go
  • Corn is emerging in Kansas
  • Phosphorus and potassium management can be difficult, because we don’t always get the response we’d think we would
  • Soil tests have taken us a long ways in understanding potassium and phosphorus
  • We might not talk about potassium as much as we should…it’s so incredibly important
  • Potash and potassium are buddies!
  • There are different tests for phosphorus, depending where you are
  • It’s pretty easy to grow 30 bushel beans without fertilizer…not so easy to grow 100 bushel beans
  • Background fertility might be more important than applied fertilizer
  • Soil types play a huge part in this, in regards to all crops — soybean is very good at accessing soil P and K
  • Megan has run trials in Manitoba and now Kansas, so she understands the difference that soil types play into all of these responses. She wishes she could find the same Ontario bean response to K in Manitoba!
  • Also a lot of surface broadcasting in Kansas, like Ontario. So we have to think about how we apply it
  • Is there a negative to having zero phos in starter on a high soil test?
  • Are soybeans similar to flax with pea acquisition?
  • Soybeans outshine flax, oats, and canola when it comes to the uptake of soil phosphorus. Up to 2x!
  • Mineralogy makes a difference
  • It’s important to make sure the P & K are balanced, and managed across the rotation
  • Soybeans hog the P & K
  • Thinking of the future of the soil is important, even if you are towards the end of your career…
  • Are beans and peas interchangeable in their response to P & K. Generally the responses are less frequent in other crops than in soybeans
  • Spring temp swings is something we have to pay attention to more than the temperature date

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