The Agronomists, Ep 13: Peter Johnson and Jeff Schoenau on seed-placed fertilizer strategies


If you’re not putting some starter fertilizer down at seeding and planting, you could be leaving yield potential on the table. But there are risks to seed-placed fertility, and just how much is too much depends on several factors including soil type, fertilizer type, crop species and more.

For this episode focused on all things early fertility, host Lyndsey Smith is joined by RealAg’s own Peter Johnson, and professor of soil science with the University of Saskatchewan, Jeff Schoenau.

Catch a new episode of The Agronomists every Monday night at 8 pm E! 


  • “Wheat Pete” has his own agenda, he wants a hat. But really, he comes up with “the things” to talk about (sometimes)
  • Ok, we’re talking phosphorus, potassium, and even sulphur
  • Seed-placed fertility risks. Jeff starts with phosphorus because it’s immobile, it has to be close to the roots of seedlings, “pop-up”
  • Cereals are the most tolerant to P2O5 in the seed row. 40 to 50 lb actual
  • The higher the yield, the more phosphorus will be removed. Strategize how P will be left over for the next crop, building fertility. Don’t let it get stranded on the surface or left there to fertilize weeds (heaven forbid!)
  • Canola and peas are pretty sensitive.
  • Jeff shows us a handy diagram, created by one of his MSc students (M. Shao) on seed-bed utilization. Very useful concept! Opener width/row spacing
  • Don’t push the limits of maximum safe rates.
  • How much can I put down? What’s the maximum rate we can chuck down with the seed?
  • There’s a similar concept for Ontario, they just don’t call it Seed-Bed Utilization
  • Salt effect: soybeans, peas, more sensitive than cereals to starter fertilizer
  • Dry sand? Can’t take as much starter fertilizer, not as much as a wetter clay. Publication 811
  • First clip — Wheat School: Boosting yields with seed-placed phosphorus
  • The plant can only take up ortho-phosphorus. Poly-phosphorus is a whole bunch of molecules strung together. The fertilizer has a higher affinity for water than the seed, so seed-placed starter fertilizer has to imbibe water before the seed can catch up and uptake can start. Pete explains.
  • Soils with high amounts of extractable or available P, there’s still a response to P, especially in cold soils or when phosphorus and potassium uptake is restricted. Heavy textured clay soil with a massive structure limits P ability to move through mass diffusion
  • Soils that are deficient in P, especially with cereal crops, that P can hasten maturity — heads more evenly, makes for better
  • Soil pH of 7.5 or 8.0 (or greater), highly calcareous will affect how P will “fix” or get bound to soil. Soil pH will matter.
  • The rhizosphere of the crop is also important. Microbial inoculant like Pencilium bilaii can help take up any residual P
  • How deep is too deep, if you are banding the starter in a secondary operation to seed? Pre-seed banding app of P and N together. Root proliferation a bit deeper down in the soil where the moisture is. 3 to 4 inches for a pre-seed band app. It also means that the seed needs to get to it quickly though.
  • Pete brings up the relay method… something to think about
  • Is there a difference between N vs P vs K, as it relates to depth? Yes!
  • Second clip — Corn School: Maximizing yield with dry or liquid starter fertilizer
  • Dry set-ups vs liquid set-ups. Switching between the two, how do you make that decision? What’s your base fertility, how many acres do you have to cover?
  • How much MAP to you need to apply to increase your available P by 1 ppm if you’re building fertility? This is for a peat soil! Those high organic matter, soils lacking in minerals can bind lots of available P but release it as well.
  • Phosphorus applied with a John Deere 750 box drill? No fertilizer capability, so the fert’s mixed with the seed. It can be done, but make sure the seed cup is on setting 2, if it’s on setting 1 it’ll grind up the mix and just turn into a mess.
  • Using a fertilizer to decrease the pH of a high pH soil? Ammonium sulphate tend to be acid forming, and in a calcareous soil that can help to bring the pH down, but Jeff also brings up that putting ammonium sulphate down in the seed row that there would be additional damage from salt-effect and free ammonium.
  • Those low soils with low pH can cause problems with Rhizobia inoculant for peas, lentils, faba beans
  • What is the best way to build P in deficient soil? Invest in your soil’s bank account. A split application might be a good strategy.
  • Liquid phosphate placement? Can get damage from that too close to seed just as easily as dry P.
  • Can phosphorus or potassium soil test levels be too high? Manure is an excellent source of K, repeated apps can have high K test levels, especially in relation to Ca or Mg. Forage would be susceptible to that, if fed to livestock, bad news bears — grass tetany. Phosphorus, don’t normally think of direct toxicity. Zinc deficiency is a possibility, especially on eroded knolls.
  • How do we navigate all the new products coming on? Biologicals or enhancers. Test plots everyone, set them up with enough replications so you can even run some basic stats on the data. Sort out what works and what doesn’t and make sure your soil test levels are maintained.
  • Third clip, even though they didn’t get to it during the episode, you should still check it out — Canola School: Management of nitrogen, phophorus, and sulphur

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