Corn School: Fine-tuning 2022 nutrient application


With high fertilizer prices heading into 2022, corn growers can’t afford to over-apply nutrients. But they also can’t risk losing money by shorting the crop of its fertility needs.

On the season-ending episode of RealAgriculture’s Corn School for 2021, University of Guelph associate professor Dr. David Hooker returns to comment on this conundrum and share fertility tips and strategies.

In part one of this discussion, Hooker calculated the most economical rate of nitrogen for corn in 2022. First up on this episode is the important contribution phosphorus and potassium make to corn yield. He shares research from long term trials that highlights the yield hit growers can take when planting corn into low test P and K soils. In these plots, yields averaged 155 bu/ac. But when P and K is applied in a starter form (6-28-28, 90 to 270 lb/ac in a 2 x 2 band) yield increased to 186 bu/ac.

“That’s over 30 bushels per acre and that easily paid for that starter fertilizer,” says Hooker. “When soil tests are relatively low we need to pay attention and at least apply our P and K fertilizer based on the soil test recommendations.”

Hooker also notes how nitrogen performance is linked to potassium levels. He points to U.S. research that clearly shows that when K is deficient in the corn crop, N use efficiency drops. “In this case yields plateau and the most economic rate of nitrogen is actually lower when potassium is deficient,” he says. “So when we want the most out of our nitrogen dollar we also need to bring in potassium sufficiency. We really do need to fertilize according to soil test recommendations for potash in our soil.” (Story continues after the video.)

For 2022, split nitrogen application is another strategy growers need to consider. Hooker says applying 30 to 50 lbs of N per acre close to the crop row at planting will ensure corn has an opportunity to reach its yield potential. Growers then have to decide when to apply a second N application and the optimum rate.

Peak nitrogen demand for corn begins at the V6 growth stage. “If I had to pick a timing I would apply part of the N at planting  — 30 to 50 lbs — and then apply the balance between V8 and VT (when the plant takes up 50 percent of its N needs),” says Hooker. He adds that this strategy helps reduce environmental N losses and also allows growers to assess yield potential later in the growing season. If the crop has enjoyed good growing conditions and suffered minimal stress, growers can then apply an optimal second N application rate to maximize yield potential.

In the video, Hooker also discusses how and where nitrogen inhibitors and stabilizers fit in 2022 and their potential contribution.

Click here for more Corn School episodes.

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