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John Kempf

Nutrient Application Timing

The best way to reduce our nutrient applications by 30% – 40% or more is to time application so the product release curve matches the crop demand curve.

We know that many crops will have a  nitrogen and potassium demand peak during fruit or seed fill.

A peak calcium demand generally occurs during the cell division stage in the weeks immediately after blossoming and pollination.

If you have a crop with a high calcium demand, consider using gypsum as a calcium fertilizer, not simply as a calcium soil amendment. The difference between the two uses is application quantity and timing. (and intent)

Using gypsum as a calcium fertilizer you might apply 100-200 lb per acre of a pelletized gypsum 30-45 days ahead of calcium demand peak. You would choose this timing because the calcium release curve of gypsum begins peaking in this time frame and then begins dropping off about 90 days after application.

Applied products don’t all release on the same curve. While there are variations because of particle size, temperature, and soil moisture, you can find general guidelines of when a product begins supplying nutrients.

For tree fruit crops, which bloom right after breaking dormancy, a gypsum application would need to be applied late winter or early spring so the calcium peak occurs during and just after pollination.

For a crop such as sunflowers or millet that blooms in late summer, a fall application of gypsum delivers just a fraction of the crop benefit as a spring application because the calcium release peak occurs before the crop demand.

Different potassium and phosphorus fertilizers all have different release curves.

We observe significant economic gains from managing nutrient application timing. This seems like an obvious point and is one of the best ways to get a bigger crop response with smaller nutrient applications.

It is also a single entry on the long list of reasons why nitrogen applications in the fall for the following years crop are a thoughtless and ill-informed choice.