Performance, ROI Come Down to Timing, Testing

As seen in Illinois Agrinews on June 12th, 2015

ASHKUM, Ill.—As crops are emerging across the Midwest, growers who hold different nitrogen-management views and techniques all generally share the same question: “Do I have enough nitrogen to maximize my yield?”

The good news is, even after emergence and faced with the typical unknowns about the weather ahead, growers still have options.

Application Rates and Methodology

Multiple studies and on-farm reports point to a sound rule that says for every bushel of yield, a corn plant demands approximately 1.3 to 1.5 pounds of actual nitrogen. In Illinois, where 200-bushel fields are rather mainstream, this 1.5 conversion rate translates to somewhere in the neighborhood of 300 pounds of actual N necessary to achieve a full-season effect.

Whether relying on a commercial fertilizer or an organic source, growers are generally better served with a management program that calls for applying about 60–70 percent of nitrogen at the pre-plant stage or, at least, early in the growing season, before seeding starts. Then, the remaining 30–40 percent ought to come in behind that prior to the V8 developmental stage or 30-inch tall corn.

The product options at this point, depending on the grower’s preference, run fairly wide—whether a UAN solution, ammonium nitrate, urea or anhydrous—but the corn’s growth stage has some influence here (see illustration) and the goal is simple.

To maximize that nitrogen dollar, growers should time the supply as close to tasseling as possible, when corn is processing its largest amount of nitrogen uptake.Source:, type and timing for sidedress, May 11, 2015

The Most Underestimated Program Component

As with reaching any goal, however, the key is knowing what the starting point is—in other words, getting a clear idea of a field’s current nitrogen profile before making any application decisions.

Using a popular technique known as a pre-sidedress nitrate test (PSNT), growers should pull 15 to 20 core samples at a minimum 12" depth—24" is ideal—avoiding areas where starter fertilizer or nitrate banding has already been applied. Mix the soil together and take the sample to a reliable lab for a nitrate test.

 If the results register greater than 25 parts per million (ppm), the field should have enough nitrogen to finish out that crop and achieve top yield potential. If results register 24 ppm or less, growers can make an educated sidedress application based on growing conditions, planting date and the field’s historical yield potential (see the chart).


Source: Purdue University Cooperative Extension Service, Agronomy Guide, AY-314-W, April 2003]

Jordal, Sean. "Full-Season Nitrogen Effect". Illinois Agrinews. June 2015. B5. Print. 

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