By Aaron Saeugling

Beginning in late May and early June every year, my phone begins to ring with numerous questions concerning the physical appearance of corn. With more technological advances in equipment, hybrids and herbicides, we strive for the perfect stand of corn. Discussion soon turns to fertility and nitrogen management.

As farmers and agronomists, we really need to step back and refer to basic nitrogen cycle charts to understand specific soil, weather and forms of fertilizer applied to discuss maximizing nitrogen availability to our corn crop. The more we try to speculate and control nitrogen in the soil, we soon realize Mother Nature and soil type have the trump card and will not reveal that until the fall harvest.

Despite all the technology, one basic premise we need to understand is that the word nitrogen is actually generic. For an in-depth look at nitrogen management in Iowa, I recommend reading “Nitrogen Use in Iowa Corn Production,” CROP3073, an ISU Extension publication. What we are discussing in most Iowa soils is the uptake of the nitrate or ammonium forms of N. The corn plant will harvest this nitrogen from the soil. We need to understand the conversion process, and how soil and moisture play a bigger role than we sometimes want to admit.

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Looking at cornfields in late May and early June that have a less-than-excellent appearance, we begin to turn to inadequate nitrogen as a symptom. Notice, I said symptom, not cause. This would be the part of the service call an agronomist makes that may feel like an interrogation for a farmer. Each and every field is different across the state, and most farm operations vary with their specific management style.

Predicting nitrogen needs
Several tools attempt to predict nitrogen usage for corn, and some tools may be more accurate than others. However, we need to keep each field as a separate database for future management. With the ability to track yield history and nitrogen application rates with technology, we can improve our odds of managing nitrogen. Just keep in mind nitrogen prediction models are just that — a model! Without the ability to track actual soil nitrate levels in fields, we are merely guessing.

Where practical and timely sidedress applications are possible, the use of the late-spring soil nitrate test can increase your odds of successful nitrogen management. For guidelines on how to properly use this test, you should refer to another newly revised ISU Extension publication, “Use of the Late-Spring Soil Nitrate Test in Iowa Corn Production,” CROP 3140.

Now back to those early-season corn service calls. Questions about the need for more nitrogen, and avoiding nitrogen deficient corn, come up for discussion. This soon turns to the painful discussion of patience. We need to focus on the initial amount of nitrogen applied and weather conditions after application. What we are attempting to predict from a visual standpoint is how much nitrogen does it take to avoid this uneven color appearance with corn plants? While I have no magic wand to wave, often tillage, crop residue and corn emergence patterns become apparent and contribute greatly to the “pattern” seen in most early-season cornfields.

Springtime rainfall key factor
Springtime rainfall is a key factor to pay attention to, as it can help identify when we may have the need to apply additional nitrogen. The best tool to consider is your local rain gauge or possibly a weather app on one of those fancy smartphones. When we begin to reach the threshold of 16 inches of rainfall occurring after March 1, we need to ask ourselves where some of our nitrogen went. For a refresher of the impact of spring rainfall, refer to a June 6, 2016, ICM news article Precipitation and nitrogen this spring. It’s available on the ISU ICM newsletter website.

The two ISU Extension publications we’ve mentioned and this ICM news article are helpful in understanding nitrogen management for corn. The No. 1 thing I want farmers to realize is the fact that nitrogen is a moving target, and no silver bullet has been developed that consistently will 100% accurately prescribe the magic application rate needed every time. While we continue to increase our odds of predicting an acceptable application rate for N, Mother Nature always has the last laugh.

Saeugling is the ISU Extension field agronomist for southwest Iowa. Contact him at [email protected].