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Nitrogen basics for 2018

TAGS: Fertilizer
cornfield with yellow spots
SEASON AFFECTS PERFORMANCE: Yellow spots across this cornfield indicate heavier soils that stayed wet. More nitrogen loss may have occurred there. Wet seasons can affect N performance.
Here are reminders about forms of nitrogen used in corn, types of loss that can occur and much more.

One of the hot-button issues in the early 1980s was talk by a few agronomists claiming they could design nitrogen programs built around specific corn hybrids. Their premise was that hybrids respond differently in how they take up N and respond to N rates.

A few people bought into the idea. Many people wrote it off as untrue or not practical. One prominent university corn specialist, long since retired, wouldn’t consent to doing an article on the topic because he didn’t want to give it credibility.

The spotlight soon faded. However, some 35 years later, many seed companies can tell you which hybrids need nitrogen earlier than others. Some have data showing that certain hybrids respond to more nitrogen than other hybrids. The problem is they also have data showing that response is inconsistent from year to year. Weather is an overriding factor.

Brian Denning, an agronomist with Stewart Seeds, talked about nitrogen rates and other factors related to N at grower meetings during the off-season. He also discussed Agronomy in Motion, or AIM, research, which he helped carry out.

Basic nitrogen facts
Here is a brief primer on nitrogen based on information provided by Stewart Seeds. Some of this information comes from the 2017 edition of “Stewart Seeds AIM Agronomy Results.”

• Denitrification. Nitrogen-loving bacteria that thrive in water-saturated soils without oxygen convert nitrate-N into gaseous forms of N. N gas can be lost by volatilization. Under severe conditions, loss of nitrate-N by this method can amount to up to 5% per day.

• Leaching. This process allows water to move nitrate-N down through the soil until it is out of the root zone. Some of it can reach tile lines and become lost from the field. It’s more common on coarse-textured soils when lots of rain occurs. Denning says both UAN and nitrate-based fertilizers are prone to leaching.

• Volatilization.  This is the loss of nitrogen in gas from the soil. When urea-based fertilizers are applied on the surface and not incorporated by rain or tillage, up to 20% of the urea-based N can volatilize and be lost within a week of application in warm, sunny weather. 

• N rate by hybrid. Denning says in a replicated test in 2017, two different hybrids, both refuge-in-a-bag brand blends, produced peak yield at two different N rates. One peaked at 180 pounds per acre and the other at 220 pounds per acre. This showed that nitrogen utilization varies by product. However, Denning says this and other studies show it also varies by environment.

This site received heavy rains early, but then only a total of 4 inches after July 10. Denning cautions that since it was a single study at one location, broader conclusions about nitrogen use trends of the two hybrids can’t be made. In other words, just because there was a significant difference in 2017 between N use and hybrids at that location doesn’t mean it would happen on your farm in 2018. The study indicates that nitrogen use efficiency of a hybrid varies based on specific environmental conditions, Denning concludes.  

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