Make A Nitrogen Plan

Balance the “4Rs” for each field to improve fertilizer efficiency.

By Jason Jenkins | Photos By AGCO Corp.

Dan Emmert knows it. So do the corn growers he advises.

“The soil is a terrible place to store nitrogen,” says the southwest Indiana-based field agronomist for Pioneer. That’s why he helps growers plan and implement the “4Rs” of nutrient stewardship: putting the right source of fertilizer at the right rate at the right time in the right place.

Even though nitrogen management practices have changed for the better in the past 25 years, quite often, more of this essential nutrient still is applied to fields than is needed to nourish the corn crop as a hedge against potential environmental losses. That may have penciled out as a low-cost “insurance” in the past, but with today’s rising input costs and low grain prices, it’s a strategy that many growers say they can no longer afford to employ.

“Nitrogen management is one of the most delicate balancing acts of all the decisions for corn production,” Emmert says. “Even within a producer’s operation, there can be variations from field to field that’ll make a huge difference in how nitrogen is handled.”

Emmert recently completed a review of agronomic research related to the form, timing and placement of nitrogen fertilizer in corn. While no one-size-fits-all approach exists for managing nitrogen, Emmert says that, based on the latest research, growers who consider weather patterns, soil types, and labor and equipment availability can feed their corn crop more efficiently and economically.

The Right Form

When fertilizing corn, producers can choose from a number of nitrogen sources. Each has advantages and disadvantages, Emmert says.

Anhydrous ammonia remains popular because it is the slowest of all nitrogen forms to convert to nitrate, at which time it becomes subject to leaching and denitrification. However, anhydrous must be injected and can be hazardous. Conversely, urea is safe and easy to handle, but it is prone to large losses through volatilization if it’s not incorporated into the soil or used with a urease inhibitor. Polymer-coated urea is less prone to volatilization, but it’s more expensive. Urea ammonium nitrate is more stable than urea, but it still can be lost through leaching and denitrification, as well as volatilization.

“Growers need to consider both the price of nitrogen and the logistics of getting it to the field and applying it,” Emmert says. “Take into account your predominant soil types, and figure out your limiting factor. Are you on sandy soil where leaching is an issue? Is it poorly drained soil where your biggest problems are denitrification and just getting in the field? Adjust your strategy to overcome those factors.”

The Right Time

According to Emmert, the best time to apply nitrogen to corn is just before the crop needs it. This limits risk of nitrogen loss and maximizes nitrogen efficiency, allowing a grower to apply less. Understanding when a corn plant needs nitrogen can help determine the timing.

While corn uses less than 10% of its total nitrogen needs prior to the V5 stage, yield potential can be reduced if nitrogen is applied too late and a deficiency occurs. “Corn grows rapidly from V6 through tasseling and is determining potential ear size, so it’s crucial to make sure the plant has all the nitrogen it needs then,” Emmert explains.

“However, research shows that 37% of the total nitrogen need is taken up after tasseling. So whether you’re doing a preplant application or spoon-feeding, you want to make sure there is enough nitrogen available beyond silking that the plant can put into the grain.”

In southwest Indiana, Emmert sees many adopting split nitrogen applications. Some are moving away from preplant nitrogen altogether, while others are moving at least one application later in the season. “That’s the biggest trend in nitrogen management right now,” he adds. “If they put nitrogen on in-season, they may be able to reduce their [overall] rate by 10%.”

The Right Place

Placement is just as important as timing and form when managing nitrogen needs. Emmert says even though the soil may be a terrible place to store nitrogen, it does help protect against volatilization.

“Nitrogen efficiency will be influenced by the nitrogen source and its placement,” he says. “Nitrogen that’s injected or incorporated will be less vulnerable to loss. Banding fertilizer rather than broadcasting it also is more effective.”

The Right Rate

By understanding the loss mechanisms that influence nitrogen fertilizers, and by optimizing timing and placement, growers can increase nitrogen efficiency and decrease rates.

Conventional wisdom once held that corn required 1.2 pounds of nitrogen for every bushel. “But what we’ve learned in the past 10 years is that it actually takes much less than that,” says Corina Ardelean, marketing manager, AGCO Commercial Strategic Initiatives. “It only takes 0.8 pounds or even 0.7 pounds. If we implement these best management practices, it allows us to maximize nitrogen use and still grow record yields.”