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The Challenge of Nitrogen

December 8, 2012
By: Darrell Smith, Farm Journal Conservation and Machinery Editor
p38 The Challenge of Nitrogen 1
Successful nitrogen management requires applying the right amount of nutrients in the right place, at the right time. It also involves assessing the risk of those nutrients being lost on various soil types throughout the season.  

In your quest for high yields, nothing is more crucial, or more difficult, than managing corn’s most important nutrient

After coping with the worst drought in decades, most farmers couldn’t wait to get whatever corn  they had harvested off their hands. While some of their frustration was sent down the line with the grain, complications still linger.

Because parched plants can’t take up nutrients, there’s a gold mine of nitrogen fertilizer buried in corn fields. The kicker, though: it is in the highly mobile nitrate form, and only the best crop managers will be able to carry these valuable nutrients over to the next corn crop. Mother Nature will play a large role in the success rate.

"You might be able to underapply phosphorus or potassium and still grow a good crop," says Farm Journal Field Agronomist Ken Ferrie. "That’s not so with nitrogen. It’s not just applying the right total amount—it’s having nitrogen present at crucial times in the crop’s life, all season long. Nitrogen management requires timing, placement and managing risk.

"From emergence to knee-high, you need to ensure that nitrogen doesn’t fall below 10 ppm [parts per million] in the top 12" of soil," Ferrie says. "From knee-high on, after the corn roots have some depth, you want to maintain 20 ppm of nitrogen in the top 2'."

That requires a basic understanding of nitrogen processes and the products you apply. Knowing your product will help ensure nitrogen is used by corn plants and not lost as a gas or leached away by water, downward into groundwater or laterally through tile lines into drainage ditches. Lost nitrogen not only costs yield, but nitrogen in water sources causes environmental problems as well.

There are a variety of nitrogen products available. "Anhydrous ammonia is the basic ingredient of all these products," Ferrie says. "It can be applied directly to the soil or used to create other products."

Besides anhydrous ammonia (a gas, shipped under pressure in the liquid form), the most common nitrogen fertilizers are urea (a solid), ammonium nitrate (a solid) and urea-ammonium nitrate (UAN) solutions. Other solid products include potassium nitrate, calcium nitrate and ammonium sulfate.

Corn production requires ammonium and nitrate, the only forms of nitrogen plants can use. However, Ferrie says, "plants need larger amounts of nitrate. Inside the plant, nitrate is stored in bulk and translocated to help with ear fill."

Calcium nitrate and potassium nitrate fertilizers are in the nitrate form, Ferrie explains. Ammonium nitrate is half ammonium and half nitrate. But anhydrous ammonia and urea must be converted to ammonium and nitrate after you apply them.

Prevent nitrogen loss. Nitrogen management is a challenge because the ammonium form of nitrogen is fairly stable in the soil, but the nitrate form is easily carried away in water. That’s because the ion carries a negative charge, which repels negatively charged soil particles.

You need to make nitrogen available to your corn plants all season long, but if you provide nitrate too far ahead of time, it might be lost before they can use it.

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FEATURED IN: Farm Journal - December 2012

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