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Managing nitrogen key for these farmers

Gil Gullickson 11/22/2010 @ 9:52am Crops Technology Editor for Successful Farming magazine/Agriculture.com

Remember the three Rs of your school days? Reading, w(R)riting, and a(R)ithmetic?

Well, Ron Alverson and son Keith, Chester, South Dakota, have their own R series -- the four Rs of nitrogen (N) management for corn.

  1. Right form.
  2. Right place.
  3. Right time.
  4. Right rate.

It’s not that easy, though. Pegging the optimal N rate for corn often mimics hand-catching a slippery salmon in a fast-flowing stream.

“N use is variable from year to year,” says Ron, who also farms with his brother, Larry. “One year, you may get by just throwing it on top in the fall and disking it in. You don’t lose any and get full utilization. Then along comes a year with a warm and wet spring, and you just get hammered with losses.”

That’s why following the four Rs of N management is so important for the Alversons.

“Nitrogen management is one of the biggest factors for corn yields,” says Ron. “If you do it right, the rewards are huge. We see it every year.”


Managing N Immobilization

Eastern South Dakota may be on the fringe of the Corn Belt. Yet, corn yields can compete with central and eastern Corn Belt states when all goes well. Glyphosate-resistant weeds are present but not as much as in some other Midwestern and Southern states. Less humidity also means less corn foliar and stalk diseases.

Still, management is key. “Managing N is not easy,” says Keith. Challenges the Alversons face include continuous corn residue resulting from planting corn on their acres four out of every five years in most cases.

“We’ve always grown more corn than soybeans due to our irrigation ground,” says Ron. Irrigation has been more conducive to corn than soybeans.

Still, the prolific residue corn-on-corn triggers can immobilize N, which makes it unavailable to corn plants.
“The recommendation over the years for continuous corn was to put 30 to 50 pounds of additional N on to overcome immobilization,” says Keith. “This assumes the average application where it is mixed in with N and dirt and all the stalk residue.”

The Alversons say they can get by with more moderate rates. “Our system overcomes the nasty effects of immobilization," says Keith.

Ridge-Till Keys System

That’s because ridge-till removes the N-immobilizing residue from the planting path. “With ridge-till, we clean off all the trash at planting, so the soil is pretty much black,” says Ron.

Removing the residue also enables seeds to quickly germinate and get off to a quick start. They build the 6- to 8-inch high ridges just before the corn canopies at an approximate 2-foot corn height.

Spoon-feeding N several times before and during the season to add 150 to 165 pounds of N per acre over the season also helps them obtain the most bang for their N buck. The Alversons first set a yield goal of around 175 bushels per acre of dryland corn and 210 bushels per acre irrigated.

In fall, they band phosphorus (P) and potassium (K) at soil test rates 3 to 4 inches deep laced with 10 to 20 pounds per acre of N.

At planting, they dribble 20 pounds per acre of actual N in a 28% N starter solution over the cleaned off row. A planter-mounted coulter from B&H Manufacturing aggressively tears trash out between rows and clears a strip for both seed and fertilizer.

“By dropping the starter on top of the black strip, the N doesn’t have a chance to be immobilized by stalks,” says Keith.

Sidedressing Starts Early

If soil conditions permit, the Alversons start sidedressing anhydrous ammonia as soon as the corn emerges. The Soil Doctor, a unit that measures soil nitrate N and N mineralized from organic matter, automatically adjusts N rates.
Environmental reasons first spurred the Alversons to start sidedressing, as a share of their land permits only small amounts of fall-applied N.

“When we apply when N is needed (when the plant is growing), there is less N loss potential,” says Ron.

Increased N-use efficiency is possible with sidedressing because N is applied closer to the time plants need it, points out Fabian Fernandez, University of Illinois Extension specialist. The window for potential N loss also narrows.

Burning can be a risk with anhydrous ammonia applications, particularly if application occurs within close proximity to the seed. By injecting anhydrous ammonia 4 to 5 inches deep right down the middle of their 30-inch-wide rows, the resulting buffers on both sides diffuse any anhydrous ammonia coming in contact with the young seedlings.

Timing is crucial. “We are equipped to get it done,” says Ron. They have three sidedressing rigs that quickly inject anhydrous ammonia over 2,000 acres of corn.

Wet weather can thwart N sidedressing if it’s too wet to enter the fields.

In 2010, they couldn’t sidedress one poorly drained field. To supply N, they applied dry urea (46-0-0) with a urea spreader over the top.

“That is risky because you need rain to move it into the root zone,” says Ron. Fortunately, forecasted rain did occur to incorporate the urea into the soil.

“If rain wouldn’t have been in the forecast, we would have dribbled (liquid) 28% N.” This would have been more expensive, but 28% N can better enter the root zone without rainfall.

Soils Matter

Initially, the Alversons figured that low-field areas were most productive. Accordingly, they would raise N rates in these areas. Meanwhile, they would cut back on hilltops, figuring they were lower-producing areas.

“The Soil Doctor just turned that upside down,” says Ron. “Those soils with higher yield potential had higher organic matter content and don’t need as much applied N. The N mineralization from organic matter is obviously higher.”

Consequently, the lower-producing areas had lower organic matter and needed more commercial N.

“Fertilizer N rates are not the primary determinant of corn yield in highly productive soils,” says Emerson Nafziger, University of Illinois (U of I) Extension agronomist. That goes against the grain, particularly in yield contests, where N rates of 250 pounds per acre and upward are common.

But U of I trials show little correspondence between corn yields and the N rate to reach those yields on corn following soybeans. There’s some evidence that higher N rates are needed for continuous corn, but this relationship is not strong, says Nafziger.

Instead, the bin-busting corn yields you see in yield contests are also keyed by soils rich in organic matter and ideal weather that helps mineralize organic matter. In some cases, yield contestants apply high N rates without accounting for soil organic matter to also provide N, says Nafziger.

The Alversons’ credit ridge-till continuous corn -- with its increased corn and stover yields -- as keys for improving soil organic matter levels.

“This would not be possible in a corn-soybean rotation,” says Ron. “In some of our long-term irrigated continuous corn fields, we have moved our soil organic carbon content up around .5% over the last 25 years. That doesn’t sound like much, but in the minds of soil scientists and agronomists, that is huge. The fact that we are adding to soil organic matter due to higher corn yields and conservation tillage has huge implications for Corn Belt soil sustainability.”

Corn stover also adds nutrients to the soil. At 2007 commodity prices, the late Wally Wilhelm, an ARS-USDA soil scientist in Lincoln, Nebraska, calculated these values for 1 ton of corn stover.

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