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Maximize nitrogen with multiple applications

Back in 2014, one of Wayne Johnson’s employees was sidedressing 32% nitrogen (N) as corn neared the tasseling stage. Late at night, the employee ran out of 32% N with one more round to go. 

“He called and asked if he should come back home and fill the tank and finish up the round,” recalls Johnson, who farms with his son, Lucas, near Forest City, Iowa. “I told him to come home, as we would just use it as a test plot for the season and see if there was any difference at harvest.”

There was. 

“Those spots that we didn’t sidedress yielded 28 bushels per acre less,” says Johnson. “I didn’t have a lot of hope for that crop, as it was super wet in June. But applying 32% N at that late date was absolutely the right thing to do.”

Spoon-feeding Nitrogen

Nitrogen applications used to be a one-shot-and-done deal. No more. These days, a corn hybrid takes up 37% of its N between tasseling and black layer, says Travis Kriegshauer, senior services manager of Encirca Services for DuPont Pioneer. That late-season shot of N can help corn hybrids realize their full yield potential going into this stage.

Spoon-feeding N in several shots also eases environmental concerns. Nitrogen unused by corn that converts from the ammonium to the nitrate form of N can end up in tile lines and ultimately drinking water. Matching N with crop uptake can help reduce this possibility. 

Then there are economics. Shrinking crop margins make it imperative that every pound of N that’s added goes to your corn.

“If we apply too much N across our farm, that’s the equivalent of $25,000,” says Johnson. “So, we squeeze it down, using tools that measure applications tightly. It’s all about business.” 

Trying to match N uptake with rapidly growing corn, though, is akin to catching a slippery salmon through a fast-flowing mountain stream. 

“You never want to be caught short,” says Johnson. 

Spoon-feeding N in several increments can help to ensure N is present when corn needs it – but not at excessive levels.   

“Rather than putting a whole bunch of nitrogen down at one time, we apply it as the plant uses it,” says Johnson.

Application rates can hinge on a soil’s organic matter. Soil organic matter is a reservoir of N. University of Minnesota data show that a soil with 3% organic matter can house about 3,000 pounds of N per acre.

Trying to peg how much N annually can be gleaned from organic matter is difficult, though. In Minnesota, decomposition rates are typically about 2%. Thus, in 3% organic matter soils, corn can access about 60 pounds of N and 6 pounds of phosphorus per acre from soil organic matter.

There are hurdles that compound this, though. “Organic matter is inconsistent across a field,” says Johnson. 


A tool that accurately predicts mineralization doesn’t yet exist. The Johnsons use several tools to help them apply optimal N rates. They use a FieldView Pro product from The Climate Corporation to assess soil N status. 

“It helps us know when to apply N, and it enables us to be better stewards of the land,” says Lucas Johnson. 

Soil samples are also teamed with Iowa State University’s N calculator to N application strategies. The Johnsons use these tools to guide them through their fertility program. For example, soybean ground that’s going into corn gets an N credit of 40 pounds per acre.  

After harvest, they apply either 18-46-0, poultry litter, or hog manure. The hog manure is buffered by Instinct II. This N stabilizer helps prevent N in the manure from converting from ammonium-N to the unstable nitrate form prone to leaching. It also aids slow release of the N contained in the hog manure. 

Once the growing season starts, the Johnsons aim to space out N applications every 30 to 45 days. 

They apply a 6-gallon-per-acre rate of a 10-34-0 starter at planting. Starter fertilizer gives corn plants an early start in cool spring soils. 

They then later apply around 75 units per acre of 32% N with post-emergence herbicide. 

Late-season n

As corn continues to grow, a critical decision soon arrives: Apply late-season N or not? 

In a drought year when a mediocre crop is on the way, it’s an easy choice. More N won’t bail out corn. 

In a year where an inch of rain falls like clockwork every week amid constant 86°F. temperatures, though, it’s a no-brainer. 

It’s tougher in those in-between years. It might work; it might not work.

Then there are the challenges of entering the field. The Johnsons come into corn with a high-boy with an N toolbar that drops 32% N via the Y Drop on the ground next to cornstalks.

This isn’t always easy. Rainfall can prevent a rig from entering the field.

Normally, the Johnsons aim to finish sidedressing by June 20. Applications can occur later, though. 

The first year the Johnsons sidedressed N, the earliest they could apply it was on July 6. 

“That scared me to death, but we got N on all the acres we needed by sidedressing during the month of July,” says Wayne Johnson. “One of the problems with tall corn is if it doesn’t dry out, you can get stuck. To get another tractor to pull it out, you destroy crop.”

Overall, though, the FieldView Pro tool has helped guide them. It alerts them to N levels in the soil throughout the growing season. This helps monitor a 25- to 50-pound-per-acre buffer while they decide whether or not to add a late-sidedressed N application.

“I don’t want to be caught short 25 bushels per acre in yield,” he says. “In most years, that can mean the different between profit and loss.”

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