Two Routes For Late-Season Nitrogen

July 11, 2016 02:00 PM
 
Two Routes For Late-Season Nitrogen

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By Aimee Cope and Charlene Finck

The nitrogen (N) landscape is changing briskly. The number of tools to assess the amount of N available to the crop and the options for making late-season applications are growing while the environmental pressure is wildly different and escalating. Add that many of today’s hybrids respond more strongly to late-season N than previous hybrids, and it’s no surprise the way farmers approach their N programs is rapidly evolving. 

Some farmers play catch-up with their N program by using a rescue approach, while others have a formulated, planned program.

What Ken Ferrie Thinks 
You Need to Know
Make sure you understand the nitrogen cycle and how environmental factors impact the amount that is ultimately available to the crop. 
The amount of nitrogen needed by corn varies by the growth stage of the plant. 
Plan to never let corn have a bad day, but if it happens, react to get nitrogen on pronto. 
Today’s tools—nitrate samples, tissue samples, stand and projected ear counts, aerial imagery and computer modeling—are no substitute for in-field scouting.

“Each approach has its place,” explains Ken Ferrie, Farm Journal Field Agronomist. “In either scenario, it’s essential to not only take care of the plant on the front end, but to monitor the N system—to keep an eye on potential midseason loss and supplying power of the soil. On the back end, you want to ensure the crop has a strong finish. No matter what, remember: Never let corn have a bad day.” 

Tissue samples; nitrate tests; aerial imagery, including satellites, planes and drones; soil mineralizable nitrate tests; nitrogen sensor technology; chlorophyll readers; and computer modeling are some of the tools that can be used to determine how much N is available for the crop—and by extension, how much N to apply. At the same time, be sure to scout the trouble spots. That’s because N deficiency has some look-alikes in today’s tools. Those include sulfur deficiency and saturated soils, among others. 

Planned programs that automatically build in a late application are good for fields that are at high risk of running short of N. High-risk fields have heavy clay soils, sands or highly variable soil with poor drainage. 

Fields with high clay content soils run into trouble after heavy rains, when the clay hangs onto the water, leading to denitrification. On the opposite end of the spectrum, sandy soils are a high risk for leaching—especially with big weather events. 

Late-season N applications can be made with fertigation through center pivot systems. “This is especially effective with sandy soils,” Ferrie says. “Some guys are not set up to or refuse to put N through their center pivots because they’re worried it will rust up the pivot. But if fertigation is possible, putting 20 lb. of N on every other turn of the pivot will make a big difference.”

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Another option is to fly on granular N with a plane or helicopter. 

With a planned program, N applications are staged to give corn a steady diet of N. For instance, put a portion of your N down pre-emergent, sidedress another application at V5 to V7, and add a last dose between V10 to tasseling. The later you make the final application, the more N needs to be put on in the front end versus the back end. 

A well-rounded N program begins with split-applying N throughout the growing season. This planned approach is based on a field-by-field basis. When farmers split N applications, Ferrie says, they pick up 10% efficiency by applying closer to the time when the plant will use those nutrients—making it easier to manage loss. The key to splitting N applications is to sidedress green corn.

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 Fields that only occasionally run short on nitrogen  might not require a late-season application  automatically built into a fertilizer program. Even  so, you need to be ready to add one if Mother  Nature throws you a curveball that undermines  yield potential. 

“If a farmer is not going to do a late application, I like to have half to two-thirds of N up front—to take care of the vegetative stages—then sidedress for earfill,” Ferrie says. “When corn shows a strong visual response right after sidedress, it’s telling you there wasn’t enough N for the vegetative stages and growth was slowed. In an ideal program, you’d sidedress dark green corn that doesn’t need that supply of N for weeks out. As a program, we always want corn to have a good day, and we always want the plant to have the N it needs.”

After several years of playing catch-up with his N program, Aaron Gingerich, who grows corn and soybeans near Lovington, Ill., decided to switch from a rescue N program to a planned program.

“We were putting on all the N needed in the fall, and we’d lose those hot spots,” Gingerich says. “We’d come back then put on extra in those areas.”

Since 2009, Gingerich has modified his N program to include pre-emergence and sidedress applications. Today, 50% of his N is applied pre-emergence and the remainder is with a variable-rate sidedress pass.

Planning a variable-rate nitrogen program should begin after harvest. First, use yield maps to pick out high-risk areas within management zones. “It’s trusting in the yield zones and management zones you created after years of collecting data for each field that make variable-rate N possible,” Gingerich explains.

He estimates he saves 8% on his N costs each year by using variable-rate application methods.

Depending on your ability to get your nitrate sample results turned into an application map, Ferrie recommends pulling soil nitrate samples two to four days before you want to sidedress. The nitrate test should be your baseline, but depending on cost and the turnaround time, you can also get the lab to measure the ammonium level in the soil. Nitrate and ammonium are the two mineral forms of N the plant can pick up.

At the same time, tissue tests can provide a snapshot of the concentration of N in the plant. 

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  In a planned program where you are  staggering your nitrogen  applications and implementing a  late-season pass, the payback might  not be in increased yields but in  reduced nitrogen usage per bushel.  

“To determine N supply and demand, consider soil availability and plant uptake. You—or the soil—need to make up the balance in between,” Ferrie explains. “Do stand counts. Predict your yield potential. Then you can calculate the rate you think you need.”

A rescue program can be used with fields that only occasionally run out of N. These are often loam soils with good drainage and water holding capacity. In cases like this, N loss is minimal and the additional application cost of a late season dose might be hard to pay for. 

“If you only run into a rescue situation, one of every five years or even one in every 10 years, you’re better off staying with your existing N program and monitoring the crop for problems,” Ferrie says. “A big rain or a prolonged wet season can create the need for another dose of N.”

When that happens, the more timely your response is, the more bushels you will be able to save in the end.

Let nitrate samples guide what’s needed. Be strategic on your sampling starting with high-risk areas (low spots, sandy areas and spots with sidehill seep). If those areas are okay, there’s a good chance the rest of the field will be fine. 

Keep in mind nitrates move up and down with the water front, especially after a rain or irrigation. Also, the plant can be pick up as much of 10 lb. of N per day from the soil.

While all the new tools farmers can use are valuable and can point to the need to apply rescue N, they are no substitute for in-field scouting. The findings from today’s cool tools need to be ground truthed. 

“We’d all like to have a magic bullet that is a precise science, it isn’t here yet,” Ferrie says. 

And, he cautions, it is important to tailor N use to match the specific yield potential of the field. 

“N is a critical component of yield, but it is not the only factor,” Ferrie explains. “Be sure to determine the yield potential of the crop before applying more N. 

“Ultimately, you’re looking for the highest ROI per acre and what’s best for the environment. For some farmers, the payback for the late-season application might be reduced N usage while maintaining yields.”

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