Varying Planting Populations

Once you have established management zones, the next step is to vary planting populations by zone. The basic guidance is to plant higher populations in your better fields, and lower populations in your poor-performing ones. But as Margy Eckelkamp explains in the following article, there are important nuances to this approach.

By: Margy Eckelkamp, Farm Journal Media

When a field is planted to a uniform population, the farmer settles for the happy medium, explains Farm Journal Associate Field Agronomist Missy Bauer. If he increases or decreases populations based on the soil's potential, he may see much better yields.

"By using what we know about our management zones, farmers can prescribe planter populations for maximum yields with more confidence," Bauer says. "This is no different than manually lowering populations on the sand hills, for example. When we use prescriptions overlaid with management zones, it’s much more precise."

The momentum behind variable-rate populations has never been greater, thanks in part to a push from service providers such as Monsanto FieldScripts, Pioneer Field360 and the Winfield R7 tool. These tools help farmers make better data-driven decisions in the field.

Many of the same factors guide variable-rate population decisions that influence the mapping of management zones.

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"To start, farmers should factor in their soils, yield history and productivity of the zone," Bauer says. "Is it a high-, medium- or low-yielding zone? What’s your soil data, cation exchange capacity, organic matter and water-holding capacity? The overall philosophy is to enable farmers to increase populations where there is higher water-holding capacity and decrease population where there’s lower capacity."

There are two ways to gain yields using variable-rate hybrids. The first is to maximizing the good ground and reduce population in poor soils. But variable-rate population can also maximize a soil’s water-holding capacity and improve yields.

"With today’s technology and machi­nery, variable-rate populations by management zone have never been easier to execute," says Jack Hardwick, regional agronomist with AgriGold Hybrids in Missouri and Illinois. "In fact, it’s setting up your management zones and layering data that requires most of the work and time."

Hardwick advocates that farmers seek out advice and help from a local team of experts, whether that be the dealer who sold the desktop software, an ag retailer, a consultant or your seed rep.

"For example, when you write your population prescription map with your seedsman, you’re drawing on their expertise, as well. Together, you can really bring out the potential of a field," he adds. "It’s not an easy task to bring all of the pieces together. Farmers shouldn’t hesitate to ask for help with file transfer from their desktop to the tractor cab. File compatibility can cause a lot of frustration, and it’s better to manage it on the front end."

The first step in variable-rate populations is working with a seed representative to select the right hybrid.

"First, I have the farmer tell me all they can about the history of the field. Knowing things like yield environment and soil types help us then walk through the hybrid capabilities of stress tolerance, ear style and drainage tolerance," Hardwick says. "That is what will increase our success when varying the population."

Know your hybrids. Since variable hybrid systems aren’t commercially available yet, farmers should select a hybrid that will perform best across a majority of their management zones.

Without proper hybrid selection, farmers might be surprised by how their variable-rate populations perform in the field.

"We need to know all we can about our hybrids," Bauer says. "I see many mistakes made by not correctly taking that into consideration."

Farmers should understand the hybrid type and where the hybrid falls on the spectrum of fixed to flex ear types, Bauer says. Does the hybrid like high, medium or low populations? Work with your seed rep to find the base population rate for that hybrid.

For example, a hybrid might have a base rate of 36,000 seeds per acre, and depending on the management zone, that could go from 38,000 to 32,000, Bauer explains. On the other hand, another hybrid that is more of a flex ear type might have a base rate of 32,000, and based on soil characteristics, its variable-rate population could range from 36,000 to 28,000.

"Typically, we adjust by 1,000 or 2,000 plants per acre increments based on the water-holding capacities of the zones," Bauer says.

Working with your seed rep to fine-tune the seed populations will help increase confidence in the prescriptions.

"In soils with low water-holding capacity and the toughest parts of the field, pull back the population," Bauer advises. "Farmers are often nervous about reducing populations because they are used to higher rates. But we’ve seen certain hybrids in sandier areas increase yields by reducing population." 

That resistance to the lower populations might be the biggest struggle that farmers face.

"Farmers have a population number in mind that they don’t want to go below. It’s beyond their comfort zone, but 26,000 might be what a low-producing management zone needs," Hardwick says.

The rules still apply. Bauer reminds farmers that even as they adopt advanced technologies, the fundamentals don’t change. In fact, ear counts and uniform emergence could be even more important.

"When we are trying to be precise in our management, it’s even more important we know our planters are properly calibra­ted and we’re achieving the actual rates in the field," she says. "Achieving uniformity and plant spacing are key across the range of plant populations, and a farmer’s planter has to be ready for that."

Bauer says that as you increase populations, ear count must also increase accordingly. If not, yields could go backward. The target to shoot for is no more than 1,200 difference on average between population and ear count in a corn-after-soybean rotation and no more than 2,000 difference in that ratio in corn on corn.

As farmers gather additional data each year using variable-rate technology, it’s important to analyze the yield results on a continual basis.

"During the year, spend time in the field. Go out to the management zone and evaluate ear fill. You’ll want to see a little pull back on the ear tip—perhaps . If you aren’t seeing that, you could have gone higher in your populations," Bauer says.

Year to year, hone your population rates by running uniform population strips across management zones.

Review your data and compare to your variable-rate prescriptions.

"There’s a lot to learn. We’ve seen that when we push populations, farmers have to support that with the appropriate nitrogen. High plant populations in certain zones may require more nitrogen per acre," she says.

Bauer encourages farmers to keep asking questions as they adopt variable-rate technologies and continue to refine their management zones. 



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