Establishing Accurate Farm Zones

No two fields on your farm are alike, but they are often similar enough to group into zones. Establishing accurate management zones is essential to reaping the benefits of precision agriculture. Here's a primer on how to group like pieces of ground --  based on everything from their soil, to their moisture content, to their insect history -- to make sure you get the most from your precision ag investment.

By: Margy Eckelkamp, Farm Journal Media

Farmers have long known that all fields aren’t created equal and that every acre in each field is not the same. Today’s technol­ogy now allows producers to easily do something about it. Zone management links precision ag and agronomic practices into one seamless outcome with three key benefits: maximizing yields, improving stewardship and boosting bottom lines.

"For 20 years, we’ve been working to get technology in farmers’ hands, and now it’s time to use the data collected through this technology," explains John Fulton, associate professor and Extension specialist at Auburn University.

In the Zone
The foundation of zone management is identifying the variability in the field. A simple starting point is recognizing the differences in soils. The photo indicates the high and low ground and the lighter and heavier soils.


Using information on the natural variability in a field, rather than a superimposed grid, allows you to pave your own path. Regardless of where you are on the technology adoption curve, there are zone management techniques that can be used.

"Zone management enables you to pick the areas where can you influence a problem by applying the right agronomic practice," explains Farm Journal Field Agronomist Ken Ferrie, who has worked with dozens of farmers to implement and employ zone management.

Use current information. The first step is to review what you know to identify the management zones within fields. Soil characteristics, water and fertility management, hybrid selection, pest and disease profiles, and yield history all play key roles. Thankfully, most farmers have already collected a gold mine of information.

"Since 1991, we have looked at yield maps as a way for fields to tell us where to identify management zones. Now, we not only have yield maps but data available throughout the season," Ferrie says.

Hybrids have one of the largest impacts on yield, not only from field-to-field but within fields. For example, drainage issues in low-lying zones of the field could be managed by selecting a hybrid that does well in wet conditions. Other examples could include recognizing high pH and planting with a hybrid that is tolerant to those soil conditions, or identifying a corn nematode hot spot and managing it with a seed treatment.

"The data we glean from management zones helps us make an informed decision on treating a whole field when a farmer’s equipment is not yet ready for variable-rate technology [VRT] or the technology to vary that input isn’t on the market yet," Ferrie adds.

Gather more data. After examining hybrids, analyze soil characteristics for existing zones. Look at texture, slope, depth, organic matter, fertility, pH, drainage and hardpans.

"Any zone that you develop must respect soil type, but a lot of management zones are within the soil type," Ferrie says. "We start with soil type or soil texture, and from there the zone may be divided out due to depth of topsoil, drainage or pH issues."

Soil information can be gathered from ground-truthed government maps, soil sampling, RTK elevation maps and soil conductivity maps.

Review and verify results. "Once we identify the zones, we have to investigate what’s causing those differences. One thing you’ll look at is the overall soil fertility. Look for clues for what is happening," Ferrie advises.

Don’t be surprised if low-yielding zones have higher fertility, he adds. "If the field has been treated uniformly for years, the poor yields have a lower removal rate. But you occasionally find that fertility is the problem, and it may be a fertility imbalance, low/high pH or micronutrient problem," he says.

Overlap layers. Factor in all possible causes for why a zone can appear.

"Farmers ask me how they can change their farm operation to maximize profit, and my answer is data. The most important data layer is the farmer’s knowledge followed by the one that depicts the farm’s variability," says Auburn’s Fulton.

Look for ways that one influencing element impacts another.

"Drainage could be the problem, but there’s a chain reaction that takes place. If you have a wet spring, which reduced emergence, caused nitrogen loss due to leaching or denitrification, and the resulting reduced stand led to increased weed problems, it would be hard to single out the factor influencing the management zone unless we were in the field the entire season to see what took place," Ferrie says.

To build confidence in your man­agement zones, use a two-pronged approach: good-quality data and boots on the ground.

"What makes good data is being able to show spatial variability in the field," he says. "Spatial variability is any type of data that tells you where the good, bad and ugly are and the differences in the field. We are looking for repeatable differences—that’s key."

It’s best to have three years of good-quality data and maps.

"You have to prove that, by using multiple maps across multiple years, you can define the same zones," Ferrie says. "Some only show up in legumes, some only in grasses. A zone may only be identified in the wet years or the dry years. We need to be able to literally stack the data and it all line up."

Develop a strategy. Well-defined and verified management zones lay the foundation for VRT. As you develop the zones, it’s important to make sure they match your technology and equipment.
"Management zones should be big enough that we can manage with the size of equipment we are working with. We might have pockets in the field that are too small to be applied with a 80' planter or 90' boom," Ferrie notes.

Sometimes a management zone might demand you implement a new production practice.

"In a field, we may have sand hills where blowing sand is cutting off the young corn in high winds. We could map those areas and control the wind erosion by planting cover crops on the hills," he says.

The return on investment can be measured in maximizing the placement of inputs and practices to improve bottom lines.

"I’ve worked with farmers who have used variable-rate population and variable-rate nitrogen and increased yields up to 15 bu. per acre on average," Ferrie says.

In the journey to implement management zones, Ferrie warns farmers about being too reliant on the tech-nology dictating your management zones. "The biggest misstep I see farmers making is allowing a computer to map management zones without input of their own experiences in the field," he notes.

The more effort you invest in verifying the management zones, the greater the payback to your bottom line.  

Decades of Data: One Farmer’s Perspective

Rod Wilson

Using zone management is a journey—not a destination—and well worth the effort. Illinois farmer Rod Wilson has been working with management zones since applying variable-rate lime in the 1970s based on soil topography maps.

"As technology developed, we overlaid soil type maps to refine management zones," Wilson says. "In 1994, we used our first yield monitor, which helped take this to the next level. Early on, though, it was frustrating to match technology and expertise to show the zones well enough to know we had something to work with."

To better understand where to look for zones, they started with the farms where they had the most experience. "Even on those older farms, we had a learning curve," he says.

It’s the trials and failures of zone management that have taught him the most. "The biggest success we have had with zone management is that it has helped us manage the variability. It’s provided a balance in the economics of our inputs while maximizing yields," he says.

Ten years ago, Wilson started using variable-rate population. He has three years of experience in variable-rate sidedressing of nitrogen.

Before variable-rate technology (VRT), his average population was 36,000 plants per acre; with VRT, his average population is 32,450 plants per acre. His VRT sidedress nitrogen rates increased over his previous uniform rate by 49 lb. per acre. In the past three years, using management zones and VRT has increased Wilson’s yields 5 bu. to 15 bu. per acre.