Field management zones can help maximize yields with fewer inputs. By Jason Jenkins
Skeptics, cynics, naysayers. Tayler McLane has encountered them all while advocating for precision agriculture and the use of field management zones across Missouri’s Bootheel.
When more bushels bust the bin at harvest, however, even the most reluctant growers become staunch supporters, she says. As the precision agronomist for MFA Agri Services in Bernie, McLane uses the power of persuasion, backed by solid data and proven in-field performance, to help customers say yes to setting up zones that can help increase yields with fewer crop inputs.
From GPS and aerial imagery to yield monitors, soil probes and moisture sensors, emerging technologies are making massive amounts of data available to growers. More and more are deciding to make the most of it and maximize their precision agriculture investments by creating management zones as the next step toward increased profitability.
“Here in Bernie, we have almost 48,000 acres in our Nutri-Track system,” McLane says, referring to MFA’s precision ag program that uses in-field management zones. “With prices being what they are, you need to make money where you can and not waste it anywhere. That’s what guys like about [Nutri-Track]. If we fertilize the best we can and put the nutrients where they really need to be, then yields are going to be that much better and make them that much more money.”
Turning Precision Crop Data Into Decisions
At its most basic, a management zone is a portion of a field that is treated agronomically different from adjacent ground due to varying characteristics. Even across a 40-acre field, there may be a number of soil types, each with a different texture and water-holding capacity.
Fertility within those soils—due to the availability of both macronutrients and micronutrients—can vary, as can other properties such as organic matter, pH and cation exchange capacity (CEC). Topography from one end of a field to the other can change significantly. Hilltops, side slopes and bottoms all impact the success of a crop. Understanding and accounting for these differences can help producers make the most of their overall yield potential.
“You need to be analyzing the data and information on a field-by-field basis,” says John Fulton, associate professor of food, agricultural and biological engineering at The Ohio State University. “You can’t expect any of these variables to correlate to the adjacent field.”
McLane can attest to such variability, both within and between fields. The territory she works in southeast Missouri includes Crowley’s Ridge, an unusually narrow, rolling region that rises above the flat alluvial plain of the Mississippi River.
“You’ll be out there sampling, and it’ll be a clay-type soil. Then all of a sudden, you’re in nothing but sand,” she says. “It might be just an acre, but it’s totally different from the rest of the field.”
Creating Field Management Zones
The first step toward understanding a field’s characteristics is to consult the USDA soil survey database (https://websoilsurvey.sc.egov.usda.gov) maintained by the Natural Resources Conservation Service. This resource—the only one of its kind in the world—provides baseline information on the physical properties of the field.
Ground-truthing that data through grid soil sampling is the next step. For example, MFA’s Nutri-Track program overlays a grid on a field, McLane explains. Six to 10 samples are pulled from each 2.5-acre cell in the grid. Samples are mixed and sent in for analysis, returning a panel of results for fertilizer recommendations on an acre-by-acre basis.
“Generally, we’re looking at variable-rate phosphorus, potassium and lime pre-plant based on grid soil testing. Those are the big three. Nitrogen will go out midseason in corn and rice,” says McLane, whose MFA location received one of three national Precision Impact Awards from the Agricultural Retailers Association in 2016. The award recognizes local retail operations for their use of technology, input efficiency, grower engagement, environmental stewardship, innovation and profitability.
“Every now and then, the manganese or boron will be limiting, and we’ll have to take a closer look,” says McLane. “Once I get out there and get the sample, I can make a recommendation for any product on the market.”
Testing also reveals the soil’s CEC, which is influenced by both organic matter and soil texture. As soils get heavier and contain more organic matter, CEC increases, allowing the soil to hold onto nutrients more readily. In general, the size of zones depends on the characteristics you intend to manage, Fulton says. The smaller the zones, the more effectively a producer can distinguish variability.
“We typically think about the limitation on zone size being tied to two things: economics and equipment,” he explains. “How many samples can I afford to take and still get a return? What size is my equipment, and how quickly can it adjust across the field?”
Layering Data, Refining Decisions
Once a field has received a variable-rate fertilizer application and the crop has been planted, zone management isn’t over for the year. For example, normalized difference vegetation index (NDVI) imagery can be used to identify in-season zones based on crop health.
“As the crop develops, its health and vigor can vary within or across the field differently than we zoned out initially,” Fulton says. “What we’ve seen with our research is that you can take imagery data to understand crop health or disease variability, and use that to establish zones for applying [in-season] nitrogen or fungicides.”
When harvest time arrives, another layer of data becomes available: yield. “Yield monitoring has become a real necessity,” Fulton says. “It’s one of those base layers that any service provider with precision ag services requires.”
Back in the Missouri Bootheel, McLane can use her company’s precision ag program to incorporate a field’s yield data with its soil-test data. This allows her to determine the crop removal rate of nutrients and accordingly adjust variable-rate fertilizer recommendations based on management zones for the next season.
“If you have 300-bushel corn on 20 acres in a field, we’ll put 300 bushels of removal on top of what the soil test calls for,” McLane says. “If another part of the field yielded 80 bushels, we’ll only put on 80 bushels worth of removal. Now, if we just flat-rated for 100 bushels removal across the field, look how much we’d short the 300-bushel area.”
Though her title may be precision agronomist, McLane sees her role more simply. Innovation isn’t new to agriculture, and she views the tools and technologies she uses today as the next evolution for the industry. With a soil probe in one hand and an iPad in the other, she can quickly convince farmers to discover the benefits of management zones.
“Precision agriculture used to be a thing, but now it’s just agriculture,” she says. “With some farmers I say, ‘Let’s try it on 100 acres.’ After we can get them talked into one farm and they see the results, they come back the next year and want it on all their acres.”