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Aerial Imagery Takes the Guesswork Out of Fertility Decisions

The images farmers gather from unmanned aerial vehicles (UAVs) may look cool on a computer screen, but until recently, they did little to help farmers improve their bottom lines. A growing number of firms are developing new aerial tools to equip farmers with information that identify problem spots in fields and, ultimately, deliver more profit per acre. 

Kansas wheat farmers are getting an early shot at some of these tools, including the new VariMax offered for the 2016-2017 wheat crop. VariMax combines aerial imagery, crop sensors, and customized algorithms to augment what farmers already know about their fields, says Shane Ohlde, CEO of Ohlde Seed Farms, a regional wheat, corn, and soybean seed company that has licensed VariMax from Kansas State University.  

Tools like VariMax require a high-quality aerial image, which is processed and plugged into an algorithm that churns out the information to help producers. In the case of VariMax, the result is a variable-rate fertilizer prescription farmers can use to fine-tune spring nitrogen applications. 

Why Wheat?

Winter wheat is a good application for aerial image-based decision making, as it is an inefficient user of nitrogen. Farmers apply N to wheat in two shots. One is administered prior to planting to promote fall growth, too much of which uses precious soil moisture. Then in the spring, a topdress application of N is made.  

Ideally, a wheat field will be flown at Feekes Growth Stage 4. Farmers can use the resulting imagery to determine how much N to apply, says Ray Asebedo, assistant professor of precision agriculture at KSU and developer of VariMax.

“Wheat typically has a lot of yield potential at that time,” he explains. “But it isn’t easy for farmers to determine the optimal yield level for their growing environment at that time.”

Local is Better

Asebedo has spent years fine-tuning algorithms for winter wheat specific to Kansas. The VariMax algorithm combines wheat crop biomass, the crop’s photosynthetic capacity, geographic-specific nitrogen-use efficiency, plus past yields for a site-specific nutrient-management plan.

The local nature of VariMax makes it stand out in a crowded lineup of national service providers, like Climate Corporation, FarmLogs, and Encirca. 

“The algorithm we use takes into account site-specific management practices to help farmers determine the optimal nitrogen rate,” Asebedo says. 

In conversations with farmers while building the algorithm and field-testing VariMax, he knew the technology had to be easy to adopt.

“Farmers only care about two things: yield potential and nitrogen recommendation. VariMax tells growers what they want to know and what they need to fix it,” he says. 

And it works. Ohlde’s research finds that VariMax saves $12 to $15 per acre in N costs. He has four years of on-farm research in which N was applied at topdress. 

“We flew the field at green-up, and the program recommended 50 pounds of nitrogen to reach maximum yield potential,” Ohlde says.

On their plots, they applied 50, 75, and 100 pounds of topdress N. “We found no statistical economical yield difference between 50 and 100 pounds,” he notes. The savings more than offsets the $4.50-per-acre cost.

According to Asebedo, VariMax seeks 90% to 95% of the maximum obtainable yield and focuses on optimizing profit per acre. “Sometimes, we maximize profit by increasing yield; other times, it’s by reducing inputs. Ideally, we want to increase yield and reduce input expense,” he explains.

Many national products are more generalized and use crop modeling within the algorithm, across a wide geography. But agronomy is local. The more dialed-in a product is to local conditions, the better. 

“Generalized algorithms may work everywhere, but they don’t work well,” Asebedo says. “They are like a one-size-fits-all hat. It works, but doesn’t fit quite right.” 

How it Works

An accurate prescription requires a lot of behind-the-scenes effort. First, the flight must record a usable image. Optical sensors on machines see a crop in the same way human eyes do. Paired with the right algorithm, they can interpret what the plant is saying. 

Someone has to aggregate the information, though. That’s where a provider like Beau Dealy steps in. “Data from aerial images is like drinking from a firehose. We need to make sure we get the information we need to help farmers make sound economic decisions,” says Dealy, who is managing partner of APIS Remote Sensing in Hays, Kansas. In April, Dealy’s firm worked with Heartland Soil Sampling, a southern Kansas soil sampling firm, to map crop health in a wheat field. 

Soil sampling gives a baseline of nutrient deficiencies in the soil prior to planting. Remember, though, that winter wheat is in the ground for nine months from planting to harvest. A lot of things can go wrong that nutrient application alone cannot solve. 

Landon Oldham, owner of Heartland Soil Sampling, collected an NDVI image from one of his customer’s fields. Taken with a UAV, the image showed crop stress on two sides, where cation exchange capacity is low, and magnesium and potassium levels are below normal. The aerial imagery closely correlated with a grid soil sample map from the fall of 2016. 

“We didn’t expect the correlation to be that spot on, but it was,” Oldham recalls. “We determined that a variable-rate prescription would fix the problem.” 

With crop prices at historic lows, Oldham knows farmers are hesitant to spend additional money on aerial imagery. Input costs can be saved as farmers begin to isolate zones within fields. “The information can be used to manage those zones accordingly,” he says.

That’s key, adds Dealy, who collected and processed Oldham’s imagery to make a usable map. “If you can’t tie aerial imagery to specific acres in a field, you’re not getting the maximum value out of that image.” 

Drone, Plane, or Satellite?

Ohlde’s VariMax was intended to be used with UAVs for the aerial image. Those images are fine, but airplanes and satellites can also provide high-resolution imagery for the farm. 

“They all have their use,” says Dealy, who is editor of the website, AgFlyers.com. “If you need timely, high-resolution imagery, drones are where it’s at. For getting a lot of images over time, however, manned flights or satellites are a good option.” 

For more tips on turning data into decisions, download our Precision Decisions e-book.

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