More and more farmers are investing in drones to help locate areas in fields under crop stress, suffering nutrient deficiencies, and much more.

"Remote sensing is what you're doing right now," says Kevin Price, Chief Emerging Technologies Officer at Air Data Solutions. Price spoke at the December USA Rice Conference in Little Rock, Ark. "You're sensing something without being in physical contact with it, and you can sense in different wavelengths of the electromagnetic spectrum," he said.

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"Remote sensing with drones allows us to detect if a plant is sick or stressed by seeing the gradual change in pigmentation. Healthy plants show a darker green pigment while plants that are stressed appear yellow because they are fighting free radicals using antioxidants that come in the form of a pigment called carotenoid."

Healthy plants appear dark because the plant is absorbing a lot of light instead of reflecting light.

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"If a plant has more plant material or biomass, then more of the light is transmitted in the near-infrared and reflects back up to the remote sensor," he said. "The near-infrared light increases to the sensor and the visible light is absorbed for photosynthesis, so it decreases. All we're doing is measuring the difference between the near-infrared and the visible light. The greater the difference, the healthier your plants are, which means a higher possible yield."

Using drones, farmers can map every square inch of a field to detect crop stress or low biomass through the Normalized Difference Vegetation Index (NDVI) used in remote sensing.

Types of drones

"There are basically three types of drones: a multi-rotor, a fixed-wing, and a hybrid drone. Multi-rotors are fairly easy to learn to fly. The problem is you can't fly as much acreage since they fly for only about 20 to 30 minutes," Price said.

A fixed-wing plane can fly for a longer time, but the challenge is takeoff and landing.

"You have to have a landing strip or place to skid land it," he said. "We usually belly flop ours on the grass or the crop since you can't put a landing gear on it; otherwise, the drone will do somersaults as its landing gear catches in the plants or uneven landing surface."

A hybrid drone has vertical takeoff and landing, which allow it to lift off the ground, and then it kicks in the motors that make it go forward.

"They can fly a lot faster than a multi-rotor aircraft. You don't have to worry about having a place to land, but they're more expensive," Price said.

Using drones in farming

There are several applications for using drones on the farm.

"We worked in a soybean field collecting spectrometer data," he said. "The cameras on the drone are typically using three or four wavelengths. The spectrometer instrument we have used collected 2,151 wavelengths. What we learned is that about three spectral components can explain up to 98% of the variation in the color infrared imagery, or in other words, a green, a red, and a near-infrared band explained about everything we were going to get out of the data."

At China, Price and his colleagues flew a drone over a rice field to collect imagery for a Chinese agronomist.

"The resulting imagery showed one particular area of the field was the poorest in the entire rice field, but the rice field looked good to me from the ground," he said. "The aerial imagery didn't look good, though, which was because when I looked at it from an oblique viewing angle by looking at the sides of the plants which makes the area appear much greener."

Aerial imagery provides a bird's eye view of the plants as opposed to a limited ground view. Drones are great at helping to scout a field since a farmer, crop consultant, or crop damage appraiser covers a lot more ground in a short amount of time, and then selectively scouts the field as needed.

Drones can also help with weed detection, nutrient management, and detection of moisture stress and water conditions with aerial imagery.

One word of caution, Price said, is that the results from aerial technology are just one part of the puzzle.

"A farmer still needs to know his fields well to be a good judge over what the plants and the soil really need," he said.