BLACKSBURG, Va. — At Virginia Tech’s Eastern Virginia Agricultural Research and Extension Center, researchers are testing aerial sensor technology to help small grain growers assess the progress of their crops without setting foot in the field or wasting valuable time and money.
College of Agriculture and Life Sciences faculty at the Warsaw, Virginia, facility are using sensors attached to drones to help determine nitrogen rate and timing of wheat, a crop that has experienced a sharp rise in production across the commonwealth. Virginia farmers harvested 10.2 million bushels of winter wheat during the summer of 2022, up 27 percent from 2021, according to the U.S. Department of Agriculture. Also on the rise is the cost of nitrogen, an element important to wheat’s overall health and reproductivity.
A key indicator that a wheat plant will succeed is the number of branches, called tillers, it produces throughout the growing season. Wheat is usually planted in October and harvested in the summer.
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Three to four tillers are ideal. Too many tillers lead to competition. Too few results in less yield. Should the crop need a boost, nitrogen fertilizer is often applied. Growers assess tiller numbers from late January to mid-February. Traditionally, the count is done on foot, a method that is both time-consuming and with inconsistent results.
“When you go out into the field to count tillers, you’re only going to do this in certain spots, so you’re not getting adequate representation,” said Eastern Virginia Agricultural Research and Extension Center Superintendent Joseph Oakes. “You might be in a fairly weak spot or a strong spot that is not represented in the entire field.”
Virginia Tech researchers recognized these inconsistencies, and in the early 2000s, they began testing a new way to measure healthy vegetation. Normalized Differential Vegetative Index –commonly called NDVI – quantifies vegetation by measuring the difference between near-infrared and red light. Healthy vegetation reflects more near-infrared and green light, compared to other wavelengths – hence the reason human eyes see vegetation as the color green.
Researchers took handheld devices equipped with NDVI sensors into the field and developed a promising relationship between NDVI and tiller density.
“Studies showed that NDVI is a good proxy and that it can be used to determine tiller density,” Oakes said.
It was an innovative discovery for the time, Oakes said. Twenty years later, though, the research was ready for a change as technology evolved.
“How can we take this one step farther?” he asked.
Or, hundreds of feet higher?
In 2017, Oakes and his colleagues launched a study examining the relationship between tiller density and aerial NDVI collected with a drone. They started testing small plots of wheat at the Eastern Virginia Agricultural Research and Extension Center and several other ARECs throughout the state.
“Research revealed that NDVI collected through the drones recommended the same amount of nitrogen as tiller density,” Oakes said. “Both methods recommended applying the same of nitrogen at Growth State 25 if the tiller density was below 50. Therefore, there is no difference in yield on whether nitrogen is applied based on tiller density or NDVI.”
The aerial method is saving growers both time and money, Oakes said. No longer will they need to physically count tillers or spray an unnecessary amount of nitrogen fertilizer. The environment will benefit, too. If growers can reduce the amount of nitrogen applied, the lower the risk of it running off into nearby water systems.
With the help of a grant from the Virginia Agriculture Council, the project has expanded onto larger farms across the state. Oakes is now valiating drone and tiller density data and comparing yield results on these farms. If researchers continue to see similar correlations between tiller density counts and data collected from the aerial NDVI, they aim to eventually create a software system.
“Our ultimate goal is to partner with a drone start-up company to develop a prescription file that growers can plug into their sprayer that will help calculate the rate of nitrogen that needs to be sprayed,” he said. “Maybe one portion of the field needs 20 and another needs 50. It will be able to make that change based on the data in the prescription file. There are still many steps to take, but we are making progress.”
–Max Esterhuizen, Virginia Tech
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