The Nebraska On-Farm Research Network launched the project Sensors for Efficient Nitrogen Use and Stewardship of the Environment (SENSE) three years ago on about 20 on-farm research sites. It is a partnership of the University of Nebraska-Lincoln (UNL) Extension, the Nebraska Corn Board and Nebraska Natural Resource Districts (NRD). The research, now in year three, focuses on crop canopy sensors directing variable-rate, in-season nitrogen application in corn.
Sensors mounted on the bar of high-clearance application equipment emit light onto the crop canopy and then measure reflectance from the canopy with photodetectors. The light source simultaneously emits visible and near infrared light.
These wavelengths are combined to create various vegetation indices that are indicative of crop condition. Algorithms then translate the indice values into an in-season nitrogen recommendation.
In simpler terms, the greener the plant is, the less nitrogen is applied. More fertilizer is applied to less green plants.
"We basically took a commercially available system off the shelf with no modifications. The goal of this is to show the grower what it would look like if they purchased a system themselves," said Joel Crowther, UNL grad student and member of the Project SENSE team, at a field day near Schuyler, Nebraska, in early August.
UNL Extension provides the sensors and applies the recommended nitrogen during the growing season. This eliminates producers having to invest in equipment they are not completely sold on, Crowther said.
The team tries to apply nitrogen in the V8 to V14 stage of growth. Nitrogen can be applied in earlier stages of growth, but the sensors need a full canopy of crop, which usually happens at the V8 stage.
Participating farmers applied a base rate of nitrogen earlier in the growing season, usually around 75 lbs./acre. Then, an in-season nitrogen application trip uses sensors with application rates ranging from 76 lbs. to 254 lbs./acre. Crowther said 172 lbs./acre was the average in 2017.
John Parrish, Project SENSE technician, said two treatments were made in the field: One was the grower's normal nitrogen management, and one that was recommended by the sensors. A high nitrogen reference point also is applied to the field. Most sites had around a 20- to 30-acre research plot.
"In 2015, we ended up reducing the amount of nitrogen applied by 40 lbs./acre but also reduced the yield some by 5 bushels per acre," Parrish said. "You see this sensor-based equipment lowering yields some, but you are saving money in the end."
By using the sensor-based nitrogen application, growers would have saved about $8 per acre compared to their normal nitrogen application management, he said.
Similar results were seen in the second year of the research in 2016, Parrish said. Applications were reduced by about 35 lbs./acre and yields were only reduced about 3 bpa. The cost of savings by being more efficient with applying nitrogen was at $7 per acre, he said. Results are not in yet for 2017, but in-season assessments look similar to the two previous years.
The goal of using sensor-based equipment is to improve fertilizer efficiency while improving profit per acre.
Parrish said that by using the 2016 calculations, researchers wanted to see what a breakeven cost on acres would be in using a sensor-based system to apply nitrogen. Research factored in a cost of the complete sensor system at $15,000 and didn't include the cost of the high-clearance applicator.
To pay off the cost of the sensor system, you would need to use it on 720 acres every year for three years, Crowther said.
The researchers also carried out pay-off to six years, roughly the lifespan of a sensor system before new technology likely would appear. A grower would need to cover only about 360 acres a year to pay off the system in six years.
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