Florence County, SC, farmer Al Cribb was among trial participants and admittedly was surprised that the use of sensors and mathematical calculations could outperform farmers’ time-tested rules of thumb.
After successfully demonstrating savings of up to $60 an acre in on-farm trials, Clemson University has made available to cotton growers a new sensor-based nutrient management plan that can reduce expenses and environment impact.
“I could look at the plants and tell that (Clemson’s) were just as good as mine without as much nitrogen,” Cribb said. “I was surprised. I found out I could cut back.”
As part of the on-farm trial conducted by doctoral student Phillip Williams, Cribb agreed to cut his nitrogen applications in half on about eight acres of cotton based on a sensor reading of nitrogen content in the plants and an algorithm created by a team of scientists led by Ahmad Khalilian, a precision agriculture engineer at Clemson’s Edisto Research and Education Center.
While Williams applied around 45 pounds per acre of nitrogen in his test plot, Cribb stuck with 90 pounds per acre, a common practice he has use for years. Based on the 2015 trial, Cribb cut nitrogen applications throughout his cotton field this year as well.
Per their sensor-based nitrogen management plan, Khalilian and Williams plant one “nitrogen-rich” strip of cotton to find the maximum, or target, yield. That determines the amount of nitrogen needed to reach desired yields. They then use handheld, optical sensors to measure nutrient content within the plants. That information, along with planting date and historical yield data, is plugged into an algorithm to tell how much fertilizer should be added during side dressing, the application of nutrients in shallow bands next to growing plants.
Cotton growers can take advantage of the product by visiting http://www.clemsonnitrogencalculator.com/ or by contacting their local Clemson Cooperative Extension Office. Williams has supplied several Extension agents throughout the state with the handheld optical devices that will allow them to assist growers with the program.
Williams also is working on a smartphone app that could be used in place of the website and is testing a similar sensor-based nutrient management plan for corn growers. Once available, the app will be available for download at both the Apple and Google stores, he said.
Approximately nine million tons of nitrogen is applied in cotton, corn and wheat fields annually in the United States. Just a 20 percent reduction in nitrogen usage would save U.S. cotton, corn and wheat growers more than $1.8 billion annually, Khalilian estimates. There are substantial environmental benefits to reducing fertilizer usage as well. The nitrate form of nitrogen moves freely into surface and groundwater and is a significant source of water contamination.
In three years of testing, the Clemson sensor-based nutrient management method applied 48 percent less nitrogen than farmers’ rule-of-thumb methods without affecting crop yields. Williams has conducted on-farm trials with six cotton growers in South Carolina and has shown savings of $27 to $60 an acre. The sensor costs around $500. That is the only investment needed to participate.
Williams said he worked with one grower who was shocked the sensor reading and algorithm informed him not to apply any fertilizer at all. The grower had planted a winter cover crop and applied poultry litter before planting. That supplied all the nutrient his cotton needed to produce, Williams said.
“I put out nothing. He put out 90 pounds an acre,” Williams said. “At the end of the year, our yields were within a pound of each other, so he started becoming a believer.”