- PRODUCTION -
N Sources, On-The-Go Sensors
By Carroll Smith
Welcome to our world, cotton farmers might say, especially when it comes to strategies for reducing the cost of nitrogen (N) on their farming operations and getting the most out of the N source they do decide to use.
Charles Mitchell, Alabama Extension agronomist and Auburn professor of agronomy and soils, offers four options for keeping fertilizer costs under control:
• If soil testing done by your land grant university indicates that your fields are high in certain nutrients, don’t add more of them. If high levels of nutrients have built up in the soil, start taking advantage of them. This applies especially to phosphorous, the retail prices of which have tripled in the past couple of years.
• Compare the cost of applying more than 120 pounds of fertilizer N at a cost of $100 per acre to planting winter legumes for $30 to $50 per acre.
• Use chicken litter if you can get it. The N alone in litter is worth more than $40 a ton.
• Buy commercial fertilizer, but compare prices. Take advantage of lower-cost materials like dry, granular urea sidedressed. It usually costs less than UAN solutions and is not as volatile. If you have to use a UAN solution, include a urease inhibitor like Agrotain. This adds more cost, but in some situations, such as applying the liquid N on the surface during a hot, dry summer, it probably will pay off.
Taking advantage of different sources of N is one way to contain costs, but application methods may have potential in that arena, too.
For example, University of Missouri scientists Peter Scharf, who is in charge of the project; David Dunn; Gene Stevens; Earl Vories; and Andrea Jones have been involved in an experiment funded by Missouri State Support Committee and Cotton Incorporated to study “on-the-go” sensors to control variable rate N applicators for mid-season cotton fertilization.
They used GreenSeeker, Crop Circle and CropScan equipment-mounted sensors for applying N on silt loam, sandy loam and clay soils.
“In a practical system, sensors are mounted on a tool bar attached to the front of the tractor directly above the row,” Dunn says. “The sensor, which can distinguish between cotton plants and bare soil, shoots a beam of light onto the cotton row.
“Light reflected by the cotton plant and received by the sensor is evaluated, and the information is fed into an on-board computer,” he adds. “The computer then controls a variable rate applicator mounted behind the tractor, and the N rate is varied as the machine moves through the field.”
Gene Stevens, University of Missouri soil fertility specialist, also points out, “With sensors, there is no lag time compared to aerial remote sensing,” he says. “You are measuring N and applying it where needed at the same time.”
Taking It To the Field
After conducting small plot tests in 2006-07, they conducted the first on-farm test in 2008 with cooperating producer Jim Steuvers, Bernie, Mo. The research team compared Steuvers’ standard sidedress rate (120 pounds of N/acre) in alternate strips with variable rate N applied based on algorithms developed from 2006-07 small plot calibration research.
“We saved an average of 46 pounds of N/acre on the variable rate applications, and in the fall of the year the cotton in the variable rate strips defoliated and opened up better than the standard N rate strips,” Stevens says. “We didn’t harvest the field until all of the cotton was ready, consequently, we may have lost some lint on the variable rate strips because the yield monitor indicated that they picked 71 pounds less than the standard rate strips.”
The team notes that this was its first on-farm test, so the researchers did learn a lot.
Stevens concludes, “Anything we can do to help farmers lower costs by lowering inputs where feasible is good. We plan to keep working on this variable rate N study again this year.”
Contact Carroll Smith at (901) 767-4020 or firstname.lastname@example.org.