By Dusty Sonnenberg, CCA, Ohio Field Leader: a project of the Ohio Soybean Council and soybean checkoff.
The Ohio State University’s Precision U winter meeting series wrapped up with a look at sprayer application tips and technologies. Joe Luck, Associate Professor and Precision Agriculture Engineer in the Department of Biological Systems Engineering at the University of Nebraska – Lincoln was the featured presenter.
When farmers make a chemical application with a sprayer, the goal is ultimately to protect their crop.
“The first step in achieving this crop protection is to make sure the application is on target and accurate,” Luck said. “This involves proper mixing, including any pre-mixing of products, proper agitation, and direct injection.”
Achieving the desired application rate is a part of the accuracy.
“This can involve the use of a rate controller,” Luck said. “It can be enhanced by minimizing speed changes during application, and monitoring boom overlap, including turns on the ends.”
Maintaining a uniform spray pattern is important for consistent application results.
“A uniform spray pattern involves selecting the correct nozzle spray angle, nozzle overlap, and boom height,” Luck said. “Spray droplet size also contributes to effective crop protection. This is impacted by selecting the correct nozzle size and spray pressure for mitigating drift, while maintaining efficacy.”
Proper batching and mixing of the product are the pre-application factors to consider.
“Applicators need to make sure that the correct chemical/adjuvant rates are being used, and that they have been mixed in the proper order,” Luck said. “Another important part of the process is the boom clean-out. Some chemicals and adjuvants won’t mix. Water hardness and pH can affect the chemical saturation.”
Post-evaluation of a chemical application is necessary to determine the effectiveness.
“Farmers need to consider how they will measure the effectiveness of their spray applications,” Luck said. “Some will involve post-application scouting. As-applied data can also be utilized.”
When evaluating the application effectiveness, there are several factors affecting field application rates.
“Rate controllers do have limitations,” Luck said. “As the sprayer equipment speeds up and slows down, the rates controller and system have physical limitations to adjusting quickly. This can lead to under application and over applications.”
Turning movements also impact the speed of the outside/far side of the boom, versus the inside/close side of the boom. The outside moves much faster and under applies, while the inside moves slower and over applies
“The nozzles selected also have a specific speed range to make the correct application rate, and as the speed exceeds that range, a misapplication can occur,” Luck said.
There are also spray overlap situations that occur on end rows, and point rows.
“Section control can help reduce the over application in these situations,” Luck said. “As the sections are turned on and off, the pressure has short term changes while the system reacts, this can result in over or under application.”
Drift has become more of an issue in recent years as well.
“Spray drift is a growing issue as we have more urban and suburban sprawl,” Luck said. “Nozzle selection and pressure settings are critical for achieving proper droplet sizes. Temperature inversions can carry small particles a long way. Monitoring wind speed can help minimize drift potential. Weather monitoring is also important. For in-field weather monitoring, and planning there are many tools available in the market. There are also several on-line weather sources that can be monitored.”
Auto boom section control has multiple opportunities for paybacks.
“Payback can be significant depending on the shape of the field and size of the field,” Luck said. “Section control gains value on irregular and shaped fields. The boom size and boom section distribution can significantly affect overlap. The more a spray boom is divided into multiple sections that are automatically controlled, the lower the over-application error.”
Pulse Width Modulation (PWM) Nozzle Control maintains pressure and droplet spectra, while accommodating flow changes through speed changes.
“Individual nozzle control allows for the duty cycle to vary across the boom and maintain a target rate during turns,” Luck said. “Some commercially available products offer individual nozzle shutoff.”
With PWM Nozzle Control, during each pulse, the on/off percentage is quantified as the “duty cycle”, which has a linear, directly proportional relationship to the flow.
“PWM benefits in turn compensation and improved rate control,” Luck said. “In a study we conducted, PWM systems improved application accuracy compared to a traditional control.”
Variable-flow orifice nozzles are also available.
“As system pressure changes, flow rates are extended as the orifices open,” Luck said. “The droplet spectra and spray pattern are typically maintained. The variable-flow nozzles can extend turndown rations from 4:1 to 8:1 across typical operating pressures.”
Boom height also has an impact on application accuracy. Automatic boom height adjustment controls help reduce errors, especially in uneven terrain.
“Maintaining proper boom-to-target height is critical and can affect application uniformity,” Luck said. “This often occurs if it is too low. It also impacts off-target movement of spray particles, especially in situations when the boom is too high.”
Other beneficial technologies include Auto-steer/guidance systems.
“Traditional light-bars or integrated hydraulic steering systems are great for minimizing turning,” Luck said. “Row sensing systems are available using mechanical or advance machine vision sensors to guide applicators between crop rows. These can improve field efficiency and reduced damage to the crops.”
Weed sensing technology is also gaining popularity.
“Reflectance-based systems work much like crop canopy sensors for detecting weeds. Machine vision assess the presence of weeds and nozzle valves are actuated on or off,” Luck said. “Challenges to adoption continue to focus on economics, and payback depends on weed density in fields and acres in production. These have the potential to greatly reduce chemical usage. Preliminary research shows approximately a 75% reduction in chemical use, compared to broadcast applications.”