FEATURE ARTICLES
The spray drift potential of several commercial sprayer nozzles is a major area of research at the AgTech Centre in Lethbridge, Alberta.
Substantial chemical spray drift observed with some twin nozzles
Early research offers results that may be the 'canary in a coalmine' of a bigger issue, says a Lethbridge-based researcher.
Posted: February 11, 2009
Three twin nozzles from industry, from top to bottom: ABJ, Turbodrop, TeeJet
According to preliminary research, some twinned air induction and conventional nozzles may substantially increase the drift of chemical spray compared to single venturi and variable rate nozzles, says a project manager with the AgTech Centre in Lethbridge, Alberta.
Early results in a series of trials at the AgTech Centre have revealed that, depending on the nozzle being twinned, certain twin nozzles can increase drift from 30 to 60 percent over single nozzles. Although the results are limited to one set of speed, water rate and wind factors, Brian Storozynsky says they may be the canary in a coalmine of a larger issue.
"It's a 'heads-up' that if a single nozzle has an inherent weakness, twinning that nozzle essentially doubles that weakness," he says. "At the same time, it's important to recognize that not all twin nozzles are created equal, and some are successful at both increasing coverage and minimizing drift. At this point, however, it may pay to be cautious."
Coverage better with twins
Single air induction (also known as venturi) nozzles, introduced around 10 years ago, have played a key role in reversing a two-decade trend of increasing spray drift. However, because of their coarser droplets, venturi nozzles have a tendency to reduce coverage in the process of minimizing drift. Because of this, twin air induction and twin conventional nozzles were introduced a few years ago in an effort to increase coverage on both sides of growing weed leaves.
Most twin nozzles perform very well in terms of coverage, particularly on hard-to-cover vertical targets such as grassy type weeds. For example, AgTech research shows that, at an application rate of 224 L/ha, nozzle pressure of 400 kPa and a ground speed of 7.2 km/hr, a green Twin Air Bubble Jet 015 angled at 30 degrees forward and aft can result in between 14 to 16 percent coverage on a vertical target facing spray and between 3 to 5 percent coverage on the same target away from the spray.
On the side facing the spray, this is roughly comparable to a blue single Air Bubble Jet 03. However, the green twins reveal better coverage on the side away from the spray than the blue single. "In terms of coverage, the bottom line is that twin nozzles apply more spray to grassy type weeds, especially away from the spray and at lower application levels," says Storozynsky.
However, depending on the final results of the twin nozzle trials, twin nozzles could set overall spray drift on an upward climb again, says Storozynsky. "The question producers have to ask themselves is if the extra two to four percent coverage they get by using twin nozzles is worth all of the extra drift."
Substantial drift
That extra drift can be substantial, says Storozynsky. AgTech trials compared various twin air induction nozzles to single venturi nozzles. Using a water rate of 7.5 gal/ac and a spraying speed of 15 mph in a 15 mph wind, researchers found the twinned Air Bubble Jet measured an average of 105 airborne spray droplets per square centimetre downwind while the single nozzle measured 59.
"Essentially, what happens when you twin, for example, a single Air Bubble Jet 04, it produces two spray streams with a finer spray that is more exposed to wind. As a result, drift increases," says Storozynsky.
An even higher difference was found with conventional and low drift twin nozzles. With the Turbo TwinJet, using the same water rate, spraying speed and wind speed as the above example, researchers counted 197 spray droplets per square centimetre downwind of the operation. By comparison, the single Turbo TeeJet 04 under the same factors measured 134 spray droplets per square centimetre, comparable to the variable rate VariTarget yellow cap at 128.
"Overall, twinning air induction nozzles rather than conventional or low drift nozzles is a better choice for keeping spray drift levels low," says Storozynsky.
It's important to recognize that not all twin nozzles are created equal. The TurboDrop TwinFan, for example, excels both in terms of coverage and minimizing spray drift, says Storozynsky. In AgTech trials, this nozzle, at a ground speed of 8.3 km/hr, achieved 9.5 percent coverage on a vertical target facing the spray and 5.1 percent away from the spray. In terms of drift, it measured 44 spray droplets per centimetre under the conditions listed above - comparable to a VariTarget green cap, which sprays very coarse droplets.
Spray drift research ongoing
Because of its long term commitment to developing sustainable commercial systems for producers, the AgTech Centre's study of spray drift reduction is an ongoing process. Results of AgTech's machinery evaluations, applied and scientific research, and information on its development of innovative agricultural technologies are available to producers to help them make management decisions. For more information, contact the AgTech Centre at (403) 329-1212.
Author: Jeff Melchior
Sponsored by: AgTech Centre
