The ability of so-called ‘airbag’ sprayers to hit the target more effectively than spraying systems relying solely on nozzles has been put to the test in comparative trials in Denmark.
Researchers concluded that using the Hardi Twin ‘air curtain’ system to help propel spray droplets to their target in challenging situations can reduce off-target drift by up to 80% and achieve more even spray coverage across the working width when spraying in a cross-wind.
Hardi says this ability to achieve more controlled spray deposition in less than ideal conditions gives users many more potential spraying days to hit timing targets and cope with a large workload.
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The Twin system is used in conjunction with conventional spraylines and the same choice of nozzles as other sprayers but for each half of the boom adds a fan and a tapered air bag with outlets along the underside. The angle of the resulting ‘air curtain’ is adjustable, its strength can be altered through infinitely variable adjustment of fan speed.
This enables the operator to fine-tune the system for different crop and ambient situations, and also the target location – insect pests on the underside of broad-leaf crops, for example, or foliar disease on the flag leaf of wheat plants.
For the comparison trials at Arhus university’s Flakkebjerg research facility, a Hardi Commander 4500-litre trailed sprayer equipped with the Twin system was used for all tests, comparing performance of ISO LD-025 tips with and without air assistance across the 24m (79ft) boom. The Hardi LD-025 is a low-drift tip using a pre-orifice to regulate flow and a chamber to reduce pressure at the outlet.
This results in a ‘medium’ spray quality when used at a system pressure of 3 bar (43psi), with a droplet size comparable to the ISO F-04, which is the reference nozzle used by Germany’s official body for spray tip classification trials.
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Researchers wanted the trial to reflect the most challenging spraying conditions faced by growers, so they were conducted on short crop stubbles in a cross-wind. Spray deposits were collected in 4 positions beneath each boom across 5 rows of Petri dishes raised just above stubble height; each test was carried out 3 times to obtain valid results.
As a further variation, the sprayer was operated at 8kph and 12kph (4mph and 7mph), with the Hardi Twin system also recorded at 16kph (8mph).
Lead researcher Peter Kryger Jensen reports that spray drift using air assistance at that speed was significantly lower than the values generated spraying conventionally at the two slower operating speeds. Further significant reductions in drift were attributed to the Twin system at the lower speeds, while also giving the most even deposition across the 24m boom, when spraying conventionally resulted in large variation between the ‘upwind’ and ‘downwind’ sections of the boom.
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“The variation in the minimum deposit under the boom between the conventional and Twin system was up to 30%, which indicates a possible PPP reduction of 30% in an open crop/bare soil situation, which would be higher in a dense crop,” said Peter Kryger Jensen. “In terms of drift reduction, Twin reduced sedimentation drift by up to 80% versus conventional spraying with the same nozzles, driving speed and wind speed.”
From this, Hardi draws the conclusion that the Twin system provides greater control over spray deposition, which can result in more effective treatments with the potential to use less chemical, while also allowing treatments to be applied in timely fashion on days when a conventional sprayer is parked up in the shed.
Operators do need to have a clear understanding of how air assistance affects the dynamics of droplet movement in order to fine tune the set-up for each circumstance, so is best handled by ‘professional’ farm sprayer users rather than inexperienced operators.