NOT so long ago, 36 metres was considered a large spray boom.
But in recent years the rise of engineered aluminium has made 48.5m and even 54.5m booms increasingly appealing.
Larger booms boost productivity by getting more ground covered in the available weather window and sparing the operator many hours on the sprayer.
But the tip-to-tip speed difference across a wide, turning boom is also driving the need for faster, precise nozzle control technology.
As HARDI Australia's product manager for large sprayers Steve Lancaster points out, the outer tip of a 48.5m boom travels considerably faster than the inner tip in every turn - leading to significant under and over-dosing around headlands or any obstacle in the paddock.
"HARDI solves the problem by combining multi-tiered spraying with the H-SELECT system," Mr Lancaster said.
"It provides accurate target rate control over the widest possible speed range."
H-SELECT co-ordinates up to four different nozzles at each nozzle body to continually maintain the required target rate across the boom and speed range.
"H-SELECT calculates the speed of the sprayer and automatically activates the best combination of nozzles for each boom section," he said.
This rapid, blended switching between nozzle combinations means H-SELECT can achieve a target rate accuracy of 90 per cent or better over the entire paddock - virtually eliminating patches of over or under-dosage.
The nozzles can be activated individually and together.
For example, a nozzle in the Number 1 position can be selected in any of eight combinations: 1, 1-2, 1-3, 1-4, 1-2-3, 1-2-4, 1-3-4, or 1-2-3-4
Similar selections are also possible with each of the Number 2, 3, and 4 positions.
Discounting duplications (like 1-2 vs. 2-1), H-SELECT effectively functions as a 16-tier spraying system.
The nozzle switching is controlled by a solenoid-activated air pressure system, which also enables constant fluid recirculation and lets the boom be operated in unlimited sections. (18 sections is standard.)
Air switching frees the system from the electrical losses incurred by electronic platforms when the wire runs exceed about 18 metres per side or 36 metres overall.
Precise droplet control also makes H-SELECT an effective drift management system.
Because it uses combinations of nozzles to manage the target rate at a constant pressure, the droplet size doesn't change with the rate adjustments.
"The operator can set a droplet size and even change it on-the-go, using the in-cab Run Screen," Mr Lancaster said.
"It means operators can adjust their droplet size throughout the day, to manage wind speed, temperature and humidity changes.
"There's also the option to use a coarse droplet to spray the paddock perimeter, then change to a finer setting once you're away from the fence lines."
Operators are able to plan their H-SELECT set-up with the complementary Nozzle Watch desktop application for Windows PCs.
This software automatically calculates the optimum nozzle selection for a desired droplet size, target rate and speed range.
Alternatively, operators can specify nozzles or specify fewer than four (keeping one position free for a fertiliser nozzle, for example).
Nozzle Watch then displays nozzle combinations and speed bands, plus overall rate accuracy for the job.
Use all four recommended nozzles and that will usually be 90 per cent or above.
Readers can get an overview of Nozzle Watch and download the software to try, via a video hosted by HARDI's territory manager for Queensland/northern New South Wales, David Wooley.
Simply search 'HARDI Australia' on YouTube.
Meanwhile, Mr Lancaster feels sure H-SELECT is the solution that large-scale spray operators have been waiting for.
"We believe the combination of air switching and multi-tier nozzle selection makes H-SELECT an effective nozzle control technology for booms 36m and above," he said.
"And with so much riding on sprayer productivity, these big booms are the way of the future."
H-SELECT is currently available on HARDI RUBICON and SARITOR 62 ACTIVE self-propelled machines, and HARDI COMMANDER trailed sprayers.
The system integrates with the on-board ISOBUS.