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Calibrate your rate

Calibrate your rate

Summer is the season for looking after your paddocks and the combination of extraordinary rain and chemical prices will make this summer a critical one. Whether you’re applying snail pellets, lime, other soil treatments or herbicide, it’s essential to calibrate your machine before you start – and the process is similar for spreaders and sprayers.

Calibrating your machine will ensure you apply products accurately – reducing the wastage of over- or under-application and helping to minimise leftover chemical in the sprayer tank when you finish.

For detailed instructions, always consult the manual for your machine.

Spreader calibration

Calibrating your spreader is an essential first step every time you dispense a different product. Granulated fertilisers, lime and snail baits will all fly off the spreader at different rates and for different distances.

To calibrate your spreading rate for a product, you need to know the swath or spread pattern width for that specific product in metres. You can find this by spreading some product over bare ground and inspecting the fall, or by driving over a line of collection trays.

The application rate at the edge of the swath must be at least 50% of the rate at the centre and your runs should be overlapped to compensate.

The weight of product dispensed can be measured by running the spreader for 60 seconds while collecting the output. Either removed the spinner(s) so the product falls into a container or use tarpaulins to catch the product, then weigh what you collect.

Finally, check the travel speed of your spreader or tractor by timing it between two points 100 metres apart with your forward gear and engine rpm set for spreading.

Your Travel Speed (km/h) =  [100 (m) x 3.6] divided by [Elapsed Time (Seconds)]          

You can now work out the calibrated application rate for that specific product:

Your Application Rate (kg/ha) =   [Total Output (kg/min) x 600] divided by [Swath Width (m) x Travel Speed (km/h)]

Remember that application rates vary with granule size, shape and density, so even the same product from different suppliers should be calibrated before application.

A particular point with snail baits is that they need to be spread to a specific ground coverage rate, usually 30 pellets per square metre or more. (Check the label instruction for your product.)

This is best calibrated by spreading over a small patch of bare ground and then counting the pellets in a measured square meter – ideally located about half-way between the spinner and the outer edge of the swath.

Sprayer calibration

For sprayers, the first step is to make sure your nozzle output is what it should be. Set up your sprayer to spray clean water at about 1500 rpm engine speed (with the gearbox disengaged) and hold a measuring jug under a nozzle for exactly 60 seconds.

The amount of water in the jug (in litres) is the nozzle output (in litres per minute).

Check several nozzles along the boom. None should be more than 10% off the manufacturer’s specification.

For the next step, put pegs 100 metres apart and time how long it takes you to travel from one to the other with your forward gear and engine revs set for spraying and a half-full tank.

Your Travel Speed (km/h) =  [100 (m) x 3.6] divided by [Elapsed Time (seconds)]

Now you’re ready to calculate your actual application rate.

Multiply your average measured nozzle output by the total number of nozzles, to get the total output across the boom in litres per minute.

Then find your swatch width in metres. This will be the boom width, plus whatever extra your end nozzles cover. 

Your Application Rate (L/ha) =  [Total Output (L/min) x 600] divided by [Swath Width (m) x Travel Speed (km/h)]

If you need new nozzles or more advice, your Ramsey Bros branch will be happy to help.

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