Are sprayer issues hitting your pocket?

Correct spreader settings are machine specific and are based on the type of fertiliser being spread and the bout width chosen
Correct spreader settings are machine specific and are based on the type of fertiliser being spread and the bout width chosen
Derek Casey

Derek Casey

It's amazing how year after year farmers pay big money for fertiliser and yet don't bother setting up their spreader properly.

Those who overlook calibrating their spreader face financial losses as costly fertiliser is either over-applied, under-applied (leading to yield drops) or spread in uneven patterns (leading to striping).

Some farmers may have specified a calibration and tray kit with their spreader when they were buying the machine.

If you didn't, consider the option of asking the machinery agent who sold you the spreader to calibrate it for you.

This shouldn't cost any more than €250 for entry level spreaders. It's a good idea to have the spread pattern checked at least once every two seasons.

A tray test is simple. After laying the trays out across the machine's spreading width, a run through the trays is made with the tractor and spreader as it would be operated in the field.

Level ground and wind free conditions are essential. Fertiliser collected in the trays is then transferred into corresponding test tubes and the contents are recorded. From this data something called the Coefficient of Variation (CV) is calculated by measuring the variation in each tray from the average.

The lower the CV the better. A CV of 10-15pc is seen as being acceptable and most industry experts agree will prevent crop striping. However, surveys indicate that a lot of spreaders in use today have CVs of 30pc or more leading to financial loss and inefficient application.

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Research has shown that improving the CV from 30pc down to 10pc will bring a yield benefit of around 0.25t/ha in wheat, so it is a worthwhile job.

If your CV is well off target it could be an issue with worn vanes, incorrect spreader height or sometimes even top link setting. Consult your local machinery agent to fix the problem.

10 steps to more accurate spraying

1 Safety first: ensure the spreader has  an intact PTO shaft cover in place.

2 Correct spreader settings are machine specific and are based on the type of fertiliser being spread and the bout width chosen. Basic information is given in your spreader's instruction manual. If you don't have these, spreader manufacturer websites and phone apps are also a great source for up-to-date settings.

3 Spreading discs should be slightly higher on the back than on the front in order to give the granules the required trajectory when they leave the spreading vanes. Lift controls should be set to allow correct disc height (as determined by the manufacturer and fertiliser type) from the crop or ground.

4 Tighten the lift arm stabilisers to prevent the spreader jolting on rough ground and giving unpredictable spread patterns. Make sure both lift arms are level to minimise bias.

5 Once you set your forward speed is set it is essential to maintain the same forward speed all the time, e.g. 7km/hr. The same applies for PTO speed; this should not be altered once spreading begins.

6 Headlands can be awkward and potential areas of over application, so shut off the spreader once the back wheels of the tractor meet the inside track of the headland run. This prevents covering an area already spread. GPS based switching can automate this process and improve accuracy on wide spreading machines.

7 Borders with water courses and field boundaries also pose a challenge. Manufacturers offer a range of mechanisms to help. These include tilting the spreader down at the boundary side; changing disc speed; adding a deflector; reversing disc direction or changing the graunule drop point to use a different disc vane.

8 Only buy quality fertiliser that has good spreading characteristics with at least 80pc of the granules in the 2 - 4 mm size range and preferably granules of smooth round shapes. This will ensure a good even spread pattern.

9 Clean and lubricate the spreader after every working day.

10 Check the spreading vanes for wear, pitting or indentations. Vanes on a 12m spreader typically last 3-4 seasons, an 18m spreader 2-3 seasons and a 24m spreader 2 seasons. A new set of vanes cost from €350-€450.


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