Over the course of the spreading season, a fertiliser spreader, like any piece of machinery, should be checked over. A spreader should be calibrated often to ensure the desired application rate is met. With fertiliser being such an expensive commodity, it is important that it is spread precisely. The spreader will only do this if it is set up and working correctly.

Machine inspection

Although this would have been done at the start of the season, it’s no harm to have another quick glance around the machine mid-season. Inspect the frame, the hopper and spreading mechanism for any signs of wear or fatigue, such as cracks or severe corrosion that may affect its overall load carrying ability. Similarly, the hopper should be crack free and its shutters in good physical working condition, closing and opening fully. Worn linkages or other regulator components can affect a spreader’s output and may result in an uneven application.

Vanes that were borderline on needing to be replaced earlier in the season may now need replacing. Good vanes are critical in achieving a good spread pattern. Vanes that have a rough or wrinkled surface and leading edge that isn’t straight will need to be replaced. What you may think is a small bit of wear here may have a large effect on the machine’s spread pattern, especially at wider bout widths.

A spreader's accuracy depends on the operator and how well it has been set up. \ Donal O'Leary

Bearings should be given a quick check over for unwanted movement. On a disc machine, do this by shaking each of the discs vertically. Ideally there should be no bearing wobble, but if present it may be worthwhile investigating further to identify the problem. Usually this is as a result of bearing failure and is solved by replacing bearings and/or shafts depending on condition.

The agitators in the hopper should be checked over and be in good working order. Check that any other parts which should move, are moving freely. All grease points should get grease before mounting on the tractor. If there is a headland management system fitted, make sure it is engaging and disengaging fully. These are important to ensure that the environment is protected in addition to ensuring accurate application up to the hedge. On some machines this is just a matter of changing the direction of the discs so that discs rotate in the opposite direction. Make sure the directional change lever on the gearbox slots into position once changed.

A wagtail spreader's flow rate setting should also be calibrated throughout the season.

Tractor mounting

The drop arms should be measured with a tape to ensure they are the same length. It’s also important that the stabilisers are nice and snug, with the spreader mounted centrally. Any play here will affect the spreading pattern.

Once fitted, raise the spreader to the correct working height and adjust the toplink so that the spreader is sitting at the correct angle as advised by the manufacturer or spread chart. Most spreader manufacturers tend to follow similar spreading heights which is 75cm from the top of the crop to the spreading mechanism – whether this be to the spreading discs or the wagtail.

If you have the time, it may be worthwhile checking rear tyre pressure. Both sides should be equal. The two factors critical for accurate spreading are the tractor’s forward speed and PTO speed. Once the PTO speed has been set to 540rpm, forward speed can be altered by changing gears.

The spreader's overall condition should examined for damage or wear.

Machine setting and calibration

Setting a spreader is relatively straightforward. On a disc machine there are two main areas of adjustment – fertiliser flow rate from the hopper, and disc and vane settings. A wagtail spreader has only one area of adjustment – flow rate. The steps involved in setting the flow rate on wagtail and disc machines are similar.

Flow rate is adjusted by moving the regulator. Naturally, the one regulator setting will not work for all fertilisers as flow rates vary depending on the characteristics (shape, size and even the brand) – no two fertiliser samples are the same. Knowing the flow rate is necessary to achieve a correct application rate (kg/ha). Once this is set and the spreader is calibrated it ensures the correct amount is leaving the hopper.

Disc machine

Depending on the make and model of the spreader, a number of the following adjustments may need to be made: vane type and position, fertiliser drop point, disc size and toplink angle. All may need to be adjusted in accordance with the spreading chart at the set working width (m), application rate (kg/ha), forward speed (km/h) and type of fertiliser being applied.

These adjustments vary from brand to brand so you will need to refer to the manufacturer’s settings and spread charts. This information is generally in the spreader manual or settings book, although not always easily followed.

Most manufacturers now have mobile phone apps that show spread charts and have calculators that allow you to input information such as fertiliser type, application rate, forward speed and spreading width and then display the machine settings to achieve this. Most manufacturers have a huge selection of fertiliser types and brands already tested in their test halls.

The spread chart will also indicate the accurate kg/min for each particular fertiliser for a machine. To calibrate, shut off one side, and remove the disc on the other side before fitting on the calibration container. The spreader should be run for one minute while the container gathers the fertiliser. The container’s weight after one minute should match the kg/min rate as displayed by the app or spread chart.

Wagtail calibration

A wagtail requires no further setting up once mounted correctly and the the flow rate has been set. This is done using the regulator, depending on working width (m), application rate (kg/ha), forward speed (km/h) and type of fertiliser being applied.

Similar to disc machines, many manufacturers have mobile apps that allow you to input all these variables along with the fertiliser type. The app will then provide you with a setting or spread chart to suit the fertiliser being used – granular, prilled or even seed.

A wagtail spreader's flow rate should be calibrated to ensure that it spreads what it is set to spread.

The calibration procedure is similar to that of a disc machine. You remove the spout and fit on a calibration container. The app or spread chart will provide a rate in kg/min which should match that coming from the spreader. Run the spreader at the setting recommended by the app or spread chart and then weigh the fertiliser that comes out over the course of the minute. If the two figures don’t match up, some fine-tuning may be required.

In the field

Once the machine has been correctly set up, the operator is the final piece in the puzzle – they need to drive accurately, ensuring both the PTO and forward speed is correct and the correct bout width is being maintained.

When using a wagtail/pendulum type spreader with a working width in the region of 10-12m, it’s reasonably easy to maintain an accurate bout width by eye.

Once working with wider bout widths or spreading in a recently cut field, it becomes much more difficult to maintain accuracy. Recent years have seen a huge uptake in entry level GPS. These systems can help to cut out overlapping and reduce fertiliser usage.