Top tips to calibrate your fertiliser spreader

Fill the hoper with sufficient fertiliser for the spreading you will be doing, or at least 100kg for calibration. Remove one of the discs from the spreader and place the manufacturer-supplied calibration chute onto the machine. Hang a bucket onto the back on the calibration chute.

Using a slide rule or similar calculator from the machine manufacturer, calculate the test distance you need to drive for the working width you will be spreading. This is roughly one fortieth of a hectare in area.

If you do not have a slide rule or calculator, divide 500 by the working width, to give you the distance in metres.

Mark your required distance out in the field, giving yourself space to ‘run-up’ to the first mark, and sufficient space to turn around after the second mark.

Set the test opening on the rate slide on the machine, according to manufacturer guidelines. Start tractor, run the PTO at 540rpm, select the gear you will be using and drive towards your first mark in the field. Allow yourself sufficient space to run-up to the first mark to ensure you are at your planned forward speed.

When you hit the first mark, open the shutter your bucket is under, and when you hit the second mark, close the shutter.

Turn the tractor off, remove the bucket and weigh the quantity of fertiliser collected, minus the weight of the bucket.

If you have a manufacturer’s slide rule, use it with the weight of fertiliser collected to achieve the required rate scale settings for the spreader.

If you do not have a slide rule, simply multiply the net weight of fertiliser collected by 40, this will give you the amount of fertiliser being applied in kg/ha.

To check this rate setting is correct, repeat the test using the new setting. If the result is a little different from the rate you set, tweak the settings on the spreader up or down accordingly.

Remove calibration chute and replace the disc.

Check that the spreader settings are giving you the correct amount of overlap. Use the spread width settings determined in Step 1, set the height of the spreader to at least the minimum required distance from the ground and ensure it is level.

Using four trays, place them equally across half the working width on the ground from the centre of the first tramline. For example, for a 24m working width you need the trays to cover 12m, by placing the trays at 3, 6, 9, and 12m from the tramline.

With the trays on your right hand side, drive up the tramline with the machine spreading at your chosen settings. Turn the tractor right handed at the top of the test run, and come down the next tramline, still spreading over the trays, which will now be to your left.

Collect the fertiliser from each tray in individual test tube. If you have collected an equal amount in each tray the spread pattern is correct.

If you have collected less in the trays nearest the tractor and more in the middle two trays, the machine is spreading the fertiliser too widely, creating an excess of fertiliser in the overlaps. In this case, reduce the working width setting.

If you have more fertiliser in the trays nearest the tractors, and less in the middle two trays, you are not spreading wide enough. Increase the spreading width setting to allow it to throw the fertiliser out further.