How to cut costly fertiliser wastage during the spring spreading season

FERTILISER spreading has started as farmers strive to boost grass growth this spring. This is a really expensive farm input, so you want to make sure all of your fertiliser is going exactly where it’s needed.

Keep in mind that the correct settings of your spreader are determined by the physical properties of the fertiliser: particle size distribution, bulk density and flow rate all influence the fertiliser spreader calibration settings. Always check the information on the bag of fertiliser and remember to change the settings every time you switch to a different kind of fertiliser.

You can find the correct settings on the spreader manufacturer’s tables. These are based on tests under ideal conditions in test stations and give information on how to set the spreader for optimum even spreading at the desired application rate (kg/ha) and at a specific working width. Set the spreader at the right height above the crop when you are out in the field.

This measurement is also found in the spreader manufacturer’s tables. To make sure you’re achieving the best possible spreading result, you can perform a tray test using your particular combination of spreader settings and fertiliser. A tray test will help you fine tune the settings, so you can rest assured that the fertiliser is spread evenly across the entire spreading width. A separate test should be conducted for different fertilisers.

You can either do this yourself or hire a fertiliser spreader calibration expert to conduct the tests. Those who overlook calibrating their spreader face financial loss as Derek Casey costly fertiliser is either over applied, under applied (leading to yield drops) or spread in uneven patterns (leading to striping). It’s a cheap step that will pay for itself in multiples.

Some farmers may have specified a calibration and tray kit with their spreader when they were buying the machine in the first instance. 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-€300 for entry level spreaders. It’s a good idea to have the spread pattern checked at least once every two seasons.

The spread pattern is assessed by a full tray test where for every 0.25m or 0.5m width of the spread, a tray is placed on flat ground and the spread pattern is measured. The weight of fertiliser from each 0.25m or 0.5m wide tray is then weighed and the evenness is assessed by the shape of the plotted graph and the calculated coefficient of variation (CV). From this data, the CV is calculated by measuring the variation in each tray from the average.

The lower the CV, the better. A CV of 10pc-15pc is seen as being acceptable and most industry experts agree it 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. 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 very 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. Be sure to consult your local machinery agent to fix the problem.