A key factor that would encourage farmers to use a Global Positioning Satellite (GPS) fertilizer spreader is its ability to automatically calibrate material delivery up to 12 times per minute.

The load cells are crucial in this respect, as are the electronic links between the GPS software and the belt speed of the front drive of the tractor spreader.

This was a question discussed in depth by Topcon’s Craig England in a recent Tillage Edge podcast.

GPS Fertilizer Spreader Operation

According to Teagasc, there is a range of technology on the GPS-controlled spreader, which supports calibration and flow adjustment for the operator. The load cells on the hopper work the same way as those installed on a diet feeder.

A set of electronic cylinders regulates the openings of the shutters at the bottom of the hopper. The in-cab control box allows the operator to enter the application rate and desired working width.

The GPS system senses the forward speed of the tractor and with all this information combined, the machine can automatically calculate the desired flow rate.

The machine will then measure the actual rate by weighing the amount of fertilizer that has left the hopper over a set period of time and it will automatically adjust the flaps at the bottom of the hopper to maintain the required rate.

It constantly rechecks the calculation and recalibrates the spreader. If forward speed increases, it will increase throughput, if speed decreases, it will decrease throughput, and so on.

“One thing that could mess the system up a bit would be the simultaneous inclusion of wet and dry bags of fertilizer in the hopper,” England explained.

“But the big advantage of a GPS-controlled spreader is that it will adjust the rate of fertilizer delivery as the tractor moves.”

According to the Topcon representative, the GPS systems act to open or close the shutter on a three-point hitch fertilizer spreader.

The intelligence of GPS?

So how does a GPS fertilizer spreader know to differentiate between the various physical characteristics of different types of fertilizer? At a very fundamental level, some are true compounds while others are mixtures.

“Each manufacturer now provides an application. The operator adapts to the make and model of the machine as well as the discs to be used,” said England.

“The type of fertilizer to be spread is also entered, as is the desired spread width and average ground speed.

“The app will then advise you what width of seam should be used on the disc. Some trailed spreaders change the location of the drop point.

“Many Irish distributors have sent samples of actual fertilizers from that country to spreader manufacturers, to ensure that the applications available have been fully programmed to perform well in local conditions.”