The physics of muck spreading

Physicists have to tread carefully when it comes to fertiliser, but the first tentative steps to a better understanding of the ancient art of fertilising the soil are described in a paper published today in the Institute of Physics publication, The Journal of Measurement Science and Technology.

Frederic Cointault, Philippe Sarrazin and Michel Paindavoine of the University of Burgundy in Dijon, France show how to take a snapshot of particles of fertiliser as a centrifugal spreader spits them out. Their findings could improve efficiency in the spreading of fertilisers and reduce environmental damage along field margins.

It may seem a simple task load up your centrifugal spreader with fertiliser, start it up and drag it up and down the field with a tractor.
`But,` explains Cointault, `centrifugal spreading is a very important step in precision agriculture.`
If the fertiliser misses the target things really hit the fan in terms of wasted product and potential harm to the neighbouring environment.

Although mechanically simple, centrifugal spreaders used for fertilization rely on rather complex physics. Cointault and his colleagues are hoping to put a new spin on centrifugal spreaders. The researchers describe a high resolution imaging system that can be used to track particles of fertiliser as they are flung from the spinning disc of the spreader by centrifugal force at speeds up to 70 miles per hour (118 kilometres/hour). The team hopes to be able to work out how the flight paths of these fertiliser particles are affected by disc speed and other factors.

The imaging system uses a high-speed camera and multiple flash units to take multiexposure photographs of a muck spreader in action. The photographs then allow the physicists to work out the particle flight paths by applying equations usually used by firearms and forensics experts.

`The determination of the initial conditions of flight is very accurate,` says Cointault, `and they can be introduced as input data for ballistic models so as to evaluate the repartition on the ground.`

In other words, they can work out where the muck will land. However, you are unlikely to see the imaging system down on the farm because it is a rather expensive piece of kit.
`The system will help farmers indirectly by providing input into the design of muck spreaders and allow optimum settings for best distribution to be used,` says Cointault.
He adds that there might also be applications in fluid mechanics, medicine and sports