Accurate spreading of slurries and farm yard manures a Silsoe perspective
Agricultural slurries and manures are valuable sources of plant nutrients; however their highly variable physical characteristics make them difficult to spread accurately. Poorly controlled application rates or inaccurate distribution decreases the uptake of these nutrients and increases the risk of pollution.

Relatively simple machines are commonly used for spreading and have been designed to maximize the convenience of loading and to accelerate the rates of spreading, with relatively little regard for accuracy.

To help improve this situation, spreading systems for both slurries and farm yard manures have been producedat the Silsoe Research Institute, which achieve controlled application rates and improved distribution without the loss of convenience.

Slurries: Prototype slurry spreading system and fluidic diode.
The prototype slurry spreading system was based on a commercially available pumped slurry tanker. The main features of the system were a positive displacement slurry pump, an electrically operated flow control valve and a novel spreading boom. The positive displacement pump enabled discharge rate to be determined from pump speed.
However, because pump speed was proportional to engine speed and to the forward speed of the tractor in any particular gear, changing engine speed could not solely be used to control the application rate. The flow control valve enabled a proportion of the flow to be re-circulated to the tanker.
Thus, using a combination of engine speed, forward speed and valve position, the application rate could be controlled. The novel spreading boom featured fluidic diodes to improve the lateral distribution. These consisted of a simple liquid tight casing with no internal or moving parts.
The tangential entry caused the slurry to swirl and to build up a back pressure at each slurry outlet, thus equalizing the flows without constricting the pipework.

Farm Yard Manure (FYM)
The prototype solid manure spreading system was based on a commercially available side discharge spreader also known as a dual purpose spreader. A fast spinning discharge rotor at the front of the spreader threw the material from the machine. The rotor was fed with material by an auger fitted in the base of the spreader and a sliding gate controlled the flow rate of the material onto the rotor
The sliding gate was operated electro-hydrualically. A novel torque transducer was used to measure drive line torque thus enabling direct measurement of FYM discharge rate in real-time.


Automatic Control
An on-board controller enabled data from the sensors and actuators on the spreading systems to be passed to and from a control system, fitted in the tractor cab. Once a desired application rate had been selected, via an operator interface, the control system responded to output variations by automatically adjusting the spreader and/or tractor settings to maintain a consistent application rate. Thus the operator was relieved from taking action to maintain the application rate, during the field spreading operation.
For further information, please contact:

Trevor Cumby, Andy Scarlett or Ian Scotford at SRI

Tel: +44 (0)1525 860000; Fax +44 (0)1525 860156