Putting slurry on to cereals or oilseed rape is a practice that attracts mixed reactions. Few people can fault the agronomic principles, but many object to the damage caused by the heavy machines needed to apply the material. There have also been concerns about whether slurry can be applied evenly enough to avoid over or under-dosing.
Manufacturers of slurry spreading equipment have been grappling with these issues in recent years. In fact, the trend now appears to favour boom-type machines which can use tramlines and employ either trailing shoes or dribble pipes to apply the slurry.
Injection systems have their fans too, but their relatively narrow working width means that there are more passes to make and more wheel marks as a result. By definition, slurry injection equipment needs the weight of a tanker to be able to penetrate the ground.
Which is the best way to do the job, though – a tanker with a boom or an umbilical feed system? A lot depends on the geography of your farm and the position of your fields relative to the slurry store. Long distances can create high pumping demands and take time to set up for an umbilical system.
Equally, a tanker has to travel back and forwards to the slurry store – unless there is a nurse tank employed – and output will be reduced as a result. And the heavy loads involved may not be welcome on the fields even if the tractor and tanker are shod on flotation tyres.
Terry Baker of slurry spreading equipment specialist company Tramspread is convinced that umbilical systems have the edge.
“The output that can be achieved with an umbilical feed system usually exceeds that of a tanker,” he says. “Most importantly, it can be used in conditions that would keep a tanker in the barn.”
Mr Baker’s company, based near Stowmarket in Suffolk, markets a range of umbilical equipment. It also offers a contract spreading service throughout the eastern counties, treating some 13,350ha (33,000 acres) a year.
Tramspread’s Terry Baker: “We aim to keep the boom as low as possible while retaining an even spread.”
He says out that most of his customers in this area are arable farmers who also run large pig units and want to spread slurry on to their cereal crops.
“We analyse the slurry for N content. Typically, it contains about 1kg N per cubic metre of slurry which means, depending on the volume we apply, an allowance can be made when applying inorganic N,” he says. “If a more comprehensive analysis is required for P and K and trace elements we have to send it away to the testing laboratories.”
Setting-up time can be an issue and Mr Baker charges £42/hour for this part of the job – actual spreading is charged at £73/hour.
First off, a mobile pumping unit is set up at the store. This involves a 170hp Deere diesel engine driving a Bauer centrifugal pump which delivers slurry at about 200psi through 10cm (4in) diameter piping.
The pump, depending on the terrain and the viscosity of the slurry, is capable of delivering to a distance of up to 2000m. For longer distances, a second pump is brought into action.
At the field, laying out the hose is a science in itself. There are many variables (point of entry, field shape and size, telegraph poles) but the general rule is to pull the feed hose across the middle of the field at right angles to the tramlines. The tractor then works up and down the tramlines.
As the first tractor moves across the field a second tractor pulls the feed pipe back to keep it clear. “The idea is to prevent the pipe from kinking or twisting and reduce the amount of pipe being pulled along behind the tractor,” says Mr Baker.
“A pipe full of slurry needs quite a bit of pulling. It’s interesting to stop the tractor on the headland and feel the pipe pulling you back several metres as the stretch is taken up.”
A rear-mounted 12m boom with three outlets gives a 24m spread. During headland turns the flow to the boom on the inside of the turn is turned off which then increases the flow to the outside boom.
The main limit to the quantity of slurry that can be spread isn’t surface run off, but slurry escaping via land drains. Mr Baker says he always asks to see a map of a field’s drainage system so that he can monitor the system’s outlets. Application rate is typically 33cu m/ha with a maximum of 52cu m/ha
“The driver has the application rate displayed in the cab. The volume being pumped is constant, so application rate is adjusted by changing in forward speed,” he explains. “Output is about two hectares/hour.”
With several thousand hectares to spread each year, slurry is applied to crops at most times of the year.
Cereals or oilseed rape best utilise slurry nutrients is in the spring but spreading can continue until the crop is quite tall with no lasting damage being caused by the hoses. Autumn application on to stubbles, while essential for some pig producers who need to have their slurry stores emptied, doesn’t make the best of the nutritional value of the slurry.