Slurry may be an unfortunate by-product of livestock production but financial pressures have ensured there can be few who would not hope to cash in on its potential for reducing fertiliser bills.

At least, that is what contractor William Weld hopes. Based near Wareham in Dorset, Mr Weld recently invested in a slurry injection system using a 240hp Terra-Gator 2204 and a 7.5m wide Veenhuis grassland injector unit.

“My reasoning is that as herds get larger slurry disposal becomes an ever bigger issue.

There are at least a couple of permanently housed 800-cow herds in this area and more than a few with over 300,” he explains.

“The volume of slurry produced by these large herds is now so great that the traditional annual emptying of the lagoon on the ground destined for forage maize is no longer possible.

“It has to be spread at set times of the year on grazing areas – and that means being able to inject it so the grazing cycle is not interrupted.”

But Mr Weld has taken his slurry injection service one stage further – he is offering a slurry analysis which will provide
his customers with precise application rates of nitrogen and phosphates – and their value when compared to bought in inorganic fertiliser.

A kit capable of analysing 25 samples put another 1500 into the investment pot and enables N and P content to be displayed in gm/kg – the kit does not provide an analysis for potash content.

A dairy farm slurry analysis would be typically about 4.9gm/kg for N and about 5.6gm/kg for P.

“If I inject slurry at 30cu m/ha it will supply, in round figures, 125kg of N and 145kg of P.

At current fertiliser prices this would equate to a total of over 100/ha just for the N and P and the potash content also has a value,” explains Mr Weld.

“Bearing in mind I charge about 70/ha to inject it, there is a good financial argument for using slurry properly.”

When slurry has been spread Mr Weld provides his customer with a detailed breakdown of how much was applied, where it was spread and the nutrients it provided – a written accountability of the way the farm’s slurry was applied.

While emphasising the importance of knowing the analysis of the slurry he also believes the ability of the injector unit to place it at the right level for root take-up is essential.

In this way, he believes, grass areas can be treated several times during the year with application rates adjusted to manage growth.

Once set, application rate is maintained, irrespective of changes in forward speed.

This is achieved by using a hydraulically driven positive displacement pump and altering its speed accordingly.

The same pump is used to fill the tank from the lagoon – no vacuum is employed.

The system also includes a chopping unit to prevent solid material – straw, for example – blocking the smaller tubes feeding slurry to the injection outlets.

“I just input the volume I want to apply and leave it to it,” he explains.

“Working speed is about 10kph which results in a pretty reasonable output but this should improve even more when a nurse tank arrives to haul slurry from the lagoon to the field.”

fwmachinery@rbi.co.uk