Why use a Dribble Bar or Trailing Shoe?
Nutrient losses from slurry spreading
In Ireland most slurry is land spread by the splash plate method. This method of application can result in up to 80% of the available Nitrogen (N) applied in the slurry being lost to the atmosphere in the form of ammonia.
Not only does this result in a loss of this valuable nutrient but it also causes atmospheric pollution.
Following surface spreading, approximately 30% of the total ammonia loss takes place in the first hour and the 80% above within the first 12 hours. A basic concept to minimise such losses is to reduce the surface area of the spread slurry that is exposed to the air.
Grassland slurry spreading systems
Systems of slurry spreading that minimise the surface area of the spread slurry exposed to air and lower ammonia loss are widely used across Europe.
These alternatives mainly include:
Dribble bar spreading
Deep injection (150 mm; 6 inches) is limited by soil texture, soil moisture, stone content and slope. Therefore, in Ireland deep injection is only suitable for a relatively small area. Dribble bar spreading of slurry reduces the surface area of slurry exposed to the air. In addition, dribble bar spreading can achieve a more uniform spread pattern and less contamination of herbage by slurry solids.
The design of the Slurrykat dribble pak using hard straight cured hose ends on the booms means that the dribble bar can achieve the effect of the trailing shoe by combing the grass/ crop aside and delivering the slurry directly onto the soil surface. An alternative to the dribble bar is the trailing-shoe application system in which a metal shoe parts the herbage and slurry is deposited in bands on the soil surface, with the minimum of herbage contamination.
Benefits of alternative slurry spreading systems
In Germany, research has shown that application of slurry by Dribble bar leads to lower ammonia losses, better N use efficiency and higher crop yields than either splash plate or injection spreading. In Holland, slurry applications by dribble bar and trailing-shoe, have resulted in 69%, 86% and 99% less ammonia emissions respectively than splash plate spreading.
Recent research at AFBI-Hillsborough has compared slurry application by splash plate, trailing-shoe and dribble bar methods in May after the first silage harvest. Slurry was applied 9, 17 and 23 days following the first silage harvest. Average application rate was 50 m3/ha. Compared with the conventional splash plate method, the dribble bar and trailing-shoe methods increased grass yield by 19 and 21% respectively averaged over the three spreading periods. The increased yields obtained with the dribble bar and trailing-shoe methods were equivalent to applying inorganic fertiliser N at, on average, 79 kg/ha compared with 18 kg/ha when slurry was applied with the splash plate. In addition, the ability to apply slurry up to 23 days after silage harvest is a major advantage.
Grass contamination from slurry
In recent research at Hillsborough, observations at the time of harvest indicated less contamination of herbage when slurry was spread by the alternative methods rather than by splash plate. Similarly, research in England has shown that slurry can be applied six weeks before a silage harvest by the new method with no contamination of the herbage or adverse effects on silage quality.
Window of opportunity for spreading
Research in England and at Hillsborough has shown that it is possible to spread slurry with a dribble bar or trailing shoe system much later after silage harvest than is feasible with a splash plate. The AFBI work indicated yield benefits from spreading up to 3 weeks after the first grass harvest.
Financial benefits of alternative slurry spreading systems
Based on N fertiliser at a cost of £288 per tonne for 27% Calcium Ammonium Nitrate (CAN, 27-0-0), the slurry plot trials indicate the value of the nitrogen gained by applying slurry with a trailing-shoe or dribble bar to be £64 per hectare more than if the same slurry was applied with a splash plate.
Taking average cattle slurry (6% dry matter) at an application rate of 50 m3/ha. Using trailing-shoe application systems rather than splash plate spreading, the chemical fertiliser required to supplement the available N from slurry for second cut silage could be reduced by 27 kg per hectare. This represents a saving in fertiliser costs of £28.80/ha.
The net savings from using alternative slurry spreading systems will depend on the additional charges (if any) made by contractors for the use of such equipment. Where a farmer is using his own machinery, the extra operating costs will depend on the specification of the machinery purchased.
Slurry is a valuable source of nutrients. Recent research at AFBI-Hillsborough highlights important opportunities to recover more of the nutrients present in livestock slurry. Furthermore, new methods of application can increase the flexibility of slurry management by permitting a longer period of application after a silage harvest.
Although these new methods can be more costly, they provide important opportunities to minimize environmental pollution and improve availability of nutrients from slurry for plant uptake.
Dribble Bar Applied Slurry Trailed Against Compound Fertiliser
The grass on the right received an application of compound artificial fertiliser whereas on the left slurry was applied using the SlurryKat dribble bar system precisely at the same nitrogen application rate as the compound fertiliser. Both applications were carried out at the same time and the picture taken eighteen days later. The results from applying the slurry with a SlurryKat system not only demonstrates that nutrient uptake is dramatically increased and sward thickness is also visibly improved.