The College of Agriculture, Food and Rural Enterprise (CAFRE) advisors have been profiling the benefits of improved slurry management over recent weeks.
The focus of this activity was the hosting of two slurry management events, one of which was held on the Banbridge dairy farm of Ian McClelland.
Mark Scott, head of CAFRE’s Sustainable Land Management Branch, used his presentation at the Co. Down venue to highlight the importance for farmers in getting the best possible value from all animal slurries.
“There are four key sustainability challenges coming up for farmers. These relate to phosphorous (P), nitrates, ammonia and carbon.
“Slurry management and how farmers devise their future nutrient management plans will have a strong influence on all these issues into the future.
“Ammonia emissions from slurry can be controlled by the use of low emission slurry spreading equipment (LESS).
“Where [P] is concerned, the issue is very much focused on the run-off of slurry into water courses.
“The same principle holds when it comes to reducing the level of nitrate ending up in our rivers and lakes,” Scott explained.
Low emission slurry spreading
Scott continued: “LESS will also reduce the amount of greenhouse gas (GHG) emissions associated with the spreading of slurry.
“Slurry management has such an integral impact on each of these four, key sustainability challenges that now is an appropriate time to deliver a comprehensive update to farmers on this important issue.”
Where low emission slurry spreading is concerned, the CAFRE representative highlighted the growing use of the technology in Northern Ireland.
“We are also seeing a lot of contractors using LESS equipment with umbilical systems, which is very positive,” he added.
Significant numbers of farmers in NI have availed of grant aid to purchase new vacuum slurry tankers in tandem with a trailing shoe or dribble bar.
However, it is important that they calibrate these systems properly to ensure that actual slurry application rates are in line with a specific crop requirement.
“Operators must take full account of the spreading capacity generated by all of the pipes, the band width of the system and the forward speed of the tractor,” he said.
According to Scott, tractors drawing a tanker fitted with a dribble bar or trailing shoe should be driven at faster speed in the field relative to what would have been the case if a splash plate-based system had been in use.
“Most farmers who have bought a new slurry tanker over the past five to seven years would have secured a machine that had been specified for the future attachment of either a dribble bar or trailing shoe.”
Turing to the issue of slurry capacity on livestock farms in NI the CAFRE representative indicated that the issue very much hinges on the weather at the shoulders of the year – late autumn and early spring.
“By law, farmers must have access to at least 22 weeks slurry capacity,” said Scott
“Farms are randomly inspected by the Northern Ireland Environment Agency (NIEA) to ensure these standards are being maintained.
“The priority for all farmers is to best integrate the use of slurry into the management of all the crops they grow – arable and grass.”
Slurry application rates
CAFRE has devised a two step calculation, which will allow farmers and contractors work out the required forward speed of a tractor when using a low emission slurry spreading system.
The variable to be included are the actual application rate required, the capacity of the tanker being used, the width of the trailing shoe or dribble bar and the estimated time to empty the tanker.
A standard example of this process would centre on an application rate of 3000gal/ac (33 m3/ha) using a 3,000gallon (13.5 m3) LESS tanker, with a bandwidth of 7.5m – emptying in four minutes.
Step one of the calculation involves the volume of the tanker being divided by the projected emptying time (in seconds) to give a projected discharge rate.
In terms of the example referenced above, this works out at 0.056 m3/sec.
The required forward speed of the tractor is then calculated by multiplying the discharge rate by 36,000, and then dividing this figure by the product of the systems band with in metres and the application rate in m3/ha.
The final answer for the example given above works out at 8km/hr.