The theme of this year’s Moorepark open day is Delivering Sustainability, which is often brought up when discussing nitrogen (N) use on Irish dairy farms.

Michael O’Donovan opened up the discussion by breaking down the N inputs and N outputs on dairy farms.

Inputs include chemical N, purchased feeds, livestock purchases and imported slurry.

Outputs are made up of milk sales, livestock sales, forage sales and slurry exports, with milk and livestock sales making up the majority of N outputs.

Nitrogen use efficiency (NUE)

O’Donovan outlined the key areas where farmers can increase NUE and reduce the surplus N going into the system.

He said by measuring grass, using predicted growth rates, the PPI and the N planner, you are clear on what, when and how much N is being spread.

He discussed the need for N applications to be reduced where low emission slurry spreading (LESS) equipment is being used, which accounts for up to 80% of slurry spread on Irish dairy farms.

The key thing for us to drive forward ... is to have better clover swards in paddocks

With an average of 1.2t of concentrate being fed to dairy cows across the country, reducing the crude protein content to 10% to 12% will also reduce the N in the system.

O’Donovan said that “the key thing for us to drive forward with grass production and reducing N is to have better clover swards in paddocks”.

He also pointed out the importance of having clover on the farm before reducing N applications, as without it there will be a reduction of dry matter production.

Clover trials

Michael Egan discussed the success of clover trials that have been ongoing with Deirdre Hennessy in Moorepark for the last seven years.

Clover has been seen to increase milk production, create potential to reduce N fertiliser and increases herbage production.

The next thing to look at is the positive influence that having good levels of clover in the sward has on the environment.

Clover trials in Moorepark have seen an increase in NUE to 55%

Farmgate NUE is 24% and rises on average by 1% per year, with the best farms in Ireland hitting 35% to 40% NUE and an N surplus of 170kg/ha.

Clover trials in Moorepark have seen an increase in NUE to 55% and a reduction of surplus N to 80kg N/ha, which is in line with the target of below 100kg N/ha.

Egan pointed out the key to all this is getting enough clover established in the sward, with the target of 20% to 25%.

Grazing management

Soil fertility, grazing management and timing are all key aspects highlighted by Egan, which can determine the successful establishment of a grass clover sward, but it does not end here.

“It's not just a matter of putting clover into the sward and leaving it there," he said.

Grazing management for better nitrogen use efficiency board, with Michael O'Donovan and Michael Egan at Moorepark 21.

"Soil fertility is an ongoing process, improving herd EBI is an ongoing process and maintaining clover in the sward at the required levels is also going to be an ongoing process.”

O’Donovan and Egan’s take home messages were:

  • The importance of getting clover in the sward and maintaining it in sward.
  • Using LESS as a better use of slurry and reduce chemical N in line with that.
  • Reducing N surpluses and increase NUE on farms using all the above methods together to increase grass production and increase profitability.