Video: How slurry application method and timing can affect on-farm emissions

In the third instalment of the ‘Farmer Feedback Report Series’ – an initiative brought to you by Bord Bia and AgriLand – we will examine the area of slurry management, and how certain practices can help farmers reduce associated emissions when it comes to storing and applying slurry.

In the video (below), Dr. Eleanor Murphy, Origin Green data manager, Bord Bia, explains that slurry emissions can be associated with approximately 17-20% of the total emissions on farm, and factors such as how long the slurry is actually stored for and application method can influence this figure.

However, she also notes that a certain proportion of those emissions will come from manure that is excreted from animals during grazing.

In relation to the timing of slurry application, Dr. Murphy highlighted that the greatest value of nitrogen (N) in slurry is available to the soil in spring, with Teagasc recommending that 70% of slurry should be applied at this time.

“What’s happening here is that, at this time of the year, the N demand by the plant can be met by the application of the N content in slurry.

“Also, there’s less interference with sunlight and wind when the slurry is being applied – that’s why the springtime is associated with lower emissions with manure management on farm,” Dr. Murphy explained.

The other aspect to consider is how farmers actually apply the manure. In the past, the splash-plate application method was the typical system used on Irish farms, but Dr. Murphy noted that there now has been a move towards Low Emission Slurry Spreading (LESS) equipment.

For example, the use of a trailing shoe can decrease the loss of N to the atmosphere at the time of spreading. Additionally, where there is a difficulty using a trailing shoe, a trailing hose or an umbilical system can be considered.

“What these do is apply the slurry under the canopy of the grass at a slower rate than the splash plate and this means that there is less volatilisation of the N in the slurry itself.

“There’s also a greater uptake of N that is available and there is less interference with the environment such as sunlight and wind when it’s being applied,” she said.

However, following this process it is important to note the increased utilisation of N from slurry when it comes to chemical N application.

Summary

Moving slurry application from summer to spring and doing so in conjunction with the use of low-emission application methods, can significantly reduce greenhouse gas (GHG) emissions.

How?
  • Spring application reduces emissions following land spreading due to the more favourable weather conditions (cool, low sunlight) at that time of year;
  • Storage losses are reduced due to the shorter storage period;
  • Reduced ammonia losses increases the fertiliser replacement value, reduces fertiliser N and associated manufacture and spreading emissions;
  • Low-emission application technologies, such as a trailing shoe, leads to reduced ammonia losses and increases the fertiliser replacement value of slurry.

A 20% shift to spring application can reduce farm GHGs by 1.3%, while a shift to a  trailing shoe can lead to a reduction of 0.9%.

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