The way we spread slurry here in Ireland is changing and will change even further in the coming years.

To reduce the loss of nitrogen (N) from slurry, a move away from the splash plate to low-emission slurry spreading (LESS) techniques, such as trailing shoe/hose or band spreader is happening on farms.

These methods reduce ammonia–N losses during application, resulting in extra N availability from spring or summer slurry applications.

Retaining more slurry N results in a larger proportion of N from slurry to grow grass, while providing opportunities to reduce chemical fertiliser N inputs.

The use of LESS is one of the key tools available to meet our national ammonia gas reduction target between now and 2030.

N, P K and S values

We now must look at cattle slurry in a different light and focus on utilising all of the major nutrients as efficiently as possible.

LESS techniques help to supply a larger proportion of the crop’s total N requirements than ever before. This change delivers a double dividend in that it helps to reduce agricultural emissions and our overall farm fertiliser bill annually.

The first step to utilising the nutrients in slurry is to know how much N, P and K is in each 1,000 gallons of slurry.

On farms where dirty water / parlour washings are entering the slurry tank, a more dilute slurry is available.

Table 1 shows the available fertiliser values (N, P and K) for a range of cattle slurries at different dry matters(DM) applied by LESS.

Typical cattle slurry has a dry matter (DM) of 6% and a nutrient profile shown in Table 1. More dilute slurry (2% to 4 % DM) will have reduced N, P and K values, which may result in the under-fertilisation of crops such as grass or maize silage if the slurry is assumed to have more typical nutrient content. These crops generally receive a large proportion of their N, P and K in the form of slurry.

Take slurry DM percentage into account and make adjustments to application rates to ensure sufficient nutrients are applied to meet crop requirements during the growing season.

The DM percentage of slurry can be measured on a farm with a slurry hydrometer or, alternatively, by sending a sample of agitated slurry for nutrient analysis to a laboratory (N, P, K and DM percentage).

Timing of applications

The second step to increasing slurry N efficiency is optimising the timing of slurry applications.

Spring applications of cattle slurry typically have higher recovery of N by up to 50% compared to summer applications (Table 2).

Weather conditions in spring will be more favourable to improving the recovery of N from the slurry, eg cool (< 13°C), damp, overcast cast days when N loss through ammonia emissions are lowest.

Spring application using LESS further increases N availability by 65% compared to summer application. For example, where a grass silage crop receives 33m2/ha (3,000 gallons/ac) in springtime, this will supply 33kg/ha N (~25 to 30% of the crop’s N requirement). However, when applied in summertime, it will only supply 20kg/ha N.

Other benefits of LESS

  • Improved flexibility with applications as a result of reduced contamination of herbage leading to a quicker return to grazing.
  • Opportunity to apply slurry into larger grass covers which creates a wider window for application in better soil conditions, particularly in spring.
  • More even application of slurry across the spread width.
  • Smells released during and after application are reduced.