With fertiliser prices at an all-time high, cattle slurry will be a key resource on the farm to reduce the impact of high nitrogen (N), phosphorus (P) and potassium (K) prices.

Retaining more slurry N results in a larger proportion of N from slurry to grow grass in the early part of the year.

This will provide opportunities to reduce chemical fertiliser N inputs in 2022.

The use of low-emission slurry spreading (LESS) equipment such as a trailing shoe or a band spreader is one of the key technologies available to meet our national ammonia-gas reduction target between now and 2030.

Know the value of slurry N, P K and S

We now must look at cattle slurry the same as bag fertiliser and focus on utilising all the major nutrients as efficiently as possible. LESS techniques help supply a larger proportion of the crops 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 or 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 matter (DM) contents applied by LESS.

Typical cattle slurry has a DM content 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 should receive a large proportion of their P and K in the form of slurry in 2022.

Take slurry DM 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 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 slurry 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 springtime will be more favourable to improving the recovery of N from the slurry. For example, during cool (< 13°C), damp, overcast days, N loss through ammonia emissions are lowest.

Using the right equipment

Spring applications using LESS further increases N availability by 65% compared to summer applications. For example, where a grass silage crop receives 33m3/ha (3,000 gallons/ac) in springtime, this will supply 33kg N/ha (approximately 30% to 40% of the crop’s N requirement). However, when applied in summertime it will only supply 20kg N/ha.

Apply cattle slurry to first-cut silage fields to supply the majority of crop P and K requirements and maximise N recovery.

Other benefits of LESS

  • Improved flexibility with applications as a result of reduced contamination of herbage leading to 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.

    • Slurry calibration tool

    Teagasc has created a simple online calibration calculator to eliminate the guesswork. The tool can be used with any type of slurry tanker no matter what applicator is being used on the back. It works on your smartphone so it can be accessed from the tractor seat. It is simple to use.

  • Sliders allow you to input the size of tanker, spread width and the time taken to empty the load.
  • Select your desired application rate.

    • It will give you the correct forward speed needed. This will ensure you are making the most of the valuable fertiliser source.