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Using Slurry To Grow Grass In 2022

William Burchill PhD, Teagasc/Dairygold Joint Programme 

The value of slurry has essentially doubled in the last twelve months due to the increase in fertiliser costs and now stands at around €40 per 1,000 gals of cattle slurry. With this in mind here are 3 steps to maximise the use of slurry on your farm in 2022;

1. Apply slurry to silage ground to maximise its P and K value

We need to remember that the majority of the value of slurry is from its P and K and thus slurry should be targeted to areas of the farm with the highest demand for P and K i.e. silage ground. When spreading slurry on the milking platform target paddocks with low P and K indexes first and the lowest grass covers in spring.

2. Apply slurry in spring using dribble bar or trailing shoe to maximise its N value

Moving from spreading in the summer time with a splash-plate to a spring time with a dribble bar or trailing shoe will give you an extra 6 units of N/1,000 gals from your slurry. While spreading slurry in spring has the potential to improve slurry N values this is reliant on good grass growing conditions, so ensure conditions are right for spreading i.e. trafficability, soil temp, weather forecast etc. Trailing shoe and dribble can be used to apply slurry to grass covers up to 1,000 kg DM/ha. 

3. Know what’s in your slurry and adjust your application rate to suit

Slurry can be tested for it N, P and K content relatively easily and cheaply by a number of labs across the country. In the winter of 2020/21 up to 128 slurry samples from dairy farms within Teagasc/Dairygold Joint programme discussion groups where tested for its DM%, N, P, and K contents. On average the slurry contained 10.7 units N/1,000 gals (applied using LESS in spring time), 5.3 units P/1,000 gal and 27 units K/1,000 gals and varied compared to the standard Teagasc values (Table 1). Based on these results, slurry applied at 2,000 gal/acre using a trailing shoe/dribble bar in spring will supply 21 units N/acre.

The standard N recommendation in spring is to apply 23 units N/acre in early February if ground and growth conditions are suitable. Based on this recommendation and the results of the slurry tests we can see that using a trailing shoe/dribble bar at a rate of 2,000-2,500 gals/acre will be the most efficient method to meet these N requirements using slurry. Heavier applications of slurry using a trailing shoe/dribble bar will supply more N than is required at this time of the year. Instead the slurry should be spread out over a larger area and used to replace the standard ½ bag urea or 23 units N/acre to reduce your fertiliser N cost this spring.

Table 1: Slurry test results from dairy farms across the Dairygold Catchment spread using LESS (low emission slurry spreading) in spring.








Slurry Dry Matter %

Units N/1000 gals

Units P/1000 gals

Units K/1000 gals

No. Samples Taken

Standard Teagasc values






Average Teagasc/Dairygold JP






Covered tanks






Open towers






Open tanks













PastureBase Review 2021 Dairy

Michael O’Leary from PastureBase Ireland reviews the 2021 grass production data on dairy farms where the national figures indicates a reduction of 400kg DM/ha across dairy farms measuring 30 covers or more compared to 2020.

 Grass measuring and budgeting is the cornerstone of all ruminant production systems in Ireland. PastureBase Ireland has seen a steady increase in the number of farmers using in application in recent years with 2,623 farms now recording >10 covers in 2021 an increase of 11%. The following analysis describes the findings from dairy farms who have recorded 30 covers or more in 2020 (810 farms) and 2021 (1,010 farms).

The national picture shows that the average dairy farm on PBI grew 400kg DM/ha less grass in 2021 when compared with 2020 (13,011 vs 13,407kg DM/ha).

However when a matched sample of 650 dairy farms, was analysed a reduction of 300kg DM/ha was seen with the south east most affected with a reduction of 434kg DM/ha while farms in the north west were least affected, with a slight reduction of  just 8kg DM/ha.

As a result of less grass growth in 2021, 247kg DM/ha less silage was conserved for this matched group of dairy farms. Another key finding saw the number of grazings increased slightly (0.3) from 7.4 in 2020 to 7.7 in 2021. This lead to a decrease in pre grazing yield from 1,576kg DM/ha in 2020 to 1,527kg DM/ha in 2021. Both the increase in the number of grazings and reduction in pre-grazing yield shows that farmers are making proactive informed decisions.