Slurry storage seems to always be in the limelight when it comes to farm developments and Department rules in the last few years, with farmers keen to increase storage where possible to better utilise nutrients, prevent runoff to watercourses and stay above the law.

Changes to minimum requirements on both soiled water and slurry storage have been continually happening over the past few years, with legislation becoming stricter and storage capacities increasing.

Minimum requirements for slurry

For each dairy cow on a farm, a minimum of 0.33m3/week of slurry storage is required, equivalent of 74 gallons. A typical 100 cow herd requiring 16 weeks minimum storage will therefore need 528m³ of storage (116,143 gallons).

However, having 528m³ of storage is not enough. A gap between the top of the slurry and the bottom of slats in the form of 200mm of freeboard is required to allow for agitation and to prevent animal welfare issues.

The recommendation by the Department is to have 20% of a buffer for dairy farms and a 10% buffer for drystock past the minimum requirement.

Suckler cows require a minimum 0.29m³/head/week, with a requirement of 0.26m3/week for over two-year-old animals, 0.26m3/week for animals aged 18-26 months, 0.15m3/week for animals aged 6-18 months and 0.08m3/week for animals aged 0-6 months.

Where tanks are located outdoors, the rainfall that will enter the tank will have to be subtracted from the slurry capacity. In order to do this, the mean rainfall for the closed period in your county (e.g. 450mm over the 16-week period) will have to be subtracted from the tank depth when calculating capacity.

Soiled water storage

Soiled water storage increased to four weeks of a minimum requirement last year for all farmers bar those in a liquid milk contract, with a closed period for spreading soiled water running from 1-31 December.

Farmers on a liquid milk contract will have to be compliant with the four-week storage rule this year, which means that no soiled water can be spread on any farm for the month of December.

Current recommendations from Teagasc would be to allow for 30l/cow for every cow in the herd when calculating requirements. This is irrespective of the size of the parlour, the number of runs per milking or if flush wash systems are used for cleaning collecting yards.

While 30 litres per cow does not seem like much, this translates to 0.21m³/cow/week. Extreme caution needs to be exercised around separating soiled water and slurry storage.

The threshold for soiled water is 1% dry matter and anything above this is classed as slurry and will have to be held over for the slurry closed period (16-22 weeks). Buffer feeding cows in collection yards is an example of where soiled water thresholds can be breached.

Interim results from study

Last December, interim results from year one of a two-year study headed up by Dr. Pat Tuohy, Teagasc Moorepark, showed what many believed to be true for many years; that the current minimum requirements fall short of the actual storage needed.

The results showed that storage requirements for dairy cows were actually 20% higher than Department requirements, with 0.41m³/dairy cow/week required, while soiled water storage requirements were actually 33% higher than Department requirements.

The year one study was conducted between July 2023 and June 2024 which was an exceptionally wet period for Irish farming. The year one results also suggested that there is a significant volume of water getting into storage tanks on farms, amounting to the equivalent of approximately 20-40 l/cow/week on average.

Peak volume collected

The highest volume of slurry collection was seen in October 2023, with 626.7 litres/cow/week collected.

Total volumes collected included rainfall runoff amounting to the equivalent of approximately 20-40 litres/cow/ week on average. The contribution from rainfall runoff varied between farms and week by week. Table 1 shows the results for year one with regard to slurry collection in litres/week.

For soiled water, the mean volume collected in peak months, July-October and March-June was 300.0 litres/cow/week, which includes rainfall runoff amounting to the equivalent of approximately 20-40 litres/ cow/week on average.

Again, the contribution from rainfall runoff varied between farms and week by week. The lowest volume recorded across the 12-month period was seen in January, where just 50 litres/cow/week was collected, while just under 150 litres/cow/week was collected in December, the month of the closed period for spreading soiled water.

The preliminary results note that ‘a second year of monitoring is required to provide a full understanding of overall volumes collected’ and ‘while this project will provide data to DAFM to inform policy associated with the Nitrates action programme, any changes to current regulations will be dependent on the consideration of a range of associated issues by DAFM, in addition to this data.’’