Huge pressure on slurry and grain storage facilities
Massive pressure was placed on slurry storage facilities this year with capacity inadequate for the prolonged winter on many farms.

What felt like the never-ending winter of 2018 will be etched in farmers’ memories for a long time to come. Slurry storage capacity was under pressure on many farms because housing went on longer than planned. Expansion in herd numbers exacerbated the issue. Many farmers had to find out the hard way that storage was not up to spec on their farms.

Now that the tough spring is behind us, maybe it is worth looking at slurry storage capacity on the farm. It may be a good idea to sit down with your adviser to discuss the capacity requirements and put a plan in place to ensure you do not get caught out in the future.

As the old saying goes, it is better to be looking at it rather than looking for it. It doesn’t always have to be a case of building a new store, there are other options.

Some farmers will rent a shed for the winter or put their cattle in a B&B arrangement. Some might consider reducing livestock numbers over the winter period if it fits their system.

Where other arrangements are not feasible, increasing storage on the farm should be considered. Tom Ryan from Teagasc and the Irish Farmers Journal have outlined three popular options for storing slurry on farms:

  • Slatted tanks
  • Lagoons.
  • Circular tanks.
  • The costs and some of the specifications required for these options are covered here. It can be used as a starting point when gathering information to choose the best system for your farm.

    Stephen Robb has also looked at weighing system options for grain storage in this Focus, which offers a useful guide to what’s on the market.

    Slurry storage capacities compared
    Tom Ryan outlines the county by county slurry storage capacity requirements for four different storage types.

    The table shows the rainfall per week in mm and the mandatory storage periods required across the 26 counties. The net storage per cow is also shown and is based on the storage period and 0.33m3 of net storage per week. The total slurry storage capacity required per cow for the storage period is shown for four different storage systems.

    The four storage methods are – the indoor slatted tank, the outdoor slatted tank, the circular slurry store and the geomembrane-lined store.

    The other variables chosen are the tank depths of 2.4m, 2.7m, 3.6m and 4.23m which are common depths for these types of storage systems.

    If, for example, four extra weeks’ storage are required in Galway, divide the capacities by the storage period (18 in this case) and multiply by 22. So, the values in the table for net and total storage will become 7.26m3 7.92m3, 10.96m3, and 11.72m3 and 9.28m3 . While the specified storage periods are mandatory, any extra storage will depend on particular needs and affordability. Ask your adviser to calculate your storage needs based on existing storage, future needs and storage systems being considered.

    Slurry storage: circular storage tanks
    Tom Ryan and Peter Varley look at the main points to consider and costs of building a circular slurry store.

    Circular slurry stores are a good option for increasing the slurry storage capacity of existing farmyards. Below we have listed some of the advantages and disadvantages of such stores.

    Advantages

  • Ideal for increasing the slurry storage capacity in an existing farm without major construction work.
  • Speed and ease of construction (can take just one week to erect).
  • No major dig-out costs involved. Very little excess clay to take care of.
  • Can be a safer option compared with open slurry stores that require safety fencing.
  • Have the option of taking down the store again and moving to another site. This would be specifically appealing to farmers with leased land.
  • Disadvantages

  • Slurry usually needs to be pumped from a reception tank to the over-ground tank. This takes time and there is a cost even if you have your own slurry pump.
  • In a greenfield site, a reception tank would have to be built, adding significantly to the cost. The reception tank should have at least two weeks’ slurry storage to save the amount of times a farmer has to pump his slurry to the over-ground tank.
  • A propeller agitator usually needs to be purchased to fit inside the tank. Some farmers find even with a propeller agitator the slurry can develop a crust on top which can be difficult to break down.
  • Bunding may be required around the store.
  • The Department of Agriculture has outlined specifications for the construction of over-ground circular slurry stores. These specifications can be found on the Department’s website under S122. The main specifications include:

  • Hard core must be laid and compacted in the area where the slurry store is to be erected.
  • Hard core must be compacted in 150mm layers using a vibrating or heavy roller.
  • A 1,000 gauge polythene membrane must be laid on the finished hardcore with 600mm overlaps.
  • Steel mesh must be laid in all floors.
  • The concrete must be thoroughly compacted using a vibrating screed, and compaction around steel reinforcement must be carried out with a poker vibrator.
  • The sides of the tank must be constructed and placed by the store contractor.
  • An access ladder must be supplied to the side of the tank to enable viewing of the upper surface of the slurry in the tank. This ladder must be provided with a back safety cage.
  • If agitation is to be performed using a jetter affixed to the top of the tank, then a safety platform with rails must be provided for the jetter operation.
  • All points for emptying the tank through either the side or base of the tank must be controlled by at least two valves in series.
  • Costs

    The Tables 1 and 2 outline the costs of circular slurry stores of different capacities based on the TAMS II reference costs. Storage periods of 16 and 20 weeks are shown for a range of cow numbers from 50 to 200. The net storage needed for the 16 and 20 weeks is shown. For a tank height of 4.23m the diameter of the tank is shown which will provide the total capacity required. In practice, the tank diameter and height will be chosen with the help of the supplier taking account of the commonly available diameters and heights as well as present and future storage needs.

    The tables show the effect of economies of scale in reducing the cost per cow and per m3 as tank size increases. When the diameter is doubled the side wall length is doubled but the capacity is quadrupled for the same depth. The floor area of the tank is also quadrupled.

    Table 3 shows costings for over-ground steel tanks based on information from a supplier. Prices exclude VAT. Prices don’t include pumps or through-the-wall propeller agitators. Tank price includes tank, jetters, steel ladder and platform, reinforcing mesh, valves, advice and all labour involved in erecting the tank, doing concrete work, etc. Price does not include any sumps/reception tanks and costs associated in getting the slurry to the reception tank. Suppliers ask that they are presented with a level site with hard core placed. TAMS II reference costs for tank number three are €53,659, which are a little behind this supplier’s costs.

    Slurry storage: geomembrane-lined lagoons
    Tom Ryan and Peter Varley look at the main points to consider and costs of building a geomembrane-lined slurry lagoon.

    Geomembrane-lined lagoons are very popular on expanding dairy farms or greenfield sites that are being converted to large dairy enterprises. They are the least expensive option for storing slurry on farms. Like the other options, they come with a number of advantages and disadvantages that we have listed below.

    Advantages of a lagoon

  • It is one of the more cost-effective options for storing large volumes of slurry.
  • Once planning permission is obtained, installation should be very fast (some contractors claim installation can be achieved in two to three weeks).
  • Slurry agitation is reasonably easy.
  • Disadvantages of a lagoon

  • Planning permission for lagoons can be difficult to achieve in some county councils.
  • Some sites are not suitable for lagoons (very rocky areas).
  • A safety fence must be erected.
  • Difficult to extend at a later date.
  • Can gather a significant amount of rainwater.
  • Farmers planning to install a lined slurry store (lagoon) through TAMS II must use a contractor from the approved Department list. The specifications for geomembrane-lined slurry stores is listed on the Department’s website under S126. The main specifications to note are:

  • A storage facility must be located not less than 50m from any water body in the case of new farmyards, and not less than 10m in the case of extensions or modifications to an existing facility.
  • The banks of the store must be a minimum of 600mm high above ground level and be well-compacted.
  • The slope angle should normally be 45°, but in certain soils the angle may be steeper. In no circumstance can the bank slope be steeper than 55°.
  • The excavated and made-up ground must be finished uniform and smooth and free of any sharp protrusions.
  • The anchor trench (which holds the liner in place and prevents it from slipping) must be carefully formed and compacted, and any undisturbed top soil beneath it must be removed.
  • A leak detection system must be installed underneath the geomembrane lining.
  • A proper agitation point(s) built to the specifications outlined in S126.
  • Costs

    Tables 1 and 2 outline the various capacities and costs associated with geomembrane lined stores. Table 1 is calculated for 16 weeks and Table 2 for 20 weeks. Other assumptions for both tables are a depth of 3.6m, freeboard of 0.3m and a rainfall figure of 23mm per week. The costs are calculated using the TAMS II reference costs for the construction of geomembrane-lined stores plus €54.7 per metre for the surrounding protective fence.

    Table 3 outlines the costs of construction (provided by one contractor of geomembrane stores) of various sizes of these types of slurry stores. A list of all contractors (S126A) supplying geomembrane-lined stores is available on the DAFM website. The cost of channels or pipes for bringing slurry to the store is not included.

    Looking at all the tables, the most notable feature is the benefit shown due to economies of scale. The bigger these storage systems are, the cheaper they are per m3 and per cow. Comparing Table 1 and Table 3, it appears that the TAMS II reference costs are lagging a little behind the contractor costs.