Over the past three weeks the Irish Farmers Journal investigated the main slurry storage options available to farmers. There are pluses and minuses to every option and the slurry storage choice a farmer will end up selecting comes down to farm circumstances. The main options we looked at were concrete tanks, geomembrane lined slurry stores (lagoons) and over-ground circular slurry stores (round tower). This week we provide a summary of the main findings. Firstly, one should remember that there are several different points to consider when choosing slurry storage including:

  • Site: The physical characteristics of the site on which you are planning to erect slurry storage will play a factor in selection. If it is a very rocky area, you may run into issues regarding dig-out, which could add to costs. Wet areas where springs may be present can also be problematic.
  • Financial situation: Your farm’s financial situation will also dictate the option that you end up choosing, with some types of slurry stores cheaper than others, especially at larger scales.
  • Future planning: Farmers should also try and look at long-term plans when selecting slurry storage. The option that is suitable now may not be suitable in 10 years’ time if livestock numbers are predicted to increase substantially in the future.
  • Existing slurry storage: The existing slurry storage may also play a role in any extra storage farmers need. For example, if building large livestock facilities on a greenfield site, farmers may decide a lagoon is the best option. Especially if they are building a large cubicle shed and want an easy method of scraping passageways to the lagoon. However, if there are existing tanks in a yard and a farmer needs to increase storage, a round tower may be best.
  • Rainfall: The level of rainfall in an area can have a huge bearing on the type of slurry storage a farmer should choose. For example, a farm in Kerry can expect to get 2m of rainfall annually while a farm in Dublin could get less than 900mm per annum. Large open slurry stores will gather more rainwater and this has to be allowed for when measuring capacities.

    • In this article we have compared the three main slurry storage options for a 100-cow herd. The aim is to show what is available. Each can play a role depending on the farmers situation.

    Concrete slurry tank

    Advantages of concrete tanks

  • Can be upgraded and slatted for animal housing in the future.
  • Some county councils prefer to give planning permission for concrete tanks rather than other slurry storage options.
  • Possibility of extending the tank to increase capacity in the future.
  • Long working life.

    • Disadvantages of concrete tanks

  • It is an expensive option.
  • Dig out, fill and hard core costs.
  • Removed soil must go somewhere and there is a cost for this.
  • If the tank is not covered, a safety fence is required and this can be costly and needs to be maintained.

    • Costs

    Figure 1 shows the plans for a concrete tank that a farmer may build for slurry storage. The concrete tank has capacity for 16 weeks of slurry storage for 100 cows. The tank is 56.5m long, 4.7m wide and 2.7ft deep (9ft). It has a usable volume of 571.05m3.

    Table 1 shows the Department reference costs for building this tank and the maximum grant aid available for a successful TAMS II application. This concrete tank would cost €39,020 excluding VAT, according to those reference costs. A safety fence to surround the tank would cost €6,432 excluding VAT and a circulation pipe system would cost a further €811 excluding VAT. The 100-cow tank could be slatted at a cost of approximately €12,605 excluding VAT.

    Comment

    Some farmers prefer to install a concrete tank because they feel it is the most durable option – there is the possibility of building animal housing above the tank in the future and some county councils prefer to give planning permission for concrete tanks rather than lagoons. However, on the other hand, not every site is suitable for constructing a concrete slurry tank. The cost of building a concrete tank can also be enough to prevent farmers choosing this option.

    Interestingly, in the costings we found there was not a huge difference between erecting a safety fence around an open slurry tank to kitting the tank out with slats instead.

    Geomembrane lined slurry stores (lagoons)

    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).

    • Disadvantages of a lagoon

  • Planning permission for lagoons can be difficult to achieve in some county councils.
  • Some sites are less 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.

    • Costs

    Figure 2 shows the plans of a lagoon designed to hold 16 weeks of slurry for a 100-cow herd on unroofed cubicles. The lagoon has capacity for 350,000 gallons of slurry. It is 25.5m long, 25.5m wide and 3.6m deep. There are two concrete-based agitation points at either end of the lagoon to support a tractor and lagoon agitator. Table 2 shows the Department’s reference costs for building this size of lagoon and the maximum grant aid available for a successful TAMS II applicant. This lagoon costs a total of €37,485 excluding VAT to build.

    Comment

    In our comparisons, lagoons seemed to be the least advantageous of all the options. However, the comparisons in this 100-cow example may be somewhat unfair because the real benefit of lagoons in my opinion are on greenfield sites where large-scale slurry storage is required at lower costs. Typically, the cost benefit only really kicks in when lagoons are erected for 200+ cow herds built to accommodate slurry from new large cubicle sheds and dairy washings.

    Over-ground circular slurry stores

    Advantages

  • Speed and ease of construction (can take just one week to erect according to manufacturers).
  • No major dig-out costs involved. Very little excess clay to take care of.
  • A safer option compared with open slurry stores that require safety fencing.
  • Can suit a rocky site.

    • Disadvantages

  • Slurry usually needs to be pumped from a reception tank to the over-ground tank.
  • 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 mixer usually needs to be purchased to fit inside the tank.

    • Costs

    Figure 3 shows the plans of a tank designed to hold 16 weeks of slurry for a 100-cow herd. The tank has capacity for 155,450 gallons or 707m3 of slurry. The tank has a radius of 7.26m and is three rings (4.27m) high. Table 3 shows the Department’s reference costs for building this size of over-ground tank and the maximum grant aid available for a successful TAMS II applicant.

    This tank costs a total of €37,507 excluding VAT to build. Included in this cost is the floor of the tank, a ladder and platform, pipe work from the reception tank to a jetter, a jetter, slurry release valves and a mixer. A slurry reception tank is not included in the cost.

    Comment

    Most farmers who erect over-ground slurry stores already have some form of slurry storage on the farm and use the over-ground tank to expand capacity. This option would be less suitable for a greenfield site because a decent reception tank is required to collect slurry before pumping into the over-ground tank and this would add significantly to the overall cost of this option.