When discussing slurry storage with farmers, two words are often used to describe the adequacy of their storage capacity: “on paper”.
The fact of the matter is that the vast majority of dairy farmers in Ireland have enough slurry storage. On paper. This paper exercise counts the capacity of all slurry stores on the farm plus concrete straw-bedded sheds and divides it by the number of livestock on the farm and how many weeks the slurry needs to be stored for.
It appears that on most farms, slurry storage is creaking to capacity on or before the opening dates for spreading. This forces farmers to either spread some slurry during the closed period, or to spread in unsuitable conditions after the closed period ends. Neither are good outcomes, either for water quality or farmers’ reputations.
Some farmers complain about calendar-based farming, suggesting that slurry should be spread when conditions are suitable. However, they need to remember that the reason for the closed period is not necessarily that ground is wetter during those weeks, it is more to do with grass growth being lower.
How can there be uptake of nutrients when grass growth is practically zero? The opening date coincides with the normal start of grass growth in each region.
Another thing to keep in mind is that the slurry storage requirements extend beyond the duration of the closed period.
So in Zone A, the requirement is for 16 weeks of slurry storage and the closed period is for a duration slightly less than 12 weeks. Farmers in Zone B need to have 18 weeks of slurry storage but have a 12-week closed period while farmers in Zone C need to have 22 weeks of slurry storage but have a 14-week closed period.
The difference between the duration of the closed period and the slurry storage requirement is to build in flexibility to hold slurry for longer than is required, due to weather and ground conditions being unsuitable for spreading.
So, if farmers have enough storage on paper, how come many are under pressure to spread at the end of the closed period? There are many possible reasons.
For some, the winter will have started earlier than expected or the tanks weren’t fully emptied when animals were housed. For others, there may be water getting into the tanks.
It appears that on most farms, slurry storage is creaking to capacity on or before the opening dates for spreading
In other situations the allowable capacity in straw bedding isn’t actually utilised. Another possible reason is that dairy cows are doing “their business” more often now than in 2005, when the rules around storage were written into law.
Is there a benefit to having extra slurry storage? The answer can only be yes. It gives more flexibility to store slurry and spread at times when nutrient uptake will be higher. This is particularly the case when slurry is spread with low-emission technology as slurry can now be applied to higher covers in a grazing rotation and this can be used to replace chemical nitrogen.
The big down side to having additional slurry storage is the cost. According to Teagasc, the cost of net slurry storage ranges from €34/m3 to €100m3 depending on the type of slurry store.
The costs of building materials have increased sharply over the last 12 months and this has increased building costs by between 30% and 50%.
So, for a typical farm with 100 dairy cows and 25 weanlings, adding an extra four weeks’ worth of slurry storage will cost in the region of €12,000 excluding VAT and before any TAMS grants.
It is difficult to quantify the payback from such an investment but there are two ways of looking at it. Firstly, slurry that would normally be spread in late January or early February can now be spread in March, at a time when more of the nutrients can be utilised, so less chemical fertiliser will be required.
Once you have sufficient storage on paper, and presuming everything else is in order, then you should be able to apply for the grant.
Secondly, spreading slurry in March, or at a drier time of the year, will mean less damage is done to fields compared to slurry applied earlier in the year when field conditions are less favourable to heavy slurry equipment.
The cost of travelling on land when soil moisture levels are high is compaction. How many times have we seen fields with poorer grass growth where the tracks of the slurry tanker travelled?
Can we quantify the reduction in growth in the wheel tracks over the course of the year? What percentage of the field is compacted?
The rules for TAMS II state that slurry storage cannot be grant-aided where insufficient slurry storage exists. This means farmers who are offside for slurry storage won’t be able to apply for a grant to build the slurry storage, even though they are in most need of it.
One way around this is to temporarily lease additional slurry storage and then apply for the TAMS grant. Once you have sufficient storage on paper, and presuming everything else is in order, then you should be able to apply for the grant.
The TAMS II grant subsidises the cost of the investment by between 40% and 60% depending on the age of the applicant. The maximum amount of funding that the grant can be applied for is €80,000 or €160,000 where the farm is in partnership.
Almost all types and shapes of slurry storage facilities are eligible for grant aid, including unroofed stores and lined lagoons.
According to the Government’s AgClimatise report, all new external slurry stores are to be covered from next January and all existing external stores are to be covered by the end of 2027. This measure is designed to reduce ammonia losses in stored slurry.
Details on the type and specification of suitable covers are yet to be released by the Department of Agriculture. The issue is that gases such as ammonia are released from slurry at varying rates depending on the air speed over the slurry.
So external, open slurry stores release more ammonia than slatted internal tanks. Outdoor slatted tanks are likely to release a lot less ammonia than outdoor tanks with no slats.
Any roof coverings over lagoons or concrete tanks will need to be close to the surface of the slurry. Plastic membranes are available and are widely used in the US and UK. They do not need to trap the gas, nor indeed do they need to prevent water from entering the slurry. In some cases a tarpaulin-type cover can rest on the slurry and act as the barrier between the slurry and air flow.
The key point here is that covering a slurry store to prevent rainwater from entering is not the same as covering a slurry store to reduce ammonia losses.
Deep and wide tanks are more economical to construct than shallow and narrow tanks per cubic metre of capacity. According to Teagasc, steel accounts for 20% of the build cost of a concrete slurry store. A double slatted tank is 11% cheaper to construct than the equivalent single tank because a wall is shared.
Tanks built to TAMS specification require a double layer of steel whereas some builders opt to go for a single layer where a grant is not being claimed, which obviously lowers the cost.
Outdoor slatted tanks are likely to release a lot less ammonia than outdoor tanks with no slats
Lined lagoons are still a popular choice in some larger farms but it is important to recognise that they do tend to capture more rainwater than concrete tanks with straight walls.
It is also important to discuss with the installer options for fixing covers to lined lagoons without impacting on the integrity of the liner.
Over the last 20 years there has been a big increase in the use of topless cubicles, many of which have replaced woodchip out-wintering pads.
These facilities tend to collect large quantities of rainwater which needs to be stored and spread. In some facilities, it is possible to divert runoff to storm water drains when the facility is clean and not in use.
Roofing these facilities and slurry stores will prevent rainwater from entering the slurry store. This increases capacity for slurry in the tank and reduces the costs of spreading as there will be no dilution of the slurry with rainwater.
A typical 60-cow cubicle facility with feed face will measure 15m by 28m which has a total footprint of 420m sq. Presuming rainfall is 1,000mm annually, a total of 420m3 of rainwater will have to spread.
This is the equivalent to 30 loads of a 3,000gal slurry tank. Presuming it takes 45 minutes to empty a load, at €60/hr the total annual cost of spreading the water will be €1,350.
However, if extra storage is required, roofing the facility might be more cost-effective
If the cost of a roof is €80/m sq, the total cost of roofing the 60 cubicles would be €34,000. This means it would take 25 years to get a payback on the roof if the only reason for putting on the roof was to prevent water from entering the tanks.
However, if extra storage is required, roofing the facility might be more cost-effective. A lot depends on the county the farm is in.
Weekly rainfall during the closed period varies by county. For example, in Kerry the weekly rainfall allowance is 45mm while it is just 17mm in Dublin.
Taking an average of 30mm over a 16-week closed period roofing the tank would increase capacity in the store by 480mm. Using the above example, this would create and extra 201m3 of slurry capacity.
At a cost of €80 per m3, this would be worth just over €16,000, roughly half the cost of the roof and reducing the payback on slurry spreading costs to 13 years.
A dairy cow requires 0.33m3 of slurry capacity per week of housing so roofing a yard measuring 420m2 will create extra slurry capacity for 38 cows.