Lime - the forgotten fertiliser

Eddie Webb, B&T Soils & Environment Adviser, Teagasc Galway/Clare

In the 1970’s and early 1980’s, Irish farmers applied an average of 1.7 million tonnes of lime to control soil acidity. The total annual tonnage of lime applied nationally in recent years, including on those farms ineligible under the Liming Programme, has ranged from 0.7m tonnes in 2017 to 1.4 million tonnes in 2022. Teagasc research has shown that on a low pH soil where only lime was applied an extra 1 tonne of grass dry matter was grown. One tonne of additional grass production each year over a typical 5 year liming period (5 t/ha lime applied) represents a 6:1 return (grass €181/tonne; lime €31/tonne) on investment in lime. Indeed the return is much greater if one has registered for the National Liming Programme. The cost of rectifying the soil pH is an investment that will deliver a financial return.

Lime is a natural and cost effective soil conditioner, and corrects soil acidity by neutralising acids present in the soil. This allows the soil biology and earthworms to thrive and break down plant residues, animal manures and release nutrients required for health plant growth. By neutralising soil acidity, the availability of nitrogen (N), phosphorous (p), potassium (k), sulphur (s) and calcium (Ca) increases. Soil pH has a major effect on availability of soil phosphorous which is the engine currency that drives most biochemical processes. Lime also has a beneficial effect on soil structure, particularly on some of our heavier soils, by assisting in building up soil crumbs, keeping heavier soils open and friable.

Soil pH is a measure of soil acidity/alkalinity and is measured a part of a standard soil test. Soils above 7.0 indicate alkalinity whilst soils below pH7.0 indicate soil acidity. The aim is to maintain grassland soils between pH 6.0 and 6.3. Lime requirement is determined by measuring the soil buffering capacity. The buffer pH determines the lime requirement to adjust the soil pH to the target pH for the crop. The buffering capacity will depend on soil type, such as whether it is a light soil or a heavy soil. In general, heavy soils will tend to have higher lime requirements compared to lighter type soils.

Lime has to be applied on a regular basis to control soil acidity as lime is continuously leached from the soil, mainly through drainage water. The use of N fertilisers, and removals in crops and livestock also remove lime from the soil. Loss through drainage will vary from 250 to 625 kg/ha/year. Lime required to neutralise acidity produced by fertiliser will vary from 180 to 220kg/ha/year per 100 kg/ha of N applied as CAN or urea. Offtakes by grazing animal are relatively small with a bullock accounting for 25kg, 1000 litres of milk accounting for 3 kg of lime. Silage crops account for 15kg per tonne of DM.

Based on the most recent soil test reports identify where lime is required on the farm, and when and at what rate lime lime should be applied. Having a liming plan in place will open up opportunities to get lime applied over the year when conditions are suitable and land is available. One should not exceed 7.5t/Hass in one application with the remainder applied on very acidic soils in 2 years’ time.

The deadline for the National Liming Programme is 31^st October and lime needs to be applied and invoices uploaded by this date. The Liming Scheme grant aids Calcium ground limestone or Magnesium (dolomitic) ground limestone, the description on the Invoice must indicate the type of lime supplied as opposed to Grolime which is a Certification mark. The Liming programme does not grant aid granulated lime. Where a contractor spreads the lime, this Invoice should also be submitted.

All Invoices/ receipts/ statements should be original, on headed paper and at least include the name, address, phone number and VAT number/Tax Reference Number TRN of the Licenced Quarry. 

In addition, the receipt must indicate:

• the name and address of the Approved Applicant
• the invoice number and date
• the quantity of ground limestone (tonnes) purchased and price charged per tonne.
• Invoice from contractor showing cost of lime spread per tonne (If Invoice from quarry does not include spreading)
• all invoices must be marked paid

All invoices must be uploaded in advance of the deadline on 31^st October and I encourage all farmers to get in touch with their agricultural agent to ensure same.