Bennettsbridge Limestone is a member of GROLIME, Ireland’s only agricultural lime quality assurance scheme.
“Correct soil pH status will improve soil nutrient availability and maximise the return from each kg of applied N, P & K fertilizers” Teagasc, Johnstown Castle, Wexford.
Soil pH is a measure of the acidity or alkalinity of a soil. Crops differ in their sensitivity to soil pH. In addition, the optimum use of fertilizers containing N and P is obtained when soil pH is between about 6.2 and 7.0.
Lime is a soil conditioner. It corrects soil acidity by neutralising the acids in soils so that the micro-organisms can thrive, break down plant and animal residues and liberates the elements necessary for healthy plant growth. It helps in the release of N and other nutrients from organic matter; it increases earthworm activity which improves soil structure and it assists the growth of clover and the survival of N fixing bacteria.
How does soil become acidic?
Soils naturally become acidic over time as a result of fertilizer, manure, leaching and crop off take. Lime must be added to restore the soils lime status back to the desired pH for optimum fertility.
The south east of Ireland is unique in that it is one of the few areas in Ireland with a source of Magnesium based agricultural lime. Most of Ireland would only have Calcium based limestone within an economical transport distance.
Typically Calcium based limestone is made up of greater than 95% Calcium Carbonate (CaCO3). Dolomitic Limestone or Magnesium based limestone is typically 55% Calcium Carbonate and 45% Magnesium Carbonate.
Bennettsbridge Limestone’s has a High Calcium reserve of limestone, with consistent results of greater than 98% Calcium Carbonate.
How do you know whether you need calcium or magnesium lime?
Ideally get your soil tested and include magnesium in the analysis. The Teagasc S6 Soil Test includes Magnesium and is only €2 more than the Basic Teagasc soil test.
Teagasc offer the following advice in the “Teagasc Green Book”.
“Where dolomitic limestone is used as a liming material, it is important that it is not used repeatedly without monitoring the soil Mg levels. The release of such Mg can be very slow, and frequent use of dolomitic limestone can cause soil Mg to rise to very high levels where it can impede the availability and uptake of other nutrients such as K.”
See below map from the Teagasc Soil Atlas – Available Magnesium for the South East. It show that the South East is Index 4 / Sufficient or excess Magnesium.
Extract from Teagasc Soil Atlas of Ireland – Available Magnesium.
Teagasc Magnesium (Mg) Index System
Soil Mg Index
Soil Mg Range (Mg / l)
0 – 25
25 – 50
51 – 100
|Sufficient / Excess|
Calcium is Essential for Good Soil Structure
Good Soil Structure Associated with Correct Calcium Levels:
- Calcium flocculates the soil.
- Drainage improves. Topsoil allows excess water to pass through to subsoil, when the ratio between air, water, minerals and organic matter is correct in the soil.
- Longer growing seasons. Warmer soils mean growth starts earlier in spring and goes on later at the back end.
- Soils become robust and more resistant to slumping. Soils are harder to damage and recover sooner after poaching or compaction when exposed to traffic by machinery or animals in wet conditions.
- Plant roots penetrate deeper. The roots forage in the whole soil for nutrition, making the best of what’s available from nature. Costs are decreased.
- Less leaching of expensive fertilizer & nutrients into soil water occurs
- Nutritionally better balanced plants result, which are healthier for the animal consuming them. Fewer problems are experienced by farmers when balance is achieved. Profits improve.
- Biological life in the soil improves. Earthworms, insects, fungi and bacteria thrive and speed up the recycling process of animal and plant residues.
Not all lime is the same. The effectiveness of agri lime relies on 2 Criteria.
- Total Neutralising Value (TNV)
- How finely ground the lime is.
Total Neutralising Value (TNV)
TNV is a measure of how effective a lime is at neutralising the acidity in the soil. All lime sold in Ireland has to have a TNV greater than 90% to conform to the Department of Agriculture specification.
Bennettsbridge Limestones Hi-Calcium Agri Lime has a consistent TNV of 98%.
The more finely ground a lime is the more surface area it has and the more available it is to react with the acidity in the soil to neutralise it. The Department of Agriculture specification states all lime sold in Ireland has to be 100% less than 3.35mm and 35% of that has to be less than 0.15mm. (Lime less than 0.15mm has a similar consistency to baking flour).
Bennettsbridge Limestone Hi Calcium Agri is manufactured to a higher spec than the The Department of Agriculture specification. Our High Calcium Lime has greater than 40% less than 0.15mm (Powder).
The availability of plant nutrients is affected by the pH of soil. The major plant nutrients nitrogen (N) and phosphorus (P), show a marked reduction in availability in acid conditions.
Recently there is a renewed focus on the role lime plays in Fertilizer Efficiency.
Maintaining the optimum pH in grassland soils will improve the release of soil N by 50 to 70kgN/ha/ yr from soil organic N reserves. This reduces the requirements for applied N and offers a large financial saving in the region of €60 to 80/ha/yr.
Source Teagasc, Johnstown Castle
Phosphorus is now the most expensive nutrient to buy and world P stocks are decreasing thus making it more expensive into the future.
Maintaining the correct soil pH will pay dividend in terms of increasing the utilisation of both soil and applied P as manure or bag P fertiliser. To maximise P uptake in grassland aim to maintain pH 6.3 and for tillage soils aim for pH 6.5.
Source Teagasc, Johnstown Castle