Maintaining the right soil pH is one of the simplest, most cost-effective ways to boost grassland productivity. But still, it’s often overlooked.
Many soils are too acidic on drystock farms in particular, which limits plant growth and leads to wasted fertiliser.
In this article, we’ll discuss the importance of lime in boosting the pH of acidic soil and how this benefits farmers.
Table of Contents
What Is Soil pH & Why Does It Matter?
Soil pH measures how acidic or alkaline the soil is on a scale of 0 (very acidic) to 14 (very alkaline), with 7 being neutral. For grassland, the target is usually a slightly acidic to neutral pH of around 6.2 to 6.5.
Soil pH influences nearly every aspect of soil health and crop performance:
- Nutrient availability: A poor pH can “lock up” nutrients in the soil, making them unavailable to plants.
- Microbial activity: Beneficial microbes, which recycle nutrients, thrive only in the right pH range.
- Soil structure: pH impacts how soil particles, affecting water movement, aeration, & root development.
- Fertiliser & pesticide efficiency: Both are less effective outside the ideal pH range.
- Environmental safety: Poor pH increases the risk of nutrient runoff, which can harm waterways.
The Problem: Acidic Soils in Ireland
A 2024 Teagasc Soil Fertility Report revealed that nearly two-thirds of Irish soil samples tested had a low pH, below the ideal range for grass growth (6.2–6.5). This means most grassland soils are more acidic than they should be.
Acidic soils limit the availability of key nutrients like nitrogen (N), phosphorus (P), and potassium (K). A low soil pH also reduces the effectiveness of both chemical and organic fertilisers.
When soil pH isn’t right, plants struggle to absorb nutrients – even if those nutrients are present. Mark Plunkett of Teagasc gives the example of a farm spreading 100kg/ha of chemical N/ha/year.
- Where pH is suboptimal, just 35% is usable (35kg/ha of N).
- If the pH is corrected, nitrogen use efficiency can rise to over 50% (50kg/ha of N).
What Is Lime?
Lime is a natural material used to adjust the acidity of soil. It comes from limestone rock, primarily made of calcium carbonate (CaCO₃). When processed and ground into a fine powder, it becomes agricultural lime, often just called “lime.”
There are two main types:
- Calcium lime (ground limestone): Contains mostly calcium carbonate and is the most common form.
- Dolomitic lime (magnesium lime): Contains both calcium carbonate and magnesium carbonate.
Lime isn’t a fertiliser – it doesn’t add nutrients to the soil. Instead, the importance of lime lies in its ability to increase the availability of nutrients already there. However, soil testing is essential to manage lime levels properly. A soil’s lime requirement is determined by its buffering capacity (the amount of lime needed to raise the pH to target levels).
The Importance of Lime for Your Soil
Key benefits highlighting the importance of lime applications include:
✔️ Increased nutrient cycling: Lime helps unlock nutrients already in the soil.
✔️ Improved fertiliser efficiency: By enhancing nutrient availability, lime reduces fertiliser needs.
✔️ Boosted grass yields: Soils restored to a pH of 6.3 can release up to 80 kg N/ha more nitrogen, resulting in up to 1 tonne more dry matter per hectare annually.
✔️ Better soil biodiversity: By raising soil pH, lime increases microorganism and earthworm populations – leading to improved soil aeration and structure.
✔️ Improved livestock nutrition: Lime adds calcium and sometimes magnesium – important for animal health and crop productivity.
Economic & Environmental Benefits of Lime
The importance of lime for your soil means lime applications translate to increased profits. But also, applying lime to your soil benefits the environment, making your farm more green.
✔️ Return on investment: For every €1 spent on lime, farmers can see a return of €5 on drystock farms and €7 on dairy farms.
✔️ Lower greenhouse gas emissions: Correcting soil pH cuts emissions of nitrous oxide (NO), a potent greenhouse gas. Agriculture contributes 90% of Ireland’s NO emissions, so this can make a big difference.
Getting Started – Test, Then Treat
By making pH correction your first step, you create a solid foundation for all other soil and nutrient management efforts. Without the right pH, you’re not getting full value from your fertilisers or your land.
With that in mind, if you’re managing grassland and want better yields, healthier soils, and lower input costs, start with lime. But every farm is different, so before applying lime, a soil test is essential. It will tell you:
- What your soil’s current pH is
- How much lime is needed
- What type of lime is best
Testing with Southern Scientific
Southern Scientific is the largest agricultural soil testing lab in Ireland. By testing your soil with us, you benefit from:
➜ Experience: We have 30+ years of experience with clients, including Teagasc.
➜ Accurate Testing: Our ISO-accredited laboratory provides reliable results for soil analysis.
➜ Fast Turnarounds: With offices nationwide, we offer a quick service no matter where you are.
➜ Expert Guidance: We provide clear, actionable recommendations for soil management.
