Guide to Liming and Soil Productivity

The most commonly used liming materials in soil productivity are ground limestone, dolomitic ground limestone, chalk, ground chalk, burnt lime and hydrated lime; almost 70% of the material currently used in the UK is ground limestone.

For example, ground limestone’ means sedimentary rock consisting largely of calcium carbonate and containing not more than 15% of magnesium expressed as MgO and of which 100% will pass through a sieve of 5 mm, not less than 95% will pass through a sieve of 3.35 mm and not less than 40% will pass through a 150‐micron (150 μm) sieve.

The seller must also declare the neutralizing value (NV) and the amount of material as a percentage by weight that will pass through a 150‐micron sieve.

Liming Materials

A liming material can bring the pH of a soil to optimum levels for crop production if used properly. Liming materials also provide calcium (Ca) and/or magnesium (Mg) to the soil for plant uptake.

Materials that can cause an increase in pH include carbonates, oxides or hydroxides of calcium and magnesium. When looking at liming materials it is often hard to distinguish one material from another.

Quality standards used to differentiate liming materials include: Total Neutralizing Value (TNV), Calcium Carbonate Equivalence (CCE), Fineness, and Effective Neutralizing Value (ENV).

Quality Standards Used To Differentiate Liming Materials

1. Total Neutralising Value (TNV)

This is the percentage of the material that can neutralize acid expressed as the calcium carbonate equivalence (CCE) of the product.

2. Calcium Carbonate Equivalence (CCE)

This standard compares the liming material to pure calcium carbonate (CaCO3). Some materials such as hydrated lime and burned lime will have a CCE higher than 100%.

Pure magnesium carbonate (MgCO3) will neutralize about 1.2 times more acidity than CaCO3 so dolomitic limestone will have a higher CCE than calcitic limestone.

3. Fineness

The rate of reaction of a liming material is determined by the particle sizes of the material; 100% of lime particles passing a 100-mesh screen will react within the 1st year while only 60% of the liming materials passing a 20-mesh sieve (but held on 100 mesh sieve) will react within a year of application.

Material that does not pass the 20 mesh sieve is not expected to react within a 1 year following application.

4. Effective Neutralising Value (ENV)

The ENV is the fraction of the material’s CCE that will react with soil acidity in the first year of application.

The ENV is calculated by multiplying a liming material’s CCE and its fineness. As an example: a liming material with CCE of 90% and a fineness of 0.86 has an ENV of 90*0.86 = 77.4.

5. Commonly Used Lime Materials

The Neutralisation Values (NV) of the material defines the amount of acidity that it will neutralise and is based on a reaction with HCl in a laboratory. Typical NVs of the three most commonly used materials are as follows:

Limestone (CaCO₃), NV = 50–55% depending on the geological strata;

Dolomitic limestone (CaMg(CO₃)₂, usually 42% CaCO₃ and 53% MgCO₃), NV = 56%;

Chalk (CaCO₃), more readily broken down and absorbed into the soil solution than limestone, NV = 48–54%.

However, the effectiveness of a liming material also depends on its reactivity, effectively its rate of dissolution, which depends on particle size and hardness.

For example, the difference between ‘ground’ and ‘screened’ limestone is the amount that will pass through a 150‐micron sieve: that is screened limestone is a coarser material and so it reacts more slowly.

Throughout Europe, each country has its own specifications for liming materials but the European Union has proposed harmonising regulations.

Read Also : Liming of Soils and Causes of Soil Acidity

EC Regulation 463/2013 adds liming materials to the European Fertiliser Regulations so that they can be sold as ‘EC Fertiliser Liming Materials’, in which case sales documentation must state the parent rock type (e.g. Chalk), the grade of product, the NV and the Ca²⁺ and/or Mg²⁺ content.

6. Other Acid‐Neutralising Materials

A number of ‘waste products’ are available that neutralise acidity: sugar factory lime, basic slag, wood ash, coal combustion products such as fly ash and bottom ash, calcium humates and fulvates from oxidised brown coal and by‐products of the paper and pulp industry (e.g. Bolan et al., 2003; Gagnon et al., 2014).

The NVs of some of these, compared with lime‐based products, are shown in the table below. Sugar Factory (or Spent) Lime is a by‐product of sugar beet purification.

It also contains some nutrients, approximately 3–5 kg N, 7–10 kg available P₂O₅, 5–7 kg MgO and 4–6 kg SO₃ per tonne of lime and has a fine particle size, so is fast‐acting.

Table: The Neutralising value of various liming materials expressed as a weight percentage of pure lime (CaCO₃) adapted from Bolan et al. (2003).

Positive Effects of Liming on Soil Properties

Liming increases Ca²⁺ concentrations and ionic strength in the soil solution, causing clay flocculation and thus an improvement in soil structure and hydraulic conductivity (Haynes & Naidu, 1998).

Liming also increases earthworm activity and therefore macroporosity (Bolan etal., 2003).

Because of the beneficial influence of lime on soil structure, there has been much research on the use of lime and other acid‐ neutralizing materials for improving degraded soils, especially in arid and semi‐arid countries, for example Kirkham etal. (2007).

Bennett et al. (2014) found that lime applied at 5 t/ha was still improving aggregate stability, hydraulic conductivity, vegetation cover, total C and N and soil respiration 12 years after application.

Dolomitic limestone is recommended for soils deficient in Mg²⁺ but using it too frequently can result in Mg²⁺ indices >3 and so poor K⁺ availability. In such a situation, farmers should ensure that there is sufficient K⁺ available and so no risk of K⁺ deficiency in the crops grown.

In summary, liming has strong effect on soil productivity as it helps to reduce the acidity of the soils. The acidity is mostly due to the deposits of hydrogen and aluminum in agricultural soils.

Application of lime neutralises the acidity due to hydrogen and aluminum. When levels of hydrogen or aluminum become too high and the soil becomes too acid, the soil’s negatively charged cation exchange capacity (CEC) becomes clogged with the positively charged hydrogen and aluminum, and the nutrients needed for plant growth are pushed out.

Liming material can bring the pH of a soil to optimum levels for crop production when it is properly used. Liming materials also provide calcium (Ca) and/or magnesium (Mg) to the soil for plant uptake.

Materials that can cause an increase in pH include carbonates, oxides or hydroxides of calcium and magnesium. When looking at liming materials it is often hard to distinguish one material from another.

Quality standards used to differentiate liming materials include Total Neutralizing Value (TNV), Calcium Carbonate Equivalence (CCE), Fineness, and Effective Neutralizing Value (ENV).

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