Neutralising Value

During soil amendments, it is imperative to know the neutralising value of the products being used. But before we look at that number, let's find out what it means in order to make the most of its capabilities.

When it comes to making a liming amendment, it is not always possible to find the desired liming amendment material in a nearby area. And there are different considerations when deciding which material to use, its granularity, purity, cost, availability or distance, so the range of options is considerably reduced.

Limestone amendments are used to correct acid soils or soils affected by high sodium concentrations.

If the objective is to increase the pH, a multitude of materials can be chosen that would fulfil this function in the soil. For example, all kinds of carbonates or calcium and magnesium oxides and hydroxides can be used. Sometimes these materials are even mixed. That is why different parameters have been determined to unify the Neutralising Value of the material:

• Total Neutralising Value (TNV)

A base material has been established to which the rest of the materials are compared in order to know the capacity to neutralise the sources of acids in the soil. This value is established with reference to the effect that the calcium carbonate equivalent.

• Calcium carbonate equivalence (ECC)

In order to compare different materials, it is established that calcium carbonate (CaCO3) has an alkalinising capacity of 100%.

Depending on the material it may be more or less effective than calcium carbonate and sometimes the material may contain other less pure materials whose source is the quarry or other additions.

• Effective Neutralising Value (NEV)

In the end, in order to know the neutralising value of a material, there are more variables than just its chemical nature.

A very important variable is its particle size. A material that passes through a 100 mesh (with a clearance of 0.149 millimetres) will react in the first year. The material described above will have an effectiveness of 1.

If we have another material that 50% of the material passes through the 100 mesh and 90% passes through the 20 mesh (with a clearance of 0.841 millimetres) it will have a lower effectiveness. Exactly the effectiveness factor will be [(90-50)*0.6+50]/100=0.74

After explaining the fineness, the Effective Neutralising Value is determined as the fraction of material that will react with the acidity of the soil in the first year of application. A liming material with a calcium carbonate equivalence (CCE) of 85% at the fineness of the example above (0.74) will have an Effective Neutralising Value of 85*0.74=62.9.

The above is important to know the real cost of the product. It is not only the distance from the quarry that has an influence when making this type of application, it is also important to know the amount of material that is going to be needed, as it depends on the source and the texture.

FieldScout SoilStick pH Phimeter