Neutralising value is an excellent measure of the acid neutralising potential of a lime source but what is it?

Neutralising value is the neutralising capacity of a liming material as compared to pure Calcium Carbonate. Eg 100% NV means a liming material has the neutralising capacity of a 100% pure calcium carbonate.

High NV, as a component of lime quality assessment, is an important factor. Bulk NV is a representative neutralising value for the submitted sample looked at as a whole sample. Individual sieve ranges provide further detail of the neutralising capacity of specific particle size fractions of the submitted sample. It is typical for the neutralising value to vary, sometimes significantly, between the sieve ranges. It is also typical for the Bulk NV and the Weighted Average NV to vary slightly.

Current industry assessments focus primarily on chemical purity of the lime source, expressed as NV or neutralising value.

But do remember, NV is not a guarantee of success. It tells us very little about the reactivity of a lime source when applied to the soil, or the capacity for the lime to move into contact with sub-soil acid.

If a lime is slow acting or unable to come into contact with acid, the return on investment for the grower is slow and limited – unless they make a costly mechanical intervention to access more of the neutralising capacity of their applied lime.

This is why a structured soil pH plan should be commissioned – to find the right lime source for your farm.

Fine particles move through the soil more efficiently and have a faster impact on changing soil pH.

The 2 landmark studies that support this are:
1995– Conyers, Scott, Fisher and Will publish “Predicting the field performance of twelve commercial liming materials from Southern Australia”. Research conducted supported Barber (1984) conclusions that particle size analysis and surface area do not necessarily relate. A strong linear relationship was discovered between measured surface area and % of product below 50 microns.

That is, material larger than 50 microns made a relatively small contribution to total measured surface area. This paper concluded that “fineness influences not only rate of dissolution but the proportion of soil volume in contact with the particles.” and also that “To obtain the maximum possible benefit from a liming material we recommend the use of the finest possible product that can be accessed and handled”.

The decision to opt for finer particle lime sand is further backed up by the national standards developed by CSIRO. These standards are far tighter that the DPIRD developed local ones. DPIRD who ascribe 100% efficiency value to under 500 microns (0.5mm).CSIRO only ascribe a 100% efficiency value to lime particles below 75um (0.075mm).

Our recommendation. Opt for the finest particles to get the best results.

The more soluble the product, the more easily they dissolve in rainfall. This means more particles from the product will move easily through the soil, resolving your acidity problems in the subsoil more quickly.

Added value lime products like, Agri-Cal, have up to 50 times more soluble neutralising fractions than typical lime sand.

Let’s be very clear. WA lime sand is an excellent pH adjustment tool when it is used in the appropriate way. It has great power to change the soil pH, but it is not necessarily the best lime product to use in every situation.

We use lime sand extensively in WA for 2 reasons. Firstly, the availability of the resource and proximity of it to the farmland where it is needed. Secondly, on the recommendation of DPIRD in the early 1990s. who decreed it was the best way for farmers to improve their soil pH.

Technology has come a long way since those recommendations and there are now a range of manufactured lime products that are more appropriate for use in certain situations. At Optima we believe in the power of lime sand where appropriate and the power of added value lime products where appropriate.

We offer one standard price – it will be the same price direct from the pit as it will be from our retail partners at Rural Stores across WA.

Purchasing from your local rural store is putting money back into businesses in your local community – and it doesnt cost you anymore money.