How Lime Works

Lime increases soil pH

Productive farming leaves excess hydrogen ions (H) in the soil, causing acidity.  This restricts root growth which limits the plants access to water and its ability to grow.

When limesand comes in contact with wet acidic soil, the calcium carbonate (CaCO3) in the limesand separates into calcium (Ca) and carbonate (CO3) ions.

The carbonate ions react with the hydrogen ions, turning into carbon dioxide and water.

The hydrogen ions are neutralised, reducing soil acidity and increasing pH. This increases the plants access to water and ability to grow.

Neutralising value

As it is the carbonate ions that react with the hydrogen ions, the percentage of carbonate (calcium carbonate or magnesium carbonate) in the limesand is an important factor.  This percentage is called the Neutralising value or NV.  The NV is proportional to the amount of acid the lime can neutralise if its particle size is sufficiently small.

Particle size

Particle size is the other important factor, especially in low rainfall WA.  Lime dissolves in soil as acid eats away the surface of the lime particle. When the acid attacks the surface of the lime, carbonate is released and that neutralises the acid.

The soil next to the lime particle is neutralised and can’t dissolve any more lime. The lime particle sits in a pocket of neutralised soil and is no longer effective.  Large particles of lime may never dissolve, surrounded by neutralised soil.