Aluminium (Al) toxicity is often a major constraint of acid sub soils. Many of the soils along the east coast of Australia have acidic subsoil, partly naturally, partly as a result of cropping.
Al3+ions are toxic to plant roots, which go to great lengths to avoid acidic subsoil. This restricts their growth to the topsoil layer, where they can rapidly deplete the soil of water and nutrients, leaving deeper water and nutrients untouched.
Gypsum is used to reduce Al toxicity in countries such as Brazil and South Africa, but is still not generally recommended in Australia.
Gypsum normally provides a quicker response compared to lime and/or dolomite offers more immediate returns.
Silica can buffer the soil by binding with iron and aluminium to nutrients like phosphorous to be more plant available. Pacific Fertiliser has some silica products suitable for agriculture.
