It has been widely believed in the Agricultural / Horticultural sector over many years that Gypsum is used to improve soil structure in alkaline soils and Lime is used to counteract acid soil conditions which is an inevitable consequence of growing pasture and plants, this process has an acidifying effect, or alternatively from the acidification as a result of prolonged use of nitrogenous high analysis fertilizers.
This theory has been shattered over the past several years by extensive research and field trials. The combined application of gypsum and lime on acid soils has demonstrated a broad spectrum of benefits for plant health, nutrition, yield and soil structural improvement benefits. Gypsum also has a liming effect on acid soils including other benefits such as dispersion prevention resulting in improved drainage and aeration while improving calcium and sulphur deficiencies.
The mistaken belief that gypsum had no value unless soils had a high ph and high in exchangeable sodium binding the clays and therefore alkaline has been disputed by scientists around the world. The scientists have discovered that gypsum improves soils with dispersive clays even when they are very acidic. Gypsum sulphates react favorably in many acid soils by hydroxyl replacement with sulphate on clay.
Lime is highly effective in raising ph and is a source of calcium nutrition on surface soil. But many acid soils also have acid subsoils, which interfere with root development, nutrient transportation and absorption.
Calcium from lime does not migrate to the subsoil and requires a chemical reaction in the soil to become available to the growing media. The calcium in gypsum , on the other hand is readily available because it is water soluble and leaches down through the soil profile into the subsoil depths. In many cases liming of acid soils will greatly decrease the water infiltration rate, but when co-applied with gypsum, it will open up the soil for water penetration and aeration enabling root penetration-from the surface to the subsoil.
Acid soils need lime, but to gain optimum benefits and improved yields gypsum and lime blends are recommended. Gypsum is also a good option to lift calcium levels and improve soil compaction issues without raising ph.
Application Rates
Gypsum is normally applied at application rates of between 3-6 tonnes per Ha to improve soil structure are recommended. Gypsum Lime Blend ratios of 50/50, 60/40 are common. Effective treatment will require around 5t/ha 60/40 mix of lime +gypsum. Ploughing or deep ripping after application will improve the effect of the treatment.
