Effect of Gypsum in Reducing Aluminum Toxicity

Almost 50% of the potentially arable lands in the world are faced with the acidification problem. Use of the agricultural gypsum in the soils with the high aluminum concentration, such as the soils in lands under the tea cultivation and those near dried up swamps used in the agriculture, reduces the aluminum toxicity and promotes the growth of plant roots.

Al + SO4  AlSO4

This equation shows that toxic aluminum is replaced with aluminum sulfate, an ionic compound that has low toxicity. Moreover, the increase in the soil calcium transfers aluminum adsorbed on the surface of clay particles into the soil solution. It is noteworthy that gypsum does not have a very noticeable effect in the increase in the pH values of acidic soils.

High magnesium content soils

Use of gypsum in soils with high magnesium content

Soil-Mg + Ca²⁺  Soil-Ca + Mg²⁺

At equal concentrations of calcium and magnesium, calcium is more inclined to be adsorbed on clay than magnesium. Research by scientists has shown that applying gypsum at the rate of 2 t/ha has no effect on magnesium concentrations in surface and deep soil. Consequently, in some soils that are not rich in magnesium, this gypsum application rate has no negative impact on soil magnesium content. However, in soils with excessive magnesium content, applying gypsum at 20 t/ha reduces soil magnesium content to the desirable level.