Soil pH is usually adjusted to a required
range using an appropriate method. Common methods of modifying soil pH include
the addition of amendments or liming materials, uses of fertilizers, tillage
practice, using organic matter, and improving drainage.
An amendment is any inorganic materials
added to the soil to change the pH of the soil. The methods chosen depends
on whether the soil acidic or alkaline.
Alkaline soil
A common amendment used to acidify alkaline
soil is sulphur (S). Element sulphur is oxidized by microorganism to produce
sulphate ions and hydrogen ion, the hydrogen ion lower the pH of the soil.
Iron (II) sulphate (FeSO4) and
aluminium sulphate [(Al2SO4)3] can also be
used to lower the pH of the soil, this is because they contain acidic cations
(Fe2+ and Al3+)
The amount of amendment applied depends on
properties of the products (particle
size, oxidation rate) and soil condition
(original pH and mineral presents)
Ammonium based fertilizer and soil inorganic
matter are also used to lower the pH of the soil, ammonium based fertilizer
such as urea (46-0-0) and ammonium phosphate (11-52-0 0r 18-46-0), are oxidized
by soil microorganisms producing hydrogen ions.
Acidic soil
The most common method of increasing the soil
pH is liming.
Liming is the application of calcium in
various forms to soil in order to increase the pH of the soil.
The most commonly used liming materials are
limestone (CaCO3), quicklime (CaO) and slaked lime [Ca(OH)2].
The liming materials react with carbon dioxide
and water in the soil to yield hydrogen carbonate. The hydrogen carbonate
ions neutralize acid farming cations in the soil, thereby raising the soil pH.
Magnesium carbonate is also used to raise the
pH of the acidic soil, wood ash can be also used as a liming materials.