Soil is a composed of organic and inorganic matter, minerals, gases, liquids, and organisms that together support life. It varies from place to place due to its structure and composition.
1. It is a medium for plant growth.
2. It is a means of water storage, supply and purification.
3. It is a modifier of Earth's atmosphere.
4. It is a habitat for organisms.
The Alkaline or Alkali Soils are the soil with high pH value (>9). It has a poor soil structure and low infiltration capacity. These types of soil have dominated presence of minerals such as Sodium Carbonate which causes the soil to swell. They are generally noticed in arid and semi-arid regions where there is low rainfall and high temperature causing intense evaporation.
The causes of soil alkalinity can be natural or man-made which are given below:
1. Presence of soil minerals producing Sodium carbonate (Na2CO3) and Sodium bicarbonate (NaHCO3) upon weathering.
2. Industrial and domestic waste such as Sodium carbonate, Sodium bicarbonate (baking soda), Sodium sulphate, Sodium hydroxide (caustic soda), Sodium hypochlorite (bleaching powder), etc. in huge quantities during their production process or consumption enhancing water sodality.
3. Coal-fired boilers / power plants, when using coal or lignite rich in limestone, produce ash containing calcium oxide. CaO readily dissolves in water to form slaked lime– Ca (OH)2 –and carried by rain water to rivers / irrigation water.
4. Use of softened water in irrigation (surface or ground water) containing relatively high proportion of sodium bicarbonates and less calcium and magnesium.
Gypsum (Calcium Sulphate, CaSO4.2H2O) is a sedimentary mineral. It is very important for the treatment of alkaline soil, which is discussed below:
1. It is an excellent source of sulphur for plant nutrition and improving crop yield.”
2. It can reduce Aluminium toxicity particularly in subsoil.
3. It helps in reducing runoff and erosion by keeping Phosphorous and other nutrients from the soil.
4. It replaces Sodium and leached downward and out of reach of plant roots.
5. It can be applied a source of Ca++ions to replace the Sodium at the exchange complex in the soil.
While using Gypsum, there must be enough natural drainage to the underground, or else an artificial subsurface drainage system must be present, to permit leaching of the excess sodium by percolation of rain and /or irrigation water through the soil profile. Apart from the use of fertilizers, the alkalinity of the soil can be reduced by cultivating grasswort or saltwort or Barilla plants.