Chemical Properties of Soil

Soil consists of mineral matter, organic matter, soil air, and soil water. All these four components are closely related with each other. The chemical properties of soil are important as they are closely related to the capacity of the soil to supply plant food Nutrients.

1. Mineral matter :The Mineral matter of the soil consists of inorganic substances derived from rocks. Minerals are of primary and secondary type. Primary minerals are similar to that of parent material and secondary minerals are those derived from chemical weathering of rocks, secondary minerals are also called as clay minerals.

2. Inorganic components: The main chemical compounds in the soil are silicon, calcium, magnesium, iron, potassium, sodium and aluminium. The total amount of elements present in the soil depends partly on the nature of the parent material and partly on their age and extent to which soluble products have been leached down. Also chemical composition of different horizons of a soil shows a great deal of variation.

3. Ion exchange: It is a reversible process by which cations and anions are exchanged between solid and liquid phases and between solid phases which are in close contact with each other. Ion exchange is the most important of all the processes occurring in soil. Cations are the positively charged ions and anions are negatively charged ions. The capacity of the soils to adsorb and exchange cations and anions varies greatly with the nature and amount of clay and the organic matter. The cation-exchange capacity (CEC) is defined as the amount of cation species bound at pH 7 and is expressed as milliequivalents (m.e.) per 100 grams.

4. Soil acidity (pH of soil): - It is a important chemical property of the soil. Suitability of the soil as the medium for the growth of plants and desirable micro-organisms depends considerably on the soil reaction. This reaction is measured in terms of pH. The pH scale has a range from 0 to 14. Its central point i.e. pH 7 indicates a neutral reaction. Values less than pH 7 denotes acidity while more than 7 indicate alkalinity. The pH range for most agricultural soils is about 5 to 8.5.

5. Buffering capacity of soil: Most of the soils can resist the pH changes, when large amounts of either strongly acid or bases forming materials are added. This ability to resist the change in pH is called as buffering capacity of the soil. Carbonates, bicarbonates and phosphates present in soils act as buffering agents. Buffering capacity of soil depends upon the amount and nature of clay and organic matter content.

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(Soil Mgmt.)