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In this article, we would discuss the basic composition of soil and the contributing factors in its formation.
What is soil?
a. It is a complex mixture comprising weathered and eroded rock materials along with decayed organic matter.
b. Chemical and biological factors like sunlight, sediments deposited by water and wind, salts, organic residues and nitrogen from bacterial fixation result in weathering. Weathering breaks down rocks into loosened particles, which then react with the decayed organic material (plants and animals) to form various types of soil.
Soil forming factors
Apart from weathering there are five primary factors that influence soil formation either individually or combined, to develop various types of soils.
1. Parent Material: The material from which soil develops is known as parent material. The chemical composition and nature of the parent material largely influences the soil type and its properties. For example: a weakly cemented stone forms soil with sandy texture while shales (fine-grained sedimentary rocks) form soil that is fine in texture. Parent material also affects the fertility of soil. For example: parent material rich in soluble ions like calcium, magnesium and potassium forms fertile soil and the ions are easily available to the plants growing in it. However, material with low amount of such ions forms less fertile soil.
2. Climate: Soil composition is greatly affected by climate. Precipitation and humidity have an impact on both chemical and physical composition of soil. Acidic soils are mostly formed in areas with high humidity and precipitation, which is responsible for leaching of ions. On the other hand, low rainfall results in higher alkalinity in the soil due to retention of lime. Climate also affects the vegetation cover, which in turn influences soil quality.
3. Biota: Both living and dead organisms affect soil composition. Roots of living plants release weak organic acids that accelerate the process of weathering. Burrowing animals like earthworms, moles, ants and termites decompose the organic matter thus dissolving the minerals faster. Organic wastes and residues, dead plants and animals also release nutrients into the soil making it richer.
4. Topography: It refers to the detailed map of surface features of land and its distribution in a specific area. It includes mountains, hills, slopes, bumps and depressions on a land surface or the orientation of the land with respect to the direction of the Sun. Steep hillslopes tend to have thin soil cover as surface runoffs result in soil erosion. On the other hand, hillsides with a gentle slope tend to have a rich vegetation as sufficient water passes into deeper levels. Landlocked depressions also have dense vegetation but with a slower decomposition rate due to oxygen deficiency.
5. Time: Time required for a particular soil to develop in favourable conditions will be lesser unlike with unfavourable conditions. Thus, the rate of soil development is determined by the effects of time with other factors that influence it.
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