Soil Geography

Pedogenesis, or soil formation, is a continuous process regulated by the effects of environment, time and geological history. It involves biogeochemical processes that act to both create and destroy order within soils leading to development of layers, termed as soil horizons, distinguished by differences in colour, structure, texture, and chemistry.

There are various factors responsible for soil formation

a. Active factors, whose influence over soil development, is directly observed. These include:

• Climate: Temperature and moisture affect the rate of weathering, organic decomposition and biological activity. The high rate of heat and humidity accelerates the microbial action, on the other hand colder and drier climate slows down these processes.
• Biosphere/Organism: Soil formation is influenced by organisms and microorganisms, burrowing insects, animals and humans as they add up to the soils.

b.Passive factors, as their effects are not immediately observed. They control how climate and organisms affect soil development and formation. These include:

• Parent material: Soil minerals are the basis of soil and they are produced from parent rocks through the process of weathering and other processes of natural disintegration. The type of parent rock and the conditions, under which it broke down, deeply influences the property of the soil.
• Topography/Relief: Topography and relief of a region affects the climatic conditions, which ultimately influences soil formation processes and its characteristics.
• Time: Young soils retain many of the characteristics of the parent material. Over time they acquire other features resulting from the addition of the organic matter and the activity of the organism. The most important feature of the soil is that they pass through a number of stages as they develop, resulting in a deep profile with many well-differentiated horizons.

Processes involved in the soil formation: Soil formation takes place through various stages like addition, losses, transformation and translocation which takes place through various processes like.

• Weathering: The changes in climate factors such as temperature, moisture, frosts etc. disintegrates rocks, breakdown and decomposes the minerals. It includes physical weathering, chemical weathering and biological weathering.
• Decomposition and humification: Decomposition is the process of breakdown of plant derived materials into its simpler organic constituents which is accomplished by enzymes, earthworms, mites and other organisms. On the other hand, Humification is the breakdown of plant remains leading to the formation of different types of humus.
• Leaching: The soluble minerals are leached or removed from the soil profile due to percolation of water from top of soil. Continuous leaching tends to impoverish the upper mineral horizon. This process helps in the formation of laterite soil due to leaching of parent rocks.
• Translocation: The movement of minerals in solution or suspension from one horizon to another is referred as the translocation. The upper mineral horizon from where the components are carried is called Eluvial horizon and the lower horizon where these components are deposited are called Illuvial horizon.

There are also other soil forming processes, which are much important in the macro-scale pattern of Podzolization soil formation, which includes

• Podzolization : It is a complex process of formation of Podzol soil where dissolved organic minerals are accumulated. These are moved from the upper horizon to the lower part of the soil profile depositing deep down under.
• Calcification/ Salinization: Calcification involves the accumulation of calcium salts in the soil profile, while salinization is the process of accumulation of salts in the soil.
• Gleization: It is the process of formation of the clay soil or wetland soil due to poor drainage conditions.

The collective interaction of these processes sets a course of soil forming process, which determines the characteristics of soil.