5 FACTORS INFLUENCING THE DEVELOPMENT OF SOIL PROFILE

 Soil profile refers to the vertical arrangement of the various soil layers from the top layer down to the parent rock or bottom layer.

It is a vertical section through the soil horizons extending into the parent material or the bedrock.

5 FACTORS INFLUENCING THE DEVELOPMENT OF SOIL PROFILE

It describes the sections downwards through the soil which comprises differing characteristics in terms of texture, color, mineral composition, the ratio of the combination of organic and inorganic matter, hardness, and rate of weathering.

The different layers are referred to as horizons.

A soil horizon is a well-defined layer within the soil profile parallel to the local round surface. There are four main horizons namely:

A horizon, B horizon, C horizon, and D horizon. Each horizon has different physical and chemical properties, which result from various soil-forming processes such as weathering, the introduction of humus, and the movement of minerals.

O-HORIZON

This is the topmost/ surface layer of the soil comprising organic matter.

The constituents of this layer include un-decomposed litter, decomposing organic matter, and humus.  

A-HORIZON

This is also known as the topsoil and it is rich in organic matter which organic matter accounts for dark colour.

Leaching and Eluviation may at times impoverish the topsoil.  

B-HORIZON

This is known as subsoil. Nutrients removed from the A horizon through leaching and Eluviation accumulate or are deposited in this horizon.

The process of plant nutrients precipitating or accumulating in this horizon is known as illuviation.

This horizon may also be characterized by hardpans due to the accumulation of large quantities of clay and other nutrients.  

C-HORIZON

This consists of partially weathered rock, this is because weathering and other soil-forming processes may not effectively operate at this depth.

D-HORIZON

This consists of solid parent rock or unweathered rock or fresh parent material. It is also known as the bedrock.

It has no soil particles but has potential for future soil formation

The nature of the soil profile may be such that it is fully developed or partially developed implying that soils may be deep or skeletal or soils of medium depth. 

5 FACTORS INFLUENCING THE DEVELOPMENT OF SOIL PROFILE

Soil profile development is influenced by a number of factors namely:

Nature of the parent rock

The parent material is the nature of rock upon which weathering and other soil-forming processes operate to create to create soil.

In the first place, the parent material provides the basis for soil profile development. It influences soil profile development in the following ways;

  • Hard or resistant rocks lead to the development of thin soils i.e. with poorly developed profiles. On the other hand softer rocks are easily weathered and acted upon by other soil forming processes leading to the formation of deep soils with a well developed profile.

  • The rocks with lines of weakness or joints have facilitated weathering and other soil forming processes leading to the formation of fairly deep soils. Such soils normally lead to a well-developed soil profile.

  • Young parent material has led to poorly developed soil or poor soil profile while older rocks have had enough time to be weathered and to develop into well developed soil profiles.

  • Permeable or porous rocks have enabled the easy infiltration of agents of weathering resulting into deep weathering and consequently deep soils with a well developed profile unlike impervious rocks.

Climate

Rainfall and temperature determine the nature and rate of weathering and soil-forming processes.

Climate also determines the growth of plants and animals that contribute to the soil profile through weathering and through the addition of humus.

Therefore different climatic conditions influence soil profile developments differently.

In areas where the climate enhances weathering and other soil forming processes there is a well-developed soil profile.  

Living organisms

Vegetation provides the needed organic matter for the soils therefore a well-vegetated area has a better-developed soil profile.

In addition, animals influence the mechanical breakdown of rocks, therefore, contributing to soil profile development.

Man’s activities such as cultivation, mining, construction tend to physically weather rocks thereby contributing to the development of soil profile therefore areas of abundant biodiversity have a well-developed soil profile as compared to those with limited biodiversity  

Topography/Relief

The nature or shape of the earth’s surface influences soil profile development.

Highly or steeply sloping areas tend to have less developed soil profiles unlike areas of gentle slopes.

This is because the rate of erosion is greater on the steep slopes and this removes the topsoil resulting in shallow or skeletal soils.

On the other hand, in the gently sloping lands and generally flatlands, soil profile tends to be more developed i.e. there are deep soils.   

Time

It takes time for the soil profile to be fully developed.

A typical or well-developed profile of soil must have undergone adequate time, therefore the longer the time to which the rocks are exposed to weathering and other soil-forming processes, the more the developed profile.

Young rocks normally yield skeletal soils i.e. with a poorly developed profile

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