Factors of Soil Formation:
The five factors, which control the formation of soil, are parent rock, relief, time, climate and plant and animal organisms.
Parent rock, relief and time these three factors are called the passive factors.
Climate and plant and animal organisms are the active factors.
The parent material and climate are the most important because these two affect the other factors.
A soil is derived from the underlying rock or the parent rock material containing different minerals.
The parent rock gets broken into tiny pieces and is decomposed slowly by physical and, chemical weathering.
It furnishes inorganic mineral particles of the soil.
The parent rock influences the rate of soil formation, the chemical composition, colour, texture, structure, mineral content and fertility.
Topography of an area affects the degree of erosion of the parent rock material and the rate of surface run off of water.
Thus, the relief affects, directly and indirectly, the processes involved in soil formation.
Steep slopes are subjected to more rapid run-off of surface water than the gentle slopes.
Therefore, there is less infiltration of water on steeper slopes, which retards soil forming processes.
In addition, rapid run-off on steep slopes often erodes their surface faster than soil can develop.
It is because of this that the mountainous topography develops coarse, thin and infertile soil and the plain areas have rich well developed fertile soils.
The soil forming process is very slow.
A well-developed soil results as an end product of physical, chemical and biological processes operating collectively for a very long period of time.
It not only tends to reduce the difference caused by the parent material but also influences biological activities within the soil.
Due to this factor, two different parent materials may develop the same type of soil in one type of climatic region.
For example, granite and sandstone have developed into sandy soil in dry Rajasthan desert.
On the other hand, two different types of soils may develop from the same parent material in two climatic regions.
For example, the crystalline granites have developed laterite soils in monsoon regions and non-laterite soils in sub-humid regions.
The process of weathering, its effectiveness and the type of plant and animal organisms in a region are directly linked with the seasonal change of temperature and distribution and nature of precipitation.
Plant and Animal Organisms
Plants and animals play an active role in transforming parent materials into a mature soil.
Dead plants and animals contribute to the organic content of the soil.
The process of decay, added by bacterial action, transforms organic matter into humus.
Humus is responsible for the fertility of the soil.
Humus also enhances water retention capacity of the soil.
The plant cover, in turn, protects the rich upper layer of the soil from erosion by increasing the proportion of rainfall entering into the soil rather than running off the surface.
It also prevents greater evaporation of soil moisture by its thick canopy, thus allowing soil to mature and become fertile.