Introductory of Soil Science

Concepts of Soil and Branches of Soil Science

Concepts of Soil

The term soil is derived from the Latin word “Solum” which means floor. For a layman or an urban people, soil is the dirt or debris on the surface of the earth or inert, uniform brown coloured materials in which plants find their foothold.

To an agriculturist soil is a natural medium for plant growth. The concept of soil has been changing with the accumulation of more knowledge.

Whitney (1892) develops the concept of soil as a nutrient bin i.e. all soils were considered to be naturally high enough in nutrients for satisfactory plant growth.

A new concept of soil developed with the development of geological science. Geologists considered soil to be the product of rock weathering.

Ruffin (as quoted by Simomson, 1968) conceived soil as a mixture of earth’s uppermost mantle of weathered rock and organic matter. The deeper part of this mantle (the regolith) were note considered soil.

According to Hilgard (1892) soil is more or less a loose and friable material in which plants, by means of their roots find a foothold for nourishment as well as for other conditions of growth.

V.V. Dokuchaev (1900) viewed soil as a natural body composed of mineral and organic constituents, having a definite genesis and a distinct nature of its own. He is considered as the father of pedology.

According to Jenny (1941) soil is a naturally occurring body that has been evolved owing to combined influence of climate and organisms, acting on parent materials, as conditions by relief over a period of time.

An agricultural definition of soil is "a dynamic natural body on the surface of the earth in which plants grow, composed of mineral and organic materials and living forms" (Brady, 1974).

As a general rule, soils should be recognized as 3-dimensional natural bodies, having length, breadth and depth. It is the interface between the atmosphere and lithosphere. Soils are natural bodies developed due to the action/influence of climate and vegetation on the parent materials as conditioned by relief, over a period of time. Soils contain more living organisms per unit volume than any other part of the biosphere. Most soil show marked variation with depth that is the reflection of basic soil forming factors and processes.

Land and soil are often confused by students as synonyms. It is not true. Land includes not only soil but also all the living organisms, the air and water bodies within or on it, and the rocks below. Soil is a part of land having definite physical, chemical and biological properties.

Soil Science:

Soil science is the branch of science that deals with the soils as a natural resource on the earth surface including pedology (soil genesis, classification and mapping) and the physical, chemical, biological and fertility properties of soils.

Definition of soil:

Soil is a dynamic natural body developed as a result of pedogenic processes during and after weathering of rocks, consisting of minerals and organic constituents, possessing definite physical, chemical, mineralogical and biological properties having a variable depth over the surface providing a medium for plant growth.

(Biswas and Mukherjee, 1994)

The Soil science has the following well defined branches:

1. Soil Physics:

Soil physics is the division of soil science that involves with the study of physical properties of soil.

2. Soil Chemistry

It is a division of soil science concerned with the chemical constituents, the chemical properties and the chemical reactions of soil. It is the study of chemical composition of soil in relation to crop needs.

3. Soil microbiology

Soil microbiology is that branch of soil science which deals with microscopic population of the soil, its role in various transformations and its importance in plant nutrition and crop production.

4. Soil conservation

It is a division of soil science dealing with the protection of soil against physical loss by erosion or chemical deterioration either natural or artificial means.

5. Soil Fertility

It deals with the nutrients status or ability of soil to supply nutrients for plant growth under favorable condition.

6. Productivity

It the capacity of a soil in its natural environment to produce crops under a specified management system.

7. Soil Mineralogy

It deals with the minerals present in the soil and their contribution to the chemistry, physics biology and fertility of soil.

8. Pedology

Pedology deals with the genesis, survey and classification of soils for land use planning.

Soil genesis:

The mode of origin of the solum from the parent materials by the action of various soil forming factors and processes.

Soil survey:

A systematic study, description, classification and mapping of soils of an area.

Soil classification:

The systematic categorization and arrangement of soils on the basis of their characteristics.

Book Ref.

1. Pedology concepts and applications-- J. Sehgal

2. Principles of soil science--- M M Rai

3. Text book of soil science--- T D Biswas & S K Mukherjee

4. The nature and properties of soil ---N C Brady & R R Well

5. Fundamentals of soil science--- Shivanand

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