CONCEPT OF SOIL SCIENCE

Concept of SoilThere are two concepts of soil-Soil is considered as a natural body, a biochemically

weathered and synthesized product of nature.

Soil is considered as a natural habitat for plants and other living organisms.

Soil: in different point of view-

On Pedological point of view- Soil is a weathered product of rocks and minerals.

Weathering

Rocks and Minerals Soil

On Edaphological point of view or Agricultural point of view -

Soil is a natural medium for plant growth.

On Composition point of view- Soil is a three-phase system consisting of solid, liquid and gases. 

On Engineering point of view- Soil is a foundation material for buildings and roads.

On General point of view- Soil is the loose surface of earth.

Definition of SoilAccording to C. E. Kellog

(1960):“The soil is a collection of natural bodies occupying a portion of the earth crust that supports the plant growth which have properties due to integrated effect of climate and vegetation acting upon parent material as conditioned by relief over a period of time”.

Definition of Soil According to Joffe and Marbut:“ Soil is a natural body developed by natural forces acting on natural materials. It is usually differentiated into horizons from mineral and organic constituents of variable depth which differ from the parent material below in morphology, physical properties and constituents, chemical properties and composition and biological characteristics”.

Definition of Soil

According to Buckman and Brady:

Soil may be defined as “ A dynamic natural body on the surface of the earth in which plants grow, composed of mineral and organic materials and living forms”.

Scope of Soil ScienceSoil Geology: The study of the geological

materials from which soil is derived and its process of formation.

Soil Chemistry: Study of the chemical components of soil, their interaction with one another.

Soil Physics: Study the effects of physical laws on the evolution of chemical and physical properties of soil.

Soil Biology: Study the effects of plants, animals and soil microorganisms on the evolution of soils.

Branches of Soil Science

There are two main branches of soil science-

1. Pedology : Pedology deals with soil formation, soil genesis, soil classification and description of soil properties.

2. Edaphology : Study of soil in relation to growth, nutrition and yield of crops or plants.

Other subjects studied in soil science are-

Soil Genesis Soil PhysicsSoil Mineralogy Soil ChemistrySoil Morphology Soil MicrobiologySoil Taxonomy Soil FertilitySoil Survey and Soil Pollution etc Classification Soil Conservation

Distinguish between Pedology and Edaphology

Pedology Edaphology1. Pedology is the word which come from the Greek word ‘Pedon’ which means soil or earth

1. Edaphology is the word which come from the Greek word ‘Edaphos’ which means soil or ground

2. Pedology deals with soil formation, soil genesis, soil classification and description of soil properties.

2. Edaphology deals with soil in relation to growth, nutrition and yield of crops or plants.

3. Pedology considers the soil as a natural body and places minor emphasis on its immediate practical utilization.

3. Edaphology considers the various properties of soils as they relate to plant production.

Major components of soil

Soil consist of four major components-

1. Mineral matter…………….. 45% Solid portion2. Organic matter…………….. 5%3. Water………………………. 25% Liquid portion4. Air………………………….. 25% Gaseous portion

Major components of soil

Fig. Volume composition of mineral soil.

25% water

25% air

5% Organic matter

45% Mineral matter

1. Mineral matter (45%):

Mineral matter includes-Primary minerals (e.g. quartz, feldsper, pyroxenes etc.)Secondary minerals (e.g. clay minerals such as kaolinite, vermiculite, muscovite, biotite etc.)CaCO3

Oxides of Fe and AlMineral matter provides mechanical support and

nutrients to the plants.

2. Organic matter (5%):

Mainly plant and animal residues such as- cowdung, urine, green manures, plants parts etc.Living organisms (e.g. plant roots bacteria, fungi, algae) may be considered into organic matter as they add organic matter after death.Organic matter is a storehouse of plant nutrients.It improves physical, chemical and biological properties of soil.

3. Air (25%):

Soil air comprises O2, CO2, N2, etc.CO2 content in soil (0.5%) in higher than in atmospheric air (0.03%)Composition of soil air is quit dynamic and various greatly from place to place.Soil air contains higher moisture than atmosphere.Soil air regulates gaseous exchange between soil air and atmospheric air which ensures fresh supply of oxygen and thereby prevents CO2 toxicity.

4. Water (25%):

Ground water table, rainfall, irrigation are the source of soil water.It is held with in the soil pores with varying degree of forces depending on the around of water present.Soil water consist of various salts in solutions such as SO4

=, NO3-, HCO3

-, of Ca, Mg, K, Na etc.Soil water keeps nutrients in solution and acts as a reservoir for supplying water to plants.

Keep in mind Under field condition pore spaces are occupied at all

times by air and water. The relative amount of air and water in the pore space

fluctuate continuously. It varies depending on some conditions like season, soil depth, intercultural operations (e.g. weeding, irrigation, mulching etc.).

In rainy season--- more water less air. In dry season --- less water more air. At weeding--- air increases. Air more in top soil, low in sub soil. Water more sub soil, less in top soil.

“The soil as a three phase system”- Explain

Soil as a phase system 

Soild phase Liquid phase Gaseous phase

 Organic matter Inorganic matter

Or Mineral matter 

Primary mineral Secondary mineral (eg. Quartz) (eg. Kaolinite)

1. Solid phase: The solid phase is 50% in total of the earth crust which having 5% organic matter and 45% inorganic or mineral matter.A. Organic matter: Only a small fraction of the solid phase is organic origin. The sources of organic origin are plants, animals, and organisms (micro & macro) in nature.B. Inorganic matter: The inorganic constituents which from the bulk of the solid phase. It contains silicates both primary and secondary minerals.i. Primary minerals: Primary minerals are found in rocks. The original sources of all primary minerals are soil.ii. Secondary minerals: Under condition of weathering, the Primary minerals are broken down to small fragments.

2. Liquid phase: 50% of the bulk volume of the soil body is generally occupied by soil pores (macro & micro), which may be completely or partially filled with water and that water is the liquid phase which is 25% in the mineral soil.

3. Gaseous phase: The air fills the pores and constitutes the gaseous phase of the soil system. The volume of the gaseous phase is thus independent on that of liquid phase. Air that is gaseous phase which is 25% in the mineral soil.