Course Content
Concept, definition, scope and branches of soil science
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Soil
Various definitions of soil
Concept of soil
Branches of Soil Science
Scope of Soil Science
Approaches of Soil Study
Historical development of soil science and soil institutions in Nepal
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Historical development of soil science
Soil institutions in Nepal
Evolution and composition of earth
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Theories about origin of Earth
The Age of the Earth
Interior of the Earth: A Layered Structure
Exterior of the Earth
Elemental Groups of the Crust (based on bonding behavior)
Land system, land forms and land units
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Land
Soil Formation from Rocks
Materials deposited from water
Common land units
Land units in Nepal
Weathering of rocks and minerals
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Introduction
Factors affecting weathering of rocks and minerals
Rocks
Minerals
Classification of minerals
Physical properties of minerals
Basic and pedogenic processes of soil formation
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Soil Pedogenesis
Basic soil forming process
Fundamental Soil forming Processes
Specific Soil Forming Processes
Soil as a Natural Body & Its Ecological Functions
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Introduction
Ecological Functions of Soil
Kinds and distribution of soil flora and fauna
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Soil Flora
Soil Fauna
Physical properties of soil
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Introduction
Relative size of soil mineral particles
Soil texture
Importance of Soil Texture
Soil structure
Types of Soil Structure
Classes of soil structure
Grades of Soil Structure
Formation of Soil Structure
Importance of soil structure in agriculture
Bulk Density, Particle Density and Porosity
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Bulk Density
Particle Density
Porosity
Importance of bulk density, particle density and porosity
Soil Color
Soil Consistence
Moist Soil Consistence: (Crushability test)
Dry Soil Consistence: (Hardness test)
Importance of soil consistency
Chemical properties of soil
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Introduction
Importance of Soil Colloids in Soil Chemistry
General properties of soil colloids
TYPES OF SOIL COLLOIDS
Fundamental structure of silicate clay
Charge Development in Silicate Clays
Mineralogical Organization of Crystalline Silicate Clays
Expanding 2:1 Silicate Clays
Non-Expanding 2:1 Silicate Clays
Importance of Silicate Clays in Agriculture
Mixed and Interstratified Clay Minerals
Genesis of Silicate Clays
Ion Exchange in Soils
Cation Exchange (Base Exchange)
Cation Exchange Capacity (CEC)
Factors Affecting Cation Exchange Capacity (CEC) of Soil
Cation Exchange & Nutrient Availability
Importance of CEC in Soil Fertility & Agriculture
Anion Exchange in Soils
Importance of Anion Exchange Capacity (AEC) in Soil
Concept of Soil pH
Acids & Bases in Soil Chemistry
Soil Alkalinity
Managing Soil pH in Agriculture
Buffering Capacity of Soil
Soil pH Classification
Reactions of Lime in Soil
Effects of Lime on Acid Soils
Management of Acid Soils
Salt-Affected Soils
Effects of Salt-Affected Soils on Plants
Management of Salt-Affected Soils
Learn Fundamentals of Soil Science and Geology with Rahul

Soil pH Classification

pH Range

Reaction

6.6 – 7.5

Neutral

6.1 – 6.5

Slightly acidic

5.6 – 6.0

Moderately acidic

5.1 – 5.5

Strongly acidic

4.6 – 5.0

Very strongly acidic

< 4.5

Extremely acidic

Influence of pH on Nutrient Availability

  • pH 6-7.5: Optimal for most nutrients.
  • pH < 5.5: Fe, Mn, Zn increase (toxicity risk).
  • pH > 7.5: P availability decreases, Mo increases.
  • Microbial activity: Bacteria prefer neutral pH, fungi thrive in acidic soils.

Management of Acidic Soils

Liming Materials & Neutralizing Values

  • Quicklime (CaO): 178%
  • Hydrated lime (Ca(OH)₂): 134%
  • Calcitic limestone (CaCO₃): 100%
  • Dolomitic limestone (CaMg(CO₃)₂): 95-108%

Key Reactions in Liming

CaCO₃ + H₂O → Ca²⁺ + HCO₃⁻ (Neutralizes H⁺)

CaO + H₂O → Ca(OH)₂ (More reactive, requires careful handling)

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