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Course Content
Concept, scope and importance of soil physics in agriculture
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Introduction
Importance of soil physics
Structure of Water
Physical Properties of Water
Soil Water Energy Concept and soil moisture characteristics curve
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Introduction
Factors affecting the potential energy of water
Soil Water Potential (SWP)
Water Movement Based on Soil Moisture Levels
Gravitational Potential (yg)
Matric Potential (ym)
Osmotic Potential (yo)
Submergence Potential (ys)
Soil Moisture Content
Soil Moisture Measurement
Soil moisture characteristics curve (SMCC), moisture extraction/retention curves or Soil water potential curve
Factors Affecting Soil Moisture Characteristic Curve
Hysteresis
Quantitative Description of Soil Wetness or Classification of Soil Water
Plant Water Availability
Soil water movement under saturated and unsaturated conditions
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Introduction
Poiseuille’s Law
Darcy’s Law
Saturated Water Flow in Vertical Column of Soil
Saturated Hydraulic Conductivity and  Unsaturated Water Flow in Soil
Key differences between saturated and unsaturated water flow in soil
Relationship between k and ym
Air and heat movement in soil and infiltration characteristics in soil
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Water Vapor Movement in Soils
Heat movement in soil
Factors affecting soil thermal regime
Modes of thermal energy transfer
Conduction of heat in soil
Latent heat transfer (LHT)
Soil temperature management
Surface sealing, its effect on soil and crop growth and its management
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Surface sealing
Soil crusting
Renewal of soil air
Impact of poor aeration
Structural management of arable soil
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Introduction
Soil management
Factors involved in genesis and stability of soil aggregate
Aggregate stability
Soil profile development
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Soil Profile
Horizon boundaries and horizon continuity in pedon
Surface and subsurface soil horizons
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Introduction
Diagnostic surface horizons (Epipedons)
Diagnostic Subsurface Horizons
Soil moisture and temperature regimes
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Soil Moisture Regime
Soil Temperature Regime
Soil classification on the basis of USDA soil taxonomy
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Introduction
Soil taxonomy (USDA Soil Taxonomy)
Bases for Soil Classification in Soil Taxonomy
Major Soil orders of Nepal according to USDA taxonomy
Baldwin and Associate’s Genetic Approach
Orders of Genetic Approach
Limitations in Genetic Systems of Soil Classification
New Comprehensive System of Soil Classification (USDA Soil Taxonomy)
The FAO-UNESCO soil classification system
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Introduction
Concept and development of land capability classification
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Introduction
The USDA Land Capability Classification System
Master Soil Physics, Genesis and Classification – Notes, Case Studies & Practical Insights – with Rahul

Soil Water Potential (SWP)

  • Soil Water Potential (SWP) measures the energy state of soil water compared to pure, free water in a reference state (a hypothetical pool of pure water at atmospheric pressure, zero elevation, and isothermal conditions).
  • Since soil water has lower free energy than pure water, energy is required to move it from soil to the reference state, this energy is the soil water potential.

 

Components of SWP:
SWP is influenced by multiple forces, each contributing to the total potential:

  1. Gravitational Potential (Ψ₉): Due to elevation differences.
  2. Matric Potential (Ψₘ): Results from soil’s adsorption and capillary forces.
  3. Osmotic Potential (Ψₒ): Caused by dissolved solutes.
  4. Submergence Potential (Ψₛ): Pressure from overlying water in saturated soils.

 

Significance:

  • Determines water movement (flows from high to low potential).
  • Helps estimate plant water uptake effort—lower SWP means plants must expend more energy to extract water.
  • All components collectively influence soil water behaviour.
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