Course Content
Concept, scope and importance of soil physics in agriculture
0/4
Introduction
Importance of soil physics
Structure of Water
Physical Properties of Water
Soil Water Energy Concept and soil moisture characteristics curve
0/15
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
0/7
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
0/7
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
0/4
Surface sealing
Soil crusting
Renewal of soil air
Impact of poor aeration
Structural management of arable soil
0/4
Introduction
Soil management
Factors involved in genesis and stability of soil aggregate
Aggregate stability
Soil profile development
0/2
Soil Profile
Horizon boundaries and horizon continuity in pedon
Surface and subsurface soil horizons
0/3
Introduction
Diagnostic surface horizons (Epipedons)
Diagnostic Subsurface Horizons
Soil moisture and temperature regimes
0/2
Soil Moisture Regime
Soil Temperature Regime
Soil classification on the basis of USDA soil taxonomy
0/8
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
0/1
Introduction
Concept and development of land capability classification
0/2
Introduction
The USDA Land Capability Classification System
Learn Soil Physics, Genesis and Classification with Rahul

Diagnostic Subsurface Horizons

Diagnostic subsurface horizons can be categorized as weakly developed horizons in lower surface. They are characterized by an accumulation of clay, organic matter, or inorganic salts as cemented horizons, or as strongly acidic horizons.

  1. Agric: this horizon form under a plow layer. It normally has lamellae (finger-shaped concentration of materials) of illuvial humus, slit and clay.
  2. Albic: clay, humus and other coating have between leached from this eluvial horizon, leaving light-colored sand and silt particles.
  3. Argillic: this illuvial horizon has mostly of high activity clay coating on the face of peds or some indication of clay movement. Exchangeable sodium is less than 15% in this horizon.
  4. Calcic: measuring 15 cm or more thick, this horizon is not cemented, and has evidence of calcium carbonate movement. If the horizon is cemented, it is classified as petrocalcic.
  5. Cambic: this horizon shows some evidence of alteration but is very weakly developed between A and C horizons. The cambic horizon has less illuviation evidence than found in the argillic and spodic horizons.
  6. Duripan: this subsurface horizon is cemented by silica in more than 50% of its volume. It dissolved in concentrated basic solution, but does not slake in HCl.
  7. Fragipan: a fragipan is brittle horizon situated at some depth below an eluvial horizon. It has a low organic matter content, lower bulk density than overlying horizons, and hard or very hard consistence when dry.
  8. Petrocalcic: this transitional horizon has part of an eluvial horizon and the remnants of a degrading argillic, kandic or natric horizon.
  9. Gypsic: an illuvial horizon, the gypsic is 15 cm or more thick with 5% or more gypsum. If the horizon is cemented, it is classified as petrogypsic.
  10. Kandic: the kandic is a horizon with an illuvial accumulation of 1:1 (kaolinite-like) clay that has a CEC of less than 16cmol/kg clay. Organic carbon constantly decreases with increasing depth.
  11. Nartic: the natric horizon is similar to the argillic horizon with yhe additional characteristics of columnar structure. It has an exchangeable sodium percentage of 15% or more.
  12. Oxic: the oxic horizon contains highly weathered clays. It is 30 cm or more thick and has a CEC of less than 16cmol/kg clay. Less than 10% of the minerals are weatherable.
  13. Palic: this subsurface horizon is cemented by iron, iron and manganese, or iron and organic matter.
  14. Salic: measuring 15cm or more thick, the salic horizon contains at least 2% soluble salt. A 1:1 soil to water extract has an electrical conductivity of 30 dSm-1 (decisiemens per meter) or more.
  15. Sombric: the sombric horizon has an illuvial accumulation of humus that is not associated with aluminum (spodic) or sodium (natric).
  16. Spodic: the illuvial horizon contains high pH dependent charge material. A sandy-textured horizon, it has an accumulation of humus with aluminum and/or iron.
  17. Sulfuric: the sulfuric horizon forms as a result of draining soil with a high sulfide content that is oxidized to sulfates, drastically reducing the pH. It is at least 15cm thick and has pH of 3.5 or less.
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