Soil Forming Factors
The unconsolidated material at the earth's surface that serves as a media for plant growth.
Soil Profile Definition
Soil profile is the order top to bottom of the master horizons
Size and texture of "sand", "silt", and "clay"
1.Sand= 2-.05 (immovable) 85% Sand Particles
2.Silt= .05-.002 (immovable) 80% Silt Particles
3.Clay= <.002 (movable) 40 % Clay Particles
Soil Texture Definition
Soil Texture is the amount of sand, silt, and clay percentage
Soil structure 3 requirements
1. Must be soil aggregates
2. Must be brought together
3. Must be cemented together.
A layer or zone of soil somehow different from the
zone above and below it
The soil horizons, in sequential order, from the
O - Organic - Occurs on top of the inorganic soil
A - Topmost inorganic horizon
E - The eluvial zone - zone of loss - some material is lost from this horizon
Eluviation is the process of loss
B - The illuvial zone - zone of gain - some material is generally gained in this horizon
Illuviation is the process of gain
C - The "parent-like" material. It is NOT parent material since it has been
R - Bed rock - is NOT a "soil" horizon
L for Limnic
Layers of organic and mineral materials
Found only in certain organic soils
W for water
Layers of water (frozen or liquid)
Found within not overlying certain soil profiles
Solum - "The soil" - A, E, and B horizons
Regolith - All the soil horizons above the bedrock
A horizon that possesses characteristics of two of the master horizons. The transition horizon is designated by two capital letters
The amount or percentage of the sand, silt, and clay sized materials in the soil. Determined by Strokes Law or by feeling the soil
The arrangement of the primary and secondary soil aggregates.
pieces of soil
are the sand, silt, and clay sized particles.
are small "groups" of the primary aggregates.
Structureless soils are:
mass per unit volume
Bulk Density (Db)
is the mass of the whole dry soil divided by the total, dry volume.
Bulk density ranges from 0.8 to 1.8 g/cm3 or (Mg/m3). The average value 1.3 g/cm3.
Particle Density (Dp)
is the mass of the dry soil solids divided by the
volume of soil solids.
fraction of the total soil volume that is pore space
Bulk Density Influence
Root growth,Water contents,Air movement, Germination, Support
physical condition of soil that describes ease of breaking the soil peds.
Hard - not easily broken
Friable - ideal - easily broken
Plastic - molded when wet
formed from temperatures and pressures under the earth's surface
formed from eroded and deposited sediments with some added pressure but no high heat
known as the transformation of particle material into soil. This occurs by geologic erosion, deposition and reformation
Smallest unit of soil that totally describes the soil variability in terms of horizontal and vertical dimensions
Pedons that are associated with one another
Fundamental unit of soil classification
Soil series plus other information
1. Hierarchical - hierarchy - few general classes divided into many specific classes
2. Utilitarian - based on use
Soil Survey Reports
1. Descriptive section
A HASH DIRT
a layered aluminosilicate that is comprised of one or more tetrahedral layers and one or more octahedral layers
any small particle that has a large surface area - soil examples are clay and organic matter
Clay micelle or clay crystal
a small clay colloid that generally is plate shaped and negatively charged
positively charged particle
negatively charged particle
charge of one
charge greater than 1
The CEC of a soil depends upon:
1. Amount of clay and organic matter
2. Type of clay
-log [H+] moles/L; pH is the negative logarithm of the hydrogen ions; Acid= less than 7, Base= Greater than 7
Factors that Influence:
1. Soil texture
2. Clay mineralogy
- the ability of a soil to resist an abrupt change of pH.
Salt Affected Soils
1. Saline-soil high in salt content as determined by electrical conductivity of extract.
2. Sodic-soils high in sodium
3. Saline-sodic=worst of all salt affected soils
1. Eradication - total removal of salt problems, hard or impractical to achieve
2. Conversion - change the problem
3. Control - do not let the problem get out of hand
b. Irrigation management
d. Plant adapted species
Clay Differences Due to:
A. Lattice: geometrical arrangement
B. Substitution: what and where cations are replaced within 2:1 clay
C. Form: how the clay minerals stack on one another
One layer of silica tetrahedra bound to one layer of alumina octahedra
Two layers of silica tetrahedra with an alumina octahedral layer sandwiched between them
CEC of Soil
The charge, in centimoles, that a soil can hold or be able to exchange per kilogram of soil.
gaseous interchange from the soil atmosphere to air atmosphere and air atmosphere to soil atmosphere
Soil AERATION Status Methods
1. Percentage of gas components
2. Redox potential
3. Oxygen Diffusion Rate
Soil factors influencing AERATION
4. Water content
Gas Movement Mechanisms
1. Mass flow - all gases move together
c. Water entry
d. Barometric pressure changes
2. Diffusion - one gas at a time - movement by gradient
physical, biological, and chemical processes
Heat balance of the earth factors:
1. Color (albedo)
Soil temperature factors:
1. Time of year
2. Color (albedo)
Heat movement mechanisms
1. Reradiation: radiation emitted from previous absorption of radiation
2. Conduction: transfer of heat between objects
3. Convection: movement of heat from soil to air
4. Latent heat: heat gain or loss by phase change
1. Physical properties
2. Biological properties
3. Chemical properties
Saturated - All pores water filled, very seldom happens very hard to achieve.
2. Unsaturated - Not all pores are water filled - most of the time soils are unsaturated.
Soil-water potential equation
ψt = ψg + ψm + ψo
ψt - Total Soil-water potential,ψg - Gravitational potential,ψm - Matric Potential,ψo - Osmotic Potential
Water always moves from high to low potential, when it can move.
Field Capacity - The water content/potential of a soil that has been wetted and drained for two to three days. ψm = -0.033 MPa for most soils ψm = -0.01 MPa for sand.
Permanent Wilting Point - The water content/potential of a soil that can no longer supply enough water to keep the plant alive. ψm = -1.5 MPa.
Plant-Available Water - The difference between the Field Capacity and the Permanent Wilting Point.
Saturation - ψm = 0
Excess Water - The water between Saturation and Field Capacity.
Plant-Nonavailable water - The water held within the soil at lower potentials (move negative) than Permanent Wilting Point.
water entry into soil
water movement within a soil. Usually
thought to be in the vertical downward direction.
water movement within a soil. Can be up, down, or horizontal.
Water balance equation
Equation: P + I + Ron = Roff + E + T +D + ΔS
P = Precipitation: any form of water falling to the earth
I = Irrigation: supplemental application of water
Ron = Run on: water that run onto the soil from upslope
Roff = Run off: water that does not infiltrate and is lost down slope
E = Evaporation: water loss as a gas directly from the soil to the air
T = Transpiration: water loss as a gas directly from plant stomata
D = Deep Drainage: water that drains below the root zone
ΔS = Change of Stored Water
Water determining Methods:
is removal of excess water from the system. This can occur before water enters the soil or after water enters the soil.
supplemental addition of water to the system
algebraic sum of evaporation and transpiration
Plant Growth External Factors
2. Mechanical Support
6. Nutrients→ Fertilizer
element required by plants to complete vegetative and/or reproductive growth
Status of soil amount and availability of the essential nutrients. Amounts, forms, and proportions for maximum plant growth.
one that is fertile and has no other limiting external factor
soil adsorbed and solution
chemically and/or position.
Macronutrients: N, K, Ca, Mg, P, and S, and
Micronutrients: Cl, Fe, B, Mn, Zn, Cu, Mo, and Ni
two step process of soil loss; Detachment, Transporation
Sheet-whole soil moves in mass down slope
Rill -small channels - crossed by tillage tools
Gully-large channels - cannot be crossed by conventional equipment
Saltation (50-75% loss/fine sand)
Creep (5-25% loss/coarse sands)
Suspension (15-40% loss/silt and clay)
Mineralization of Organic Matter
1. Aminization: enzymatic hydrolysis of protein OM →RNH2
2. Ammonification: R-NH2 →NH4+
3. Nitrification: NH4+ →NO2- →ΝΟ3-
Nitrification Factors Influencing
5. Water content
6. C:N ratio
8. Other salts
is the primary source for commercial, inorganic fertilizer
compression of unsaturated soil resulting in less air
compression of saturated soil by squeezing out water
1. Surface Crust
a. pedogenic: compaction due to soil formation
b. authogenic: compaction due to human actions
utilize CO2 as carbon source. Two types of autotrophs are as follows:
1. Photoautrophs - use sun for energy—think of plants as this type of organism. This is the concept behind the plant in the above figure. There are also algae that use sunlight for energy sources.
2. Chemoautrophs - use chemical reactions for energy—there are microorganisms (Small) that do NOT use light for an energy source. Those organisms use chemical reactions as a source of energy, but still use CO2 as carbon source
utilize fixed carbon as carbon source
1. Aerobes - require O2
2. Anaerobes - requires lack of O2
3. Facultative anaerobes - can function with or without O2
one decreases the amount and the toxicity of the trash that one throws away.
reusing containers and products rather than using new ones.
using over and over again
2.inorganic elemant polutants
4. Chemical reaction
5. Microbial metabolism
6. Absorbed and detoxified within plants