Physical Properties Flashcards
What is soil?
45% Mineral Matter
5% Organic Matter
25% Air
25% Water
Weathering
Breakdown of parent material (rock) into smaller pieces
2 types: chemical and physical
Physical weathering
Mica loses K+ and turns to vermiculite which loses more K+ and becomes smectite (montmorilinite being the most important smectite)
feldspars lose K+ and become kaolinite( a low CEC clay mineral)
Decomposition: Organic material to inorganic
biological process that includes physical breakdown and biochemical transformation of complex organic molecules of dead material into simpler organic and inorganic molecules
(C6H10O5)n+ O + F&B–> CO2 +H2O + Heat
Contributes to carbon cycling
Factors controlling rates of decomposition
Environment Factors:
Aeration, Temperature, Soil Moisture, Soil pH
Quality of added residues:
- Size of organic residues
- C/N of organic residues
Rate of decomposition of plant residue
in order from fastest to slowest decomposition rates:
- Sugars, starches, simple proteins
- Hemicellulose
- Cellulose
- Fats, waxes, oils, resins
- Lignin, phenolic compounds
Soil Texture:
Describes the proportion of soil particle sizes: Sand, Silt, Clay
influences other traits such as: Water holding capacity, Aeration
Effect of particle size
Smaller particles larger internal surface area
Small particles= many small pores (more pores= micropores)
Large particles= larger pores but fewer in number (Larger pores= macropores)
Soil Separates
Sand: 2.00-0.05mm
Silt: 0.05-0.002mm
Clay: <0.002mm
Textural Classification
12 Textural Classes, Textural Triangle
Soil Density and Permeability
Density: Mass per volume D=M/V
Two densities in Soil
Particle Density (PD) Bulk Density (BD)
Particle Density
PD average soils ~2.65 gm/cu cum
Bulk Density
BD average range from 1.0-1.8 gm/cu cm
Depends on amount of pore space
BD= wt.dry soil/ vol. dry soil = g/cu cm
eg. BD= 650g/500 cu cm= 1.3 g/cu cm
Soil Porosity
Usually expressed as a percentage
2 ways to determine porosity:
- Calculate ratio water volume to total core volume
- Calculate from bulk density and particle density
Soil Porosity examples
Water Volume to Core Volume
porosity= wet weight (g)-dry weight (g)/ soil volume (cu cm) * 100%
Soil Porosity ex
An oven-dry soil core, volume 500 cu cm, weighs 650g. When wet, it weighs 900g. Find its % porosity
Porosity= 900g-650g/500 cu cm *100%= 250g/500 cu cm * 100 = 50%
Bulk Density to Particle Density
Defines the percentage of the soil that is solid matter.
The percent solid matter is subtracted from 100% to give percent porosity:
Porosity= 100% - (BD/PD * 100%)
soil porosity ex.
an undisturbed oven-dry soil, BD of 1.3 g/cu cm, consists of average mineral composition (PD 2.65 g/cu cm) Find its % Porosity:
Porosity=100% - (1.3 g/cu cm /2.65 g/cu cm *100%)
Porosity=100% - (0.49 *100%) = 100%-49%=51%
What has greater porosity, Sand or Clay?
Clay at about 50%; sand is lower at about 30%
Why? clay has more surface ware and smaller particles so has more pores
Permeability
the ease with which air, water, and roots move through soil
depends on number, size, and continuity of pores
liken to a maze
Fine-textured soils would be impermeable if not for
Soil structure
Structure: def
the way soil particles clump together into large units called aggregate or peds
Examples of soil structure
Granular, Platy, Wedge, Blocky (Subangular or Angular) Prismatic, Columnar
Structure and texture
structure can alter the effects of texture
e.g. a fine-textured silty clay with good structure can be permeable
Structure is classified by three groups of traits
Type: refers to shape of aggregates (granular, Platy, blocky, prismatic, columnar)
Class: refers to size of peds (very fine, fine, medium, coarse, very coarse)
Grade: refers to strength and distinction of peds (weak/not visible vs strong/easily distinguished
Formation of soil structure
2-step formation:
- Individual soil particles loosely aggregate
- Weak aggregates are cemented to strengthen: clay, iron oxides, organic matter, microorganisms gums
Aspects of soil structure
The arrangement into aggregates of desirable shape and size
the stability of the aggregate
the configuration of the pores
Factors that affect aggregate stability
Kind of clay
chemical elements associated with the clay
nature of the products of decomposition or organic matter
Nature of the microbial population
Factors that affect soil structure
Kind of clay
Amount of organic matter
freezing and thawing
wetting and thawing
action of burrowing organisms
growth of root systems of plants
Soil consistence
the behavior of soil when pressure is applied; measured at 3 different moisture levels: wet, moist, dry
Soil Tilth
ease of tillage, seedbed preparation, and seedling/root movement
Compaction
results from pressure applied at the soil surface
Puddling
occurs when pressure is applied to very wet soils (esp. plowing)
Crusts
occur when bare soil is struck by raindrops; disperses soil then dries to a hardened crust
Clods
clumps in soil
Improving Tilth
best accomplished by improving structure
tilth relates to texture, structure, permeability, and consistence; however texture and consistence cannot be altered
therefore, improve tilth by improving structure and avoiding compaction
Soil Channels
Continuous macropores leading from surface to deep subsoil
Soil pans
any layer of hardened soil; includes claypans, fragipans (clays), plinthite (tropics), caliche (Ca cemented)
Soil Temperature
Varies with color, texture, O.M
Soil Color
Munsell Soil color chart
Hue, Value, Chroma
e,g 10YR3/6
Soil Color
wide range of colors (gray, black, white, red, brown, yellow and greens)
varies by horizon (helps with id)
Development and distribution results from weathering
Aerobic vs anaerobic soils
Soil Color Aerobic soils……
Aerobic soils produce uniform color changes
Soil color is
Influenced by the amount of proteins present
Dark or black color
indicates high organic matter
Water affects soil color
oxidation rate:
- oxygen rich= red or brown
- Low oxygen= usually gray
Munsell Soil color chart
Separates color into components of:
hue (relations to red, yellow, and blue)
Value (lightness or darkness)
Chroma (paleness or strength)
ex. 10YR 3/6
Determining soil color of our soils
Use the Munsell soil color book to determine the Hue, value and chroma
Soil Profiles: Soil horizons
Soils consist of one or more distinct layers called horizons
upper limit is air or shallow water and its lower limit is the depth to which soil weathering has been effective
A soil pedon
a 3D sample of a soil just large enough to show the characteristics of all its horizons
O horizon
Layers dominated by organic material.
May or may not be present.
undisturbed Bangor series ex. O is typically 3 inches thick
A horizon
The mineral soil horizon at the surface or below the O.
All surfaces resulting from agricultural practices are considered part of the A horizon.
This horizon may have accumulations of organic compounds leached from the O
undisturbed Bangor series ex. A is typically 1 inches thick
E horizon
characterized by eluviation i.e removal of silicate clays, iron, aluminum and organic matter.
Frequently not present
Used to be called A2. AKA “albic” horizon.
Found in campus forest in Monarda series. Pale colored.
bangor= 2 inches
eluviation
transportation of dissolved or suspended material within the soil by the movement of water when rainfall exceeds evaporation
illuviation
accumulation of eluviation material in lower levels
B horizon
Formed below A, E, or O.
Thicker than the above
Tree roots found here
Dominated by the obliteration of all or much of the original rock structure.
Concentrates clays, iron, Al, organic compounds.
Bangor=32 inches
C horizons
horizons other than bedrock that are little affected by soil forming processes
no tree roots usually
Bangor=25 inches
R
Hard bedrock
In Waldo County
1/4 of the land is underlain by glacial till on top of gneiss, schist or phyllite rock
Soil orders in Maine
Spodosols
Inceptisols
Histosols
Entisols
Spodosols
Subsurface accumulation of humus typically high in Al and Fe
Form in coarse textured parent material:
- Light colored E horizon overlaying a reddish brown spodic (illuvial accumulation of organic matter-due to eluviation) horizon
- Formed by podzolization
podzolization
principally involves leaching of upper layers with accumulation of material in lower layers
Spodosols occur….
under coniferous forests in cool, moist climates
Occupy ~4% of the ice free land area
Naturally infertile
-require additions of lime in order to be agriculturally productive
Inceptisols
Exhibit minimal horizon development
Widely distributed occurring across a wide range of ecological settings
Inceptisols occur…..
Often on steep slops, young geomorphic surfaces and resistant parent materials
Often found in mountainous regions (forestry, recreation and watershed)
15% of ice free land area (second most extensive soil order)
Histosols
- Composed mainly of organic materials
- 20-30% organic matter by weight
- Low bulk density often less than 0.3 g/cm3
Inhibit decomposition which in turn accumulate over time
referred to as peats, mucks (mined for fuel and horticultural products
Histosols occur
wetlands with restricted drainage
Very ecologically important:
- Accumulate large quantities of carbon
- less than 1.5% of ice free land area
Entisols
Soils of recent origin
No horizons except A
-all soils which so not fit into other orders are Entisols
Entisols occur
great diversity in both land use and setting
Many found in steep rocky settings
most extensive soils order
-~18% of ice free land area
