introduction to soils chapter 4: soil architecture and physical properties
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Introduction to Soils
Chapter 4:Soil Architecture and Physical Properties
Physical Properties
Physical Properties of the soil will deal with the particle aggregation as well as texture, colloidal properties, surface area, pore spaces, water in the soil and other physical properties.
SOIL COLOR Color plays an important role in
differentiating different conditions of the soil.
Color Classification System
Munsell color charts1) Hue – red to yellow color of the
soil2) Chroma – brightness of the color –
0 neutral gray3) Value – lightness or darkness of
the soil –0 being black
Color can give a clue to: OM content Water content Oxidation states of iron and
possibly manganese oxides.
Dark Soils Usually high in organic matter Rich soils if there is not too much
water
Light Soils Sandy High salts, gypsum or lime
Light Brown to Red Aging soils iron – oxidizing Drainage is fair
Bluish - Gray They have poor drainage Indicates no 02 in soil and could
smell rotten called - Gleying soils
Mottled Colors Indicates a period of water logged
and then drying out
SOIL TEXTURE the amount of sand silt and clay in
the soil The Soil Separates (USDA)
Sand - .05 – 2 mm Silt .05 - .002 mm
Clay less then .002mm
Soil Texture triangle allows the classification of the soil texture
into 12 classes.
Determining soil texture
Ribbon test No ribbon – sandy loam Shorter then 1” – loam, silt, silt
loam 1-2” – Sandy clay loam, silty clay
loam, clay loam 2-3” – Sandy clay, silty clay clay
Measuring the soil separates in a jar
Can one change soil texture?
Surface area considerations:
It is the surface area of the soil that has the ability to hold water and be a site for chemical activity. The greater the surface area the greater the chemical activity and possible nutrient holding ability.
Surface area of the soils and its affect
Water holding capacity, fertility and total pore space.
Sand SiltClay
Soil Porosity Total pore space of the soil
Sand has less than clay
Determining porosity %:Wet weight (grams) – dry weight (grams) Soil volume (cm3) X 100
= %
Permeability
How the water moves through the soil
• Sand is rapid and clay is slowTextural types and their characteristics ie
Soil Porosity, Permeabilitya) Clayeyb) Silty
c) Sandy
Soil Structure
Soil Structure is how the soil separates
combine to form larger aggregates
Types of structure
peds natural formation clods caused by tillage
a. Granular- ideal agronomic structure accomplished through correct cultural practices: in the A horizon Minimum tillage, done at the correct time incorporating organic matter and encouraging microbial action
b. Platy- Usually in the lower depths of the A horizon or compacted soils
c. Blocky- in the B horizon large aggregates that slows water penetration
e. Single grain- Structure less – the absence of soil structure.f. Massive- Structure less - concrete
Structure Formationa. Soil adhesives released by fungi and organismsb. Good soil structure can be encourage through
proper cultivationc. Organic matterd. Gypsum e. Culture practices done when soil is at proper
water retentionf. Avoid compaction
1) Equipment2) Reduction of traffic through the
field3) Keep vegetation on the soil
a.
Soil Consistence Refers to soils ability to resist
crushing and its ability to be molded.
Such as for most soil Loose, Very Friable, Friable, Firm, Very Firm and extremely firm.
Soil Tilth Physical condition of the soil after
tillage- usually the granular form
Compaction is detrimental to good soil tilth-
Compaction causes• Reduced porosity and permeability• Reduced gas exchange• Slow percolation rate and slow drying rate.• Restricted root growth
Soil Particle Density As to the specific weight of the soil
particles.
This is a direct correlation to the parent material and should be between 2.6 to 2.75 g/cm3
Bulk Density Is the weight over volume.
This will determine the amount of pore space in the soil.
Clay – 1.15 Silt – 1.35 Sand – 1.8
Soil Temperature Germination is dependant on proper soil
temperature.
Corn needs 65-70FMost warm season crops need warm soilRoot growth is more abundant when soil temperatures
Soil Characteristics that affect temperature Dark soils warm fast Rocky soils warm fast Sandy soils warm fast Grandular loose soils warm quicker then compacted soils
Formation and Stabilization of Soil
Aggregates:
Physical Chemical Processes: Flocculation of Clays Clays will be the first to join together as
they are attracted to each others negative and positive sides.
Together with humic acid binds together the individual particles acting like glue to bind them together.
Formation and Stabilization of Soil Aggregates:
Both biological and physical processes are responsible for soil aggregates
Biological Processes: Soil organisms – help bind
particles together Earth worms Root exudates Fungal products ie
glomalin Bacteria
OMIs the principle method of soil
aggregate stabilization.
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