Basic Soil Science: The Properties of Soil NotesDate _______________Topic___________________________________
Basic Soil Science BSS3 The Properties of Soil
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Soil Color:
Basic Soil Science: The Properties of Soil Notes
Basic Soil Science BSS3 The Properties of Soil
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Soil Structure:
Basic Soil Science: The Properties of Soil Notes
Basic Soil Science BSS3 The Properties of Soil
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Soil Texture:
Basic Soil Science: The Properties of Soil BSS3.1
Soil Matrix Color: Dark Brown, Very Dark Brown, Black
These colors are caused by accumulations of organic matter in soils. Humus coats the soil particles, giving them a dark color. Usually, the darker the color, the more organic matter the soil contains, and the more fertile and productive is the soil.
Dark colors are typical of A horizons (the surface layer of soil). In northern Missouri soils, nearly all A horizons have this color.
That is not the case in much of southern Missouri. Organic matter content is lower; therefore, the soils are lighter in color. In general, if the lighter-colored soils have been cultivated, and much crop residue has been mixed into the Ap horizon (plow layer), then the color is probably brown or very dark brown. If the soil has not been cultivated and there is not much native vegetation, then the A horizon is likely to have a light brown color.
Some soils have black colors extending well down into the subsoil. That is usually an indication of wetness. In wet soils, organic matter breaks down very slowly and the soil is darkened by the partially decomposed organic matter that accumulates.
Some very clayey, sticky soils may be black, too. In these soils, organic matter is mixed throughout the entire soil, and the soil is black, even though the organic matter content is not particularly high.
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.1
Soil Matrix Color: Light Brown, Brown, Yellowish Brown
These are the colors of well-aerated soils. Well-aerated means that air moves freely into and out of the pore spaces of the soil. As microbes and plant roots use up oxygen in soil pores, oxygen from the air above the soil moves in to replace it. Well-aerated soils, therefore, provide a healthy environment for plant roots.
Brown colors are due to iron oxide coatings on mineral grains (soil particles). Chemically, they are the same as a coating of rust on a piece of iron. These iron oxide coatings require plenty of oxygen in soil pores. If water should fill soil pores and remain there for a long time, oxygen cannot reach the iron coatings, causing the soil to turn gray. That is why brown colors indicate that the soil has good air-water relations and has not been saturated for long periods of time.
Brown colors are typical of B and C horizons (lower horizons) that are well-aerated. This is true all over Missouri. As long as there is not enough organic matter to darken the soil and there is plenty of oxygen to maintain iron oxide coatings, the soil will nearly always be brown or red.
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.1
Soil Matrix Color: Red, Reddish Brown
These colors are also caused by iron oxide coatings, and they also indicate well-aerated soil. The soil is red, rather than brown, only because the chemical form of the iron oxide is a little different.
Most red soils are very old soils and are very strongly weathered. They are more leached, more acidic, and less fertile than soils having brown colors.
Red soils occur on some of the uplands of southern Missouri. Except for the A horizon, all the other horizons in these soils usually are red. Red soils are rare in northern Missouri, but there are a few areas where the soils formed in limestone residuum and have red subsoils.
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.1
Soil Matrix Color: Dark Gray, Light Gray, White
Dark gray soils are wet soils. When soil pores are full of water, oxygen cannot get in. Gradually the yellow-brown coatings are removed from mineral grains and are leached away. The gray color is the natural gray color of the uncoated mineral grains, darkened a little by organic matter. Dark gray is typical of B and C horizons in wet soils.
E horizons (subsurface layers) are always lighter in color than the horizon above them because E horizons have lost organic matter and are leached. Some E horizons occur in wet soils. Iron is reduced and leached from the soil by water moving horizontally on top of a clayey subsoil. Other E horizons may occur in well-drained soils. In these soils, different chemical processes cause the loss of iron oxide coatings from mineral grains. These E horizons have bright-colored B horizons below them.
There are some parent materials (loess and glacial till) common in northwest Missouri that are naturally gray. It should be noted that this color is not a result of wetness.
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.2
Soil Matrix Colors
Dark Brown, Very Dark Brown, Black
Light Brown, Brown, Yellowish Brown
Red, Reddish Brown
Dark Gray, Light Gray, White
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.3
Soil Color Matching
Match the colors below to the four classes of soils:o Dark brown, very dark brown, black o Light brown, brown, yellowish brown o Red, reddish brown o Dark gray, light gray, white
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.4
Guide for Describing Mottles
Feature Description Classes
Abundance The percentage of exposed surface area occupied by mottles
Few: less than 2% of exposed surface Common: 2-20% of exposed surface Many: more than 20% of exposed surface
Size The approximate diameter of individual mottles
Fine: Diameter less than 5mm Medium: Diameter 5-15mm Coarse: Diameter more than 15mm
Contrast The relative difference between the mottle color and the matrix color
Faint: Mottles evident only on close examination. Mottle color and matrix color are very nearly the same.
Distinct: Mottles are readily seen, though not striking. Mottle color and matrix color are different, though not widely so.
Prominent: Mottles are so conspicuous that they are the outstanding visible feature of the horizon. Mottle color and matrix color are widely different.
Color Described the same way as soil matrix colors.
Most common mottle colors are: Yellowish brown Dark reddish brown Red Gray
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.5
Types of Soil StructureST
RU
CT
UR
ED
Granular: Roughly spherical, like Grape Nuts™ cereal. The structure is usually 1-10mm in diameter. It is most common in surface horizons (A horizons) where plant roots, microorganisms, and sticky products of organic matter decomposition bind soil grains into aggregates.
Platy: Flat peds that lie horizontally in the soil. Most are less than 2cm thick. Not common, but occurs mostly in subsurface horizons or dense layers (E and Bx horizons).
Blocky: Roughly cube-shaped with generally flat surfaces. Divided into two types: angular blocky has edges and corners that remain sharp; subangular blocky has edges and corners that are rounded. Sizes commonly range from 5-50mm across. Typical in the subsoil (B and Bt horizons). They form by repeated expansion and contraction of clay materials.
Prismatic: Peds are taller than they are wide. They often have five sides. Sizes are commonly 10-100mm across. Most common in the lowest part of the subsoil (B and BC horizons). The prisms in some strongly developed soils have rounded tops because the tops have lost their corners by eluviation (downward movement of material). These prisms are called columnar.
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.5ST
RU
CT
UR
EL
ESS
Single Grain: In some very sandy soils, every grain acts independently and there is no binding agent to hold the grains together into peds. Permeability is rapid, but fertility and available water capacity are low.
Massive: Compact, coherent soil is not separated into peds of any kind. Massive, claylike soils usually have very small pores, slow permeability, and poor aeration.
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.5
Types of Soil StructureST
RU
CT
UR
ED
Granular: Roughly spherical, like Grape Nuts™ cereal. The structure is usually 1-10mm in diameter. It is most common in surface horizons (A horizons) where plant roots, microorganisms, and sticky products of organic matter decomposition bind soil grains into aggregates.
Platy: Flat peds that lie horizontally in the soil. Most are less than 2cm thick. Not common, but occurs mostly in subsurface horizons or dense layers (E and Bx horizons).
Blocky: Roughly cube-shaped with generally flat surfaces. Divided into two types: angular blocky has edges and corners that remain sharp; subangular blocky has edges and corners that are rounded. Sizes commonly range from 5-50mm across. Typical in the subsoil (B and Bt horizons). They form by repeated expansion and contraction of clay materials.
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.5 Prismatic: Peds are taller than they are wide. They often have five sides. Sizes are commonly 10-100mm across. Most common in the lowest part of the subsoil (B and BC horizons). The prisms in some strongly developed soils have rounded tops because the tops have lost their corners by eluviation (downward movement of material). These prisms are called columnar.
STR
UC
TU
RE
LE
SS
Single Grain: In some very sandy soils, every grain acts independently and there is no binding agent to hold the grains together into peds. Permeability is rapid, but fertility and available water capacity are low.
Massive: Compact, coherent soil is not separated into peds of any kind. Massive, claylike soils usually have very small pores, slow permeability, and poor aeration.
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.6
Particle Size
Sand
Silt
Clay
Particles are large and can be seen with the naked eye.
Not sticky
Particles are very small and flat; can be seen with high-powered microscopes.
Less than 0.002 mm in size
Particles are smaller than sand; can’t be seen without hand lens or microscope.
Feels gritty
Range in size from 0.05 mm to 2 mm
High water holding capacity
Will not stick together when wet
Feels smooth (like flour or corn starch)
Range in size from 0.002 mm to 0.05 mm
Feels sticky; can be molded into ribbons or wires
Holds large amounts of water in a form plants can use
Low capacity for holding moisture and storing nutrients
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.7
Texture Triangle
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.8
Clues to the Feel of Textural Classes
Sand Moist sample collapses after squeezing Hands don’t get dirty working the sample
Loamy Sand Sample has very little body Moist soil barely stays together after
squeezing Just enough silt and clay to dirty hands
Sandy Loam Sand dominates noticeably Enough silt and clay to give the sample
body Moist soil stays together after squeezing Hardly forms any ribbon at all
Sandy Clay Loam Feels gritty and sticky Forms ribbon 1-2 inches (2.5-5 cm) long
Sandy Clay Feels definitely sandy Forms ribbon 2-3 inches (5-7.5 cm) long
Loam Sand noticeably present, but doesn’t
dominate Sample works easily between thumb and
fingers Contains enough silt and clay to give
sample good body Sample only forms short, broken ribbons
Silt Loam Feels smooth, like flour or corn starch Tends to be nonsticky Only forms short, broken ribbons
Clay Loam Noticeably gritty, but sand doesn’t
dominate Noticeably sticky Noticeably hard to work between thumb
and fingers Forms ribbon 1-2.5 inches (2.5-6 cm)
long
Silty Clay Loam Feels smooth and sticky Contains very little sand Forms ribbon 1-2.5 inches (2.5-6 cm)
long
Clay and Silty Clay Dry sample absorbs a lot of water before
it is moist enough to work Sample very hard to work between
thumb and finger Forms ribbon 2.5-4inches (6-10 cm) long
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.9
Estimating Textural Classes
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.10
Properties of Soil News Report Evaluation
In pairs, create a six-minute interview pertaining to the information learned in this lesson. Focus on how to determine the color, texture and structure of a given sample of soil. One person will be the news broadcaster and the other will play a role pertinent to the features of the interview.
15 points 10 points 5 points
Length 5-6 minutes 3-4 minutes 2 minutes or less
Content Factual information regarding how to determine the color, texture, structure of soil; brought in students’ personalities, humor, opinions
Factual information regarding how to determine the color, texture, structure of soil
Lacked factual information regarding how to determine the color, texture, structure of soil
Interviewee Identity
Identity of person being interviewed was appropriate for the content presented in the report
Identity of person being interviewed was not appropriate for the content being presented in the report
Overall Effect Like an interview on TV; students spoke clearly, were easily understood, showed knowledge of content
Somewhat like an interview on TV; students spoke clearly, were easily understood, showed knowledge of content.
Lacked resemblance to an interview on TV; and/or students needed to speak more clearly and show more knowledge of content
Comments:
Total __________________ / 45 points
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.11
The Properties of Soil Evaluation
Match the definition on the left with the term on the right.
1. ____ Splotches of colored soil in a matrix of different color
2. _____ A system used to identify soil color
3. ____ Structure is roughly spherical, like Grape Nuts; usually 1–10 mm in diameter
4. _____ Structure consists of flat peds that lie horizontally in the soil
5. _____ Structure consists of peds that are roughly cube-shaped with more less flat surfaces
6. _____ In the structure, the peds are taller than they are wide, often with five sides
7. _____ Every grain acts independently and there is no binding agent to hold the grains together into peds
8. _____ Largest of the soil separates, between 0.05 and 2.00 mm in diameter
9. _____ Medium-sized soil separate, particles between 0.05 and 0.002 mm in diameter
10. _____ The class of smallest soil particles, smaller than 0.002 mm in diameter
Basic Soil Science BSS3 The Properties of Soil
A. Sand
B. Blocky
C. Munsell color
system
D. Prismatic
E. Granular
F. Single grain
G. Clay
H. Mottles
I. Silt
J. Platy
Basic Soil Science: The Properties of Soil BSS3.11
List the four broad classes of soil color:
11. ___________________________________________________________________________
12. __________________________________________________________________________
13. ___________________________________________________________________________
14. ___________________________________________________________________________
Use the soil triangle to determine the correct name for the texture of a soil sample that is 40% sand, 15% clay, and 45% silt.
15. The soil is a ___________________________.
Basic Soil Science BSS3 The Properties of Soil
Basic Soil Science: The Properties of Soil BSS3.11
The Properties of Soil Evaluation
Match the definition on the left with the term on the right.
1. H ___ Splotches of colored soil in a matrix of different color
2. C ____ A system used to identify soil color
3. E ___ Structure is roughly spherical, like Grape Nuts; usually 1–10 mm in diameter
4. J ____ Structure consists of flat peds that lie horizontally in the soil
5. B ____ Structure consists of peds that are roughly cube-shaped with more less flat surfaces
6. D ____ In the structure, the peds are taller than they are wide, often with five sides
7. F ____ Every grain acts independently and there is no binding agent to hold the grains together into peds
8. A ____ Largest of the soil separates, between 0.05 and 2.00 mm in diameter
9. I ____ Medium-sized soil separate, particles between 0.05 and 0.002 mm in diameter
10. G ____ The class of smallest soil particles, smaller than 0.002 mm in diameter
Basic Soil Science BSS3 The Properties of Soil
A. Sand
B. Blocky
C. Munsell color
system
D. Prismatic
E. Granular
F. Single grain
G. Clay
H. Mottles
I. Silt
J. Platy
Basic Soil Science: The Properties of Soil BSS3.11
List the four broad classes of soil color:
(in any order)
11. Dark brown, very dark brown, black
12. Light brown, brown, yellowish brown
13. Red, reddish brown
14. Dark gray, light gray, white
Use the soil triangle to determine the correct name for the texture of a soil sample that is 40% sand, 15% clay, and 45% silt.
15. The soil is a loam.
Basic Soil Science BSS3 The Properties of Soil
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