LabWorksheet07_GettingtoKnowtheSoils
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Santa Monica College *
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Geography
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Jun 4, 2024
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Name: _____________________________ Lab Worksheet 7: Getting to Know the Soils GEOG 5, Instructor: Joy Fritschle This lab is in three parts: in part 1, you will examine soil horizons, color, and texture; in part 2, you will study several different soil orders from around the world; and in part 3, you will investigate the soils at a specific location in the U.S. Part 1: Soil Properties: Horizons, Color, and Texture In this part of the lab, you will more closely examine the key properties of soils including their horizons, color, and texture. The process of soil formation generally involves the downward movement of clay, water, and dissolved ions. The common result of that is the development of chemically and texturally different layers known as soil
horizons
. The commonly developed soil horizons are as follows: ➢
O: the layer of organic matter ➢
A: the layer of partially-decayed organic matter mixed with mineral material ➢
E: the eluviated (leached) layer from which some of the clay and iron have been removed to create a pale layer that may be sandier than the other layers ➢
B: the layer of accumulation of clay, iron, and other elements from the overlying soil ➢
C: the layer of incomplete weathering ➢
R: the parent material or bedrock English Cleveland
1.
Based on the descriptions provided in the table on the next page, label the soil horizons shown on each of the four soil profile diagrams
. (remember: not all soils have all the horizons present!) (2 pts)
Soil Horizon Labeling
Profiles and Descriptions Profiles and Descriptions Soil Profile 1.
Few horizons have formed because the parent material was recently exposed to weathering. There is some biological weathering activity initiated by moss growth. Soil Profile 2.
This is an arid environment with low rates of weathering. Caliche (calcium carbonate) deposits are found in the B horizon. Soil Profile 3.
This is a well-developed soil in a temperate environment. Soil Profile 4.
This is a soil in a tropical environment with aluminum oxide deposits (bauxite) in the B and C horizons. R Horizon
R Horizon
C Horizon
B Horizon
A Horizon
E Horizon
A Horizon
E Horizon R Horizon
R Horizon
A Horizon
E Horizon
B Horizon
C Horizon
C Horizon
A Horizon
E Horizon
B Horizon
C Horizon
Soil color
is another physical property of soil. The mineralogy of the parent material and the rates of weathering are the two main factors that determine a soil’s color. Minerals and Common Soil Colors Material Formula Common Soil Color goethite
FeO(OH) yellow, strong brown hematite
Fe
2
O
3
red lepidocrocite FeO(OH) reddish-yellow, red ferrihydrite Fe(OH)
3
dark red glauconite K(Si
x
Al
4-x
)(Al,Fe,Mg)O
10
(OH)
2
dark gray iron sulfide FeS black pyrite FeS
2
black (metallic) jarosite KFe
3
(OH)
6
(SO
4
)
2
pale yellow todorokite MnO
4
black calcite CaCO
3
white dolomite CaMg(CO
3
)
2
white gypsum CaSO
4×
2H
2
O very pale brown quartz SiO
2
light gray humus Humus is not a mineral but it influences soil color, especially in the upper horizons. Humus is organic material that forms in a soil when living organisms decay. black 2.
What colors are commonly seen when iron (Fe) is present in the parent material of a soil? (0.25 pts)
What color is commonly seen when calcium (Ca) is present in the parent material of a soil? (0.25 pts)
Soil texture
refers to the sizes of the mineral materials in a soil. All soils can be classified by the amount of sand (<2 to 0.05 millimeters), silt (0.05 to 0.002 millimeters), and
clay
(<0.002 millimeters) found in them. The soil texture triangle provides the names to classify soils with varying percentages of sand (bottom side of triangle), silt (right side of triangle), and clay (left side of triangle. The colors commonly seen when iron (Fe) is present is yellow or red.
The colors commonly seen when calcium (Ca) is present is white.
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3.
What is the soil name for a soil that has 10% silt, 85% sand, and 5% clay? (0.5 pts) ___________________ What is the soil name for a soil that has 30% silt, 35% sand, and 35% clay?
(0.5 pts) ___________________ What is the soil name for a soil that has 75% silt, 10% sand, and 15% clay?
(0.5 pts) ___________________ 4.
Loam
is the ideal soil texture for most vegetable crops. From soil texture triangle, what are the relative amounts of silt, sand, and clay for loam soils (note: this should add up to 100%)? (1 pt)
_____% sand _____% silt _____ % clay Part 2: Soil Orders
In this part of the lab, you will study several different soil orders and their distribution from around the world. You will need to make sure you have first completed Part 1 before doing this section. In the United States, soils are classified into twelve categories called soil orders
. This taxonomy is based on the dominant physical and chemical characteristics that make each soil order unique. Like many taxonomies (classification systems) within each category, there are subdivisions. You may be familiar with the taxonomy of living organisms from a biology course: domain, kingdom, phylum, class, order, family, genus, and species. With the soil taxonomy, order is the largest grouping, which can be further divided into suborder, great group, subgroup, family, and soil series. So, soil order is the largest grouping and soil series is the smallest grouping. Clay Loam
Stilt Loam 40
40
20
Sandy Loam
Before we review the key characteristics of each soil order, let’s analyze the Global Soil Regions map: 5.
Which two soil orders are most common along the equator? __________________________________ and __________________________________ (0.5 pts)
Which two soil orders are most commonly found in the world’s desert regions? __________________________________ and __________________________________ (0.5 pts)
Which soil order is most common in the highest latitudes of the northern hemisphere? __________________________________ (0.5 pts)
Entisols and Inceptisols: The two soil orders with the least soil weathering and development are entisols and inceptisols. Entisols
are soils that are recent and they have the least number of horizons than any other soil order. For example, very thin O or A horizons may be present in an entisol. Entisols are found in many different environments such as dunes, steep slopes, or a location in which parent materials have been only recently exposed to weathering. Inceptisols are a little more developed than entisols. Inceptisols have a few more horizons present, or they might have a thicker O and A horizon compared to an entisol. Oxisols
Ultisols
Aridosols
Entisols
Gelisols
6.
Return to question 1 at the beginning of this lab (in part 1). Which one of the four soil profiles that you labeled best represents an inceptisol? (0.5 pts)
Soil Profile Number ______ Oxisols and Ultisols:
While entisols and inceptisols are the result of weak weathering, oxisols and ultisols have very high weathering rates. Oxisols and ultisols are found in humid environments and have advanced rates of physical, chemical, and biological weathering.
Oxisols
are found in tropical and subtropical regions. Oxisols commonly have quartz, aluminum oxides, or iron oxides present. Oxisols are common on stable land surfaces in the tropical regions of the world. Ultisols
have clay-enriched subsoils along with quartz, aluminum oxides, or iron oxides present. 7.
Which one of the four soil profiles that you labeled in question 1 best represents an oxisol? (0.5 pts)
Soil Profile Number _____ Refer to the global soil regions map on the previous page. Which soil order is most common in the southeastern United States? (0.5 pts)
__________________________________ Andisols, Aridisols, and Gelisols: Andisols, aridisols, and gelisols are soil orders that are connected to specific geologic environments. Andisols
are found in volcanic landscapes, aridisols are found in desert landscapes, and
gelisols
are associated with permafrost. Andisols make highly productive soils because of their nutrient availability and water-holding capacity. Aridisols have limited soil development but can accumulate caliche and other materials that are usually leached out of soils in environments that have higher rates of precipitation. 8.
Which one of the four soil profiles that you labeled in question 1 best represents an aridisol? (0.5 pts)
Soil Profile _____ 9.
Refer to the global soil regions map. Both aridisols and entisols are found across the Sahara Desert. Why are these two soil orders are commonly found there? (1 pt)
Alfisols and Spodosols Alfisols and spodosols are common in forest environments. Alfisols are found in humid and temperate climates and spodosols are found in cooler climates with coniferous forests. Alfisols are rich in nutrients and make productive agricultural soils. In contrast, spodosols are more acidic and have low rates of fertility. 10.
Which one of the four soil profiles that you labeled best represents an alfisol? (0.5 pts)
Soil Profile _____ Which regions of the United States have alfisols? (0.5 pts)
Which regions of the world have spodosols? (0.5 pts)
2
4
Ultisols
2
Aridisols and Entisols are two soil orders that are commonly found in the Sahara Desert because of the arid climate and limited soil development. Aridisols form in dry environments, while Entisols deposit materials such as desert sand.
3
Northwest and Southeast
Some regions of the world that have spodosols are areas of the northern parts of North America,
Europe, and Asia.
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Histosols, Mollisols, and Vertisols Histosols
are found in wetlands and mollisols
are common in grasslands. Vertisols are not associated with a specific landscape—they are distinct from other soil orders because vertisols have large amounts of clays. Key ideas about these three soil orders are as follows: ➢
Given their wetland environment, histosols have high levels of organic content when compared to other soil orders. Little drainage in wetland areas allows for organic materials to accumulate over time. ➢
Mollisols
also have higher levels of organic materials due to the activity of plant roots in grassland ecosystems. Mollisols are productive agricultural soils. ➢
Vertisols shrink and swell due to their clay content. When wet, clay absorbs moisture and swells. When dry, clay shrinks and cracks. 11.
Peat is partially decayed organic matter. Which soil order would likely be a source of peat? (0.5 pts)
___________________________ Where in the United States are mollisols common? (0.5 pts)
Part 3: Getting to Know Your Soils
This part of the lab is to be completed in the Lab 7 Discussion board on Canvas. You will need to write a primary post (at least 150 words in length; worth 4pts
) and two secondary posts in response to other students’ primary posts (at least 75 words in length each; worth 1pt each
). The instructions for what you should write about can be found by going to the Discussion menu item in our Canvas course. Histsols
The middle latitudes are where the United Sates have mollisols, particularly in the Great Plains.
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