Transcript Introduction : Soils - Columbia University

Module
10
Cover Page
The Effects of Topography and
Parent Materials on Soil at Mount
Lemmon and Biosphere 2 Center
SEE-U 2001 Biosphere 2 Center, AZ
Professor Tim Kittel, TA Erika Geiger
Yuko Chitani
Mei Ying Lai
Lily Liew
Asma Madad
Adam Nix
Eli Pristoop
J.C. Sylvan
Introduction: Soils
Soil is one of the most important bases of terrestrial
ecology because it provides a variety of requirements for
plants and animal life. The principal properties that soil
provides for plants are anchorage, moisture storage (in that
soil is like a sponge storing water), and a supply of nutrients.
Soil creates habitats for animals by providing space for them
to live and by determining the local chemistry.
One of the many definitions of soil is: “The
unconsolidated mineral matter on the surface of the earth
that has been subjected to and influenced by genetic and
environmental factors such as parent material, climate
(including moisture and temperature effects), macro-and
microorganisms, and topography, all acting over time and
producing a product—soil—that differs from the material
from which it was derived by many physical, chemical,
biological, and morphological properties and characteristics.”
(as quoted in J. P. Kimmins, 1997, Forest Ecology: a
Foundation for Sustainable Management, 2nd edition,
Prentice Hall Press.)
Many animals play important roles in the soil, including
insects (springtails, beetles, and ants), mites, millipedes,
nematodes, annelids, mollusks, burrowing vertebrates,
mycorrhizae, bacteria, and plant roots. Desert soils are not
turned over very often, but ants and burrowing mammals do
most of the turnover that occurs. Plant roots also do much of
the initial breaking of the parent material into smaller
components.
Soil has been called the least renewable resource in
the ecosystem. Unlike biodiversity, plant growth, water
resources, and most other components, soil takes decades
to be replenished if it is lost.
Steve Slaff talks with students about the soil profile at the summit of Mt. Lemmon.
The three most important mechanical properties of soil are
texture, structure, and porosity.
Texture is the composition of the soil, or simply, what the soil is
made up of. Some soils are made up of sand, silt, and clay.
Determining the texture of a soil is a process that will be further
explained in the methods.
The structure deals with the shape, size and grade of particles.
Soil structure refers to how the individual sand, silt, and clay
particles are arranged into stable aggregates
Porosity or pore space of soils is calculated from the Bulk
Density (Db) and Real or Particle density (Dp). Texture,
structure and organic matter are all important in determining the
overall soil porosity. Coarse textured sandy soils have larger
pores but much less pore space than finer textured clay
soils.Soil is the link between the organic and inorganic world.
There are five factors that determine how a soil develops.
Parent material
•Particle size- dune sand vs. clay alluvium
•Chemistry, soluble limestone vs. decomposing granite vs.
resistant basalt
Regional Climate
•Temperature- cold favors humus accumulation {organic material
is added faster than it decays}: heat allows humus to decompose
rapidly.
•Water flux- mineral leaching by high rainfall vs. Caliche formation
under low rainfall.
Organisms
•Organic matter input- acidic pine needles vs. grass roots.
•Vegetation cover – determines rate of organic input and rate of
surface erosion.
Steve Slaff describes the parent materials in the Santa Catalina Range.
•Bioturbation due to prairie dogs, earthworms, termites, etc.
Topography
•Water flow
•Whether a soil will be eroded, stable, or covered by more
deposits.
•Solar radiation loading, which affects soil temperature and
evaporation rate.
Time
•Soil genesis – It takes time for soil to develop
•Surface stability
•Climate changes-the longer the time, the more likely that climate
will change.
•Human disturbance—grazing, land use, and fire.
Both physical and chemical weathering are
needed for soils to form. Weathering is the process of
physical and chemical changes in rocks, which are
caused by atmospheric agents such as water, oxygen,
and carbon dioxide. Weathering takes place at the
earth’s surface. Weathering may involve the
disintegration of rocks into smaller particles, or the
decomposition of rocks into different minerals. Longterm weathering often forms various kinds of clays.
In this lab we examined soils from two different
sites, analyzed, and compared them. What
differences or similarities do soils from different
topographical areas have? What differences could
topographical factors have that influence the kind of
soil and soil production?
Horizon Definitions
A LAYER
B LAYER
C LAYER
The second component of soil structure is referred to in terms of soil
horizons. The materials arriving at the surface layer, such as leaf
litter and other dead organic matter, are processed within each
horizon and then pass through to the layer beneath it. The horizons
are abbreviated to single letters, and unfortunately the nomenclatural
systems differ between continents.
The top layer is the litter layer (L), composed of litter that is slowly
decomposing and has been only recently deposited, but is rapidly
being broken down by biotic activity. The next layer is the F layer, a
rapidly decomposing layer of litter leading to an accumulation of a
layer of “raw” humus (horizons H and O - horizon O has material that
is more decomposed than horizon H) below it. The H layer has litter
that has been broken down to particles and is usually very nutrient
rich. Below the humus layer, are the alluviated layers (A horizons),
layers that are very poor in metallic elements like iron and aluminum,
elements which have been leached out (alluviated) of the forest floor
to the B horizons below. The alluviated B horizons are layers that
are rich in deposited iron, aluminum, and other minerals (alluviated)
that were leached out of the A horizons. Below the B horizons lies
material that are not considered soil—the C horizon consisting of
unweathered parent material or compacted rock materials. The C
horizon begins the bedrock layers, where biological activity is almost
non-existent.
 The soil profile at the Mt. Lemmon site; notice the four distinct layers (or horizons) in the bank.
Map of Two Sites
Mt. Lemmon
Biosphere 2 Center
Map of Regional Soil Profiles
MH2- Haplustolls- shallow,
moderately slowly to slowly
permeable soils that formed in eolian
material over residuum derived from
basalt.
TS6-Torrertic Haplustolls (New
classification: Torrertic Hoplustolls)
clayey texture and deep wide cracks
that are open more than 6 months in
most years formed in clayey
sediments, soft shales, or basic rocks,
in association with Aridisols and with
aridic subgroups of Ustolls.
TS7-The Caralampi series consists
of very deep, well drained soils
formed in fan and slope alluvium
from granitic and volcanic rock. -very
gravelly sandy loam - rangeland.
TS10-The Cellar series consists of
shallow and very shallow, somewhat
excessively drained soils formed in
slope alluvium from granitic rock.very gravelly sandy loam – rangeland.
FH5-Mirabal Baldy- Mt. Lemmon
site. Loamy sand. Bolsa quartzite.
Climate Diagram of Mt. Lemmon Area
Courtesy of the Desert Research Institute website: http://www.wrcc.dri.edu
Methods
In this lab we wanted two different soil types,
so we collected a soil survey from Mt. Lemmon,
from an elevation of 8,500 feet. To collect proper
sample we labeled each horizon of soil, clearly
distinguishing one horizon from another. After
labeling the horizons we measured the depth of
each horizon. In order to get the purest sample of
each horizon we dug a vertical profile. This vertical
profile allowed us to dig at the side of the soil,
which helped prevent other horizons from
contaminating the sample. We then carefully
bagged the soil from each horizon and labeled
them. This method of sampling was also used on
the soil profile at the Biosphere 2 Center campus.
The second soil profile was collected at 3,852 feet.
After we took these samples, we analyzed
them at the dry lab. We performed a series of tests,
such as the sieve screen test, plasticity tests,
texture makeup tests, the smudge test, and the
Munsell soil color test. The sieve screen test has
five pans, and 4 of the pans have screens filtering
particles from largest to smallest, and the last pan
collects what remains. The mesh sizes are 5, 10,
60, and 230. A mesh size is an indication of the
number of openings per linear inch. This test
allowed us to separate soils to examine their
texture on four different levels.
Using screen sieves, we separated each horizon of the soil profile
into 5 different particle sizes (#5 mesh-gravel, #10 mesh-fine gravel, #60
mesh-course sand, #230 mesh-fine sand, bottom pan-silt and clay).
Using a balance scale, we weighed each of the particle types from each of
the horizons (Tables 1&2). We then used Excel to determine the percent
composition for each horizon at each site. Another part of testing the soils
texture was with a flow chart that helped determine the texture of the soil
by feel. We then tested each horizon from each site on the plasticity and
stickiness of the soil. Using the Munsell soil color charts for both the dry
and wet soils, we identified soil colors according to a standard that is
universally acknowledged. We then smudged these colors on a white
piece of paper for better contrast (Results).
Excavating a soil profile at the Biosphere2 site.
Geologic Formations:
Mt. Lemmon and Biosphere 2 Center
Mount Lemmon: Naco group – metamorphosed Paleozoic
sequence, mostly limestone, Bolsa quartzite
Biosphere 2 Center: Dissected Neogene basin fill, overline terrace
and pediment gravel sheets and local alluvium
O
O
A
A
B
B
C
C
R
Top: Mt. Lemmon profile (Letter denotes layer)
Bottom: Biosphere 2 soil profile
Top: Detail-view of Mt. Lemmon soil profile
Bottom: Detail-view of Biosphere 2 soil profile
A
B1
A
B1
B2
B2
Top: Mt. Lemmon soil profile analysis, Mei and
Adam working on the texture tests.
Bottom: Biosphere 2 soil profile analysis, Asma
working on the Munsell color and smudge Tests.
Pyramid of Soil Texture
Mt.
Lemmon
B
i
o
s
p
h
e
r
e
2
Table 1 – Mount Lemmon
Site Name
Mt. Lemmon
O Layer dry
wet
A Layer
wet
B Layer
wet
C Layer
Texture
Description.
% Composition
(Sand/Silt/Clay)
Stickiness Test
Plasticity Test
Loamy sand
Sand = 70-90%
Silt = 0-30%
Slightly sticky
Non-plastic
Sandy loam
Sand = 50-88%
Silt = 0-50%
Clay = 0-58%
Sandy clay
loam
Sand = 50-100%
Silt = 0-30%
Clay = 20-30% Slightly sticky
Loam
Sand = 25-52%
Silt = 25-50%
Clay = 8-25%
Slightly sticky
Slightly plastic
Moderately
plastic
Moderately sticky Slightly plastic
wet
R Layer
wet
Munsell Color
Test Color
Color Descp.
10 YR 2/2
7.5 YR 2.5/1
very dark brown
black
10YR 3/2
10YR 3/1
very dark
grayish brown
very dark gray
10YR 5/4
10YR 4/3
yellowish
brown
brown
10YR 4/3
10YR 4/4
n/a
n/a
brown
dark yellowish
brown
n/a
n/a
Lat/Long: 32.44˚ N / 110.78˚W, Elevation: 2764 meters, 8500 feet
Site Description: Old growth, near summit, cooler, breezier climate, more rainfall, more organic
materials
Soil Composition – Mount Lemmon
Adj.Total % Gravel
% Without Gravel
% of Total Lost
Adj.Total % Gravel
% Without Gravel
% of Total Lost
Adj.Total % Gravel
% Without Gravel
% of Total Lost
Adj.Total % Gravel
% Without Gravel
% of Total Lost
Mt. Lemmon
O Layer
total sample
gravel
fine gravel
coarse sand
fine sand
silt and clay
experimental
loss
A Layer
total sample
gravel
fine gravel
coarse sand
fine sand
silt and clay
experimental
loss
B Layer
total sample
gravel
fine gravel
coarse sand
fine sand
silt and clay
experimental
loss
C Layer
total sample
gravel
fine gravel
coarse sand
fine sand
silt and clay
experimental
loss
grams
% Composition
121
55
16
8
28
8
61.74%
18.18%
63.64%
18.18%
6
4.96%
76
24
7
24
13
2
44.29%
61.54%
33.33%
5.13%
6
7.89%
90
26
16
32
6
1
51.85%
82.05%
15.38%
2.56%
9
10.00%
Mt. Lemmon--O Layer
gravel
fine gravel
coarse sand
fine sand
silt and clay
experimental loss
Mt. Lem m on--A Layer
M t. Le m m on--B Laye r
M t. Le m m on--C Laye r
282
220
25
30
3
0
88.13%
90.91%
9.09%
0.00%
4
1.42%
Table 2 – Biosphere 2 Center
Site Name
Biosphere 2
A Layer (dry)
Texture
Description.
% Composition
(Sand/Silt/Clay)
Sandy clay
loam
Sand = 50-100%
Silt = 0-30%
Clay = 20-30% Slightly sticky
Stickiness Test
Plasticity Test
Munsell Color
Test Color
Non-plastic
7.5 YR 4/4
A Layer (wet)
B1 Layer (dry)
5 YR 3/2
Clay
Sand = 40-65%
Silt = 0-40%
Clay = 65-100% Moderately sticky Very plastic
B1 Layer (wet)
B2 Layer (dry)
B2 Layer (wet)
B3 Layer (dry)
B3 Layer (wet)
Sandy clay
loam
Sand = 50-100%
Silt = 0-30%
Clay = 20-30% Non-sticky
Moderately
plastic
Sandy clay
loam
Sand = 50-100%
Silt = 0-30%
Clay = 20-30% Non-sticky
Slightly plastic
2.5 YR 4/4
Color Descp.
brown
dark reddish
brown
5 YR 3/4
reddish-brown
dark reddish
brown
5 YR 5/6
5 YR 4/6
yellowish red
yellowish red
5 YR 4/6
5 YR 4/6
yellowish red
yellowish red
Lat/Long: 32.57˚ N / 110.84˚W , Elevation: 1174 meters
Site Description: Arid, Desert, grasses, small trees, succulents shrubs, less than 10" of rain, alluvial
deposition
Soil Composition – Biosphere 2 Center
Biosphere
A Layer
total sample
gravel
Adj.Total % Gravel fine gravel
% Without Gravel coarse sand
fine sand
silt and clay
experimental
% of Total Lost
loss
B1 Layer
total sample
gravel
Adj.Total % Gravel fine gravel
% Without Gravel coarse sand
fine sand
silt and clay
experimental
% of Total Lost
loss
B2 Layer
total sample
gravel
Adj.Total % Gravel fine gravel
% Without Gravel coarse sand
fine sand
silt and clay
experimental
% of Total Lost
loss
B3 Layer
total sample
gravel
Adj.Total % Gravel fine gravel
% Without Gravel coarse sand
fine sand
silt and clay
experimental
% of Total Lost
loss
% Composition
271
31
34
86
18
13
35.71%
73.50%
15.38%
11.11%
Biosphere
Site A Layer
Composition
gravel
fine gravel
coarse sand
fine sand
silt and clay
89
32.84%
256
85
65
96
8
1
58.82%
91.43%
7.62%
0.95%
1
0.39%
242
30
70
129
11
2
41.32%
90.85%
7.75%
1.41%
0
0.00%
278
65
58
143
10
1
44.40%
92.86%
6.49%
0.65%
1
0.36%
experimental
loss
Biosphere B1 Layer Com position
Biosphere B2 Layer Com position
Biosphere B3 Layer Com position
Results
Based on the Texture Analysis and the Munsell Color Test, the soil profiles of Mt. Lemmon and
Biosphere 2 are as follows:
Mount Lemmon
•O: +3cm – black/brown, charcoal, leaf litter
•A: 0~-26cm – dark grayish brown, sandy loam
•B: –26~-46cm – yellowish brown, sandy clay loam
•C: -46~-156cm – brown weathered rock, loam
•Bedrock: -156~
Biosphere 2
•A: 0~-30cm – brown, sandy clay loam
•B1: 030~-50cm – reddish brown, clay
•B2: -50~-85cm – yellowish red, sandy clay loam
•B3: -85~ - yellowish red, sandy clay loam
The Screen Sieve Analysis was affected by imprecise methods (see conclusion)
Mount Lemmon
•Gravel accounted for the largest percentage of mass from O to C layers.
•Coarse sand accounted for most of the non-gravel mass.
•With increasing depth, percentage of silt and clay decreased.
Biosphere 2
•Percent of coarse sand increased with depth in soil profile.
•Less gravel than soil from Mt. Lemmon.
•Percentage of silt and clay very variable among different horizons.
Smudge Tests
Discussion: Parent Material, Topography & Soil
“The unconsolidated mineral matter on the surface of the earth that has been
subjected to and influenced by genetic and environmental factors such as parent
material, climate (including moisture and temperature effects), macro-and
microorganisms, and topography, all acting over time and producing a product—soil—
that differs from the material from which it was derived by many physical, chemical,
biological, and morphological properties and characteristics.”
To investigate this working definition for soil, we were asked to consider two questions:
What differences or similarities do soils from different topographical
areas have? And what differences could topographical factors have
that influence the kind of soil and soil production?
To answer these we took soil from two distinct topographical locales—one from a road
cut near the top of Mt. Lemmon (elevation 8,500 ft.), the other from a road cut on the
Biosphere 2 campus (elevation 3,852 ft.). We looked at soil texture, color, consistency,
structure; we also looked at the topography, climate, and the general characteristics of
each site.
Of the five functional factors that make soil (topography, parent material, time, organic
forces, and climate) we found topography and parent material to have the most
pronounced affect on the texture, structure, and the physical and chemical
characteristics of our samples.
Not that climate, biotic activity, and time are unimportant to soil development, but
parent material and topography have shape how these other (crucial) factors function.
The parent material at a given site influences the interaction between organic and
inorganic materials—e.g. quatz and limestone weather differently and so form very
different soils. Topography is a deciding factor in the microclimate. Elevation effects
temperature and moisture levels at a given site; these in turn are limiting factors for the
vegetation growing there and the kind of organic material that they into the soil.
Eli takes a closer look at the clay.
One note about time. Though it is a passive agent in this process, it is perhaps the key ingredient in the creation of soils. The process of physical
and chemical changes in rocks caused by atmospheric agents such as water, oxygen, and carbon dioxide takes place over millions of years. Soil is a
living process (a living labyrinth, Tony Burgess calls it) and like most living things it takes time to develop.
TOPOGRAPHY: At 8,500 feet, the Mount Lemmon site is a breezy mountaintop characterized by its cool temperatures
and old growth forest. Ponderosa and Limber Pines, Douglas and White Firs all tower 60 ft or more over the forest
floor. In the space between these trees, small stands of Quaking Aspens and Rocky Mountain Maple saplings grow.
Part of the reason for high biotic productivity in the area has to do with an abundance of rainfall: 788mm of precipitation
per year on average, according to the nearby Palisades Ranger Station which has been compiling yearly climate data for
years (see above table). These forests benefit from late summer monsoons, as well as snowfall in late fall/early winter.
Referring to the local climate of the Santa Catalina Mountains, the Arizona AgNIC reports, “On high peaks at 9000 to
10,000 feet, snow persists all winter and accumulates to 20-40 inches. Summer rains fall June - September, originate in
the Gulf of Mexico, and are convective thunderstorms. Winter moisture is frontal, originates in the Pacific and Gulf of
California, and falls as rain or snow in widespread storms of low intensity and long duration. May and June are the
driest months of the year. Humidity is generally low. Temperatures are mild in the summer to cold in the winter. Freezing
temperatures are common from October through April. Frost free period ranges from 120 to 260 days.”
Mount Lemmon
We were surprised at first to discover less biodiversity of plant and arthropod life at this site, but given the colder
temperature regime--the minumum daily temperature in the Santa Catalinas drop below freezing during four months
our of the year—a chill that many plants thriving in the lower elevations around Biosphere2 could not tolerate. Thus
because of its topography, the microclimate on Mount Lemmon is much like that found in temperate forests at higher
latitudes. Vegetation contributes a substantial amount of organic material to the soil profile every year as reflected in
the L, H, and O layers of the soil profile. We estimated this to be 3cm in our profile. It is worth noting that we could
expect more given the sheer amount of organic activity at Mount Lemmon. The fact that there was not a thicker O layer
is strong evidence of the effect of erosion on overall soil formation at higher topographical points.
The deep roots of the trees, and the life forms that they support, also help to break down the soil structure through the
process of biturbation. These dense networks of roots and the burrows of vertebrates and arthropods that live on the
forest floor provide conduits for water; thus aiding in the process of weathering of the rock material. Another
contributor to the character of this O layer has been fire. Charcoal found in the litter over the O layer suggests a history
of forest fires in the area. These fires allow for a much more rapid decay of organic material and nutrients than normal
decomposition. Judging from the vegetation, there has not been a fire in recent years. Human disturbance even when it
has profound impact of a local ecology does not tend to have any long term geological effects; for this reason it is
considered more of a historical phenomenon than a geological one. In an indirect way, topography also influences
human disturbance and land use policy. Mount Lemmon is a popular tourist site and is used primarily for recreation
purposes. Land use in the immediate area is limited to these activities, though there is a great deal of construction on
roads in the area. Currently these are the only significant disturbances to the soil.
Temperate forest near
the top of Mount Lemmon.
PARENT MATERIAL: According to Steve Slaff, the rock material that forms the basis of our Mt.
Lemmon site is called Bolsa Quartzite. (He also referred to it as “Cat Mountain Rhyolite.”) The rock
formations in this area were probably laid in the Pleistocene period and influence the soil type here,
known as Mirbal Baldy. There is almost no volcanic material in the Santa Catalina Range of which
Mt. Lemmon is a part. The parent material is broken down over time in the C layer of the soil. This
fact plus the enormous amount of organic material available to the process are perhaps the two
most distinguishing factors from the Biosphere 2 site.
Topography: Compared with Mt. Lemmon, the landscape of our second
site is limited mostly by availability of water. This biome would be best
classified as Apacherian mixed scrub savanna, which, according to Dr.
Tony Burgess, is classified as “coexisting growth forms that include
grasses, subshrubs, stem succulents and shrubs” (Burgess 1994). Long
dry spells punctuated by erratic and variable rainstorms make for a very
unstable plant community. This area has a much larger percent
composition of grasses than the site on Mt. Lemmon. This makes the
whole community susceptible to frequent fire and thus limits extensive
long-term productivity. The pattern of dry periods followed by heavy
rains means that summer storms cause erosion. Plants have had to
adapt their root structure to these extreme conditions—grasses have
quick growing shallow roots to take advantage of the heavy summer
rains, trees and some shrubs tend to send deeper roots into the soil to
take of water that seeps deeper into the profile during winter storms.
Warm average temperatures protect species vulnerable to frost—trees
like the mesquite, and succulents. Sandy soils work to the advantage of
these type of trees, since they are more porous and allow for more water
during the characteristic heavy storms to penetrate deeper into the soil
profile.
Another factor in the topography of this site is extensive grazing. While
the ground directly above our sampling site did not appear to have been
grazed recently, the Apacherian savanna has historically been
overgrazed. Overgrazing can erode the soil, by trampling microorganisms
that help knit the soil structure together. They also significantly reduced
the amount of biotic material available to the soil process. When cattle
are introduced to the ecosystem, much less biotic material and nutrients
are returned to the soil. Compared to the Mt. Lemmon site, there is very
little litter at the Biosphere 2 Center. The topography is marked islands of
fertility under trees where litter and hungry nutrient grasses tend to
gather leave top soil levels vulnerable to erosion. This may have had
something to do with why we found no O layer at the Biosphere 2 site.
Biosphere 2
Parent material: The geological basis of Biosphere 2 is called the Cordones Surface. It is part of an ancient alluvial
fan deposited by runoff from the Catalina Mts. during basin and range faulting. The Cordones Surface formed from mixed
alluvial deposits of different kinds of rocks including Paleozoic sedimentary rocks, metamorphic rocks, and Tertiary granites
Since then, two processes have prevailed over time in the creation of this soil composition. Eluviation occurs when water
percolating down through the soil leaches substances out of the upper layers. The acidic water dissolves most minerals, except
quartz, and carries them deeper into the soil. Illuviation occurs as water percolating down through the soil carries materials from
upper layers into deeper layers. An illuvial soil horizon has accumulated clays or minerals transferred by water flow from
overlying soil. Over time these two processes can change a uniformly mixed alluvial deposit into a mature soil with distinctly
different horizons (Burgess). This explains why we found clay interspersed many rounded rocks in the soil horizon.
Clay comes some from weathering within the original deposit but most is brought in as windblown dust and raindrop
nuclei. This dust often consists of oxidize iron-based material which give the soil a ruddy appearance. You can see this in the
smudge tests: the samples from B2 are much redder than those on Mount Lemmon. Percolating water gradually moves
clay particles down through the soil. In early stages this forms clay films on clods and pebbles. As clay continues to
accumulate, water movement within the horizon is slowed; hence clay is not moved into deeper layers, forming with is called an
argillic horizon. On ancient alluvial fans, such as the Biosphere 2 campus, Holocene erosion has exposed the Pleistocene
argillic and calcic horizons. These exposed layers become parent material for new soil formation. This process is typical of
lower elevations in the Basin and Range Geologic Province. Over time the low level of precipitation (usually less than 12 inches
per year) forms a horizon of caliche, a cement layer made from calcium carbonate (Burgess). This layer is almost nonexistent
in areas of greater and more consistent precipitation (like the temperate forests of the Northeast), but we found that it was very
prevalent on the B2C campus. The presence of caliche was one of the major differences between the soil profiles.
McAuliffe in his essay on desert soils in the Natural History of the Sonoran Desert describes the slow process by which
caliche horizons are formed: “They start as thin, patchy coats of whitish calcium carbonate on the lower surfaces of pebbles and
small stones….These weakly-developed calcic horizons can form within a few thousand years. Accumulation of more calcium
carbonate eventually produces thicker, continuous coatings on pebbles and stones or pronounced whitish nodules in finegrained parent materials. Eventually, additional accumulation of calcium carbonate fills the soil interstices between pebbles or
nodules and the calcic horizon becomes plugged, greatly restricting the downward movement of water. Once this occurs,
calcium carbonate may continue to accumulate on the top of the calcic horizon in hard, cemented layers and may literally engulf
and obscure overlying soil horizons in the process. It takes many tens to hundreds of thousands of years for such stronglydeveloped calcic horizons to form. Sometimes hard, whitish caliche becomes exposed on the surfaces of very old soils when
erosion removes overlying, less erosion-resistant soil horizons. These partly eroded soils are very common throughout the
Sonoran Desert and are called truncated soils.”
Thus the presence of a caliche layer not only tells us something about the content of the soil, it also serves as evidence
of the climate that created it. The thick caliche layer we found in out Biosphere 2 sample would suggest that this area has
experienced extreme aridity for quite some time. It can also give us a picture of the future topography and soil composition
since caliche “erodes unevenly to create exposed or slightly buried surfaces that shed water in weathering crevices, resulting in
a landscape with patchy water infiltration and retention,” and facilitating even more run-off, and more erosion, during heavy
summer thunderstorms (Burgess). The geology of the landscape also exacerbates many of the environmental/climatic factors
that shape this community and the soil profile, and creates a patchwork of different soil textures and characteristics. This is
partly why desert soils are so hard to classify.
The Formation of Caliche in Arid Soils
From Phillips and Comus. 2000. Natural History of the Sonoran Desert. Arizona Desert Museum Press. Tucson.
Conclusion
How did the soils differ? How does topography affect local climate?
How did different parent materials result in different soils?
In this exercise, we learned various techniques for sampling and
examining soil profile. For example:
• Sieve test
• Texture tests: smudge test, ribbon (plasticity) test, stickiness test
• Munsell Color Test
Topography affects climate, and together, these two factors
significantly influence the soil composition. The higher elevation of
Mount Lemmon results in more rainfall, and a more breezy climate. The
lower elevation of Biosphere 2 results in a dryer, hotter climate.
Analysis of the soils indicated that the Mount Lemmon soil had more
gravel and organic material in it than the Biosphere 2 soil, whereas the
Biosphere 2 soil had more coarse sand in it. This is because the Mount
Lemmon site has a colder climate, where litter decomposes more slowly
than in the arid climate at the Biosphere 2. The arid climate here results
in less rainfall which, in turn, favors the formation of caliche found in
the Biosphere 2 soil.
Differences in the parent materials of the soils also influence soil
composition. Bolsa quartzite was the parent material of the Mount
Lemmon soil; this material resulted in the softer, easily broken apart,
weathered rock found in one of the soil layers. The parent material of
the Biosphere 2 soil is alluvial deposits. Rust in the alluvial deposits
results in the rust color of the soil at the Biosphere 2.
In analyzing the soil samples collected, we learned that there are not
many quantitative tests that can help us accurately describe the soil
composition percentages. Most of the results that we obtained were
from qualitative assessments, such as the Color Test and the Smudge
Test. We found discrepancies that might have a lot to do with how we
implemented these tests.
In the future, we need to collect sufficient amount of soil so that we
can replicate our test for more accurate results.
Soil profile Biosphere 2 
http://www.columbia.edu/itc/cerc/seeu/bio2/index.html
http://homepages.which.net/%7Efred.moor/soil/formed/f0107.htm
http://www.statlab.iastate.edu/soils/osd/dat/C/CABEZON.html
http://ialcworld.org/soils/nonaridisols/nonaridisols.html
http://www.statlab.iastate.edu/soils/osd/dat/C/CARALAMPI.html
http://www.statlab.iastate.edu/soils/osd/dat/C/CELLAR.html
http://interactive.usask.ca/skinteractive/modules/agriculture/soils/s
lphys/soilphys_depo.html
http://www.wrcc.dri.edu
McAuliffe, Joseph R. “Desert Soils”. A Natural History of the
Sonoran Desert. Eds Steven J. Phillips. Arizona-Sonora Desert
Museum Press: Tucson, 2000
Burgess, T. 1995 Desert Grassland, Mixed Shrub Savanna, Shrub
Steppe, or Semidesert Scrub? Pp.31-67 in The Dilemma of
Coexisting Growth Forms. University of Arizona Press, Tucson.
References &
Acknowledgements
Dickinson, William R. 1992. Geologic Map OF Catalina Core
Complex And San Pedro Trough Arizona Geological Survey
contributed Map CM-92-C. 1:125,000 Geological Society of
America Special Paper 264.
Macbeth, Gretag. MUNSELL SOIL COLOR CHARTS year 200
Revised washable Edition. MUNSELL COLOR 617 Little Britain
Road, New Windsor, NY 12553.
Steve Slaff Lecture on geology and soil. 6/19/01, Mt. Lemmon, AZ