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This lab illustrates some basic concepts of soils as individual components of the
landscape. Soils occur as natural bodies that may be mapped. Finally, soil interpretations
for various uses, as well as some problems involved with the interpretation process will
be discussed.
The pedon is the smallest three dimensional volume of soil that
can be recognized. Its lower limit is the vague and somewhat arbitrary limit between soil
and 'not soil'. The lateral dimensions are large enough to permit study of the nature of
any horizons present, because a horizon may be variable in thickness or it even may be
discontinuous. The pedon area ranges from 1 to 10 square meters, depending on the
variability in the horizons. The shape of the pedon is roughly hexagonal. Unfortunately, a
soil individual varies in characteristics more broadly than the characteristics exhibited
in a single pedon.
A soil individual is comprised of several pedons. The
characteristics of these pedons are within the defined limits described by the central
concept for the soil individual. A soil body that consists of more than one pedon is
called a polypedon. If you think about it a little, you can easily see that a very uniform
soil individual may include only one pedon. A very heterogeneous soil individual may
consist of many pedons, each one illustrating varied characteristics but within defined
limits.
The pedons render too much detail for mapping purposes, and though important in soil
taxonomy development, we are more interested in units that can be recognized on the
landscape with relative ease, and which would have practical significance. So, the soil
individual or polypedon is of primary interest here, and in turn, the clusters of polypedons which go to make up the 'soilscape'. The
term soilscape is a contraction of the term 'soil landscape' and is analogous to
'townscape' of architects. A soilscape then, is the pedologic portion of a landscape, and
it is what a soil surveyor discovers progressively while working across a terrain mapping
soil bodies on an aerial photograph. The term soilscape denotes the pedologic quality of a
terrain. As shown in the slide, there are three clusters of polypedons, or three soil
bodies. It is at this point we can attach taxonomic units to a soil body. The common body
is the soil series.
We can divide the continuum of soil into individual soils which can be arranged in a
taxonomic system. Soil bodies can be characterized not only by profile properties, but
also by a natural drainage index, a soil body pattern index, and a landscape position. The
average drainage index is simply a value expressing the average wetness or dryness of the
soil on the terrain. One such expression is drainage class described in lecture and used
in the field exercise at Heiberg Forest. The pattern index is simply a ratio of the soil
body circumference to that of a circle having the same area. The pattern index is related
to the drainage patterns of the terrain surface. Patterns are different between glaciated
terrain and terrain controlled by bedrock structure. In regions where relief is great,
there are more soilscape positions than in regions with low relief. The greater the relief
in a soilscape, the greater the differences among different slope aspects, and the more
the distribution of soil bodies is related to this feature. A particular kind of soil will
occur wherever the factors of soil formation provide the requisite state, and this may be
in more than one niche.
Because of natural variability, the soil within the boundaries of a soil body are not
purely the one designated on the map. These inclusions should not exceed 15 percent of the
area within the boundary, but often exceed this proportion. This fact must be considered
as a source of error on the map. However, most of the included soils are usually similar
to the designating soil. In addition to mapping the soil body, other factors, commonly
slope class or erosion class, are mapped. This combined information comprises a soil
mapping unit. It is the basic unit for detailed soil survey, and is roughly equivalent to
the soil individual or cluster of polypedons.
This is an example of a soil map showing the mapping units and
their symbols. Other features are shown, all superimposed on the aerial photograph
basemap. There is a minimum size area that can be shown on a soil map. The aerial photos
used as base maps are usually 1:20,000 scale. The smallest practical mapping unit
enclosing a symbol is approximately one-quarter square inch. This represents about two and
one-half acres on the ground. For broad mapping and interpretation purposes, this creates
no real problem, but for specific interpretations for areas less than two and one-half
acres, problems could arise if the area is occupied by an inclusion of soil different from
the designation. The actual procedure in mapping and compilation of the report is covered
in the laboratory manual.
Presentation of the field mapping of soils on aerial
photographs is probably the most important feature of the county soil survey report. The
written portion of the report contributes to the importance of the maps, particularly in
regards to interpretation.
The mapping legend, is essentially a list of soils found in the
county. The slide illustrates the mapping unit legend for Berks County, Pennsylvania. You
may wish to open the report in your carrel to the back of the written material, at the
beginning of the maps. Here, on a fold-out page you’ll find the mapping legend. Once
this legend is established and necessary photos are in hand, the surveyor heads for the
field. The surveyor traverses over the landscape ascertaining the location of the soil
boundaries by making frequent stops to examine the soil profile with a spade or soil
auger.
Here, you see a farmer using a tractor and spring-tooth harrow
to 'fit' his field for planting. This picture was taken in the Cortland Valley between
Homer and Preble. In the foreground and beyond the railroad tracks is the gravel bottom
material deposited as outwash when the glacier existed at Tully and the melt water flowed
southward or from left to right. This parent material extends to the foot of the slope
behind the barns. At that point there is a material that is a mixture between the gravel
and the eroded and slumped material from the hillside, forming a narrow band parallel to
the shoulders of the valley. As we ascend the hill in the background, the material becomes
increasingly influenced by the bedrock from the hillside- very thin glacial till mixed
with residual materials derived from the underlying bedrock of shales, siltstone, and fine
sandstone. Variations in profile drainage occur according to surface drainage patterns and
position on the slope. Primary soil boundary patterns are parallel to the valley. First
consideriing parent material and drainage as it relates to soilscape position, the soil
surveyor would tentatively identify the Palmyra series in the well-drained valley floor.
As the footslope is reached, drainge becomes imperfect and the Valois-Howard series are
found.
As we ascend the hill, Langford channery silt loam is crossed onto moderately well drained
Mardin series with Volusa on moist long slopes and Chippewa in drainage depressions. The
well-drained Lordstown series occurs on the uppermost portion, probably where you see the
woods. To establish the boundaries of the soil bodies, the soil surveyor moves back and
forth across the valley floor then up on the slopes, moving uphill and downhill on an
angle. The soil surveyor does not move simply parallel to the valley as many boundaries
could be missed. He moves in the direction and manner which maximizes the number of
boundaries crossed.
This is a close-up of the soil map for the areas seen in the
previous slide. The PbA and PbB are units of Palmyra soils; HbA, Howard Soils; LaB,
Langford; VaC and VaD Valois-Howard complex- which is a term used to designate a mapping
unit where two or more soils are so intricately intermingled that they cannot be separated
for mapping purposes. The MaB, is the Mardin series; VbB, Volusia, and CeB, Chippewa; and
finally LgE and LfC, Lordstown. The first two letters of the mapping unit symbol designate
the soil series and the third letter designates the coded slope class with A as 0 - 3%, B
as 3 - 8%, C as 8 - 15%, and D as 15 - 25% slope. The soil surveyor marks the boundaries
on the photos, gradually moving over each soilscape and piecing together the information
like a giant jigsaw puzzle.
Doc 12_09 One further example of mapping a soilscape may be helpful to you. Now, we are in
the Oley Valley of Berks County, near Reading, Pennsylvania.
This is a limestone valley with gently rolling slopes and little developed drainage due to
underground streams. The soil bodies tend to be larger and somewhat more uniform in this
soilscape, with some small scattered soil bodies that occur on bedrock outcropping or near
the moister stream-side soils of local alluvium. The soil surveyor is able to cover an
area such as this rather rapidly, traversing in wide sweeps.
This a close-up of the soil map of the scene in the previous slide. The DfB2 designates the Duffield silt loam, 3 - 8% slope, moderately
eroded. The latter is designated by the Arabic numeral. These areas occur on very low
ridges with shallow limestone bedrock. The WsA is Wiltshire soil derived from a mixture of
limestone and calcareous shale. Lt. is the Linseed series formed on the better-drained
floodplain material. And, Ml is the Melvin silt loam formed in poorly drained alluvium
from sediment originating from upland limestone materials. As you may gather from the
picture and he description, this is a highly productive agricultural area. You can surmise
this conclusion from the little homestead built by Mr. Fisher
in 1802.
As each aerial photo is completed in the field, the soil boundaries are correlated with
those on adjacent photos, and the entire composite is put together for the county. An
index to the photomaps is compiled and may be found at the beginning of the maps in each
soil survey report.
A general soil association map, as shown here, is compiled from
the detailed maps. Some reports will have an additional map at a scale of 1 inch equals 1
mile. These are very useful for county planning purposes.
In the text of the report, the soil associations are described
and the slide illustrates the appearance of the report.
This illustrates section giving the series descriptions along
with the mapping unit descriptions within each series. This section contains much valuable
information on each of the soils. Now that we discussed the mapping of the soils and the
generation of the soil maps, we need to address the question of how we use the information
in the soil survey report. Capability classes for general soil groupings have been
established to show their suitability for most kinds of farming. It is a practical
classification based on limitations of the soils, risk of damage when they are used and
the way in which they respond to treatment. There are eight classes ranging from Roman
numerals I through VIII. Look up the capability classes in your report.
This is a level field with soils developed on alluvium near Chittnango, New York. This is
an example of Class I land, the very best for farming. The
slides of Cortland Valley and of Oley Valley both illustrate Class I land.
Before you is an aerial view of a soilscape in central Alabama, sometimes called the Black Belt due to the color of the soil. This too is Class I land
just outside of Montgomery.
This slide illustrates a farm on Class II land. It is rated
Class II because the soils are somewhat droughty due to fine texture, and the presence of
a fragipan which limits root depth.
These are muck soils of Erie Boulevard right here in Syracuse
(before they were lost to development). These soils, to be useful, must be drained and
fertilized, as well as protected from wind erosion. Because of these limitations, they are
classed as capability Class III.
Obviously a landslide along Whiteface Mt. Memorial Highway. It
shows the problems of soils on steep slopes with shallow, impermeable bedrock below. This
is Class VIII land - land with such severe limitations that preclude its use for anything
but recreation, wildlife, water supply, or aesthetic purposes.
From the agricultural standpoint, one of the most important sections of the soil survey
report is the productivity ratings. Ratings for various crops
are given for each mapping unit. This information is derived from actual experience of the
farmers on the soils within the county, or adjacent counties with similar soils. By
examining this table you can see which crops are best adapted to certain soils. Other
ratings are given in either tables such as suitability for wildlife habitat and woodland.
This latter section, dealing with woodland, is probably the weakest section of the whole
report. Little research data exist for woodland productivity in general, let alone more
detailed information by mapping units. Also, some of the data developed by the Natural
Resource Conservation Service and others have found to be wanting for reliability.
Unfortunately, it takes a long time to develop this information, and the forest soil
scientists have not been able to produce the information fast enough. In most cases, we
are not able to quantify the relationship between soil properties and forest growth. The
variation in species composition complicates this task. In some states, reliable
productivity data for woodland has been developed through the impetus of private industry.
A productivity guide for spruce and fir in Maine was recently published by the Cooperative
Forestry Research Unit (Briggs 1994).
An example of the engineering data tables is shown. Data from
analyses and tests in highway engineering laboratories are provided. Engineers planning
highway and road construction can use maps and these data to choose preliminary routes.
Other tables may have nonfarm use interpretations for housing, farm-pond construction,
drainage ways, recreation fields and cemeteries. Because of the increasing importance of
this information from urbanization pressures, the SCS has an active program to strengthen
this information. One of the pieces of information found important by local officials and
planners is oil percolation or permeability. These data are important for rating of soils
for on-site waste disposal for single dwellings.
This soil pit has been dug and is being sampled to obtain data
for interpretation. You’ll notice the technician knee-deep in mud. This is a poorly
drained soil with severe limitations for a septic tank filter field.
The corn is rather poor in vigor because of poor drainage- a
good clue, but not recognized by home builders or buyers. The owners of the homes in the
background had overflowing septic tanks until a sewer system was installed. Mapping units
are also rated for foundations, such as one, two, or three story buildings, etc.
Soils are rated for limitations as potential landfill sites.
This is an example from Delaware County, New York. Soils for landfills should be deep to
bedrock so that the bottom of the landfill does not rest on it; the soil should be
well-drained and unaffected by floodwaters or a high watertable. However, an impervious
layer should be present to prevent the percolation of leachate into the watertable or
nearby streams.
This is a section of Interstate Route 81 South of Tully. This
section of the highway runs across a somewhat poorly drained soil, so additional drainage
structures had to be provided. The base had to be raised with gravel from local pits.
This is the related portion of the soil map before the highway
was constructed. The soil along proposed routes determine, to a great extent, the
feasibility and costs of the road along that route. Unfortunately, good farmland is lost
in the process. Soils are also rated for trafficability.
Foresters and others are concerned with trafficability for
harvesting timber crops and for other operations in the forest that require heavy
equipment. Little specific data are available for most of our soils.
Here, technicians are sampling bulk density of a soil on a
logging skidtrail near Cuyler, New York. The purpose is to get an estimate of the degree
on compaction caused by the skidder making a known number of passes over the point with
known loads. This information is used to evaluate logging patterns to minimize the impact
on soils. This aids the forester in doing a better job in forest management. The study
showed hat there is little damage to the soil and little resultant erosion when care is
used both in the design and in the operation.
One of the things you should have noticed while perusing the report is that the ratings
are given as 'slight', 'moderate' or 'severe'. They are defined in the text of the report.
These terms are satisfactory for relative ratings, but many times we need to have
quantitative ratings. Again, it is difficult to obtain the required data in the desired
form. Therefore, these ratings are the best we have and are satisfactory for many uses,
but we have a long the way to go.
