Soil Survey

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Soil Survey Chapter 19
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This short presentation focuses on the two below
topics.
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A soil survey is an inventory of soils in a
county. It shows where different soil types
occur, gives properties of them and says whether
their properties may limit uses of them. This is
one of two types of soil maps. Its low
resolution.
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Thus, soils in an association may be fairly
similar, like the loess soils on campus.
The Feliciana is on the slopes and is better
drained than Olivier, which is on broad flat
areas.
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The other type of soil map is much
higher resolution and shows what specific soil
type is at a spot. The whole county is shown in
aerial photos with soil type boundaries
super- imposed. Whats in red is a square mile,
or section of land ( 640 acres). The
small letters inside boundaries are abbreviations
for soil types (technically, mapping units).
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This is your guide to which detailed map sheet
(aerial photo) to see for a specific tract of
land. Its right before the aerial photos.
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There are usually only a few dozen soil types in
a county. The first task in making a soil survey
is to determine what soil types occur. This is
where an understanding of soil formation is very
useful. If you have information on the geology
of the county, you have a guide to parent
material. Dig some exploratory holes on
different combina- tions of parent material,
vegetative cover and topographic position, and
see what whats there, i.e., soil type. A
lot of lab work besides the detailed descriptions
of typical pedons for the different soil types in
the county.
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Auger a hole where you think a certain soil is
and one where you think another one is. Guess and
confirm location of transition along a transect.
More efficient than grid sampling (compare number
of holes in illustration).
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Old style data input.
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Spectral data correlated with soil properties.
Particularly helpful in difficult terrain.
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Maps and tables are the core of a soil
survey. However, explanations in narrative
sections and definitions in glossary are
necessary for the layman to fully understand
tables.
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The soil types delineated on aerial photos are
called mapping units. Sometimes these are soil
series or minor variations of a certain
series called phases. This might have to do with
texture (Ruston sandy loam or Ruston fine sandy
loam), slope (Ruston, 1 3 , or Ruston, 3 8
) and so forth. In some cases, different soil
types occur in such tight and complicated spatial
patterns that it is not feasible to delineate
them. There are 2 types of this kind of lumping,
consociation, with 2 soil types that are
similar, and complex, with 2 types that are
dissimilar.
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This is an important table for agricultural use
of a soil. You can farm Class I soils without
risking de- grading them. More management is
needed with Class II, even more with III.
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Lower case letter for Class II and up gives the
major limitation. Erosion and wetness are common
for soils in Louisiana. Wetness refers to
a shallow water table.
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These are estimates of relative productivity for
possible crops and are part of the Land
Capability Class table.
Numbers are per acre. AUM animal unit month,
like 1 acre of bahiagrass can support 1 cow for 7
months or you need 12 / 7 acres per cow.
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The next slide gives ratings for a few soils if
used for camp sites or golfing. Ratings
are based on several factors. You dont get much
bounce and roll on a fairway that is
water- saturated 6 below the surface.
Obviously, you dont want a fairway to flood,
ever.
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Expected high water table depth (ft).