Describing Soil Profiles
Summary
TLDRThe video script provides an in-depth guide to describing soil profiles, emphasizing the importance of understanding the geology and parent materials before analysis. Set in central Pennsylvania's Ridge and Valley Province, the tutorial demonstrates how to 'face off' a soil profile dug by a backhoe to reveal accurate soil horizons. It identifies the presence of A, B, and R horizons, explains the absence of an E horizon due to plowing, and details the depth and characteristics of each horizon. The script also covers the use of the Munsell color system for soil color identification and discusses various soil structures like granular and blocky, highlighting the significance of earthworm activity and animal burrows as indicators of soil health.
Takeaways
- πΊοΈ The script describes a soil profile in Central Pennsylvania's Ridge and Valley Province, emphasizing the importance of understanding the geology and geomorphology of the area.
- π The soil profile is developed from Limestone Bedrock, indicating it's a residual soil that has formed over thousands of years.
- π To accurately describe a soil profile, one must 'face off' the profile to remove smears caused by digging, ensuring a clear view of the soil horizons.
- π The six master horizons in a soil profile may not all be present, and the script highlights the presence of A, B, and R horizons in the described profile.
- π± The absence of an E horizon in the profile is noted, likely due to plowing which mixed the material into the AP horizon.
- π The depth of the soil profile is measured from the surface (0) down to the Bedrock, which is 28 inches deep in this case.
- π₯ The soil color is described using the Munsell color system, with the script illustrating how to compare soil color to color chips.
- 𧱠The soil structure is a key aspect of soil profile description, with the script mentioning granular and blocky structures as examples found in the profile.
- π The script points out natural soil features like animal burrows and earthworm channels, which can affect soil homogeneity and are indicators of soil health.
- πΏ The presence of earthworm channels is a good sign of well-drained soils and overall soil health.
Q & A
What is the importance of understanding geology and geomorphology before describing a soil profile?
-Understanding geology and geomorphology is crucial as it provides a background that helps predict what might be observed in the soil profile. It sets the context for the parent materials and the development of soil horizons.
What is a soil profile and why is it important to 'face off' the profile?
-A soil profile is a vertical section through the soil to the parent material or bedrock, revealing the soil horizons. 'Facing off' the profile, which means breaking off smeared areas, is important to get an accurate representation of the soil horizons, as tools like shovels or backhoes can distort the natural layers.
How many master horizons are there in a soil profile, and which ones were identified in the described profile?
-There are six master horizons in a soil profile. In the described profile, the A, B, and R horizons were identified, with no E horizon due to plowing that mixed the material into an AP horizon.
What does 'AP Horizon' signify in the context of soil profiles?
-The 'AP Horizon' signifies the plowed layer at the surface of the soil profile, where 'A' indicates the topsoil and 'P' indicates that it has been plowed.
Why is the E horizon sometimes not visible or described in soil profiles?
-The E horizon is an eluvial horizon where materials are leached out. If it is mixed with other horizons due to activities like plowing, or if it is too thin (less than 2 inches), it may not be described separately in a soil profile.
What is the significance of the B horizon and its suffixes in soil science?
-The B horizon is a subsoil layer that often shows evidence of clay accumulation (Bt). The suffixes like Bt1 and Bt2 indicate different stages or characteristics within the B horizon, such as color, texture, or structure.
How is soil color used in soil profile description, and what system is commonly used?
-Soil color is an important property that can indicate organic matter content, mineral composition, and soil development. The Munsell color system is commonly used, with specific notations like '10R' to describe the color precisely.
What are the different types of soil structures mentioned in the script, and what do they indicate?
-The script mentions granular and blocky soil structures. Granular structure is common under grasses, indicating good soil conditions, while blocky structure indicates more developed soil with natural clumps or pads.
What are the implications of finding earthworm channels in a soil profile?
-Earthworm channels, or middens, indicate good soil health and drainage. Earthworms homogenize and mix the soil, which is beneficial for aeration and nutrient cycling.
Why are old animal burrows significant in soil profiles?
-Old animal burrows can provide insights into the biological activity in the soil and can affect soil structure and properties. They can also be indicators of past land use or natural processes.
Outlines
π± Understanding Soil Profiles
This paragraph introduces the process of describing soil profiles, emphasizing the importance of understanding the geology, geomorphology, and landscape of the area, such as the Ridge and Valley Province in central Pennsylvania. The speaker explains that before describing a soil profile, it's crucial to appreciate the parent material, which is one of the key criteria. The soil profile was dug by a backhoe, which can smear the soil, so the speaker 'faces off' the profile to get a clear view. The description of a soil profile involves six master horizons, though not all may be present. The speaker identifies the A, B, and R horizons in the profile, noting the absence of an E horizon due to plowing. The depth of the profile and the specific depths of the horizons are provided, with the AP horizon indicating the depth of plowing. The speaker also discusses the significance of the B horizons, particularly the BT horizon, which shows clay accumulation.
π¨ Describing Soil Profile Characteristics
In this paragraph, the focus is on the detailed examination of a soil profile, including the identification of soil colors using the Munsell color system. The speaker compares soil colors to the Munsell color charts to determine the value and chroma. The discussion then moves to soil structure, with the speaker demonstrating granular and blocky structures found in the soil profile. The size, development, and shape of the structural units are described, with examples of subangular blocky structures. The paragraph also highlights unique soil features such as old animal burrows and earthworm channels, known as earthworm middens, which indicate soil health and drainage. The presence of these features is used to infer information about the soil's characteristics and history.
Mindmap
Keywords
π‘Soil profile
π‘Geology
π‘Landscapes
π‘Parent material
π‘Soil horizon
π‘AP Horizon
π‘BT Horizon
π‘Soil structure
π‘Earthworm channels
π‘Munsell color system
Highlights
Introduction to the importance of understanding geology, geomorphology, and landscapes in soil profile description.
Central Pennsylvania's Ridge and Valley Province characterized by limestone valleys and sandstone ridges.
The significance of parent materials in soil profile description.
The process of 'facing off' a soil profile to remove smears for accurate observation.
Description of the six master horizons in soil profiles and their potential presence in any given profile.
Identification of an A horizon and B horizons in the soil profile.
Explanation of the absence of an E horizon due to soil being plowed, resulting in an AP horizon.
Depth measurements of the soil profile, starting from the surface to the bedrock.
Differentiation between B horizons using suffixes like BT for clay accumulation.
Observation of color differences in B horizons using the Munsell color system.
Importance of soil structure in profile description, with examples of granular and blocky structures.
Identification of unique soil features such as old animal burrows and earthworm channels.
Earthworm channels as indicators of well-drained soils and soil health.
The process of describing soil color by comparing soil samples with Munsell color chips.
The significance of soil structure in determining soil type and its impact on soil function.
The role of earthworms in soil homogenization and their contribution to soil fertility.
Transcripts
well today we're going to describe uh a
soil profile so I want to give you a
little bit of a background about how do
we describe soil
profiles and the first thing we need to
do whenever a soil is described is to
get a little appreciation of the geology
the geomorphology the
Landscapes and we're in an area in
central Pennsylvania where we have what
we call the Ridge and Valley Province we
have a series of L Stone valleys and
Sandstone
ridges and then we try to get a littleit
of a understanding or appreciation of
the geology before we describe a soil
profile so this will help us understand
what we might expect to see in this soil
profile
exercise probably parent materials one
of the most important criteria that we
need to understand and know before we
write a so profile
description so with that as the
background Let's uh let's head to a soil
profile and take a look at one now this
soil profile was dug by a back ho and
what happens when a back ho or a shovel
digs a pit it smears the pit and really
it doesn't give us a very good
expression of the soil horizon so before
I describe a soil I need to go ahead and
what we call Face Off the profile which
means really break off these
smears so I'm going to do this and then
we'll take a look at the profile after
I've cleaned off the face I was to try
to describe a soil
profile and there are six Master
Horizons and in any given soil profile
we may not have all six and I'm going to
go over some of the horizons that we
have in this particular
soil now again this is the Limestone
Bedrock this is what the soil
developed from so this is a residual
soil and these soil horizons developed
over thousands and thousands of years to
form this particular
soil now I'm going to go through and
show you a few of the horizons and
hopefully they're pretty obvious to you
this is would be an a
horizon this would be both of these
would be B
Horizons and this would be the r Horizon
now you can see there's no e you might
ask well where's the E Horizon remember
that's the eluvial
Horizon well what we have here this soil
was plowed and if there was an e Horizon
it was actually mixed up in this Horizon
that we call an AP Horizon a again
Horizon the surface Horizon the P
indicating it was plowed and it was
plowed to this
depth now when when we start to look at
a soil profile we always start with zero
being at the top and in this case the
depth of this profile down to the
Bedrock is 28
in so the AP is about 9 in the depth to
this particular Horizon is 9 to 17 and
the last Horizon here is like 17 go to
20
eight so again we always start using the
tape in this direction not this
direction now what we have
here these are both B
Horizons and remember with a B Horizon
we just don't use just B we have to have
a suffix attached to it these are
subordinate Horizons so we'd have like a
BT for clay accumulation for
example and that's what this particular
soil has it has an accumulation of clay
so the clay is moved out of here into
here eluvial
Horizon exits from an uvial horizon and
goes into an aluvial
horizon now what we have here we have a
subdivision of the B so we have a b B
T1 and then a
bt2 and there's difference if you can
see in these two Horizons in
color there's also differences in play
content and probably in
structure now you might say well where
is the sea Horizon most soils have sea
Horizons this one probably if we had a
SE it might be this little thin material
material this weathered
Bedrock but it's far too thin to call a
sea
Horizon we never describe Horizons that
are thinner than 2 in so if you have a
horizon less than 2 in thick that's
usually not
described so now let's uh take a look at
some of the different features that we
might look at in this so profile one of
the first things we do when we try to
describe a soil profile is to look at
the different colors in the so oil and
to do that we use it's called the Mel
color
system and whatever I start to describe
a Sol profile I always start with the
What's called the 10 yr
page but if I pull open this page and
look at this
soil uh I think the soil is much redder
than the
10yr so the way to do this is to get a
piece of the soil
out a ped and then then compare it to
the
chips and in this case the soil is
redder than the 10 yr page so I would
flip to maybe the 7 and2 yr or maybe
even to the 5 yr page which I think this
particular color of this soil
Falls and then we decide on what is the
value in the chroma and this of course
is discussed in uh in one of the lessons
how to do determine in soil color but at
least for looking at their soil profile
I hope that you can see that there is
quite a difference in color in this BT
Horizon the bt1 is not as red as the bt2
when we look at soil profiles is soil
structure and I collected this right out
of the AP
Horizon and if you can see that this is
uh almost like little BBS in here and
this is called called granular structure
this is a type of structure that we
normally see under sod under grasses we
have this type of granular
structure now another type of structure
we have in this soil
profile is something we call blocky and
see I just broke it out of the uh out of
the soil profile and it breaks into
natural
pads and uh these pads form something
that we call blocks I think you can see
that that's looks pretty much like a
little
block a few of these fell out and they
all tend to be pretty much
blocky in
shape now when we describe structure we
describe the size of the structure how
welld developed are the structural units
and what is the shape is it
granular is it blocky usually we call it
subangular blocky because it kind of has
rounded Corners it has very sharp
Corners it's called angular
blocking but this would be a couple
different structural types some of the
others are like plat Prismatic we don't
particularly have those structural types
in this soil the structure again is an
important component of the soil profile
description I'd like to point out just
the kind of a couple of uh unique
features that sometimes we see in soils
and these are features that some
sometimes uh confuse people but right
here we have a dark feature coming down
and as you can see it's uh it's actually
material that came right out of the AP
Horizon and what that is is probably an
old animal burrow when the animal moved
down and made a burrow a horizon
material was brought down and
Incorporated in the
bee another very common feature we see
of soils are these dark streaks
here and these streaks are actually uh
channels from earthworms here's one hit
here here's another one here's a third
one so it shows you how earthworms
actually do a pretty good job of
homogenizing and mixing up soil and
these are something we call uh earthworm
middens it's What's Left Behind when the
earthworm goes through the
soil now we only usually find earthworms
in well- drained soils so it's a good
indication of the health of a soil if
you see these earthworm channels
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