Describing Soil Profiles

Summary

The 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

• 🗺️ 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.
• 🏔 The soil profile is developed from Limestone Bedrock, indicating it's a residual soil that has formed over thousands of years.
• 🔍 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.
• 🏗 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.
• 🌱 The absence of an E horizon in the profile is noted, likely due to plowing which mixed the material into the AP horizon.
• 📏 The depth of the soil profile is measured from the surface (0) down to the Bedrock, which is 28 inches deep in this case.
• 🟥 The soil color is described using the Munsell color system, with the script illustrating how to compare soil color to color chips.
• 🧱 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.
• 🐛 The script points out natural soil features like animal burrows and earthworm channels, which can affect soil homogeneity and are indicators of soil health.
• 🌿 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

00:00

🌱 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.

05:01

🎨 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.

Keywords

💡Soil profile

A soil profile refers to a vertical section of soil that displays its layers or horizons. In the video, the speaker describes the process of examining and documenting a soil profile, which is crucial for understanding soil properties and its development over time. The speaker emphasizes the importance of appreciating the geology and geomorphology of the area before describing a soil profile, as it provides context for what might be observed in the soil layers.

💡Geology

Geology is the study of the Earth's structure, composition, and the processes that shape it. In the script, the speaker mentions the need to understand the geology of the area, such as the Ridge and Valley Province in central Pennsylvania, to predict and interpret the soil profile characteristics. This is because the underlying rock types and geological processes significantly influence soil formation.

💡Landscapes

Landscapes encompass the visible features of an area of land, including its physical elements like landforms, soil, and vegetation. The video script describes the area of study as having Limestone valleys and Sandstone ridges, which are part of the landscape. These features are important in soil profile description as they provide a backdrop for understanding the soil's parent material and its development.

💡Parent material

Parent material is the original substance from which soil is formed. In the video, the speaker highlights the importance of understanding parent materials before describing a soil profile. The parent material, such as Limestone Bedrock in the example, influences the soil's characteristics and the types of soil horizons that develop.

💡Soil horizon

Soil horizons are the layers of soil that are formed due to various soil-forming processes. The speaker describes several horizons in the soil profile, including the A, B, and R horizons. Each horizon has distinct characteristics that reflect different stages of soil development and the processes that have acted upon the soil.

💡AP Horizon

The AP Horizon is a surface soil horizon that has been mixed by cultivation, such as plowing. In the video, the speaker notes that the AP Horizon is a result of human activity, indicating that the soil has been disturbed. This horizon is characterized by a mix of organic matter and mineral soil, which is different from the undisturbed soil layers below.

💡BT Horizon

The BT Horizon is a subtype of the B Horizon, which is known for clay accumulation. The speaker describes the presence of a BT Horizon in the soil profile, indicating that clay has been transported and deposited in this layer. This is an example of an illuvial process, where materials are moved downward from an eluvial horizon to an illuvial horizon.

💡Soil structure

Soil structure refers to the arrangement of soil particles into distinct shapes or units. The video script mentions granular and blocky structures as examples observed in the soil profile. Soil structure is important for water infiltration, aeration, and root penetration, and it can indicate the soil's physical properties and its suitability for plant growth.

💡Earthworm channels

Earthworm channels are tunnels created by earthworms as they move through the soil. The speaker points out these channels as evidence of earthworm activity, which is a sign of healthy soil. Earthworms help mix and aerate the soil, creating channels that can be seen as dark streaks in the soil profile.

💡Munsell color system

The Munsell color system is a color notation system used to describe colors, including soil colors. In the video, the speaker uses this system to describe the color of the soil, which is an important characteristic in soil profile description. The speaker compares the soil color to Munsell color chips to accurately document the soil's color, which can provide insights into soil properties such as organic matter content and oxidation.

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