Soils Lab 1 on soil morphology includes a review of the five soil forming factors and how they influence soil texture, soil structrure, and soil color.  Assignment activities include conducting soil textural analysis by feel for two soils of your choice and questions from the lab material and lecture material from Soil Architechture and Physical Properties (Chapter 4).   

Instructions

Create a document with answers to the questions to be uploaded to the DropBox named ‘Soils Lab Assignment 1’.

Include your name and exercise number at the top of the new document and include the questions with answers.  
You should name your file with your last name, underscore exercise number.  For instance, a word file with my lab exercise 1 would be named ‘Pope_SoilsLab1 ‘.  

Acceptable file types include Office files as well as PDFs whichever is convenient for you.    
PLEASE NOTE, points will be deducted for not following these basic instructions.  

IntroSoils – Lab 1

Soil Morphology

o Lecture Materials: Soil Architecture and Physical Properties (Ch 4)

o Labs submitted without advised instructions will result in a 3 point deduction:

 Proper document name (LastName_SoilsLab1)

 Name included in document

 Legible numbering and spacing including questions with answers

 Use of spell and grammar check

o Labs submitted early will receive feedback with the opportunity to resubmit the lab. Do not
miss out on a great opportunity to be ensure understanding of the materials and increase your
lab grade.

Lab 1 – Soil Morphology

Introduction
Soil is generally all of the unconsolidated materials on the earth’s surface. Soil is a mixture of
mineral and organic solids, gases, liquids and living organisms which can serve as a medium for
plant growth. The pedosphere develops at the interphase of the lithosphere (rock),
hydrosphere (water), atmosphere (air), and biosphere (living things). Soil serves a medium for
plant growth, recycler and provider of nutrients, modifier of the atmosphere, water purification
system, and provides a medium for animal and human structures.

The five soil forming factors influence the earth’s surface at each landscape differentiating
themselves into horizontal layers slowly giving rise to what we call soil. A vertical sequence of
these horizons is called a soil profile and is characterized by its physical, geographical, and
biological features. The major horizons include the O, A, E, B, C and R horizons.

O: Organic horizons
A: Topmost mineral horizons, darkened somewhat by organic matter accumulation
E : Zones of eluviation (maximum leaching) of clay and of oxides of Fe and Al,

generally lighter in color than A horizon.
B: Zones of illuviation (accumulation)of materials such as silicate clays and

oxides of Fe and Al, and sulfates and carbonates of Ca, and Mg. Materials may
have formed in place or may have moved in from other
horizons.

C: Material underlying the A, E, and B horizons that is generally little affected by
the processes that formed the horizons above it. It may or may not be the
same as the material from which the upper horizon formed.

R: Underlying consolidated rock.

Texture, structure, and color are three of the basic properties used to describe soil, and the
following exercises are designed to characterize them in more detail.

Soil Texture
Soil texture describes the proportion of the different-sizes fine earth particles in soil. Soil
texture is of great practical importance to everyone from landowners to soil conservationist
and farmers, as many important soil properties are based on the soil texture. For instance,
sandy soils tend to have less fertility or water holding capacity while clayey soils generally are
much more fertile, but can prove problematic to work with due to their potential for shrink-
swell and drainage issues.

Soil particles have different size ranges and are categorized into two broad classes of soil
separates. The fine earth fraction constitutes particles smaller than 2mm and makeup soil
texture, while the coarse fraction covers particles greater than 2 mm.

sand: smaller than 2 mm, and larger than 0.05 mm
silt: smaller than .05 mm, and larger than 0.002 mm
clay: smaller than 0.002 mm (2 microns)

Soils generally contain some combination of sand, silt, and clay in addition to other organic and
inorganic constituents. Soils are grouped into 12 textural classes that have similar proportions
of sand, silt, and clay. The textural triangle (Figure 1) was designed so that any combination of
sand, silt, and clay could be placed into a textural class and then assigned a name. Textural size
class can be determined by mechanical analysis which will be discussed in the following lab or
by feel.

Determining the textural class of a soil in the field is generally accomplished by feel. It is also of
great practical value for any practitioner physically characterizing soil. The major soil classes
are relatively easily discernable just by touch. Sand will feel gritty while clays sticky and loams
more like flour. A flow chart (Figure 2) is available to guide one through the process. For a
demonstration of the process, please see the Nebraska Crop Watch YouTube video
(https://www.youtube.com/watch?v=W0osjN0t-Ho). It is best to either print this flow chart or
have it handy with you outside as you determine texture yourself. An alternative to this flow
chart is available in the text as Box 4.2.

Your task for Lab 1 is to choose two soils in your area and determine their texture. Try to
choose soils that might have different textures, but this is not a requirement. The only things
you will need are an implement to take your soil sample and some water. The first step is to
take an implement (shove, spoon, etc) and dig down about 3 inches into the topsoil and obtain
approximately 25 grams of soil (about the size of a walnut) and start thru the flow chart. As
part of the assignment, please take a photo of your soil and your attempt at making a ‘soil
ribbon’ and include insert the picture alongside your determination of texture. (NOTE: If you
have any issues with taking or inserting the picture, please email instructor.)

Figure 1: Soil Textural Triangle (NRCS)

Figure 2. Flow chart for determining soil texture by feel (Courtesy of NRCS)

Structure
Soil structure is the arrangement of soil particles (sand, silt, and clay) into larger structures,
aggregates called peds. Soil structural types are defined by their shape. Figure 2 (Text 4.13)
describes the major types of soil structure and where in the soil they are commonly found.

Figure 2. Soil structure types (Figure 4.13 in text)

Soil Color
Soil color might seem the most obvious of soil morphology characterizations. Soils contain the
gamut of color scales from greys to reds and oranges. Color also helps provide evidence of
other soil characteristics. Colors in soil are derived largely from organic matter and minerals.
Organic matter darkens soils while iron oxides provide brown and reddish components. The
oxidation/reduction state can also be inferred from the colors seen. Highly reducing conditions
like wet and anaerobic conditions can produce gleying or gray-ish colors in soil. Water content
is also a major contributor to color in soils as wet soils are generally darker in color than dry.

Unfortunately, color is not observed the same by each person’s eye. To obtain a more precise
and repeatable description of color in soils, the Munsell Color System is used. The Munsell
charts use the three components of how people see color: hue, value, and chroma.
Hue refers to the dominant wavelength of the light and in soils is generally the redness or
yellowness). Value, lightness or darkness is the total quantity of light. Chroma is the relative
intensity of the dominant wavelength of light.

The following is a page from a field book of the Munsell Color chart. When possible with the
sun over ones shoulder, a soil sample is held next to a corresponding color chip in the chart.
The various cards contain one of the hues (top 7.5 YR) and then the value (left) and chroma
(bottom) are determined from each particular chip. For example, a soil from this card that
matched the chip noted with a star would be considered a 7.5 YR 5/3.

Intro Soils – Lab 1 – Assignment Questions
o Utilize lab as well as lecture materials: Soil Architecture and Physical Properties (Ch 4)
o 40 Total Points: #1, 7 points, #2-12, 3 points each

1.) Determining Soils by Feel: Indicate the following from the two soils you described.

a. Soil 1 General Location:
Texture:
Picture:

b. Soil 2 General Location:
Texture:
Picture:

2.) Name the master soil horizons and a few of their general characteristics.

3.) Define soil texture including the sizes of each particle.

4.) Why might I want to know about the soil texture of a plot of land before I purchased

it to build a new home?

5.) Name the 12 soil textural size classes; how are they determined.

6.) Explain the process of how one might determine a soil was a silty clay loam? (Hint:

Flow chart for determining soil texture by feel.)

7.) Which soil textural class might be described as having medium-to-high organic

matter and water holding capacity, is highly susceptible to soil erosion, has medium

drainage rates and a low shrink –swell potential (Text, Table 4.1)?

8.) In what horizon might one find blocky structure in soils?

9.) Define three processes by which soil structure or aggregation is formed.

10.) Why is soil structure important? Name management practices that might help

maintain soil structure.

11.) Why do soil scientists need a standard system to characterize soil color?

12.) Explain briefly the Munsell color chart and its three major components.