Guide, Part 2: Horizon Properties

Soil Characterization Step-by-Step Guide, Part 2: Horizon Properties
 

Soil Structure

Soil structure is the shape that the soil takes based on its physical and chemical properties. Each individual unit of soil structure is called a ped. Take a sample of undisturbed soil in your hand (either from the pit or from the shovel or auger). Look closely at the soil in your hand and examine its structure. Possible choices of soil structure are:

granular structure

prismatic structure
Granular: Resembles cookie crumbs and is usually less than 0.5 cm in diameter. Commonly found in surface horizons where roots have been growing.
Blocky: Irregular blocks that are usually 1.5 - 5.0 cm in diameter.
Prismatic: Vertical columns of soil that might be a number of cm long. Usually found in lower horizons.
columnar structure
platy structure
singlegrained structure
Columnar: Vertical columns of soil that have a salt "cap" at the top. Found in soils of arid climates.
Platy: Thin, flat plates of soil that lie horizontally. Usually found in compacted soil.
Single Grained: Soil is broken into individual particles that do not stick together. Always accompanies a loose consistence. Commonly found in sandy soils.
massive structure
   
Massive: Soil has no visible structure, is hard to break apart and appears in very large clods.
   

If you wish download the protocol above so that you can use it in the field, here are pict files soil texture page 2.

Below are some images of the different soil structures.

With Structure:

granular
Granular

blocky
Blocky

prismatic
Prismatic
columnar
Columnar

Platy
Platy

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Structureless:

single grained
Single Grained

massive
Massive

 

 

 

 

 

 

 

 

 

 

 

Soil Color

 

spray ped
1. Take a ped of soil from each horizon and note on the data sheet whether it is moist, dry or wet. If it is dry, moisten it slightly with water from your water bottle.

break ped
2. Break the ped

test soil color against color book
3. Stand with the sun over your shoulder so that sunlight shines on the color chart and the soil sample you are examining.

Note: Sometimes, a soil sample may have more than one color. Record a maximum of two colors if necessary, and indicate (1) the Main (dominant color) and (2) the Other (sub-dominant color).

 

Soil Color, Continued

Munsell Notation

The Munsell code below each color in the GLOBE color chart is a universal notation that describes the soils' color.

Soil color book

hue, value, chroma in soil color book

The Munsell code below each color in the GLOBE color chart is a universal notation that describes the soils' color.

hue

 

 

 

 

 

 

 

 

Hue

The first set of number and letter symbols represents the hue. Hue represents the position of the color on the color wheel (Y=Yellow, R=Red, G=Green, B=Blue, YR=Yellow Red, RY=Red Yellow).

Munsell Notation: Value

The Munsell code below each color in the GLOBE color chart is a universal notation that describes the soils' color.

Shades of Gray (value)

 

 

 

 

 

 

 

 

 

 

Value

The number before the slash is the Value. Value indicates the lightness of a color. The scale of value ranges from 0 for pure black to 10 for pure white.

  

Munsell Notation, continued: Chroma

The Munsell code below each color in the GLOBE color chart is a universal notation that describes the soils' color. 

chroma

Chroma

The number after the slash is the Chroma. Chroma describes how the "intensity" of a color. Colors of low chroma values are sometimes called weak, while those of high chroma are said to be highly saturated, strong, or vivid. the scale starts at zero, for neutral colors, but there is no arbitrary end to the scale.

Soil Consistence

Take a ped from the top soil horizon. If the soil is very dry, moisten the face of the profile using a water bottle with a squirt top and then remove a ped to determine consistence.

(Repeat this procedure for each horizon in your profile.)

Holding it between your thumb and forefinger, gently squeeze the ped until it pops or falls apart. Record one of the following categories of soil consistence on the data sheet.

spraying sample

loose soil in hand

Loose

You have trouble picking out a single ped and the structure falls apart before you handle it.*

* Soils with "single grained" structure always have loose consistence.

 

 

 

hand popping soil ped

Friable

The ped breaks with a small amount of pressure.

 

 

 

 

 

 

hand squeezing soil pedFirm

The ped breaks when you apply a good amount of pressure and dents your fingers before it

 

 

 

 

 

  

hammer breaking soil ped

Extremely Firm

The ped can't be crushed with your fingers

 

 

 

 

 

 

 

Soil Texture

The way a soil "feels" is called the soil texture.

Soil texture depends on the amount of each size of particle in the soil.

Sand, silt, and clay are names that describe the size of individual particles in the soil.

Sand are the largest particles and they feel "gritty."

Silt are medium sized, and they feel soft, silky, or like flour.

Clay are the smallest sized particles, and they feel "sticky" and they are hard to squeeze.

Relative Size Comparison of Soil Particles

Barrel

Barrel

Sand (feels gritty)

(2.00 - 0.05 mm, USDA)
(2.00 - 0.02 mm, ISSS)

Plate

plate

Silt
(feels floury)

(0.05 - 0.002 mm, USDA) (0.02 - 0.002 mm, ISSS)

Coin

dime

Clay
(feels sticky)

 

(< 0.002 mm, USDA) (< 0.002 mm, ISSS)

Step 1 (Get and moisten sample)

    Use the triangle to determine the soil texture of your horizon. 

    Place some soil from a horizon (about the size of a small egg) in your hand, and, using the spray mist bottle, moisten the soil. Let the water soak in and then work the soil between your fingers until it is the same moisture throughout. Once the soil is moist, try to form a ball. If the soil forms a ball, go on to Step 2. If the soil does not form a ball, go to Step 5.

textural triangle: main selections

Step 2 (Test for Clay)

A. If the soil:

  • Is really sticky
  • Hard to squeeze
  • Stains your hands
  • Has a shine when rubbed
  • Forms a long ribbon (5+ cm) without breaking,

Call it a clay and go to Step 3.

    Otherwise, go to B.

B. If the soil: 

  • Is somewhat sticky
  • Is somewhat hard to squeeze 
  • Forms a medium ribbon (between 2-5 cm)

Call it a clay loam and go to Step 3. 

    Otherwise, go to C.

C. If the soil is:

  • Soft
  • Smooth
  • Easy to squeeze, 
  • At most slightly sticky,
  • Forms a short ribbon (less than 2 cm) 

Call it a loam and go to Step 3. 

    Otherwise, go to D.

D. If the soil forms a ball but no ribbon, go to Step 4. 

If you wish download the protocol above so that you can use it in the field, here is a jpg file: soil texture steps 1 & 2.

To Determine Soil Texture (Continued)

Step 3 (Refine initial soil texture classification from Step 2 for relative amounts of sand and silt) Wet a small pinch of the soil in your palm and rub it with a forefinger.

If the soil:

  • Feels very gritty, go to E
  • Feels very smooth, with no grittyfeeling, go to F
  • Feels only a little gritty, go to G

E. Add the word sandy to the initial classification.

Soil texture is (check one):

  • sandy clay,
  • sandy clay loam,
  • sandy loam

 

sandy clay loam, sandy clay, sandy loam


Soil Texture is complete.

F. Add the word silt or silty to the initial classification.

Soil texture is (check one):

  • silty clay,
  • silty clay loam,
  • silt loam

Soil Texture is complete.

 

silty clay, silty clay laom, silt loam triangle


Soil Texture is complete.

G. Leave the original classification of (check one):

  • clay,
  • clay loam,
  • loam

textural triangle main colors

Soil Texture is complete.

If you wish download the protocol above so that you can use it in the field, here is a jpg file: soil texture step 3.

To Determine Soil Texture (continued)

Step 4 (Test for loamy sand or silt) If the soil:

  • Forms a ball
  • Forms no ribbon
  • And is
      H. Very gritty
        Soil texture is:
        • loamy sand

          • Soil Texture is complete.

    Or
      I. Very soft and smooth with no gritty feeling,
        Soil texture is:
        • silt

          • Soil Texture is complete.

loamy sand/silt triangle

Step 5 (Test for sand) If the soil:

    Forms no ball and falls apart in your hand,
      Soil texture is:
      • sand

sand triangle

Soil Texture is complete.

If you wish to download the protocol above so that you can use it in the field, here is a jpg file: soil texture steps 4 & 5.

 

Presence of Roots and Rocks

roots

Presence of Roots

Observe and record if there are none, few, or many roots in the horizon.

 

rocks

 

Presence of Rocks

Observe and record if there are none, few, or manyrocks* in the horizon.

* A rock is defined as being larger than 2 mm in size.

Test for Free Carbonates

Free carbonates are compounds that coat soil particles. They form under certain conditions such as in dry climates where the pH is above 7. They are also found in some soil profiles that have parent materials made of carbonates (such as limestone).

This test is performed by squirting vinegar on the soil. If free carbonates are present, they will "effervesce" or bubble when the vinegar reacts with them. Record one of the following based on your observation:

free carb spraying

no reaction

None: you observe no reaction (the soil has no free carbonates).

slight reaction

Slight: you observe a slight amount of bubbling (the soil is coated with some carbonates).

strong reaction

Strong: you observe a strong reaction (many bubbles) (the soil has many carbonate coatings present).

Continue to part 3 of the Step-by-Step Guide: Soil Sampling