Soil Characterization Protocol

Field Guide

Task

Identify, measure and record the horizons in a soil profile at a Soil Characterization Site. Measure and record the physical and chemical properties that characterize each horizon. Photograph the soil profile. Collect soil samples from each horizon.

What You Need

1. Spray mist bottle full of water
2. Acid bottle filled with distilled vinegar
3. Golf tees, nails or other marking device that can be pushed into a soil horizon  
4. Soil Characterization Data Sheet
5. Trowel, shovel, or other digging device   
6. Pencil or pen or other method of recording data
7. Soil color book
8. Paper towels
9. Marking pen      
10. Meter stick or tape measure
11. Camera            
12. Rolling pin, hammer, or other utensil for crushing peds and separating particles

In the Field

Identifying and Measuring Horizons

1. Make sure the sun shines on the profile if possible.
2. Use a trowel to scrape a few centimeters of soil off of the profile to expose a fresh soil face.
3. Determine whether the soil profile is moist, wet, or dry by lightly placing your hands on the Soil face. If the soil profile is dry, moisten it with the spray mist bottle.
4. Start at the top of the profile and observe the characteristics of the soil moving towards the bottom of the profile.
5. Feel carefully at the soil profile for distinguishing characteristics such as texture, shapes, roots, rocks, small dark nodules, worms, small animals, insects, and worm channels. These observations will help to define the horizons.
6. Working in a straight vertical line, place a marker (such as a golf tee or nail) at the top and bottom of each horizon to clearly identify it. Be sure there is a consensus from all of the students regarding the depths of the soil horizons.
7. Measure the top and bottom depth of each horizon beginning at the top (surface) of the profile. Start with the meter stick or tape measure at 0 cm at the top of the profile. Note the depths at which each horizon starts and ends.
8. Record the top and bottom depth of each horizon on the Soil Characterization Data Sheet.

Measuring Structure

1. Use a trowel or other digging device to remove a sample of soil from the horizon being studied.
2. Hold the sample gently in your hand and look closely at the soil to examine its structure.
3. Come to a consensus with other students in the group on the type of soil structure of the horizon. Possible choices of soil structure are:
   • 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: Vertical columns of soil that have a white, rounded 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.

IN certain cases, soil samples may have no structure.   These would be classified as either:

• Single Grained: Soil is broken into individual particles that do not stick together. Always accompanies a loose consistence. Commonly found in sandy soils.
• Massive: Soil has no visible structure, is hard to break apart and appears in very large clods.

4. Record the structure type on the Soil Characterization Data Sheet.

Measuring Main Color and Second Color

1. Take a ped from the horizon being studied and note whether it is moist, dry, or wet. If it is dry, moisten it slightly with water from your water bottle.
2. Break the ped and hold it next to the color chart.
3. Stand with the sun over your shoulder so that sunlight shines on the color chart and the soil sample you are examining.
4. Find the color on the color chart that most closely matches the color of the inside surface of the ped. Be sure that all students agree on the choice of color.
5. Record on the Soil Characterization Data Sheet the symbol of the color on the chart that most closely matches the soil color that covers the largest area of the ped (dominant or main color). Sometimes, a soil sample may have more than one color. Record a maximum of two colors if necessary, and indicate (1) the dominant (main) color, and (2) the sub-dominant (second) color.

Measuring Soil Consistence

1. Take a ped from the soil horizon being studied. If the soil is very dry, moisten the face of the profile by squirting water on it, and then remove a ped for determining consistence.
2. Holding the ped between your thumb and forefinger, gently squeeze it until it pops or falls apart.
3. Record one of the following categories of soil ped consistence on the Soil Characterization Data Sheet.
   • Loose: You have trouble picking out a single ped and the structure falls apart before you handle it. Note: Soils with single grained structure always have loose consistence .
   • Friable: The ped breaks with a small amount of pressure.
   • Firm: The ped breaks when you apply a good amount of pressure and the ped dents your fingers before it breaks.
   • Extremely Firm: The ped can't be crushed with your fingers (you need a hammer!)

Measuring Soil Texture

Step 1

• Place some soil from a horizon (about the size of a small egg) in your hand and use the spray mist bottle to moisten the soil. Let the water soak into the soil and then work it between your fingers until it is thoroughly moist. 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, call it a sand . Soil texture is complete. Record the texture onto the Soil Characterization Data Sheet.

Step 2

• Place the ball of soil between your thumb and index finger and gently push and squeeze it into a ribbon. If you can make a ribbon that is longer than 2.5 cm, go to Step 3. If the ribbon breaks apart before it reaches 2.5 cm, call it a loamy sand . Soil texture is complete. Record the texture onto the Soil Characterization Data Sheet.

Step 3

• If the soil:
  • Is very 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 4.

 

• Otherwise, 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 4.
• Otherwise, If the soil is:
  • Smooth
  • Easy to squeeze,
  • At most slightly sticky,
  • Forms a short ribbon (less than 2 cm)
• Call it a loam and go to Step 4.

Step 4

• Wet a small pinch of the soil in your palm and rub it with a forefinger. If the soil:
  • Feels very gritty every time you squeeze the soil, go to A.
  • Feels very smooth, with no gritty feeling, go to B.
  • Feels only a little gritty, go to C.

  A. Add the word sandy to the initial classification.

  • Soil texture is either:
    • sandy clay,
    • sandy clay loam, or
    • sandy loam
  • Soil Texture is complete. Record the texture onto the Soil Characterization Data Sheet.

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

  • Soil texture is either:
    • silty clay,
    • silty clay loam, or
    • silt loam
  • Soil Texture is complete. Record the texture onto the Soil Characterization Data Sheet.

  C. Leave the original classification.

  • Soil texture is either:
    • clay, clay loam, or loam
  • Soil Texture is complete. Record the texture onto the Soil Characterization Data Sheet.

Measuring Rocks

1. Place your hands on the surface of the profile and feel for the presence of rocks along the face of the profile that you are studying. Observe and record if there are none, few, or many rocks or rock fragments in the horizon. A rock or rock fragment is defined as being larger than 2 mm in size.
2. Record your observation on the Soil Characterization Data Sheet.

Measuring Roots

1. Place your hands on the surface of the profile and feel for the presence of roots along the face of the profile that you are studying. Observe if there are none, few, or many roots in each horizon.
2. Record your observation on the Soil Characterization Data Sheet.

Photographing the Soil Profile

1. Place a tape measure or meter stick starting with 0cm from the top of the soil profile next to where the horizons have been marked.
2. With the sun at your back, photograph the soil profile so that the horizons and depths can be seen clearly.
3. Take another photograph of the landscape around the soil profile.
4. Submit photos to GLOBE following directions outlined in the How to Submit Photos and Maps section of the Implementation Guide.