Soil Characterization Protocol

Background information

This protocol is for characterizing soils in the field near (but not in) the BeSt experiment plots. After digging a hole or using a sampler to collect a soil core, you will measure the depths of each distinct layer of soil, or horizon. You will look at the soil horizons, as well as individual peds of soil to learn about various characteristics of the soil including the texture, color and consistence. All of these characteristics help determine how well plants can grow in the soil.

Timeline/Frequency

This protocol for soil characterization should be completed at least once in the first year of the BioEnergy SusTainability experiment near each “block” (set of eight experimental plots). It can be done at any time of the year, but fall or spring is preferable.

Vocabulary Words: Horizon: A specific layer in the soil that is horizontal to the soil surface and has different

characteristics from the layers below or above it. The size, or depth, of a soil horizon can vary—it can be as thin as a centimeter, or meters thick, depending on the soil.

Ped: A single unit of soil. The size of a ped can vary. Some soils are very chunky and stuck together, and can have big golf-ball size peds (see photo below). In many soils, the peds are smaller and about a centimeter or so in diameter. In some soils, like pure sand, the particles do not stick together at all and there are no soil peds.

Soil Horizons

(source: www.sparknotes.com )Soil Horizons

(source: www.sparknotes.com ) Soil Peds

(photo: CA soil resource lab)Soil Peds

(photo: CA soil resource lab)

Materials

Site maps labeled with block and plot numbers Soil Characterization Data Sheet Clipboards Pencils Shovel/gardening trowel OR a soil corer

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Meter stick or metric tape measure Water bottle: Plastic squirt bottle filled with water Nitrile or rubber gloves Acid bottle: Plastic squirt bottle filled with vinegar Digital camera (optional)

Teacher Preparation

Before sampling, decide if you will dig a hole or use a soil corer to investigate your soils (see “Looking at Soil Horizons” below), and either delete the instructions that don’t apply to your students, or show them which set of instructions to follow.

Also decide if you will divide the class into smaller groups or sample as a whole class. If you divide into smaller groups, each group will need one adult to model some of the steps (like digging a hole/taking a core). You will also need tell each smaller group where to go to characterize the soil, so that groups aren’t too close together. For the BeSt experimental plots, this only needs to be done in at least one spot near each block of 8 plots. But, if it is done in more than one spot near the plots then that’s OK.

If possible, it would be informative to students to do this protocol once near the BeSt experimental plots and once in an area where soils are less disturbed from things like past construction, like a natural forest or grassland. The students can compare and contrast the data they get from these two places.

Instructions

Looking at Soil Horizons1. Go to a spot that is about two meters away from the BeSt experimental plots where the surface of

the soil can be exposed and you are not in another research plot. For example, see this picture:

SchoolSchool BeStBeStPlotsPlots

Soil CharacterizationSpot

About 2 metersSchoolSchool BeStBeSt

PlotsPlots

Soil CharacterizationSpot

About 2 meters

2. Mark approximately where you are on your Site Map by drawing a star. 3. If you have a GPS, record your coordinates on the BEST Soil Sampling & Characterization Data

Sheet next to “Soil Characterization Location”. If you do not have a GPS, then ignore this step.4. Decide if you are looking at the soil in this spot by digging a hole or taking a soil core. If you are

digging a hole, follow the instructions under “Digging A Hole Method.” If you are taking a core, follow the instructions under “Taking a Core Method”

Digging A Hole Method: Identifying and Measuring Horizons1. Remove the surface vegetation (push aside grass, dead leaves, or other plants) and use a

garden trowel or shovel to carefully remove the top 10 cm of soil from a small area and set it on the ground

2. If you can dig deeper, remove the soil up to 50 cm deep. Remove 10 cm of soil at a time, and place the soil you removed in piles on the ground in the order that you dig it out.

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3. Record the total depth of the hole you have just dug (your “soil characterization pit”) on your Soil Characterization Data Sheet next to “Soil Characterization Pit Depth (cm).” Ignore the place on the data sheet that says “Soil Core Depth (cm).”

4. Look at the side of hole for layers in the soil by looking at the colors of the soil, the texture of the soil, and what is in the soil. These layers are called soil horizons. For example, you might see a layer of brown soil on top of a layer of more gray, sandy soil.

5. Number the horizons from the top to the bottom so that the top horizon is Horizon 1, the next horizon down is Horizon 2, and so on. On your Soil Characterization Data Sheet write down the number, top depth, and bottom depth of each soil horizon.

Taking a Core Method: Identifying and Measuring Horizons1. Remove the surface vegetation by pushing aside grass, dead leaves, or other plants.2. Use your soil corer to take a soil core. When you take a soil core, you are removing a thin

cylinder of soil from a specific spot. This allows you to look at the layers of soil without digging a big hole.

3. Record the total depth of the soil core you removed on your Soil Characterization Data Sheet next to “Soil Core Depth (cm).” Ignore the place on the data sheet that says “Soil Characterization Pit Depth (cm).”

4. Look at the your soil core for layers in the soil by looking at the colors of the soil, the texture of the soil, and what is in the soil. These layers are called soil horizons. For example, you might see a layer of brown soil on top of a layer of more gray, sandy soil.

5. Number the horizons from the top to the bottom so that the top horizon is Horizon 1, the next horizon down is Horizon 2, and so on. On your Soil Characterization Data Sheet write down the number, top depth, and bottom depth of each soil horizon.

Measuring Structure: 1. Remove some soil sample with your hand from Horizon 1 or the pile of soil that was taken from

Horizon 1. 2. Hold it gently in your hand and look closely to examine its structure. 3. Look at Figure 1 (on page 4) to come to a consensus with other students on the type of soil

structure of the horizon, and record this on your data sheet next to “Structure”. 4. Repeat this step with the remaining soil horizons

Observing Color: 1. Take a ped (a hunk of soil, see “vocabulary” section above) of soil from Horizon 1 and record

whether it is moist, dry, or wet on your data sheet. 2. If it is dry, moisten it slightly with water from your water bottle. 3. Break the ped and look at its color. 4. Is it mostly brown? Grey? Red? Write this down on your data sheet next to “Color(s).” If there is

more than one color present, record all the colors you see.5. Repeat steps 1-4 for the other soil horizons

Measuring Soil Consistence. 1. Take a ped from soil Horizon 1. 2. Holding the ped between your thumb and forefinger, gently squeeze until it pops or falls apart. 3. Using the pictures in Figure 2 (on page 5), record which one of the four categories best describes

the hardness, or consistence, of this soil ped on your data sheet next to “Consistence”.4. Repeat steps 1-3 for the other soil horizons

Measuring Soil Texture: Follow these steps to determine the texture of soil in each horizon:

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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.

2. Place the ball of soil between your thumb and index finger and gently push and squeeze it into a ribbon (a long, thin strip that looks like a hair 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.

3. If the soil: a. Is very sticky, hard to squeeze, stains your hands, has a shine when rubbed, and/or

forms a long ribbon (5+ cm) without breaking; call it a clay and go to Step 4.b. Is somewhat sticky, is somewhat hard to squeeze, and/or forms a medium ribbon

(between 2-5 cm); call it a clay loam and go to Step 4.c. Smooth, easy to squeeze, at most slightly sticky, and/or forms a short ribbon (less than 2

cm); call it a loam and go to Step 4.4. 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 and Roots:1. Observe and record if there are none, few or many rocks or rock fragments in each soil horizon.

Write this on your data sheet2. Observe and record if there are none, few, or many roots in each horizon, and record this on

your data sheet

Measuring Free Carbonates: 1. Set aside a portion of the exposed soil in the hole or in the core you removed to use for the free

carbonates test. Make sure not to touch it with your bare hands.2. Open the acid bottle and squirt vinegar on the soil particles, starting from the bottom of the profile

and moving up. Be sure to use caution and point the bottle directly at the soil, not toward other students, especially toward eyes. If vinegar gets into your eyes, rinse with water for 15 minutes.

3. Look carefully for the presence of effervescence, or bubbles. The more carbonates that are present, the more bubbles (effervescence) you will observe.

4. For each horizon, record on the Soil Characterization Data Sheet one of the following results:

None: if you observe no reaction, the soil has no free carbonates presentSlight: if you observe a very slight bubbling action, this indicates the presence of some

carbonates

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Strong: if there is a strong reaction (many and/or large bubbles) this indicates that many carbonates are present.

Photographing the Soil Profile: 1. If you have a camera, place a tape measure or meter stick starting from the top of the soil profile. 2. With the sun at your back, photograph the soil profile so that the horizons and depths can be

seen clearly. 3. Take a photograph of the landscape around the soil profile.

Cleaning Up1. Do your best to replace the soil that you sampled: fill the hole back in with the soil that you

dug from it or take the soil out of your corer and return it to the hole you took the core from.2. Look around to make sure that you take all of your sampling equipment and data sheets back

to the classroom

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Figure 1: Measuring Soil Structure

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Figure 2: Measuring Soil Consistence

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Soil Characterization Data Sheet

School District: ______________________ Instructor/Fellow: ____________________

Date: _______________ Time: ________Weather: ____________________________

Soil Characterization

Soil Characterization Location: _______________________________________

Horizon Number: _________ Top depth (cm): ____ Bottom depth (cm):_____

Moisture (wet, dry, moist): _____________

Structure (granular, blocky, platy, prismatic, columnar, single grained, massive):____________________________________

Color(s) ________________________________________________

Consistence (loose, friable, firm, extremely firm):________________

Texture:_________________________________________-

Rocks (none, few, many): __________________________________

Roots (none, few, many): __________________________________

Carbonates (none, slight, strong): ____________________________

Other notes (animals?): _____________________________________________________________________________________________________________________________________________________

Horizon Number: _________ Top depth (cm): ____ Bottom depth (cm):_____

Moisture (wet, dry, moist): _____________

Structure (granular, blocky, platy, prismatic, columnar, single grained, massive):____________________________________

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Color(s) ________________________________________________

Consistence (loose, friable, firm, extremely firm):________________

Texture:_________________________________________-

Rocks (none, few, many): __________________________________

Roots (none, few, many): __________________________________

Carbonates (none, slight, strong): ____________________________

Other notes (animals?): _____________________________________________________________________________________________________________________________________________________

Horizon Number: _________ Top depth (cm): ____ Bottom depth (cm):_____

Moisture (wet, dry, moist): _____________

Structure (granular, blocky, platy, prismatic, columnar, single grained, massive):____________________________________

Color(s) ________________________________________________

Consistence (loose, friable, firm, extremely firm):________________

Texture:_________________________________________-

Rocks (none, few, many): __________________________________

Roots (none, few, many): __________________________________

Carbonates (none, slight, strong): ____________________________

Other notes (animals?): ____________________________________________________________________________________________________________________________________________________

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