Types by Texture. Soil Isn t a Dirty Word. Purpose Students will learn about soil texture and determine the textures of several soil samples.

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1 Types by Texture Soil Isn t a Dirty Word Purpose Students will learn about soil texture and determine the textures of several soil samples. Time: 1 1½ hours Grade Level: Middle Materials Soil samples brought in by students from home, cleaned of rocks, roots, etc. (about 1 cup) Quart jars Rulers Alum (optional) Soil samples of sand, silt, and clay (available online at utahagclassroom.org; search soil samples) Dirt Shake handout Soil Texture Triangle handout Small bowls Spoons Water Bucket Newspaper Background Soil is the foundation of agriculture. Farmers know that different soils are suitable for different crops, but how do they recognize what type of soil they have? Texture is an easily recognizable property that informs farmers about how to manage their soils. Soil texture cannot be changed, and it affects the movement of water and nutrients in the root zone of plants. Clayey soils hold water and nutrients, while sandy soils drain and dry out quickly. Farmers will make different decisions about irrigation, tillage, and what type of crop to plant based on the texture of their soil. With some practice anyone can learn to recognize different soil textures by feel. Soil is made up of four components: air, water, organic matter, and mineral matter. The mineral component, made of tiny particles of rock, determines the texture of the soil. Soil particles are categorized according to their size as sand, silt, or clay. Sand is the largest category, including particles that measure 2.0 to 0.05 mm. Silt particles measure between 0.05 and mm, and clay particles are less than mm.* Most soils are a mixture of sand, silt, and clay. When the three particles are present in approximately equal amounts, the soil is considered a loam. A soil that has more sand in it is a sandy loam, one with more silt is a silty loam, and one with more clay is a clay loam. The Soil Texture Triangle provides standardized soil textural classes based on the relative quantities of sand, silt, and clay particles in a soil. The first activity in this lesson is a hydrology test that uses water to separate soil particles. This is a quick, simple method to assess soil texture. Sand is the largest, heaviest, and most dense particle, so it will settle out of the water first within one minute. Silt, the next largest particle, will settle out in three to four hours, and clay will take days to completely settle. The layers may be easy or difficult to see, depending on the mineral composition of the soil. Soil color is not directly related to texture. Some red soils have a greater fraction of clay particles than others. Scientific laboratories shake soil samples in water for 24 hours to ensure that tiny clay particles are thoroughly separated. Two minutes of shaking is sufficient for a classroom experiment, and alum can be added to improve separation. Organic matter will separate out as debris floating on top of the water. Soil texture is based on the mineral component of the soil and does not include organic matter. When texturing soil samples by hand, students should use the following criteria: sand feels gritty; silt feels smooth, soft, and somewhat slick, like the smooth silkiness of baby powder; clay feels sticky and often stains the fingers. Soil samples containing a lot of clay can be pressed together through the thumb and forefinger to create a ribbon of soil. If the soil doesn t contain much clay, the ribbon will break before it gets very long. Clay soils stick together. This can also be demonstrated by forming a ball out of the soil and testing how much pressure is needed to break the ball sandy soils will break apart easily, clay soils will resist breaking. Many people are familiar with pottery clay. Clay soil is stickier than pottery clay but will hold together in a similar fashion. You cannot determine soil texture by color or where it is found in the soil profile, but by feeling the soil or conducting the simple hydrology test described here, you can easily identify the texture of a soil. Utah Agriculture in the Classroom 1 utah.agclassroom.org

2 Vocabulary sand: soil particle that measures between 2.00 and 0.05 mm silt: soil particle that is between 0.05 and mm clay: soil particle less than mm loam: a mixture of sand, silt, and clay; see the Soil Texture Triangle for more detail Activity Procedures Activity 1: Dirt Shake 1. Divide the students into groups of three or four. Provide each group with a soil sample or instruct each group to use one of the samples brought from home. Two notes: This activity will not work with most potting soil. Soil texture is an evaluation of the mineral component of soil; potting soil is mostly organic matter. Remove rocks, roots, and anything else that is clearly not soil from samples and break up any large clumps before beginning. 2. Provide each group with a quart jar. Instruct the students to place 2" to 4" of soil into the jar, measure the level of soil, and record the measurement as total soil. It s important to measure and record the depth you start with so that you can accurately estimate the sand, silt, and clay fractions. 3. Add water until the jar is two-thirds to three-fourths full. Add one teaspoon of alum (found on the spice aisle of most grocery stores; it does help the soil settle faster, but is not necessary). Be sure the lid is tight. 4. Shake the jar vigorously until all the particles have been separated by the water, about two minutes. Set the jar down, and allow the soil to settle. 5. After 1 minute, measure the amount of soil on the bottom of the jar. Record this measurement and label it as the sand fraction. Share the Dirt Shake and Soil Texture Triangle handouts with the students. 6. Allow the sample to settle for 3 to 4 hours, then measure again and record the level. This second layer indicates the silt fraction of your soil. 7. The remaining clay particles may take as long as a week to settle depending on the composition of the sample. However, you can use the measurements you already have to determine the amount of clay in the soil. Simply subtract the combined sand and silt measurements form the total soil measurement as shown below. Organic matter will float on the surface of the water. Generally it is a small component that won t affect your measurements, but if there is a floating organic layer large enough to measure, subtract its measurement from the total soil before calculating the clay fraction and before moving on to calculate percentages. Total soil = 2" Sand fraction (first layer) = 1" Silt fraction (second layer) = ½" Clay fraction (total soil sand+silt) = ½" 8. Now convert the measurements into percentages as shown here: Sand percentage (sand / total soil x 100) = (1 2) x 100 = 50% Silt percentage (silt / total soil x 100) = (½ 2) x 100 = 25% Clay percentage (clay / total soil x 100) = (½ 2) x 100 = 25% Utah Agriculture in the Classroom 2 utah.agclassroom.org

3 9. Once you know these percentages, use the Texture Triangle handout to determine the name of the soil type. 10. Discuss the following questions: Why do the larger particles settle out first? What is the stuff floating in the jar? How does each person s sample compare? Activity 2: Soil Textures By Feel 1. Place four soil samples of at least three different textural types (sand, silt, clay, and loamy) into four separate bowls. Samples of sand, silt, and clay can be obtained from Utah Agriculture in the Classroom (see Materials). Note: Samples can be reused if allowed to dry after each use. In each subsequent use, the samples can be moistened to a paste and textured as explained. To show students what the soils look like dry, use a mortar and pestle (a wooden dowel or carriage bolt and plastic bowl will work) to pulverize the sample to its original loose state. 2. Share the Soil Texture Triangle handout with students. Show them that there are different names for different types of soil. It will be the task of your students to determine the texture of the supplied soil samples. 3. Explain how the different soil textures feel using the information found near the end of the Background section. Tell the students that they will be determining the texture of each soil sample by feeling it. Explain that each sample is different. 4. Moisten soils to the consistency of pasty mud. Do not get them too wet. 5. Divide the class into groups of four. Invite each group, one at a time, back to the table where the soil samples are set up in the bowls on newspaper. Note: You may want an activity for students to do independently at their desks while waiting for their turn with the soil samples. Four soil-themed activity sheets are attached for this purpose. The teacher should try to remain with the texturing group as much as possible to guide them through the activity and answer questions. 6. Each student should place about a teaspoon of the mud into the palm of his or her hand. Instruct students to rub the soil between their index fingers and thumbs, feeling for the presence of sand, silt, and clay. Two notes: Hands must be rinsed between samples to prevent the samples from being contaminated and changing the feel, which will confuse the next students who use the samples. To avoid a mess, cover the entire working surface with newspaper and place a bucket of water in the middle of the table for rinsing hands. Have paper towels available. As much of the sample as possible should be returned to the sample bowl before rinsing hands. 7. As they continue to feel the samples, ask students to evaluate how much sand, silt, or clay is present. Students should record their analysis of the soil based on the names provided in the Soil Texture Triangle. 8. After all students have felt and examined the soils, discuss their findings and tell them the actual textures of the samples. 9. Discuss the following questions: What is the name of a soil that contains a mixture of sand, silt, and clay? How do sand, silt, and clay feel? How can you tell them apart? What are their similarities and differences? Utah Agriculture in the Classroom 3 utah.agclassroom.org

4 Dirt Shake Organic matter Suspended particles Clay Silt Sand Particle Size This illustration shows relative particle sizes of sand, silt, and clay. Silt and clay cannot be seen with the naked eye, but sand can. Sand Silt Clay

5 Soil Texture Triangle To find the texture of your soil, read percentages of sand, silt, and clay in the direction of the arrows at the sides. For example, a soil with 20% clay and 40% each of sand and silt is a loam.

6 ACROSS DOWN 1. soil, water, forests, minerals, wildlife, fish things found in nature (two words) 4. artificial lake where water is stored 6. weathered particles that become soil 7. natural mixture of minerals, organic matter, water and air that forms land surface 9. liquid we need to live that covers most of the earth 11. loosening and movement of soil by water, ice, landslides and wind 12. science of the history of the earth 1. food that helps soil grow 2. any living being (people, animals, or insects) 3. everything that surrounds us 5. wise use and protection of soil and water 8. planet we live on 10. material deposited by water, glaciers and wind Hint: use the glossary to help solve the puzzle

7 GLOSSARY of soil and water terms conservation wise use and protection of our natural resources ecology science of the relationships between plants, animals and their environments environment everything that surrounds us erosion loosening and movement of soil by wind, water, ice and landslides geology science of the history of the earth habitat an area in which plants and animals live, grow and reproduce mineral (a natural resource) an inorganic substance with definite chemical and physical properties and definite crystal structure natural resources found in nature -- soil, minerals, forests, water, fish, wildlife nutrient something that provides nourishment for an organism to live (it can be food or chemicals) organic matter plant and animal materials in different stages of decay (decomposition) that may be part of the soil organism a living being (people, animals and insects are all organisms) particle a very small piece or part of something bigger reservoir a body of water (often a lake) in which water is collected or stored sediment bits of sand, soil, pebbles and other material deposited by wind, water and glaciers that washes into rivers, lakes and oceans and piles up layer on top of layer soil a naturally occurring mixture of minerals, organic matter, water and air that forms the surface of the land weathering breaking down of rock by wind, water and living things wetlands freshwater or saltwater areas (swamps, bogs, marshes) with waterlogged soils or that are covered with a shallow layer of water

8 Hidden Words In Soil ANIMALS BIOME CLAY COMPOST CONSERVATION EROSION FARMS HABITAT INSECTS LEAVES MULCH PLANTS ROCK ROOT SAND SEED SOIL TREES WORMS

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10 WEATHERING AWAY In the coded message below, find out what helps make soil. Write the letter of each picture clue under the same picture in the puzzle.

11 Soil and Water Crossword Across 1. natural resources 4. reservoir 6. rocks 7. soil 9. water 11. erosion 12. geology Down 1. nutrients 2. organism 3. environment 5. conservation 8. earth 10. sediment Hidden Words in Soil Word Search Messages in Soil Beneath My Feet GRAZING ANIMALS CROPS NATURE AREAS CONSTRUCTION DAIRY OR OTHER FARMS GARDENS Decoding in Weathering Away SOILS FORM SLOWLY FROM ROCKS BROKEN DOWN BY WEATHERING TEMPERATURE CHANGE AND ICE HELP TO MAKE SOIL