THE RELATIVE SIZE OF SAND,SILT, AND CLAY - PDF document

THE RELATIVE SIZE OF SAND,SILT, AND CLAY ©2003 Project Food, Land & People sand silt clayarms outstretchedhands on hips,arms at yourfrom shoulderbent at theside3.Have all the ÒparticleÓ students represent ÒsandÓwith their arms outstretched. They should stand indegrees without hitting another student. (You mayneed to arrange some of the students.) Tell studentstheir outstretched arms represent the largeness of aparticles represents pore space. These ÒlivingÓspaces in nature are filled with air, water or livingorganisms. Place the string on the floor around all4.Add the Òwater dropletÓ students. Have them passthe Òwater dropletsÓ arenÕt allowed to go ar oundthe Òparticles,Ó but they must pass thr Òwater dropletsÓ to push their arms slightly to pass5.Discuss briefly the relative ease with which theÒwater dropletsÓ passed through the large pore6.Next have all the ÒparticleÓ students represent ÒsiltÓparticles by placing hands on their hips with armseach other with elbows just touching each other.arms of the particles.7.Discuss the differences in water movement throughpercolation, however, is reduced when all the pores arefull of water, causing the soil to be saturated. Unfortu-soil, increasing the possibility of soil erosion andThe porosity of the soil - the available pore space of asoil type - determines how quickly water will moveparticles. Gravity pulls the rest of the water, called freewater, downward. The water held by soil particles isAlong with farmers, city and town planners are con-cerned with soil texture and porosity. A heavy clay soilPercolation and other soil tests help city and townthese tests, they can learn if there is too much clay inGETTING STARTEDHave students bring in soil samples from home or anearby area; gather one (or more) empty, clear, plastic1-liter soda bottle with lid, water, string, and magnifying 1.Ask the students what they know about soil andplace. Explain that they are going to learn about2.Explain that students are going to pretend tosoil particle sizes and pore spaces between thethat they will use arm actions to represent each soilparticle. Draw these three stick people figures in a 163 ©2003 Project Food, Land & People 8.Finally, have all the ÒparticleÓ studentsrepresent ÒclayÓ particles by standing withtheir arms at their sides and touching theparticles will be bunched in together. Addthe Òwater dropletÓ students. The dropletspass through the particles by moving twoswelling action of clay. Water dropletseither removed by plant roots or9.Explain to students that when waterdry soil particle actually holds some water.water plants ÒdrinkÓ (suck up) with their roots.10.Ask students to discuss the differences in:ease of Òwater dropletsÓ passing through the up less room in the flower pot than the ÒsiltÓ(The ÒclayÓ particle size and porespace between particles are smaller.)less room in the flower pot than the ÒsandÓ(The ÒsiltÓ particle size and porespace between particles are smaller.)11.Have the ÒparticleÓ students, still in the flower pot,particles by adjusting their arm actions and theparticles. (Be sure that the different particles arethe arm positions of the particles, if the flowerpotÕs soil has a sandy, silty, or clayey texture. Ispore space is directly related to the proportionof particle sizes in the soil. (More clay particlessand means larger total pore space. You canadd the Òwater dropletÓ students to themixtures to aid in the understanding of poredropletsÓ to pass through the pore spacesor in the mixtures you created?hich soil type does water move throughSoils in nature are usually a mixture of the threeholds less water for plants and dries out morerapidly. Water moves through clay soils veryslowly and may cause plants to suffocate bydrowning the roots. Play areas in sandy soilsareas on clay soils would be wet a long timeand swell and may break up things built on 1.Distribute the 2.Add several handsful of one soil sample to the 1-liter soda bottle and fill it with water. (Break up anyclumps of soil before adding the water. Adding afew drops of detergent may help to break the clayaggregates [clumps] so they perform like individualon a table where students can observe the soil ©2003 Project Food, Land & People164 3.Discuss with students the fact that a typical soilamounts. Water allowed us to separate theparticles. Use the diagram showing the relative sizeof the particles (see Supporting Information).(Organic matter [e.g., plant and animal5.Students can identify a soilÕs texture bysoil samples in their hand, add water dropletsidentification exists when the soil stays together.information on students agree with the assignedThere are several commercially available types of and Permoplast Molding Clay, that areavailable, have students investigate its texture andwater to it. Ask, ÒWhat are some similarities and6.To increase students' understanding of soil particleEVALUATION OPTIONS1.Evaluate studentsÕ 2.Have students fold a piece of paper into thirds and3.Give students a handful of soil. Have them identifythe sampleÕs general texture of sand, silt or clay,4.Have students imagine they had three flower pots,Which pot has the smallest pore space, the largest?EXTENSIONS AND VARIATIONS1.Have students demonstrate porosity. Porosity, theavailable pore space in a soil, and water-holdingcapacity vary from one soil type to another.Porosity determines how fast water will move 165 ©2003 Project Food, Land & People A.Assemble four clear plastic cups. Punch severalB.Put an equal amount of two different types ofone cup and a sandy soil in the other.) WhichC.Pour equal amounts of water onto the soil in2.Have a student contact the office of the countyrequired before any new construction can be3.Invite a soil scientist from your local conservationprofiles or pictures of them, if4.Place different-size metalequal amount of water.5.See the FLP lesson ÒTill We or WonÕt We?Ó tolearn about soil formation, soil erosion, and soilLifeÓ to learn about the importance of roots to soil.See the FLP lesson ÒFrom Apple Cores to HealthySoilÓ to learn about soil nutrients and composting.ment of Agriculture, Natural Resources Conservation. GarethBryant-Mole, Karen. . Raintree Steck-Vaughn.. Raintree Steck-Vaughn.. NSTA Press.National Science Teachers Association. 2001. Flanagan, Alice, Linda Labbo, Terrance Young. Kohnke, Helmut, D.P. Franzmeier. . Waveland Press. 1994.Lachner, Michelle Myers. . MillbrookMurray, Peter. Dirt, Wonderful Dirt! ChildÕs World,Petty, Kate, Chris Fairclough. . Watt Franklin.Environmental. Raintree Steck-Vaughn. 1994.Sumner, M.E., editor. EDUCATOR'S NOTES Conceptual Framework Reference: I.B.1.,I.C.3, II.A.2.c., ©2003 Project Food, Land & PeoplePerc Through the Pores 1.Your teacher will mix soil and water in a clear2.What is happening to the soil particles and water in the bottle immediately aftershaking? Record your observations her3.What is happening in the bottle 30 minutes after shaking? Is anything floating?4.Observe the plastic bottle the next day. What happened? RecorDraw a picture of your prediction here. ©2003 Project Food, Land & PeoplePerc Through the Poresou and your partner(s) are going to discover the general texture of a soil sample.1.Place a small amount of soil from your soil sample in your hand, add drops of water slowly, and knead the soilto break up any clumps. When the soil is moist, not wet, it is ready to identify.2.The soil texture is feels smooth like flour,is not really sticky, andforms a short snake and then breaks apart when rolled between hands.forms a long snake when rolled between hands.3.Our soil sample is mostly _________________. We know this because4.Using a hand lens or magnifying glass, describe your sample (draw a picture too).5.With another group, compare your samples. How are they the same? Different? THE RELATIVE SIZE OFSAND, SILT AND CLAYSILTCLAY