Ogden Nature Center

Adapted from Shelburne Farms Project Seasons, Deborah Parrella

Pre-Visit Activity, Grades 3+

Objective

• Students will learn soil is composed of different sized particles and organic material.
• Students will consider how these components influence water drainage and retention and the soil's ability to sustain life above and below the surface. 

Background

Most soils are a combination of sand (large, silt (medium) and clay (fine) particles.  Different types of soil are classified based on their percentages of these three particle size components.  Some soils are better than others for sustaining life above and below the ground.  Over time, the texture and composition of all soils can be altered by adding differing amounts of sand, silt or clay, plus compost and other organic materials. 

Materials

• Student soil samples (or 2-3 teacher collected samples)
• Sample bags of sand, silt, and clay (can be obtained from Natural Resource Conservation Service)
• Paper bags (grocery bag size)
• Paper cut-outs the size and shape of basketballs, baseballs, and small confetti dots (one each per student)
• Clear bottles or jars with labels removed and tight fitting lids (12 oz. or larger), one per student (students can bring from home) or one for each teacher collected sample
• Coffee filters
• Funnels 

Procedure

1. Ask students to bring in soil samples (approximately2 cups) from home or from any other location they have access to (from a camping trip, from a park, from a forest floor, near a beach).  Students should take notes about the area from which they take their sample:  Are there a lot of plants growing there?  Is there much animal life?  What does the area look like?  Have students compare and discuss differences in appearance and texture of their samples.  If younger students collect their own samples they can draw the area from which the soils came.  If you bring in 2 or 3 different samples to use as a class, describe the areas the samples came from.  Explain to the class that soil is a composition of organic materials and minerals of three main particle sizes. 
2. Set up the sample bags of sand, silt, and clay in a central location in the room, with an empty paper bag next to each sample.  Explain to the students that in three of the bags are soil samples of the tree main particle sizes.  For older students write "Soil Particle Size Chart" on the board and post one of each size circular paper cut-out with the real-life dimensions next to each:  small, less than .002 mm; medium, .005-.05 mm; large, .05-2.0 mm (you will add more information as the activity progresses).  Pass out one of each circular paper cut-out to each student.  Explain that these represent the three particle sizes and show the relative difference in sizes between particles.  Ask the students to feel the soil samples without looking in the bags and place the cut-out they think matches its relative size in the paper bag next to that sample. 
3. Review the cut-outs placed in each bag, then reveal the sample, from largest to smallest.  Ask students to identify the first sample with the largest particles by name (sand).  Add the name next to the size listing on your Soil Particle Size Chart.  Depending on the age of your students discuss some of the basic features of each soil type and its quality with respect to gardening and growing food.  Use the paper cut-outs as a visual aid to show how the different particles would fit together.  Show how the different sized particles would fit inside a square (drawn on the board), use the same size square to show that far more silt particles (the medium sized particles) could be packed tightly in the same space where only a few sand grains fit.  Note the amount of large air space between the sand particles indicating rapid drainage and the inability to hold much water or nutrients.  How do the silt particles differ?  They have medium air spaces, moderate to poor drainage and can hold some water.  Last, look at the clay note its poor drainage.  The particles are so fine that often water is unable to penetrate into the clay.  Clay expands when wet, further reducing space between particles.  Hard packed clay soils in a garden can be very difficult to work with. 
4. Younger students skip to Step 6.  Ask older students to conjecture what might make soil more amenable to life underground?  (mixture of different soil particle sizes to enable percolation, addition of organic materials to provide nutrients).  Explain that most soils are called loam, and are a combination of these particle sizes and organic material.  As a result, some soils are better than others for gardening.  Different types of soil are classified based on their percentages of these three particle size components (see Soil Classification Chart).  Over time, the texture and composition of all soils can be altered by adding differing amounts of sand, silt or clay, plus compost and other organic materials. 
5. Explain that students will determine the composition of their soil sample by using the "soil shake" method.  Soil is added to a container of water, then the mixture is shaken to disperse the particles.  How would they predict the three particles will settle?  (The particles separate by size and weight, and distinct layers can be observed when the soil completely settles).  Which particle type would be on the bottom?  In the middle?  On top?  (Sand settles first, then silt, and lastly clay) 
6. Older students can do this activity in pairs while younger students can work as a class.  Have each pair fill a bottle or jar 2/3 full with water.  Have them add one partner's soil to the jar until it is almost full and screw the lid on tightly.  Now they shake it for 2 minutes until the soil is well dispersed and the solution looks like a rich chocolate soil shake.  Have them set the jar in a level place and not disturb it for 24 hours.  Partners should repeat the process with the other partner's sample in a different jar.  Ask the students to predict which component will make up the greatest percentage of their soil samples. 
7. After 24 hours, have students observe the layers.  Older students should also carefully measure the layers without moving their jars.  How many layers do thy see?  Can they determine which layer is sand, which layer is silt, and which layer is clay?  Which layer is largest?  What else do they observe? Older students can draw a diagram of their soil shakes, showing the relative thicknesses of their layers and drawing the floating organic materials on top.  Older students can also calculate percentages using the simple formula:  the height of a layer divided by the height of entire sample equals the decimal fraction of the layer.  Multiply by 100 to get the percentage.  Have the students name their soil type using the Soil Particle Size Chart. 
8. Students who have cloudy water with residue floating in it, chose soils with organic materials.  Direct these students to carefully pour the water (without disturbing the settled soil) through a funnel lined with a coffee filter to collect the residue.  Have them examine the residue after it dries.  Remind them organic materials such as decomposing leaves, grasses, and animals, add nutrients to the soil and enable life to go on beneath and above the soil.  Would their soil be good for gardening?  Why or why not?  How could they improve its quality for gardening? 
9. When students are finished with their soil samples, direct them to empty them outside, not in the trash or in the sink.  Recycle the bottles and jars if possible.