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Soil Soakers

Objective:  Students will observe and measure the relationship between water holding and drainage capacities of soils.

Grade Level:  3-6

Groupings:  Small groups

Materials: (per group) Dry, diverse soil samples such as sand, clay, compost, garden soil, and peat moss; metal pie plate; glass lamp chimney, or clear plastic soda bottles with bottom cut off, or clear funnels; plastic window screening; rubber bands; 1-2 quart wide-mouth jar; masking tape; clear 8 oz. plastic cup; water.

Time Allotment:  30 minutes


Directions:

1. Challenge the students to collect unique soil samples from in and around their homes and garden. Suggest they talk to gardeners to obtain special mixes or soil types. Have them bring their sample to class in a brown paper lunch bag. Ask them to keep their soil composition a secret. You might want to bring a selection of soils yourself to insure a diverse mix. Possibilities include: potting soil, compost or composted cow manure, sand, peat moss, and clay.

2. Collect and observe the students' soil samples. Select four to six distinct samples to be used in the activity. Divide the students into small groups and assign a soil sample to each. Have each group empty their sample into a metal pie plate. Ask each member of the group to use their senses to observe the soil and write down an adjective that describes their sample. Have the group record the words generated and create a short poem, descriptive verse or song about their sample.

3. Collect the samples and number each one. Display them in a central location. Ask the students to visit each of the samples and observe them carefully. Have each group then read their poem, descriptive verse or song and let the rest of the class try to guess which soil sample it describes.

4. Discuss the variety of soils, their basic characteristics and how each type might affect plant growth. Sand is composed of fairly large particles with rough edges, has a gritty texture, and a lot of air spaces between the particles. Clay is made of very fine particles with smooth edges. It is sticky and slippery when wet and can become hard and packed when dry. It is often hard to work. Loam is a mixture of particle sizes and has a crumbly texture and moderate air spaces. Soil rich in organic material tends to act like a sponge and hold water. Explain that the groups will be performing an experiment to investigate the water holding and drainage capacities of these various soil samples.

5. Pass out a glass lamp chimney (or plastic soda bottles or funnel), plastic screening, and rubber bands to each group. Ask them to attach the screening to the narrow end of the chimney with the rubber band. Provide masking tape and have each group label their soil sample with an identifying name. Ask them to add their soil to the chimney to the predetermined line (each group should have the same amount of soil in their chimney). Pass out wide-mouth jars and have each group place their chimney into the jar, screen side down.

6. Have the groups place their setup in a central location with their original soil sample in the metal pie pan for observation. Explain that they will pour water into the wide end of the chimney (about 1/3 to 1/2 full) and observe and record how quickly water passes through the sample and into the wide-mouthed jar. This is called a percolation test. They will also note how much water is absorbed by comparing the volume of water before it is poured into the sample to the volume of water after it has passed through the sample. What factors do they think will affect the percolation rate? Which sample will perc the fastest? The slowest? Suggest that they look closely and feel the samples in the metal pie plates for helpful information.student pouring water through sample

7. Ask each group to designate one student to pour water through their sample and another to monitor and record the times. Explain that when you say, "Go!" students will simultaneously pour water into the chimneys. In addition to observing and recording, the timers will announce when the first drop passes through the sample and when the water finally stops dripping steadily.

8. Discuss the results from the samples. Were there any surprises? Compare the volume of water that passed through each sample. Have the students pour the percolated water back into the plastic cups. How does it compare to the original volume? Be sure to note any differences in color and clarity.

9. Wet the soil samples in the metal pie plates. Have the students feel and describe the wet soil. Explain that they will repeat the percolation test through the wet soil samples. Explain that when evaluating soils at a building site percolation tests are done in wet soil. Do they think the results will change?

10. Compare results from wet and dry samples. What can you determine about each sample's porosity and drainage abilities versus water retention? How would these factors influence plant growth?

Extensions:

aMake squirt bottles for younger students by punching holes in the lids of plastic soda bottles. Fill these bottles with water and explain they will be using them to test absorption rates of different soil areas in the school yard. Divide the class into pairs and give each pair a bottle. Outside, have them squirt an area of soil with water. Is the water quickly absorbed or does it pool up? Have the pairs share and discuss their results.

bHave the students conduct an experiment to look at particle size, pore sizes and water-holding capacity of some common materials. Give each group a cup full of marbles and one filled with the same amount of sand. Which cup has the most empty spaces or pores, the marbles or the sand? To check their guesses, give them cups containing the same amount of water. Tell them to add water until the water level is even with the top of the marbles or sand. Direct them to remove any excess water with an eyedropper and add it back to the original cup. Which holds the greatest amount of water? (The sand can hold more water than the marbles as there are more air spaces in the cup of sand.) Were they surprised? Suggest they try filling the empty spaces in a second cup of marbles with sand. How much sand can they add? Will they be able to add any water to this mixture? Record their predictions, then test by pouring in water.


SOIL SPONGES

What do a sponge and good garden soil have in common? They are both full of holes and absorb and hold water. Good garden soil is a mix of different particle sizes and rich in organic matter, with a crumbly texture and a range of air spaces. These characteristics allow for the free flow of oxygen and water through the soil, making it easier for plant roots and soil animals to work their way through. Organic materials in the soil improve absorption and water holding capacity, encouraging healthy and vigorous root growth. These materials also help to control erosion, as surface water is quickly and completely absorbed, leaving little damaging run off. Good garden soil maintains a balance between how quickly water drains through the soil and how much water is retained; hence, the soil is never too wet or too dry.


* This material has been used with permission from Shelburne Farms, Copyright © 1995.

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