Where Does Soil Come From?

 Introduction:

The chemical elements that are crucial to life cycle through ecosystems along paths that depend on their chemical properties.  This nutrient regeneration or recycling is a key aspect of the dynamic stability of ecosystems.  If all of the organic and inorganic matter from dead organisms just piled up, the environment could never support life indefinitely.  Therefore the many organisms that are considered decomposers are crucial members of biological communities.  The final stage of a food chain involves the Detrivores, which are the decomposers and detritus feeders.  These organisms consume detritus, which is the waste of living organisms, their cast off parts, or the material that remains when they are dead.  The biomass that these organisms feed on consists of complex molecules, which are broken down into simpler inorganic molecules and soluble nutrients, which the organisms digest.  Most decomposers are bacteria and fungi. Detritus feeders are often worms, insects or other animals such as crabs.

National Standard Addressed:

From the area of life science the structure and function in living systems is something that can be stressed during this lab.  You can discuss how worms are able to dig through the soil and how their body functions as a recycling plant for many of the nutrients.  Also regulation and behavior can be talked about when looking at the worms.  Discuss with the students how the worms come to the surface to feed and how they mix the soil as they hunt for more food.

Engage the students in extended investigations and they will be more prepared to face a world where things do not always happen instantly.  Today more than ever we need to be supportive of science inquiry.  Getting the students involved in the activity enough to want to learn more by asking questions is a major focus of the teaching standards.

Objectives and Benchmarks:

Upon completion, students will recognize the significance of animals as biological decomposers.  They will be able to explain how worms convert organic matter into soil.

Materials:

Composting Worms 1,000 mL Beakers            Wet Paper Towel            Soil            Newspaper      Saran Wrap

Several Distinct forms of Detritus  (Chopped Carrots, Broken Egg Shells, Coffee Grounds, Untreated Grass Clippings)

Advance Preparation:

Obtain Worms for Experiment -           Red wigglers are excellent and many people have basement colonies to share

Collect Detritus for Food Sources

Procedure:

Students need to examine the appearance and behavior of the worms before starting their experiment.  Have students place the worms on a piece of damp paper and describe their size, color, structure, and compare their movements.  These worms are called Red Wigglers and are a special type of composting worm.  Remind students that these are living things and should be handled gently and treated with respect.

The worms should be hungry because they have not been fed in a few days.  The basic idea is for students to construct a food source, in their beakers, for the worms that consists of distinct layers of different detritus materials.  They can alternate different colored materials to emphasize the distinction of different layers.  On the top of the last layer be sure the students place 1 cm of brown dirt and finally a similar layer of damp paper towel.  Also they should moisten the soil so that it is damp, but not saturated.  Have the students count and record the number of worms they place on the damp paper towel.  Finally cover the beakers with a piece of plastic wrap and poke several holes in it.  The beakers should be placed in a dark closet or cabinet for several days before they observe them again.

Observe your experiment every time they are in the lab.  Ask, what happens? 

Have students keep a record of the progressive changes that take place.  

Things to Consider:

What happens to the organic matter in the containers with worms?

Are the worms changing the soil?  How do you know this?

Do you notice tunnels or evidence of activity?  Do you see castings?

How does the worm activity compare to a soil tiller?  Are they recycling the material?

How do worms help the environment in natural ecosystems?

Possible Integration:

This lab focuses on biology but could also be used as a lesson in Environmental Science, describing to the students the importance of worms in our environment and the many benefits they offer is a good way to bring the lesson an environmental issue.

In an Earth Science or Agricultural Education class this lab would also be helpful in talking about the formation of soil and the different ways it is produced.

Art classes may even benefit from this lesson by drawing observations of the worm farm or possibly even painting a picture to describe what it looks like.

Critical Concepts:

Functional Role- Decomposition            Animals            Invertebrates            Hermaphrodites

Ecosystems & Recycling            Oxygen Uptake by Diffusion