Got Water?
Module 2

Lesson 3 - The "Sponge and Bucket" Soil Water-Holding Demonstration
Acknowledgement: Taken from "Living on the Land 2001"

Materials Needed:

• Large sponge
• Bucket
• Water (consider coloring the water with food dyes to make it easier to see)

1. Show the students the sponge. The sponge can be likened to soil in that it has many pores of different sizes.
2. Dip the sponge into a bucket and allow it to completely wet, filling all the pores. This is called "saturated."
3. Hold the sponge and allow it to drain in front of the audience. Big pores will drain first, followed by the smaller pores.
4. Once most of the water has drained out by itself, explain to the audience that this is what is referred to as "field capacity" in a soil.
5. By squeezing the sponge further, you mimic a root taking up water and reduce the amount of available water holding capacity. The available water holding capacity is the amount of water between field capacity and wilting point.
6. Explain that water can still be in the soil at wilting point, especially in clays, but the water is held very tightly by the small pores and is unavailable to plants. The plants cannot exert enough energy to extract the water.

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