Exploring the Rate of Plant Growth in Crystals vs. Soil

Type

Life Science

Grade Level

Upper elementary (Grade 5) and/or Middle School (Grades 6-8)

Difficulty of Project

Fairly easy

Cost

$18.00 - Excluding the Tri-fold cardboard display board Safety Issues (Any safety issues to be considered?) Investigator should not ingest the crystals or drink the liquids associated with the activity. The crystals used in the project are extremely slippery when spilled. Never flush or pour these crystals down the drain, crystal swelling could possibly clog drainpipes. The supervising adult should discuss the warnings and safety information with the child or children before commencing the activity.

Material Availability

The materials are readily available.

Approximate Time Required to Complete the Project (Hours, Days, Weeks)

Two weeks depending on plant growth.

Objective

What is the project about?

A hydrogel superabsorbent crystal is long chain of molecules called a polymer, that can absorb vary large amounts of water.  This ability to hold water makes it an ideal medium for seed germination and plant growth. The research aspect of this science fair project is to compare the rate of plant root growth in water absorbing crystals to that of soil.

What are the goals?

To measure the rate of growth of a bean seed or young plant placed in a superabsorbent crystal medium to that of a simular plant placed in soil. From the measurements taken a quantitative data table of the difference in growth rates, if any, will be produced, and the results will also be displayed in the form of a graph.

The young investigator will gain an understanding of the a possible application of  hydrogel superabsorbent crystals in forestry, gardening, and landscaping as a means of conserving water by the ability of these crystals to store water in the soil and then release it as the plant’s roots need it.

Materials and Equipment / Ingredients

What materials are required?

Hydrogel superabsorbent crystals, metric ruler, potting soil, clear plastic cups, fertilizer or liquid minerals, and fast-growing plant seeds (grass, radish, or beans). With the exception of the crystals, all the other items can be purchased from the local supermarket and garden supply store. Also, a Tri-fold cardboard display board can be purchased from an art & crafts supply store.

Where can the materials be found?

The hydrogel crystals can be purchased either locally from a garden supply store or online. Fortunately the price has been coming down. Science in a Bag charges $10 plus free shipping for a pack of these crystals. They may also be ordered from Educational Innovations, or Nasco Science. 

Introduction

Background information

A hydrogel crystal (sometimes called a “Disappearing crystal,” “Water Crystal,” etc) is a long chain of molecules bonded together to form a superabsorbent polymer, that when placed in water swells into a transparent tapioca-like bubble of encapsulated water. The crystal is made up almost entirely of water. Placing a plant seed or the roots of a small growing plant into a container of these crystals allows water to be absorbed by the plant’s roots as it is needed. These crystals function similar to hydroponics which is the growing of plants in water instead of soil. The difference between the two activities is that for hydroponics to be successful, the water must be enriched with nutrients and sometimes oxygenated. Also, the plants must be placed in some type of inert medium like sand, vermiculite, or sawdust to provide mechanical support in order to anchor the roots. The physical structure of the crystals used in this science fair project serves as the plant root anchors and therefore external support is not necessary.

When comparing the growth of plants in superabsorbent hydrogel crystals to that of soil a little fertilizer or liquid minerals is added to the crystals because where as these nutrients are found naturally in the soil they will be absent in the crystal medium and if not added will affect the results of the project.

While the young instigator may consider water-absorbing crystals to be a modern convenience or curiosity, the possible impact that such applications of these crystals to farming in parts of the world that are plagued by drought could be enormous.

Diagrams/Pictures

 Digital photos can be taken during the experimenting process and/or images of crystals submerged in water can be downloaded from the Science in a Bag website for free and without copyright infringement issues.

The following sites offer down loadable images that maybe used on the display board: