Packed Tight

Materials

✓ an adult

✓ long nail

✓ ruler

✓ large tin can (16 or 32 ounces) with ends andlabel removed

✓ pitcher of water

✓ watch with a second hand

✓ science notebook and pencil

✓ hand shovel (optional)

✓ plant identification guide

How do humans impact the levels of water and oxy gen insoil?

The texture and amountof air spaces between soil particles is important to plant and animal life inan ecosystem. The growth of some plants can be slowed by highly compacted soil. That is why before they do any planting, farmers and gardeners take time tobreak up tightly packed soil. By loosening soil, they make it easier for waterand oxygen to get to plant roots. Landscapers aerate lawns for the same reason. People who raise earthworms also make sure that soil particles are loose andwell aerated to support the worm population.

When they arepreparing an area to be planted, farmers, gardeners, and landscapers maycaution people not to walk

over the loosenedsoil. Walking and driving over these areas presses the soil particles closertogether, compacting them. Certain soils, such as clay, tend to compact moretightly than others, like sand. When soil becomes compacted, water seepsthrough it slowly and little oxygen can work its way down to plant roots.

Youcan compare the productivity of soil that is loosely packed to that of soilthat is tightly packed by looking at the number of plant and animal speciesliving in each. To do so, select four different soil sites in your neighborhoodor school yard. Site A should be a place where human travel is heavy, Site B alocation where human travel is moderate, Site C where little human trafficoccurs, and Site D an area that gets no human traffic. Do not trespass on, ortake samples from, someone’s yard without permission, and take an adultwith you.

VisitSite A and record its location. In your notebook, make a note of the number ofdifferent kinds of plants and ani mals at Site A. First, check out how manykinds of plants you see growing on the surface of the soil, as well as evidenceof different plants from other places (like dead leaves or twigs). Refer to aplant identification guide for help in distinguishing different species. Alsowrite down how many different animals you see, as well as evidence of animals(like a gnawed pinecone or droppings). Finally, dig down a few inches andinspect the soil for evidence of plant or animal life, like roots, seeds, orworms.

Brushany leaf litter from the top of the soil sample. Push the long nail or ice pickinto the soil as far as possible. The nail will not be able to penetratecompacted soil as easily as it can penetrate noncompacted soil. Remove the nailand measure how many centimeters it penetrated into the soil. Record this valueinto your notebook.

Nextmeasure how fast water seeps into the soil. Areas that are highly compacted maynot be able to absorb water as quickly as less compacted areas. Reduced waterabsorption can limit the number and kinds of organisms that live in soil. Takea tin can from which the ends and label have been removed. Firmly push the caninto the soil to a depth of 2 or 3 centime ters. Fill the can with water, thentime how long it takes for the water to drain from the can into the soil. (SeeFigure 23.) Record this time in your notebook.

Repeatthe entire process at sites B, C, and D. Record your results in your sciencenotebook.

Atwhich of the four sites did you find the most kinds of plants? At which did youfind the most kinds of animals? In which site did water drain into soil thefastest? At which site was it most difficult to push the nail into the soil? From this experiment, can you make a statement about how soil com pactionaffects the plant and animal life in an area?

Packed Tight

Figure 23.

To test how compacted the soil is, you can (a)push a nail into the surface and (b) watch how quickly water seeps into thesoil. Measure how long it takes for water to seep from the can.

Science - Project Ideas

Expand this experiment and findout if compacted soil or soil that is not compacted is more prone to erosion.

Design and perform an experimentthat shows which type of soil sand, loam, clay, or silt is most likely toexperience compaction.

Earthworms require very looselyrather than tightly spaced areas between soil particles. How could you ver ifythis experimentally?

Create an experiment thatdetermines the effect of com pacted soil on seed germination. Can you use theresults of this experiment to explain why forest rangers ask hik ers to stay onthe trails in state parks?