Stephanie Hines & Robert Vest
PIE Scientists, Ball State University
Exploring Soils
Standards addressed:
Indiana State Science Standards: These are indicators that are directly addressed by
using the model or may be addressed by development of additional activities with the
model.
 6.1.3, 6.2.1, 6.2.2, 6.2.5, 6.2.6, 6.2.7, 6.3.15, 6.5.4
 7.1.2, 7.1.4, 7.2.1, 7.7.1, 7.7.2
 8.2.8, 8.5.4, 8.5.9, 8.5.10, 8.7.2, 8.7.3
Materials required for each group of students:
 3 plastic bottles of the same size (1, 1.5, or 2 L)
 Soils from 3 different locations, e.g. garden, lawn, forest floor and sand
 Mesh cut to fit the bottle holes
 O-rings to secure the screen
 3 cups to hold inverted bottles, the size of the cup depends upon the size of bottle
you are using
 Stopwatch
 500 ml beaker
 A water supply
Background information:
Soil is necessary for the survival of all species, including humans. It is an
important, and often overlooked, natural resource. Soil provides a medium for plants to
grow, nutrients and minerals for them to survive, and holds water for them to use. It
houses the microbes that decompose waste, produces and absorbs gases, and filters water
and waste. While it is technically renewable, the rate at which soil forms is so slow that
it can hardly be called so. It may take anywhere from 100-1000 years for an inch of soil
to accumulate, yet can be eroded in a fraction of that time.
Soil formation depends upon five factors: time, topography, parent material,
climate and organic matter. Together these factors determine soil properties, such as
fertility, appropriate use (e.g. landfill), color, stability, and particle size. Soil is
comprised of three particles: sand, silt, and clay. Sand is the largest particle (2.0.05mm), silt is the middle sized particle (.05-.002mm), and clay is the smallest sized
particle (<.002mm) (USDA classification). Relative particle sizes are: a sand particle is
the size of a barrel, silt the size of a dinner plate and clay the size of a coin. Particle types
have a distinct texture as well: sand feels gritty, silt floury, and clay sticky. The majority
of soils are a combination of these three particles. A preparatory activity on soil particle
size, texture & composition is recommended before conducting this activity and can be
found at: http://www.bsu.edu/web/fseec/pie/ .
General Procedures:
1. Invert each funnel with the screen secure into a cup. Rest the shoulders of the
funnel on the cup edge so that there is space between the bottom of the cup and
the mouth of the funnel. Pour one soil type into each of the funnels.
2. Ask your students to write down their hypotheses regarding what will happen to
the water in each of the funnels. Things to include are: how much time it will
take for the water to pass through, how clear the water will be, and how much
water will pass through.
3. Direct students to pour 300ml of water into one funnel at a time, recording the
time it takes from starting to pour the water until it comes out the funnel mouth.
Because the soils will all be dry, the time it takes to pass through each sample will
be similar and is not an accurate representation of the soil filtration property.
Now that the soils are all somewhat saturated, ask students to repeat this step a
second time. This second round more accurately represents the soils’ properties
and this repeat information is what they will use to compare their hypotheses.
Principles & Variables - Several different soil principles may be addressed using this
apparatus with minor variables:
 Soil porosity – The amount of space between soil particles (pores) defines
porosity. Porosity determines the amount of liquids and gases present in the soil,
which then determines the plant and organisms that can survive there.
 Bulk density – Bulk density is related to porosity because it describes how tightly
packed a soil is. It equals the weight of a given volume of soil, including pore
space. To demonstrate this principle, determine the volume of the funnel, fill it
with soil and find the mass of the soil. Dry the soil in the oven and weigh the soil
again. Calculate the bulk density by measuring dry mass/volume (g/mL).
 Soil permeability - Permeability indicates how quickly gases, liquids or plant
roots percolates through soil. This rate is largely dependent upon porosity. Septic
systems, drainfields, and landfills are constructed upon this principle. Use the
general procedures to demonstrate soil permeability.
 Soil filtration – Charged particles on the soil surface and bacteria within the soil
remove pollutants from water as it filters through the soil. Groundwater and
aquifers, as well as wetlands, depend upon soil filtration to purify the water for
future use. To demonstrate this principle, place a few drops of gentian violet
(positively charged) and eosin y (negatively charged) in saturated soil, and slowly
flush the soil with water. Compare the color of the water that filters into the cup.
Web Resources:
http://ltpwww.gsfc.nasa.gov/globe/globerel.htm
http://www.unep.org/geo/yearbook/070.htm
http://interactive.usask.ca/ski/agriculture/soils/soilphys/soilphys_depo.html
http://archive.globe.gov/tctg/bulkden.pdf?sectionId=94