1. You will need to collect FOUR different soils from different locations to represent the soil removed from the 4 suspected vehicles. It is up to you to decide what kind of soils you will collect. Collect soils that have obvious differences if you want to make it easier for students to solve the crime (different colors, different textures, different kinds of visible materials in the soil) – collect soils that are more similar if you want to make it more difficult. A one-gallon zip-lock bag full of each soil will be enough for at least 5 classes (you can use left-over soil the next year). YOU MUST ALSO CHOOSE ONE OF THESE FOUR SOILS TO REPRESENT THE FARM SOIL (the soil that will match one the vehicle soils). You should collect DOUBLE the amount of this soil (half to be used as the farm soil, half to be used as vehicle soil).
2. Spread out the collected soils on newspaper and allow them to completely dry out. You should attempt to break up any larger clumps of soil before the soil becomes completely dried (completely dried soil clumps often become so hard it requires a hammer to break them up). Keep track of the two soil samples that match.
3. When your soil samples are dried you have two options: A. use the soil samples as they are
B. customize your soil samples to give them special qualities
We always choose to customize our soil samples (our soil samples in St. Louis, Missouri are often filled with clay particles and has little sand – so we customize our soils to make them more interesting for students to test).
How we customize our soil samples:
Vehicle #1 soil – we sprinkle Glo-Germ Powder on the soil and mix it in. Glo-Germ is a white powder that fluoresces brightly when placed under a long-wave UV-A light. This allows students to see a soil that fluoresces in their ultraviolet light test. Glo-Germ powder can be purchased from different Biological Supply Companies (such as Wards Natural Science 36W9902) Vehicle #2 soil – we scatter some unusual plant, animal, or human product in the soil that is a clue to where the soil originated. Example: we add small pieces of broken clay pottery to the soil as a clue that maybe this soil came from a greenhouse area.
SAMPLE PAGES
Vehicle #3 soil AND Farm Soil (we make Vehicle #3 match the Farm Soil)– we purchase a bag of play sand from a hardware store. Mix about 40% sand and 60% soil. The play sand usually has many different colors of sand particles. It also usually gives the soil a higher percentage of larger soil particles. Vehicle #4 – we mix in several spoons of Coarse Sand. Course sand can be purchased from most Biological Supply Companies (such as Wards Natural Science 942W5608). Purchased course sand is usually all one color (usually white) and is made of larger particles with sharp edges.
How you choose to customize your soil samples will depend on the type of soil you have in your area and the materials you have available.
4. Place each of the five soil samples in some sort of container that allows easy access for students (and ultraviolet light testing). We place the soil samples on cafeteria trays. Correctly label each container – Vehicle #1, Vehicle #2, Vehicle #3, Vehicle #4, and Farm Soil. Make sure that your Farm Soil label and Vehicle #3 label are on matching soils.
5. Place the soil samples in a location where students can easily access them – and can easily perform the ultraviolet UV-light test.
6. You can tell students to throw away their dry soil samples after testing them – or you can have them pour the dry samples back into their correct soil containers.
7. Place leftover soil samples in zip-lock bags to use next year.
Comments/Problems:
This Training Lab usually takes 3 - 4 days to complete. Day 1 – texture, pH, general
observations. Day 2 – finish texture, microscopic observations. Day 3 – finish observations, calculations, begin questions. Day 4 – finish questions if needed.
It’s always a little funny watching an entire class of students shaking their soil texture tubes in unison.
Students are usually surprised by the appearance and colors of the magnified sand grains.
Typical Results:
Typical Results (what our students find testing the soils we provide) can be found in the Data Tables that follow these Teacher Notes – as well as a KEY to the Soil Training Lab Questions.
SAMPLE PAGES
SOIL AS EVIDENCE DATA TABLES NAME___________________________________ Table 1 – Soil Texture Test Results
Table 2 – General Soil Characteristics Total Number of Layers Height of Sand Layer (mm) Height of Silt Layer (mm) Height of Clay Layer (mm) Total Height of All Layers (mm) % of Sand In Soil % of Silt In Soil % of Clay In Soil Farm Soil 3 10mm 21mm 3mm 34mm 29.40% 61.80% 8.80% Vehicle #1 3 10mm 15mm 5mm 30mm 33.30% 50% 16.70% Vehicle #2 3 2mm 25mm 7mm 34mm 5.90% 73.50% 2.60% Vehicle #3 3 10mm 20mm 3mm 33mm 30.30% 60.60% 9.10% Vehicle #4 3 4mm 34mm 3mm 41mm 9.76% 82.90% 7.30%
pH Color of Dry Soil Unusual Material in Soil Appearance With UV
Light Farm
Soil 8 LIGHT BROWN LARGER ROCKS NONE
Vehicle
#1 9 BROWN GRAY MOSS AND ROCKS
MANY POINTS OF FLUORESCENCE Vehicle
#2 7 DARK BROWN
MULCH, POTTERY PIECES, AND ROCKS
FEW POINTS OF FLUORESCENCE Vehicle
#3 8 LIGHT BROWN ROCKS NONE
Vehicle
#4 7 LIGHT BROWN LOTS OF ROCKS NONE