Soil Properties Lab: Vocabulary and Procedures

Lab Introduction and Vocabulary

  • Homework Assignment: Students are tasked with finding rough or working definitions for a list of vocabulary words. This is considered an easy assignment, contributing
    10/10
    to their grade, as everything will be submitted and discussed on Monday.
  • Vocabulary Words for Definition:
    • Density
    • Pore space
    • Saturate/Saturation
    • Field capacity
    • Gravitational water
    • Capillary water/Capillary action
    • Hygroscopic water
    • Cation exchange buffering capacity
    • Origin/Parent material
  • Existing Knowledge: Some terms like "origin" or "parent material" should already be familiar from previous discussions.
  • Gravitational Water:
    • Definition: Water pulled downwards by the force of gravity.
    • Example: Rain working its way down through the soil.
  • Capillary Water / Capillary Action:
    • Definition: Any water movement that reverses the flow of gravitational water. This action is crucial for plant life.
    • Plant Mechanism: Plants pull water up through their roots, moving it in the opposite direction of gravity via capillary action.
    • Sponge Example: When a sponge is placed in water, water slowly works its way up through the sponge against gravity due to capillary action.
    • Paper Towel Experiment: Taking two containers (one with water, one empty) and connecting them with a twisted paper towel will show water seeking its own level through the towel, demonstrating capillary action and other related concepts.
    • Goal: Students need to develop a good working definition of these terms.

Lab Equipment and Materials

  • Necessity of Following Directions: It is crucial to follow the lab procedure step-by-step without skipping sections. Once one experiment is completed, subsequent trials might not require constant reference to the directions.
  • Graduated Cylinders:
    • Options: Two glass cylinders are available (handle with care; there are only two left out of an original dozen). Multiple durable plastic cylinders are also available and are recommended for less breakage risk.
    • Usage: For precise volume measurements.
  • Glass Beakers:
    • Sizes:
      200
      mL (actually
      250
      mL) or
      400
      mL.
    • Location: Available at the front and back of the lab.
  • Balances/Scales:
    • Quantity & Location: Two are set up at the back.
    • Accuracy: These are very accurate for weighing.
    • Weight vs. Volume Discrepancy: Beakers of the same volume (e.g.,
      400
      mL) do not necessarily weigh the same (e.g.,
      132.35
      vs.
      131.45
      grams). Their volume is guaranteed, but not their weight.
    • Experimental Impact: Using the same beaker throughout an experiment is vital for accurate results, as different beaker weights can affect the final outcome (potentially by a couple of grams).
    • Weight Capacity Warning: When weighing sand or peat moss, the weight might exceed the scale's capacity. In such cases, a portion must be weighed, dumped, and then the next portion added and weighed to get a total.
  • Fine Mesh Screens:
    • Purpose: Used during the process of dumping free water to determine field capacity and pore space. They prevent soil from being lost with the water, allowing it to be flicked back in for accurate measurements.
  • Stirring Rods: Available for mixing.
  • Masking Tape/Rubber Bands: Not strictly necessary due to existing graduations on beakers.

Experiment Procedure and Calculations

  • Mathematics: Calculations are integrated into the step-by-step procedure.
  • Field Capacity and Air Capacity:
    • Expected Sum: When calculating the percent of water held at field capacity and the percent of air held at field capacity, their sum should ideally be around
      100
    • Error Allowance: Some experimental error is expected; a sum of around
      96
      % or greater is generally acceptable.
  • Water Measurement: When filling the graduated cylinder, fill precisely to
    100

    mL (not
    105

    or
    95

    ). Add water slowly.
  • Pore Space Calculation: Once the total pore space is filled, calculate the exact amount of water added without rounding.
  • Soil Components for Testing:
    • Sand
    • Peat moss
    • Perlite
    • Vermiculite
    • Students may also use their own soil samples or provided lab samples.
  • Soil Preparation (Grinding):
    • Tool: Mortar and pestle are available.
    • Method: Lightly grind and move the soil to break up clumps. Do not pulverize or remove rocks; simply break up aggregates.
    • Transfer: Dump the prepared soil into the beaker. Do not add unground soil, as it will cause problems in the experiment.