Overview
This lecture explains how to determine the moisture and organic matter content of soil samples using crucibles, weighing, drying, and burning procedures.
Equipment Needed
- Crucibles for soil samples.
- Numbering system (labels) for crucibles.
- Tongs, scale, calculator, hot pads.
- Data recording method (table).
- Drying oven or kitchen oven, muffle furnace or Bunsen burner.
Weighing Procedure
- Number each crucible to keep results organized.
- Weigh and record the empty crucible.
- Add wet soil sample to each crucible, then weigh and record.
- Subtract crucible weight from combined weight to get wet soil weight.
Drying Soil
- Place crucibles with soil in a drying oven at 125°C or kitchen oven at 200°F overnight.
- Remove crucibles; weigh and record now-dry soil plus crucible.
- Subtract crucible weight to get dry soil weight.
Calculating Moisture Percentage
- Divide dry soil weight by wet soil weight, then multiply by 100 for the moisture percentage of each sample.
- Optionally, average percentages for an overall value.
Burning Off Organic Matter
- Place crucibles in a muffle furnace at 400°C for 3 hours, or above a Bunsen burner for 30 minutes.
- Weigh crucibles after burning; record the combined weight.
- Subtract crucible weight to get weight of burned (inorganic) soil.
Calculating Organic and Inorganic Content
- Divide dry soil weight by burned soil weight, then multiply by 100 for inorganic soil percentage.
- Subtract inorganic percentage from 100 to get organic soil percentage.
- Optionally, average for overall percentages.
Key Terms & Definitions
- Crucible — a heat-resistant container used to hold soil during testing.
- Moisture percentage — ratio of dry to wet soil weight, indicating water content.
- Muffle furnace — high-temperature furnace for burning off organic matter.
- Inorganic percentage — proportion of soil remaining after burning off organic material.
- Organic percentage — proportion of soil lost after burning, representing organic matter.
Action Items / Next Steps
- Prepare all equipment and label crucibles.
- Create a data table to record all weights and calculations.
- Complete drying and burning procedures as outlined.
- Calculate moisture, organic, and inorganic percentages for each sample.