Soil texture and properties lab – jar test, texture triangle, porosity, drainage, pH, nutrients and humus
GeographySoils, Biosphere & EnvironmentAges 15–16Virtual lab
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A virtual soil lab with six soil samples (coastal dune sand, pine heath soil, garden soil, floodplain soil, grassland soil on limestone and a heavy clay soil) and an unknown sample. Shake a sedimentation jar: sand settles within a minute, silt within hours and clay over days; read the layer heights on the ruler to work out the percentages of sand, silt and clay, then find the soil's name on the texture triangle. Pour water into 100 cm³ of dry soil to measure porosity, let 100 mL of water drain through a soil column to compare permeability and the water the soil holds, test the pH with universal indicator, test for nitrate, phosphate and potassium with colour charts, and heat the soil to find its humus content. All results collect in a soil report that compares the samples.
Lesson: Soils: texture (sand, silt and clay) and the soil texture triangle; porosity, permeability, water-holding capacity, pH, nutrients and organic matter as edaphic factors
What it shows
Soil texture is the share of sand (0.05–2 mm), silt (0.002–0.05 mm) and clay (below 0.002 mm) particles. In the jar test the particles settle at speeds given by Stokes' law, so sand, silt and clay form layers; the USDA texture triangle turns the three percentages into a soil name. Texture controls the other properties: clay soils have more pore space but tiny pores, so water drains slowly and more is held. Porosity, drainage and water held follow simple rules fitted to typical values, and the pH, nutrient and humus values are typical of each soil. The jar test is approximate.
How to use
Choose a Soil sample. On Texture press Shake jar; the clock speeds up and stops at 40 s, 2 h and 2 days, so press Record height each time, work out the percentages and tap the triangle. On Porosity hold Pour water until the water just reaches the soil surface. On Drainage press Pour 100 mL of water and record the volume at 10 min, 30 min and 24 h. On Soil chemistry choose a Test, add the indicator or reagents and tap the matching colour.
Parameters you can change
- Screen Texture, Porosity, Drainage, Soil chemistry
- Soil sample Coastal dune sand, Pine heath soil, Garden soil, River floodplain soil, Grassland soil on limestone, Heavy clay field soil, Unknown sample
- Add a dispersant to the jar
- Show the soil names on the triangle
Questions to explore
- Why does clay have more pore space than sand, yet water drains through it much more slowly?
- Why is a dispersant added to the jar before shaking it?
- Which of these soils suits plants that need acidic soil, and which holds the most water for crops?
