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Difficulty: MediumEcological Factors and Their Measurement

In an experiment to investigate the water-retaining capacity of three different soil types, equal masses (100 g100\text{ g}) of dried soil samples PP, QQ, and RR were placed into separate filter-lined funnels. A volume of 100 cm3100\text{ cm}^3 of water was poured over each sample, and the volume of filtrate collected in the measuring cylinders beneath after 15 minutes15\text{ minutes} was recorded as follows:

- Sample P: 25 cm325\text{ cm}^3 of filtrate collected
- Sample Q: 55 cm355\text{ cm}^3 of filtrate collected
- Sample R: 85 cm385\text{ cm}^3 of filtrate collected

Which of the following correctly identifies Sample R and the primary edaphic factor responsible for its observed drainage rate?

  1. Sandy soil, due to large coarse particles and large pore spaces that promote rapid water percolation.Answer
  2. B
    Clay soil, due to fine particles and high capillarity that impede drainage.
  3. C
    Loamy soil, due to a balanced mixture of sand and silt with optimal organic matter.
  4. D
    Clay soil, due to low porosity and small pore spaces that retain minimal water.

Answer

Sample R is sandy soil, because its large particle size and large pore spaces allow water to drain rapidly, resulting in the highest filtrate volume collected.
The sample that produces the highest volume of filtrate (85 cm385\text{ cm}^3) retains the smallest amount of water (15 cm315\text{ cm}^3). Sandy soil has large mineral particles and relatively large spaces between particles, which allows water to drain freely and rapidly under gravity.

Step-by-Step Solution

1
Calculate the volume of water retained by each soil sample.
Water retained = Initial water added (100 cm3100\text{ cm}^3) minus filtrate collected. Sample P retained 75 cm375\text{ cm}^3, Sample Q retained 45 cm345\text{ cm}^3, and Sample R retained 15 cm315\text{ cm}^3.
Determining the retained volume allows ranking the soils from highest to lowest water-holding capacity.
2
Analyze the physical properties of soil types relative to drainage.
Sample R retained the least water (15 cm315\text{ cm}^3) and drained the most (85 cm385\text{ cm}^3).
Sandy soils consist of large, coarse sand particles with large macropores between them, leading to poor water retention and high percolation rates.

Key Concept

Water-retaining capacity and percolation rates of edaphic soil types (sand, loam, clay)
Estimated Time:1m 30s
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Topics

Ecological Factors and Their Measurement

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