Question

Arrange the following soil types such that the spacing of drains (m) fall in a descending order.
A. Clay loam
B. Loam
C. Sandy loam
D. Peat
Choose the correct answer from the options given below:

• A. A, B, C, D
• B. A, C, B, D
• C. D, C, B, A
• D. C, B, A, D

Hint:

Drain spacing is directly proportional to soil permeability. The coarser the soil texture, the higher the permeability, and the wider the drain spacing can be. Coarse Soil \(\rightarrow\) Wide Spacing; Fine Soil \(\rightarrow\) Close Spacing.

Answer 1

The Correct Option is D

Step 1: Relate drain spacing to soil properties.
The purpose of subsurface drains is to lower the water table. The spacing between drains depends on the soil's hydraulic conductivity (permeability). A soil with high permeability allows water to move easily, so drains can be placed far apart. A soil with low permeability requires drains to be placed close together to be effective.
Step 2: Order the given soil types by their hydraulic conductivity.
- C. Sandy loam: Has the largest particles among the loams and clays, and thus the highest permeability.
- B. Loam: A mixture of sand, silt, and clay; has moderate permeability, lower than sandy loam.
- A. Clay loam: Has a high clay content, making its permeability quite low.
- D. Peat: Organic soil that is often highly decomposed, resulting in very low hydraulic conductivity.
Step 3: Arrange the soils in order of descending drain spacing.
Descending order of drain spacing corresponds to descending order of permeability.
Highest Spacing (Highest Permeability) \(\rightarrow\) Sandy loam (C)
\(\downarrow\) \(\rightarrow\) Loam (B)
\(\downarrow\) \(\rightarrow\) Clay loam (A)
Lowest Spacing (Lowest Permeability) \(\rightarrow\) Peat (D)
The correct sequence is C, B, A, D.