Soil Science Quiz

Grade 6 · Science · Quiz

Test your knowledge of soil composition, formation, layers, and importance.

Questions

1. What is humus?

   1. A type of clay mineral
   2. Decomposed organic matter that enriches soil
   3. The bottom layer of rock in soil
   4. Weathered sand particles
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   Answer: Decomposed organic matter that enriches soil

   Humus forms when bacteria and fungi break down dead plants and animals. It stores nutrients, retains water, and gives fertile soil its dark color.

2. Earthworms help improve soil quality.

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   Answer: True

   Earthworms tunnel through soil, improving aeration and drainage, mixing organic matter downward, and releasing nutrients as they digest soil particles.

3. Which process breaks rocks down into smaller particles to form soil?

   1. Erosion
   2. Weathering
   3. Decomposition
   4. Precipitation
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   Answer: Weathering

   Weathering (physical and chemical) slowly breaks apart bedrock and rock fragments into the mineral particles that form the base of soil.

4. The dark, fertile upper layer of soil is called ___.

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   Answer: topsoil

   Topsoil (the A horizon) is the most nutrient-rich layer where most plant roots grow. It's usually the darkest soil layer because of its humus content.

5. Which type of soil drains quickly but holds nutrients poorly?

   1. Clay soil
   2. Loam
   3. Sandy soil
   4. Silt soil
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   Answer: Sandy soil

   Sand particles are large with spaces that water moves through quickly. Sandy soil can't hold nutrients or moisture well enough for most crops.

6. Soil is made only of rock particles and contains no living organisms.

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   Answer: False

   Healthy soil teems with life — bacteria, fungi, earthworms, insects, nematodes, and more. A teaspoon of soil can contain over a billion bacteria.

7. What is the main threat to topsoil that removes it from farmland?

   1. Decomposition
   2. Erosion
   3. Condensation
   4. Infiltration
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   Answer: Erosion

   Wind and water erosion strip topsoil from agricultural land. It's a global crisis — eroded farmland loses productivity and can become barren.

8. An ideal garden soil with balanced sand, silt, and clay is called ___.

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   Answer: loam

   Loam is the ideal agricultural soil because its balanced texture (sand + silt + clay) provides good drainage while retaining water and nutrients.

9. Approximately how long does it take to form 2.5 cm of topsoil naturally?

   1. 10 years
   2. 100 years
   3. 500 years
   4. 5,000 years
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   Answer: 500 years

   Natural soil formation is extremely slow. This makes topsoil a precious, essentially non-renewable resource on human timescales.

10. The B horizon in soil contains more organic matter than the A horizon.

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    Answer: False

    The A horizon (topsoil) is richest in organic matter and humus. The B horizon (subsoil) has less organic matter and more minerals leached down from above.

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