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Soil - Soil Profile (Layers of soil)

Grade 5ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Soil is formed through the process of weathering, where rocks are broken down by wind, water, and climate over thousands of years.

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A vertical section through different layers of soil is called the Soil Profile. Each layer is called a Horizon.

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Horizon A (Topsoil): This is the uppermost layer. It is dark in color because it is rich in humus (decayed organic matter) and minerals. It is soft, porous, and can retain H2OH_2O effectively.

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Horizon B (Subsoil): The layer below the topsoil. It contains a smaller amount of humus but is rich in minerals. It is harder and more compact than topsoil.

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Horizon C (Parent Material): This layer consists of small lumps of rocks with cracks and crevices. It is the stage of transition between soil and rock.

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Bedrock: The solid, unweathered rock layer found at the bottom of the soil profile. It is very hard and difficult to dig with a spade.

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Soil contains H2OH_2O (moisture), air (in the spaces between particles), minerals, and organic matter.

📐Formulae

Percolation Rate (mL/min)=Amount of H2O (mL)Percolation Time (min)\text{Percolation Rate (mL/min)} = \frac{\text{Amount of } H_2O \text{ (mL)}}{\text{Percolation Time (min)}}

Percentage of moisture in soil=Weight of H2O lostOriginal weight of soil×100\text{Percentage of moisture in soil} = \frac{\text{Weight of } H_2O \text{ lost}}{\text{Original weight of soil}} \times 100

💡Examples

Problem 1:

A student conducted an experiment and found that it took 2020 minutes for 200 mL200\text{ mL} of H2OH_2O to percolate through a soil sample. Calculate the percolation rate.

Solution:

Percolation rate=200 mL20 min=10 mL/min\text{Percolation rate} = \frac{200\text{ mL}}{20\text{ min}} = 10\text{ mL/min}

Explanation:

To find the rate, we divide the total volume of water by the time it took to pass through the soil. The resulting unit is mL/min\text{mL/min}.

Problem 2:

Identify the soil layer that is rich in humus and provides nutrients to growing plants.

Solution:

Horizon A (also known as Topsoil).

Explanation:

Topsoil is the most fertile layer because it contains decomposed organic matter called humus, which is essential for plant growth.