JAMB Biology Note- Soil

Topics:

a) (i) characteristics of different types of soil (sandy, loamy, clayey)
i. soil structure
ii. porosity, capillarity and humus content
iii. Components of the soil
i. inorganic
ii. organic
iii. soil organisms
iv. Soil air
v. Soil water                                                                                                                                             Soil fertility:                                                                                                                  
i. loss of soil fertility
ii. Renewal and maintenance of soil fertility

Table of Contents

• Topics:
  • 1. Characteristics of Different Types of Soil
    • Sandy Soil
    • Loamy Soil
    • Clayey Soil
  • 2. Soil Structure
  • 3. Soil Properties
    • Porosity:
    • Capillarity:
    • Humus Content:
  • 4. Components of Soil
    • Inorganic Components:
    • Organic Components:
    • Soil Organisms:
    • Soil Air:
    • Soil Water:
  • 5. Soil Fertility
    • Loss of Soil Fertility:
    • Renewal and Maintenance of Soil Fertility:
  • 6. Practical Activities
  • Conclusion

1. Characteristics of Different Types of Soil

Soil can be classified into three main types based on its texture and the size of its particles:

Sandy Soil

• Characteristics:
  • Contains large particles.
  • Drains quickly.
  • Low water retention.
  • Poor in nutrients but easy to cultivate.
  • Light and easy to work with.
• Uses: Ideal for plants that require good drainage, such as cactus and some vegetables.

Loamy Soil

• Characteristics:
  • A balanced mixture of sand, silt, and clay.
  • Good water retention and drainage.
  • High fertility.
  • Rich in nutrients and organic matter.
  • Ideal for most plants, making it the best type of soil for general cultivation.
• Uses: Used for growing a wide variety of crops due to its balance of nutrients, water retention, and aeration.

Clayey Soil

• Characteristics:
  • Contains small particles that are tightly packed.
  • Poor drainage, retains water for a long time.
  • Very fertile but can become waterlogged.
  • Heavy and difficult to cultivate when wet.
• Uses: Suitable for crops that need more water, such as rice, but it requires careful management to avoid waterlogging.

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2. Soil Structure

Soil structure refers to the arrangement of soil particles into aggregates or clumps. This affects how air and water move through the soil.

• Good Soil Structure: Soil particles are loosely arranged, allowing air, water, and plant roots to move easily through the soil.
• Poor Soil Structure: Soil particles are tightly packed, leading to poor water infiltration and root growth.

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3. Soil Properties

Porosity:

• The percentage of soil volume that is pore space.
• Affects water retention and air availability for plant roots.
• Sandy soil has low porosity, while loamy and clayey soils have higher porosity.

Capillarity:

• The ability of soil to move water upward against gravity through small pores.
• Fine particles in clayey soil have high capillarity, while coarse particles in sandy soil have low capillarity.

Humus Content:

• The decomposed organic matter in the soil.
• Rich in nutrients and improves soil fertility.
• Loamy soil generally has a higher humus content than sandy and clayey soils.

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4. Components of Soil

Soil is composed of both inorganic and organic materials, as well as soil organisms and water.

Inorganic Components:

• Derived from rocks and minerals.
• Includes sand, silt, clay, and minerals like calcium, magnesium, and potassium.

Organic Components:

• Derived from decaying plant and animal matter.
• Includes humus, which adds fertility to the soil.

Soil Organisms:

• Includes bacteria, fungi, earthworms, and insects.
• Play a crucial role in breaking down organic matter and recycling nutrients.

Soil Air:

• Contains oxygen and carbon dioxide.
• Essential for respiration of soil organisms and plant roots.

Soil Water:

• Water held in soil pores.
• Available for plant uptake and is essential for plant growth.

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5. Soil Fertility

Loss of Soil Fertility:

• Can result from:
  • Loss of inorganic matter: Due to erosion or poor agricultural practices.
  • Compaction: When soil becomes too hard, restricting root growth.
  • Leaching: The loss of nutrients due to excessive rainfall or irrigation.
  • Erosion: The removal of the topsoil by wind or water, which is rich in nutrients.
  • Repeated cropping with one variety: Depletes specific nutrients, leading to reduced fertility.

Renewal and Maintenance of Soil Fertility:

• Contour Ridging: Building ridges along the contours of slopes to reduce water runoff and soil erosion.
• Terracing: Creating stepped levels on hilly land to reduce water erosion.
• Mulching: Covering the soil surface with organic matter (e.g., straw, leaves) to prevent water evaporation and add nutrients.
• Poly-cropping: Growing multiple crops together to increase biodiversity and reduce pest pressure.
• Strip-cropping: Growing crops in alternating strips to reduce soil erosion.
• Use of Organic and Inorganic Fertilizers: Adding organic material (compost) and inorganic fertilizers to replenish lost nutrients.
• Crop Rotation: Changing crops each season to prevent nutrient depletion.
• Shifting Cultivation: Practicing rotational farming in different plots of land to allow the soil to recover.

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6. Practical Activities

Experiment 1: Measuring Soil Porosity

• Collect three types of soil (sandy, loamy, clayey).
• Measure the volume of water poured into the soil and the amount that drains through.
• Calculate the porosity and compare the three types of soil.

Experiment 2: Determining Capillarity

• Fill a container with soil and add water to one side.
• Observe how water moves up through the soil and the rate at which it rises.

Experiment 3: Humus Content

• Collect soil samples from different types of soil.
• Heat the samples to remove water and weigh the remaining organic matter (humus content).

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Conclusion

Soil is a complex and vital natural resource for plant growth and agricultural productivity. Understanding the different types of soil, their properties, and how to maintain soil fertility is crucial for sustainable farming practices and soil conservation.