Chapter 20: Soil: Our Friend 🌱
A Comprehensive Guide for PSTET Paper-2 (Science)
Chapter Overview
| Section | Topic | PSTET Weightage | Page No. |
|:---:|:---|::---:|:---:|
| 20.1 | Formation of Soil | Medium | 2 |
| 20.2 | Layers of Soil (Profile) | High | 7 |
| 20.3 | Types of Soil and their Properties (Sandy, Clayey, Loamy) | High | 13 |
| 20.4 | Soil Erosion and Conservation | High | 20 |
| Practice Zone | MCQs & Pedagogical Questions | - | 28 |
Learning Objectives 🎯
After studying this chapter, you will be able to:
✅ Explain the process of soil formation through weathering of rocks and the role of various factors
✅ Identify and describe the different layers (horizons) of a soil profile
✅ Distinguish between sandy, clayey, and loamy soils based on their properties and particle size
✅ Analyze the causes and agents of soil erosion
✅ Evaluate various methods of soil conservation and their importance
✅ Apply pedagogical strategies to teach soil-related concepts effectively to upper primary students
Pedagogical Link 🔗
For Teachers: This chapter directly aligns with:
Class 7 Science NCERT Chapter 9: "Soil"
Teaching Tips:
Begin with a "Soil Sample Investigation"—collect different soil samples from the school garden, playground, and local area for students to observe and feel
Use a clear jar with water and soil to demonstrate particle separation (sand settles first, then silt, then clay)
Create a "Soil Profile Jar" using different colored materials to represent soil horizons
Connect to local agriculture—discuss which crops grow well in your region's soil type
Use the "soil ribbon test" as a hands-on activity to determine soil texture
Section 20.1: Formation of Soil
Introduction
Soil is more than just "dirt"—it is a precious natural resource that supports all terrestrial life. But have you ever wondered how soil is formed? The ground beneath our feet is the result of millions of years of geological processes. Understanding soil formation helps us appreciate why soil is truly our friend and why we must protect it .
20.1.1 What is Soil?
Definition: Soil is the upper layer of earth in which plants grow, a mixture of organic matter (humus), minerals, gases, liquids, and countless organisms that together support life .
Components of Soil:
| Component | Typical Percentage | Function |
|---|---|---|
| Mineral Matter | 45% | Derived from weathered rocks; provides physical structure and minerals |
| Organic Matter (Humus) | 5% | Decomposed plant and animal material; provides nutrients, improves water retention |
| Water | 25% | Soil moisture; essential for plant growth and chemical reactions |
| Air | 25% | Fills pore spaces; provides oxygen for roots and soil organisms |
20.1.2 Soil Formation: From Rock to Regolith
Soil formation, also called pedogenesis, begins with the weathering of rocks. Weathering is the breakdown of rocks and minerals at Earth's surface through contact with the atmosphere, water, and biological organisms .
A. Weathering Processes
Table 20.1: Types of Weathering
| Type | Process | Examples |
|---|---|---|
| Physical (Mechanical) Weathering | Breakdown of rocks into smaller pieces without changing their chemical composition | • Freeze-thaw action (water expands in cracks) • Exfoliation (peeling of rock layers due to pressure release) • Abrasion by wind and water • Root growth splitting rocks |
| Chemical Weathering | Breakdown of rocks through chemical reactions that alter the mineral composition | • Dissolution (limestone dissolved by slightly acidic water) • Oxidation (iron minerals rust) • Hydrolysis (feldspar converts to clay minerals) • Carbonation (CO₂ in water forms weak carbonic acid) |
| Biological Weathering | Breakdown caused by living organisms | • Lichens and mosses secreting acids • Burrowing animals mixing soil • Plant roots wedging into cracks |
📝 PSTET Note: Mechanical and chemical weathering reinforce each other. Mechanical weathering provides fresh surfaces for chemical attack, while chemical weathering weakens rocks, making them more susceptible to mechanical breakdown .
20.1.3 Factors Affecting Soil Formation (CLORPT)
Soil scientists use the acronym CLORPT to remember the five main factors that control soil formation :
| Factor | Description | Impact on Soil |
|---|---|---|
| C - Climate 🌡️ | Temperature and precipitation | • Warm, moist climates → faster weathering, more leaching • Cold, dry climates → slower soil formation • Rainfall amount affects nutrient retention (too much rain can leach nutrients) |
| L - Organisms 🌿 | Living things (plants, animals, microorganisms) | • Plant roots break rocks, add organic matter • Bacteria and fungi decompose material • Burrowing animals mix soil layers |
| R - Relief (Topography) ⛰️ | Slope and landscape position | • Steep slopes → thin soil (erosion > formation) • Flat areas → thick soil (accumulation) • South-facing slopes (in N hemisphere) warmer → different soils |
| P - Parent Material | The original rock or sediment from which soil forms | • Quartz-rich rocks (granite, sandstone) → sandy soils • Basalt/shale → clay-rich soils • Glacial deposits → mixed soils |
| T - Time ⏳ | Duration of soil-forming processes | • Young soils (few thousand years) → thin, less developed • Old soils (millions of years) → thick, well-developed horizons |
20.1.4 The Journey: Bedrock to Soil
The transformation of solid rock into soil takes thousands of years. Here's the step-by-step process:
| Stage | Description | Time Scale |
|---|---|---|
| 1. Solid Bedrock | Unweathered parent rock | Starting point |
| 2. Weathering Begins | Cracks form; physical/chemical weathering creates fragments | Hundreds of years |
| 3. Pioneer Organisms | Lichens and mosses colonize; their acids further break rock | Hundreds to thousands of years |
| 4. Organic Matter Accumulation | Dead organisms add organic material; simple plants establish | Thousands of years |
| 5. Soil Horizons Develop | Distinct layers form as weathering and organic activity continue | Thousands to millions of years |
📝 PSTET Note: Even under ideal conditions, soil takes thousands of years to develop. In Canada, for example, soils are relatively young because the area was glaciated until about 10,000-14,000 years ago .
20.1.5 Parent Material and Soil Texture
The parent material significantly influences the resulting soil :
| Parent Material | Resulting Soil Texture | Nutrient Content |
|---|---|---|
| Granite, Sandstone | Sandy soils (quartz-rich) | Low in nutrients |
| Basalt, Shale | Clay-rich soils | High in iron, magnesium, calcium |
| Glacial deposits | Mixed (loamy) soils | Variable |
| River flood deposits | Clay-rich, fertile soils | High in clay minerals with nutrient-holding capacity |
20.1.6 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Rock Weathering Demo | Show students different rock samples; discuss how they break down | Observation skills |
| "CLORPT" Mnemonic | Teach the five factors with hand gestures | Memorization aid |
| Time Scale Discussion | Compare human lifespan vs. soil formation time | Appreciation building |
| Local Geology Connection | Identify local rock types and discuss how they affect local soil | Real-world connection |
Section 20.2: Layers of Soil (Profile)
Introduction
If you dig a deep pit, you'll notice that the soil is not uniform—it has distinct layers, like a layered cake. These layers are called soil horizons, and together they form the soil profile. Each horizon has unique characteristics in terms of color, texture, composition, and biological activity .
20.2.1 What is a Soil Profile?
Definition: A soil profile is a vertical cross-section of the soil that shows all its different layers (horizons) from the surface down to the bedrock .
Master Horizons: From top to bottom, the main horizons are:
| Horizon | Name | Description |
|---|---|---|
| O Horizon | Organic Layer | Organic material (leaves, twigs, humus) |
| A Horizon | Topsoil | Mineral layer mixed with organic matter; dark colored |
| E Horizon | Eluviation Layer | Zone of leaching (not always present) |
| B Horizon | Subsoil | Zone of accumulation (illuviation) |
| C Horizon | Parent Material | Weathered parent material; not true soil |
| R Horizon | Bedrock | Solid unweathered rock |
20.2.2 Detailed Description of Each Horizon
A. O Horizon (Organic Layer) 🍂
Description: The uppermost layer composed primarily of organic matter in various stages of decomposition .
| Sub-horizon | Meaning | Description |
|---|---|---|
| Oi | Fibric | Slightly decomposed organic matter; original plant structures identifiable |
| Oe | Mesic | Moderately decomposed organic matter |
| Oa | Humic | Highly decomposed organic matter (humus); original structures not identifiable |
Characteristics:
Dark color (brown to black)
High biological activity (microbes, insects, worms)
Most common in forests; rare in grasslands
B. A Horizon (Topsoil)
Description: The surface mineral layer mixed with organic matter—often called topsoil .
Characteristics:
Darker than lower layers due to organic matter content
Most fertile part of the soil profile
Highest biological activity (microfauna, mesofauna, macrofauna)
Typically coarser texture than lower layers
📝 PSTET Note: The A horizon is usually the most fertile part of the soil profile, containing the highest concentration of organic matter and nutrients .
C. E Horizon (Eluviation Layer)
Description: A light-colored layer where materials have been removed (leached) by percolating water .
Characteristics:
Not always present (common in forest soils, rare in grasslands)
Light in color (grayish) due to loss of clay, iron, aluminum oxides
Name comes from eluviation (washing out)
Sandy texture due to loss of finer particles
D. B Horizon (Subsoil)
Description: The layer of accumulation (illuviation) where materials washed down from above are deposited .
Characteristics:
Often rich in clay, iron oxides, aluminum oxides
Brighter colors (reddish, yellowish) due to iron oxides
Denser and less fertile than A horizon
May contain calcium carbonate (in arid regions)
Sub-horizon Designations:
Bt - Accumulation of silicate clay
Bf - Accumulation of iron and aluminum oxides
Bh - Accumulation of organic matter
E. C Horizon (Parent Material)
Description: The layer of unconsolidated material (weathered rock or sediment) from which the upper horizons formed .
Characteristics:
Little to no evidence of soil-forming processes
May show some weathering but not considered "soil"
Plant roots do not usually extend here
Soft enough for root penetration but not part of active soil zone
F. R Horizon (Bedrock)
Description: Solid, unweathered rock beneath all other layers .
Characteristics:
Continuous mass of rock (granite, basalt, limestone, etc.)
Excavation requires specialized equipment
Roots cannot penetrate (except in cracks)
Represents the ultimate parent material
20.2.3 Visual Summary of Soil Profile
O Horizon ────► Organic debris (leaves, twigs, humus) A Horizon ────► Topsoil (dark, fertile, mixed organic-mineral) E Horizon ────► Eluviation layer (light-colored, leached) B Horizon ────► Subsoil (accumulation of clay, minerals) C Horizon ────► Weathered parent material R Horizon ────► Solid bedrock
20.2.4 Transitional Horizons
Soil horizons don't always have sharp boundaries. Transitional horizons occur where properties of two master horizons mix :
| Type | Designation | Description |
|---|---|---|
| Dominant-subordinate | AB, BC | Properties of first horizon dominate, but second's properties also present |
| Equal properties | A/B, B/C | Properties of both horizons are equally represented |
20.2.5 Why Soil Horizons Matter
Understanding soil horizons is important for :
| Application | Why It Matters |
|---|---|
| Agriculture | Topsoil (A horizon) is most fertile—protecting it is crucial |
| Construction | B and C horizons affect foundation stability |
| Waste Management | Horizons influence water movement and contamination risk |
| Ecology | Different horizons support different organisms |
20.2.6 Classroom Activity: Make a Soil Profile Jar
| Step | Procedure |
|---|---|
| 1 | Find a clear jar with a lid |
| 2 | Collect soil from different depths (if possible) OR use different colored materials |
| 3 | Layer materials to represent horizons: |
| • Top: Crumbled leaves/decomposed material (O horizon) | |
| • Dark potting soil (A horizon) | |
| • Light-colored sand (E horizon) | |
| • Reddish clay or darker sand (B horizon) | |
| • Gravel and small stones (C horizon) | |
| • Large rock at bottom (R horizon) | |
| 4 | Label each layer and display |
20.2.7 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| "Edible Soil Profile" | Use crushed cookies, pudding, and other foods to create edible horizons | Engaging hands-on |
| Horizon Sorting | Students match horizon names to descriptions and pictures | Classification skills |
| Local Soil Pit | If possible, dig a small pit (with permission) to observe real profile | Real-world observation |
| Horizon Mnemonics | Teach "O-A-E-B-C-R" with phrases like "Only Amazing Earth Beneath Colorful Rocks" | Memorization aid |
Section 20.3: Types of Soil and their Properties (Sandy, Clayey, Loamy)
Introduction
Have you ever noticed that soil from the garden feels different from soil near a construction site or from a sandy beach? Soils vary in their texture based on the size of the mineral particles they contain. The three main types of soil are sandy, clayey, and loamy .
20.3.1 Soil Texture: The Basis of Classification
Definition: Soil texture refers to the relative proportions of sand, silt, and clay particles in a soil .
Particle Size Classification:
| Particle Type | Diameter Range | Characteristics |
|---|---|---|
| Sand | 0.05 mm to 2 mm | Largest particles; visible to naked eye; gritty feel |
| Silt | 0.002 mm to 0.05 mm | Intermediate size; smooth, floury feel when dry |
| Clay | Less than 0.002 mm | Smallest particles; sticky when wet; hard clods when dry |
📝 PSTET Note: Clay particles are so small they cannot be seen without a microscope—about 1,000 clay particles could fit on the head of a pin!
20.3.2 The Soil Textural Triangle
Soil scientists use the textural triangle to classify soils based on their sand, silt, and clay percentages. The triangle has :
Vertical axis: Percent clay
Horizontal axis: Percent sand
Remainder: Percent silt (100% - %sand - %clay)
| Group | Definition | Classes Included |
|---|---|---|
| Sands | ≥70% sand by weight | Sand, Loamy sand |
| Loams | Intermediate texture; significant proportions of all three | Sandy loam, Loam, Silt loam, Clay loam, Silty clay loam, Sandy clay loam |
| Clays | ≥35% clay (often >40%) | Sandy clay, Silty clay, Clay, Heavy clay |
20.3.3 Detailed Study of Main Soil Types
A. Sandy Soil 🏖️
Composition: High proportion of sand particles (≥70%), low clay and silt .
Properties:
| Property | Description |
|---|---|
| Texture | Coarse, gritty, loose |
| Water Holding Capacity | LOW—water drains quickly through large pore spaces |
| Nutrient Retention | POOR—nutrients leach easily |
| Aeration | GOOD—large pore spaces allow air circulation |
| Workability | EASY—light and easy to till ("light soil") |
| Warmth | WARMS UP quickly in spring |
| Consistency | Dry: loose; Wet: little coherence |
Common Names: "Light soil," "warm soil"
Suitability:
Good for: Root vegetables (carrots, potatoes), drought-tolerant plants
Poor for: Plants requiring constant moisture
B. Clayey Soil
Composition: High proportion of clay particles (≥35-40%), low sand .
Properties:
Common Names: "Heavy soil," "gumbo"
Cation Exchange Capacity (CEC): Clay particles and organic matter have negative charges that attract positively charged nutrient ions (calcium, potassium, magnesium), holding them for plant use .
Suitability:
Good for: Plants that need consistent moisture, rice, willows
Challenging for: Root vegetables (can become misshapen)
C. Loamy Soil
Composition: Balanced mixture of sand, silt, and clay—typically 40% sand, 40% silt, 20% clay.
Properties:
| Property | Description |
|---|---|
| Texture | Moderately coarse to moderately fine; crumbly |
| Water Holding Capacity | GOOD—balances drainage and retention |
| Nutrient Retention | GOOD—clay and organic matter hold nutrients |
| Aeration | GOOD—sand provides pore space |
| Workability | EASY—ideal for gardening |
| Warmth | MODERATE—warms reasonably in spring |
Common Names: "Ideal soil," "gardener's soil"
Suitability:
Good for: Almost all garden plants, crops, vegetables
Considered the best soil type for agriculture
20.3.4 Comparison of Soil Types
Table 20.2: Sandy vs. Clayey vs. Loamy Soil
| Feature | Sandy Soil | Clayey Soil | Loamy Soil |
|---|---|---|---|
| Particle Size | Large (0.05-2 mm) | Very small (<0.002 mm) | Mixed |
| Feel | Gritty | Sticky when wet, hard when dry | Crumbly, smooth |
| Water Drainage | Rapid | Slow | Moderate |
| Nutrient Content | Low | High | High |
| Air Content | High | Low | Good |
| Workability | Easy | Difficult | Easy |
| Warming in Spring | Fast | Slow | Moderate |
| Agricultural Rating | Poor (with irrigation) | Good (with management) | Excellent |
20.3.5 The Field Texture Test (Ribbon Test)
Teachers can demonstrate this simple test to determine soil texture :
| Step | Procedure |
|---|---|
| 1 | Take a small handful of moist soil (not wet) |
| 2 | Squeeze it to form a ball |
| 3 | Try to form a ribbon by pressing soil between thumb and forefinger |
| 4 | Measure ribbon length and observe behavior |
| Soil Type | Ribbon Length | Behavior |
|---|---|---|
| Sand | No ribbon | Cannot form ball; falls apart |
| Loamy Sand | Minimal ribbon (5 mm) | Slight coherence |
| Sandy Loam | 15-25 mm | Forms ribbon but very sandy feel |
| Loam | ~25 mm | Coherent, spongy feel |
| Clay Loam | 40-50 mm | Smooth, plastic |
| Light Clay | 50-75 mm | Plastic, slight resistance |
| Medium/Heavy Clay | 75 mm+ | Plastic like plasticine, firm resistance |
20.3.6 Soil Texture and Plant Growth
| Soil Type | Advantages | Disadvantages | Best Crops |
|---|---|---|---|
| Sandy | Good drainage, warms early | Low water/nutrient retention | Carrots, potatoes, peanuts, melons |
| Clayey | High nutrients, water retention | Poor drainage, slow warming | Rice, cabbage, beans, wheat |
| Loamy | Balanced properties | Few (if any) | Most vegetables, grains, flowers |
20.3.7 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Soil Texture by Feel | Students handle different soil samples and describe them | Sensory learning |
| Ribbon Test Activity | Students perform ribbon test on unknown samples | Scientific investigation |
| "Soil in a Jar" Test | Shake soil in water; let settle; observe layers (sand at bottom, silt middle, clay top) | Visual learning |
| Crop Matching Game | Match crops to preferred soil types | Application skills |
Section 20.4: Soil Erosion and Conservation
Introduction
Soil is a precious resource that takes thousands of years to form, but it can be destroyed in a matter of years through soil erosion. Erosion is a natural process, but human activities have accelerated it dramatically, causing loss of fertile topsoil worldwide .
20.4.1 What is Soil Erosion?
Definition: Soil erosion is the process of detachment and transport of soil particles from one place to another by natural agents such as water and wind .
Key Concept: Soil erosion can be:
Geological (Natural) erosion — slow process that has been occurring for millions of years
Accelerated erosion — rapid loss due to human activities (10-40 times faster than natural rates)
20.4.2 Global and Indian Statistics
📝 PSTET Note: In India, nearly 80 million hectares are exposed to the threat of soil erosion, and 43 million hectares are actually affected .
20.4.3 Agents and Causes of Soil Erosion
A. Agents of Erosion
| Agent | Description |
|---|---|
| Water | Rainfall, runoff, waves, ice—responsible for most erosion |
| Wind | Strong winds, especially in dry areas with sparse vegetation |
| Gravity | Mass wasting events (landslides, slumping) |
B. Human Activities Causing Accelerated Erosion
| Activity | Contribution to Erosion |
|---|---|
| Overgrazing | 35% of erosion cases—trampling destroys vegetation cover |
| Deforestation | 30%—removes protective tree cover; exposes soil to rain and wind |
| Agricultural activities | 28%—plowing, continuous cropping, cultivation on slopes |
| Developmental activities | Housing, roads, construction—massive land disturbance |
| Mining | Extraction of minerals disturbs land and removes vegetation |
20.4.4 Types of Water Erosion
Water erosion occurs in several forms, depending on intensity :
| Type | Description | Severity |
|---|---|---|
| Splash Erosion | Raindrops hit bare soil, detaching particles | Initial stage |
| Sheet Erosion | Thin layer of soil removed uniformly from large area | Can go unnoticed |
| Rill Erosion | Small channels (rills) form on slopes | Visible channels |
| Gully Erosion | Deep, wide channels that cannot be removed by plowing | Severe |
| Stream Bank Erosion | Rivers and streams cut into banks | Can be severe |
20.4.5 Types of Wind Erosion
| Type | Description |
|---|---|
| Suspension | Very fine particles carried high into air (dust storms) |
| Saltation | Medium particles bounce along surface |
| Surface Creep | Large particles roll or slide along surface |
20.4.6 Effects of Soil Erosion
A. On-site Effects
| Effect | Description |
|---|---|
| Loss of Topsoil | Removal of nutrient-rich A horizon |
| Reduced Fertility | Loss of organic matter and nutrients |
| Decreased Water Holding Capacity | Soil cannot retain moisture |
| Poor Crop Yields | Reduced agricultural productivity |
| Ecological Collapse | Loss of habitat and biodiversity |
B. Off-site Effects
| Effect | Description |
|---|---|
| Sedimentation | Rivers, lakes, reservoirs filled with sediment |
| Water Pollution | Sediment carries nutrients, pesticides into water bodies |
| Eutrophication | Excess nutrients cause algal blooms, dead zones |
| Flooding | Sediment reduces river capacity |
| Damage to Infrastructure | Roads, houses damaged by sediment |
20.4.7 Soil Conservation Methods
Soil conservation involves practices that protect soil from erosion and maintain its fertility.
A. Agronomic Measures (Crop-based)
| Method | Description | How It Helps |
|---|---|---|
| Crop Rotation | Alternating crops (e.g., corn one year, beans next) | Beans fix nitrogen; different root structures hold soil |
| Cover Cropping | Planting crops (clover, rye) between main crops | Protects soil when main crop not growing |
| Mulching | Covering soil with organic material (straw, leaves) | Reduces splash erosion; adds organic matter |
| Contour Farming | Plowing along contours (across slope), not up-down | Reduces water runoff speed |
| Strip Cropping | Alternating strips of different crops | Strips of dense crops trap sediment |
| Wind Breaks | Planting rows of trees/shrubs around fields | Reduce wind speed; trap blowing snow/soil |
B. Mechanical/Structural Measures
| Method | Description | How It Helps |
|---|---|---|
| Terracing | Building step-like structures on steep slopes | Reduces slope length; slows water |
| Contour Bunding | Low earthen walls along contours | Traps water; allows infiltration |
| Check Dams | Small dams in gullies/streams | Trap sediment; slow water flow |
| Gabions | Wire baskets filled with rocks | Stabilize banks; trap sediment |
| Drainage Channels | Engineered channels for runoff | Direct water safely |
C. Vegetative Measures
| Method | Description | How It Helps |
|---|---|---|
| Reforestation | Planting trees on degraded land | Roots bind soil; canopy reduces rain impact |
| Afforestation | Planting trees where none existed | Prevents erosion from beginning |
| Grassland Management | Controlled grazing; avoiding overgrazing | Maintains protective vegetation cover |
| Riparian Buffers | Vegetation along water bodies | Traps sediment from fields; stabilizes banks |
20.4.8 Sustainable Agricultural Practices
| Practice | Description |
|---|---|
| No-till Farming | Planting without plowing; leaves crop residue on surface |
| Reduced Tillage | Minimum soil disturbance |
| Organic Farming | Avoids synthetic chemicals; builds soil organic matter |
| Agroforestry | Integrating trees with crops |
| Integrated Nutrient Management | Balanced use of organic and inorganic fertilizers |
20.4.9 Soil Conservation in India
| Program/Initiative | Purpose |
|---|---|
| Soil Health Card Scheme | Provides farmers with soil nutrient status and recommendations |
| National Mission for Sustainable Agriculture | Promotes soil conservation, water efficiency |
| Watershed Development Programs | Integrated development of watershed areas |
| Integrated Watershed Management Programme | Soil and water conservation in rainfed areas |
20.4.10 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Erosion Demonstration | Use tray with soil, water spray bottle to show splash/sheet erosion | Hands-on learning |
| "Before and After" | Show images of eroded vs. conserved land | Visual impact |
| School Garden Project | Implement conservation practices in school garden | Real-world application |
| Local Case Study | Investigate erosion issues in local area | Community connection |
Chapter Summary: Key Points for Revision 📝
Quick Revision Table
| Topic | Key Points | Common PSTET Questions |
|---|---|---|
| Soil Formation | Weathering (physical, chemical, biological); CLORPT factors (Climate, Organisms, Relief, Parent material, Time) | What factors affect soil formation? |
| Weathering Types | Physical (mechanical) breakup; Chemical alteration; Biological action | Differentiate physical and chemical weathering |
| Soil Profile | O (organic), A (topsoil), E (eluviation), B (subsoil), C (parent material), R (bedrock) | Name the soil horizons in order |
| A Horizon | Topsoil; most fertile; rich in organic matter | Which horizon is most fertile? |
| B Horizon | Subsoil; accumulation of clay, minerals | What accumulates in B horizon? |
| Sandy Soil | Large particles; gritty; drains fast; low nutrients; "light soil" | Properties of sandy soil |
| Clayey Soil | Small particles; sticky when wet; holds water; high nutrients; "heavy soil" | Properties of clayey soil |
| Loamy Soil | Balanced mixture; ideal for agriculture; good drainage + nutrients | Best soil for gardening? |
| Soil Erosion | Detachment and transport of soil particles by water/wind | Define soil erosion |
| Water Erosion Types | Splash, sheet, rill, gully, stream bank | Types of water erosion |
| Erosion Causes | Overgrazing (35%), deforestation (30%), agriculture (28%) | Major human causes of erosion |
| Soil Conservation | Contour plowing, terracing, cover crops, wind breaks, reforestation | Methods to prevent soil erosion |
Practice Zone: PSTET-Style Questions 🎯
Content-Based MCQs
Q1. The process of breaking down rocks into smaller pieces without changing their chemical composition is called:
a) Chemical weathering
b) Physical weathering
c) Biological weathering
d) Leaching
Q2. Which horizon of the soil profile is known as "topsoil" and is the most fertile?
a) O horizon
b) A horizon
c) B horizon
d) C horizon
Q3. The layer of soil where materials accumulate from above is called the:
a) A horizon
b) E horizon
c) B horizon
d) R horizon
Q4. Which type of soil has the largest particle size?
a) Clay
b) Silt
c) Sand
d) Loam
Q5. Clayey soil is described as "heavy" because:
a) It weighs more than sandy soil
b) It is difficult to till (requires more power)
c) It contains heavy metals
d) It has high density
Q6. Which soil type is considered ideal for most agricultural purposes?
a) Sandy soil
b) Clayey soil
c) Loamy soil
d) Silty soil
Q7. The acronym CLORPT stands for factors affecting soil formation. What does the "R" represent?
a) Rainfall
b) Rocks
c) Relief (topography)
d) Radiation
Q8. Approximately how many million hectares in India are affected by soil erosion?
a) 10 million
b) 43 million
c) 80 million
d) 100 million
Q9. Which type of water erosion involves removal of a thin layer of soil from a large area uniformly?
a) Splash erosion
b) Rill erosion
c) Sheet erosion
d) Gully erosion
Q10. The practice of plowing along the contours of a slope rather than up and down is called:
a) Terrace farming
b) Contour plowing
c) Strip cropping
d) Mulching
Pedagogical MCQs
Q11. A teacher wants to demonstrate that different soil types have different water-holding capacities. The best activity would be:
a) Show a diagram comparing soil types
b) Take three funnels with filter paper, add equal amounts of sandy, clayey, and loamy soil, pour equal water, and measure drainage
c) Lecture about water-holding capacity
d) Show pictures of wet and dry soil
Q12. To help students understand soil horizons, the most engaging activity is:
a) Memorize horizon names from textbook
b) Create an "edible soil profile" using cookies, pudding, and candies
c) Draw a diagram on paper
d) Watch a video about soil
Q13. A student asks, "Why is clay soil sticky when wet but hard when dry?" The best explanation is:
a) "That's just how clay behaves"
b) "Clay particles are very tiny and flat; they slide over each other when wet and lock together when dry"
c) "Clay contains special minerals"
d) "Because it has more water"
Q14. While teaching soil conservation, a teacher takes students to a nearby farm to see contour plowing and terracing. This is an example of:
a) Lecture method
b) Field trip/observation method
c) Textbook method
d) Demonstration method
Q15. The most effective way to teach the difference between sandy, clayey, and loamy soils is:
a) Give students samples of each soil type to touch, feel, and observe
b) Show pictures in textbook
c) Describe properties verbally
d) Write definitions on board
Answer Key with Explanations
Pedagogical Reflection for Teachers 🤔
Think-Pair-Share Activity:
Think: How would you explain to students that soil takes thousands of years to form but can be destroyed in a few years?
Pair: Discuss with a colleague how you would set up a "Soil Conservation Corner" in your school with demonstrations of different conservation methods.
Share: Design a 15-minute activity to teach the ribbon test for determining soil texture.
NCERT Textbook Linkages 📚
| Class | Chapter | Topic |
|---|---|---|
| Class 7 | Chapter 9 | Soil |
| Class 8 | Chapter 1 | Crop Production and Management |
| Class 8 | Chapter 2 | Microorganisms: Friend and Foe |
Chapter End Notes
Key Terminology Glossary
Quick Tips for PSTET Aspirants ⚡
✅ Memorize with Mnemonics:
CLORPT Factors: "Children Love Our Rich Parent's Teaching" = Climate, Life/Organisms, O (just O for organisms), Relief, Parent material, Time
Soil Horizons (top to bottom): "Only Adults Eat Butter Cookies Rarely" = O, A, E, B, C, R
Particle Sizes (largest to smallest): "Sandy Soil Can't Cling" = Sand, Silt, Clay (and Clay Clings!)
Soil Water Holding: "Sandy Sheds, Clayey Cling, Loamy Likes both" = Sandy drains, Clayey holds, Loamy balanced
✅ Common Exam Traps:
"Heavy clay" refers to tillage difficulty, NOT actual weight—dry clay is actually lighter than dry sand!
Soil takes THOUSANDS of years to form—not decades or centuries
B horizon accumulates materials; E horizon loses materials—don't confuse
C horizon is NOT bedrock—it's weathered parent material above bedrock
Loam is best but not the only soil—different crops prefer different soils
Sheet erosion is easy to overlook—thin layer removed uniformly
Overgrazing is the #1 human cause of erosion (35%), not agriculture
✅ Important Facts:
Sand particles = 0.05-2 mm; Clay = <0.002 mm
R horizon = solid bedrock
A horizon = most fertile
Answers to "Check Your Understanding"
[To be filled by student]
📝 Note for Self-Study: After completing this chapter, ensure you can:
Explain the three types of weathering with examples
List the five factors of soil formation (CLORPT)
Draw and label a soil profile with all six master horizons
Describe the characteristics of O, A, E, B, C, and R horizons
Differentiate between sandy, clayey, and loamy soils (5 points each)
Perform the ribbon test to identify soil texture
List the major causes of soil erosion with percentages
Describe four types of water erosion
Explain five methods of soil conservation
Connect soil conservation to agricultural practices
