Soil profile, texture, organisms and temperature
Use soil layers, particles, structure, living organisms, water and temperature to explain conditions for crop growth.
Section 2.2 · Soil types, composition, texture and temperature
Exam scope and assessment notes
Use this original lesson for the listed 2026, 2027–2028 and 2029–2031 Cambridge syllabus cycles. This route maps Cambridge's 2026 Version 2, 2027–2028 Version 1 and 2029–2031 Version 1 syllabuses. The 2026 update changes only a weblink; Cambridge reports no significant teaching changes for the 2027–2028 or 2029–2031 cycles. Exams are in the November series, and the qualification is not available in every administrative zone; confirm entry with your centre. Centre-selected local crop, weed, pest, disease and livestock examples must be checked against local agriculture. StudyForA does not replace supervised, risk-assessed practical work, the four assessed practical exercises, the individual practical investigation/report, teacher assessment or Cambridge moderation. Online practice is not an official mark or grade.
Before you begin
- Read the syllabus that matches your exam year and confirm your centre can enter you for code 0600. This route maps Cambridge's 2026 Version 2, 2027–2028 Version 1 and 2029–2031 Version 1 syllabuses. The 2026 update changes only a weblink; Cambridge reports no significant teaching changes for the 2027–2028 or 2029–2031 cycles. Exams are in the November series, and the qualification is not available in every administrative zone; confirm entry with your centre. Centre-selected local crop, weed, pest, disease and livestock examples must be checked against local agriculture. StudyForA does not replace supervised, risk-assessed practical work, the four assessed practical exercises, the individual practical investigation/report, teacher assessment or Cambridge moderation. Online practice is not an official mark or grade.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does soil texture describe?
What you will learn
- Describe topsoil, subsoil and underlying material.
- Distinguish sand, silt and clay and explain crumb structure, humus, capping and pans.
- Compare sandy, loam and clay soils and describe soil mineral matter, organic matter, air, water and organisms.
- Explain how soil temperature affects growth and how mulching and shading reduce extremes.
Read a soil profile
A profile shows layers through the soil. The syllabus names topsoil, subsoil and underlying material. Topsoil commonly contains much biological activity and organic matter; subsoil and underlying material differ, but their properties depend on the site.
Do not infer exact fertility from layer names alone. A profile should be observed and tested in context.
Separate texture from structure
Texture describes the proportions and sizes of mineral particles: sand is largest, silt intermediate, and clay smallest. Structure describes how particles are grouped into aggregates.
A stable crumb structure leaves pores for air and water. Humus and organic matter can support aggregation; oxidation and loss of organic matter can weaken structure. Surface sealing or capping and compacted pans can restrict infiltration, roots or drainage.
Compare soil behaviour
Sandy soil often drains quickly and holds less water; clay soil can hold more water but may drain slowly; loam often combines useful drainage and water retention. These are broad patterns, not guarantees for every field.
Cultivation, compaction, organic matter, slope, climate and crop requirements modify these behaviours. Check the actual soil before recommending a practice.
Describe soil constituents and organisms
Soil contains mineral matter, organic matter, air, water and living organisms. Water may be free or gravitational, capillary or hygroscopic; not all soil water is equally available to plants.
Bacteria, nematodes, fungi and earthworms are examples of soil organisms. They affect decomposition, nutrient cycling, soil structure and plant health in different ways; their presence alone does not prove a soil is fertile.
Relate soil temperature to crop growth
Soil temperature affects the rate of plant growth. Excessive heat can damage young seedlings; frost can damage some crops.
Mulching seedbeds can reduce extreme surface heating or cooling, and shading transplanted seedlings can limit heat stress. The method and timing depend on crop and conditions.
Sources for this lesson
Pause and explain
What does soil texture describe?
Worked example
A field has a sealed surface, compacted layer and slow drainage. Explain how structure differs from texture and identify two likely effects.
Show the worked solution
- Texture concerns the relative particle sizes; structure concerns how particles aggregate and the pore spaces between aggregates.
- Capping can limit water entry and seedling emergence; a compacted pan can restrict roots, drainage and air movement.
- Inspect a profile and test field conditions before selecting a correction.
Answer The stated problems mainly indicate poor structure or compaction; texture cannot be diagnosed from them alone. Water and root movement may be restricted.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Compare likely water movement in sandy and clay-rich soils and explain why the labels alone cannot predict yield.
Give me a hint
Link particle and pore behaviour to drainage, then consider other growth factors.
Compare my reasoning
- Sandy soil commonly has larger pores and drains more readily, so it may retain less water.
- Clay-rich soil can hold more water but may drain slowly and reduce air around roots if waterlogged.
- Yield also depends on structure, nutrients, pH, crop, weather and management.
Sandy soil may dry quickly, while clay-rich soil may become waterlogged. Actual yield depends on several soil and crop factors, so particle-size class alone is insufficient.
Look for these in your work
- Both soils compared
- Water behaviour explained
- Other yield factors stated
Explain how repeated loss of organic matter could affect soil structure and suggest what evidence a farmer should gather before changing management.
Give me a hint
Connect organic matter to aggregation, then avoid a blanket prescription.
Compare my reasoning
- Reduced organic matter can weaken aggregation and contribute to poorer crumb structure.
- Weaker structure may increase capping, compaction, runoff or restricted root growth depending on the soil.
- Inspect a profile, measure organic matter if available, check pH and drainage, and compare crop performance before choosing an amendment.
Organic matter supports structure; its loss may make a soil more vulnerable to structural problems. A soil and crop assessment should guide any change.
Look for these in your work
- Cause and consequence connected
- More than one possible effect named
- Evidence gathered before action
A student calls a soil 'clay' after a single field observation. Explain two ways to improve the description.
Give me a hint
Use particle-size evidence and profile or structure observations.
Compare my reasoning
- Describe the observed particles or use a suitable texture assessment rather than relying on colour alone.
- Record structure, aggregation, compaction, organic matter and profile layers separately from texture.
- Compare observations from multiple representative locations because a field can vary spatially.
A useful soil description separates texture, structure and profile, uses a suitable assessment and samples more than one representative place.
Look for these in your work
- Texture assessed with evidence
- Structure and profile separated
- Sampling variability recognised
Common mistakes
- Treating loam as a fixed particle size
- Saying clay always means poor soil
- Assuming humus and texture are interchangeable
- Calling a pan a soil horizon
What can you explain now?
What does soil texture describe?
Compare with the explanation
The relative sizes and proportions of sand, silt and clay particles
Texture concerns mineral particle size and proportions.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Distinguish texture and structure, then compare one water-related property of sandy and clay soils.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.