Soil fertility, nutrients, nitrogen and amendments
Explain nutrient roles and deficiency clues, plan soil tests and evaluate organic and inorganic fertility management.
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 a soil pH test directly estimate?
What you will learn
- Describe the roles and deficiency signs of N, P, K, Ca, Mg and S.
- Plan representative soil sampling and pH testing and explain the nitrogen cycle.
- Explain the roles of legumes, manure, compost and inorganic fertilisers in soil fertility.
- Explain how fertilising practice and liming can alter soil pH.
Relate nutrients to plant growth
Nitrogen supports amino-acid and protein formation; phosphorus is important in energy transfer and root development; potassium supports enzyme activity and water regulation. Calcium supports cell walls and growing tissues, magnesium is central to chlorophyll, and sulfur is needed in some amino acids.
Deficiency patterns vary by crop and conditions. Older leaves may show mobile-nutrient deficiencies first, while calcium deficiency often affects growing points; symptoms overlap with disease, drought and other stresses, so observation alone is not a diagnosis.
Sample and test fairly
Take samples from representative parts of a field using a consistent method and clean equipment. Avoid unusual patches unless testing them separately; label locations and record depth, date and recent management.
A pH test estimates acidity or alkalinity. Follow the test method, calibrate equipment when required, repeat measurements and compare results with suitable crop guidance. A pH value does not measure every nutrient.
Follow nitrogen through the system
Nitrogen moves through soil, air and organisms. Nitrogen fixation by some bacteria makes nitrogen compounds available from atmospheric nitrogen; plants take up available compounds; animals obtain nitrogen by feeding; decomposition returns compounds; nitrification and denitrification transform them.
Leaching and crop removal can reduce available nitrogen. Legumes associated with nitrogen-fixing bacteria can contribute to the system, but they do not remove the need to assess nutrient balance and soil conditions.
Maintain fertility with organic and inorganic inputs
Legumes can contribute nitrogen through biological fixation. Manure and compost add organic matter and nutrients and can help maintain soil structure and fertility; composition varies, so application should be planned from local evidence.
Inorganic fertilisers supply mineral nutrients. The syllabus requires recognition of one predominantly phosphorus fertiliser, one predominantly potassium fertiliser and one compound fertiliser. Check the product label and analysis because formulations differ.
Use pH evidence when choosing inputs
Fertilising practices can change soil pH, and liming can raise the pH of acidic soil. A change that suits one crop or soil may be unsuitable for another.
Use representative tests and crop requirements to inform decisions. Do not apply a universal lime or fertiliser rate from a general lesson; follow qualified local guidance.
Sources for this lesson
Pause and explain
What does a soil pH test directly estimate?
Worked example
A crop has pale older leaves and a low soil pH result. Explain why this evidence is not enough to prescribe fertiliser.
Show the worked solution
- Pale leaves may indicate a nutrient problem but can also result from water, root, disease or other stress.
- A pH test informs acidity or alkalinity, not a complete nutrient analysis.
- Use representative samples, crop history and appropriate nutrient tests before selecting an amendment.
Answer The signs are clues, not a diagnosis. Soil pH and nutrient availability are related but different; further sampling and crop-specific advice are needed.
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.
Plan a representative pH sampling approach for a field with one visibly waterlogged corner.
Give me a hint
Decide whether the unusual corner belongs in the general sample.
Compare my reasoning
- Divide the field into reasonably uniform sampling areas and record boundaries.
- Take several representative subsamples from the main area using the same depth and clean tools.
- Sample the waterlogged corner separately, label both samples and use the same validated pH method.
Keep the unusual corner separate so the main sample represents the field while the distinct condition is documented. Use consistent sampling depth and method.
Look for these in your work
- Representative areas selected
- Unusual patch separated
- Method and labels controlled
A farmer applies nitrogen fertiliser, then heavy rain occurs. Explain one possible loss pathway and how legumes may contribute to nitrogen availability.
Give me a hint
Trace nitrogen movement and distinguish a contribution from a guaranteed fertiliser replacement.
Compare my reasoning
- Rain can move soluble nitrogen compounds below the root zone by leaching.
- Some legumes form associations with nitrogen-fixing bacteria that convert atmospheric nitrogen into compounds in the system.
- Crop demand, soil conditions, biomass management and losses still determine how much becomes available.
Leaching may remove available nitrogen from the root zone. Legumes can add nitrogen through fixation, but the benefit depends on species, growth and management.
Look for these in your work
- Loss pathway correct
- Legume role explained
- No fixed replacement claim
Design a short investigation to distinguish nutrient deficiency from low pH as explanations for poor growth.
Give me a hint
Use separate measurements or treatments, comparable plants and repeated observations.
Compare my reasoning
- Collect representative soil samples and record pH using a consistent test.
- Measure relevant nutrients or compare a supervised, controlled nutrient treatment with a suitable untreated comparison.
- Keep other conditions similar, repeat measurements and interpret growth alongside symptoms and possible disease or water stress.
A fair investigation measures pH separately from nutrient availability and compares growth under controlled conditions. It should not change several factors at once.
Look for these in your work
- pH and nutrients distinguished
- Comparison controlled
- Alternative explanations considered
Common mistakes
- Using one visibly unusual patch to represent an entire field
- Treating pH as a direct measure of nitrogen
- Diagnosing a deficiency from a single leaf symptom
- Assuming every legume fixes the same amount of nitrogen
What can you explain now?
What does a soil pH test directly estimate?
Compare with the explanation
How acidic or alkaline the tested soil is
pH describes acidity or alkalinity.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Name three plant nutrients, explain one deficiency clue and state what a pH test does and does not show.
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.