Drainage and irrigation
Explain gravity drainage, waterlogging and leaching, and compare irrigation methods and their effects on crop yield and quality.
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 can waterlogging do to roots?
What you will learn
- Describe gravitational water moving down through soil and drainage by ditches.
- Explain effects of waterlogging on soil organisms and root respiration and identify nutrient loss by leaching.
- Compare irrigation methods and consider effects on yield and crop quality.
Drain excess gravitational water
After rain or irrigation, gravitational water moves downward through soil under gravity. Ditches can help drain waterlogged land, but poorly planned drainage may transfer water or nutrients to other places.
Leaching occurs when water carries soluble nutrients downward beyond roots. Waterlogged soil has less air-filled pore space, which can restrict root respiration and affect soil organisms.
Irrigate where and when crops need water
Irrigation supplies water when rainfall or stored soil water is insufficient. Methods include surface or furrow irrigation, sprinklers and drip delivery; choice depends on field shape, crop, water source, cost and maintenance.
Adequate water may support yield and quality, while excess can cause waterlogging, erosion, nutrient loss or disease conditions. No crop-specific irrigation programme or equipment specification is required in this syllabus.
Sources for this lesson
Pause and explain
What can waterlogging do to roots?
Worked example
A field alternates between waterlogging after storms and dry soil later. Explain two distinct management needs.
Show the worked solution
- During waterlogging, assess drainage and root aeration; ditches may remove gravitational water if designed safely.
- During dry periods, assess crop demand and water availability before choosing an irrigation method.
- Monitor nutrient loss and downstream effects because drainage and irrigation can both move water through the system.
Answer Drainage and irrigation address different water problems. Their timing and design must be balanced to protect roots, nutrients and downstream water users.
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.
Explain how heavy rainfall can both water a crop and cause a fertility problem.
Give me a hint
Describe a benefit and then trace a loss pathway.
Compare my reasoning
- Rain adds water that plants may use.
- If excess water drains downward, it can carry soluble nutrients below the root zone by leaching.
- Waterlogging may also restrict oxygen around roots; the effect depends on soil, drainage and crop.
Rain can supply useful water, but excess drainage can leach nutrients, and waterlogging can reduce root aeration.
Look for these in your work
- Benefit and risk distinguished
- Leaching explained
- Root effect stated
Choose between drip and sprinkler irrigation for two different field situations, explaining the evidence needed before deciding.
Give me a hint
Compare where water is delivered, field conditions, cost and maintenance.
Compare my reasoning
- Drip delivers water near plants and may suit targeted delivery, but needs suitable equipment and maintenance.
- Sprinklers distribute water over a wider area, but wind, evaporation, pressure and crop characteristics can affect performance.
- Compare water source, field layout, crop, energy, cost, labour, local rules and expected effect on yield and quality.
No method is universally best. Drip and sprinklers have different delivery patterns; field and resource evidence should guide selection.
Look for these in your work
- Two methods compared
- Trade-offs included
- Evidence identified
A grower proposes installing ditches beside a stream to drain a field. Identify two environmental questions that should be answered first.
Give me a hint
Think about where the water and dissolved nutrients will go.
Compare my reasoning
- Determine how much water and sediment may reach the stream during different rainfall conditions.
- Assess whether nutrients or farm chemicals could be carried with drainage water.
- Check local permissions, downstream users and site design with qualified local guidance.
Ditches can alter water flow and carry nutrients or pollutants. Their effect on the stream, downstream users and legal requirements should be assessed before construction.
Look for these in your work
- Water pathway considered
- Pollution or nutrient loss considered
- Local review included
Common mistakes
- Saying drainage removes all soil water
- Treating leaching as nutrient uptake
- Assuming irrigation always increases yield
- Confusing root respiration with photosynthesis
What can you explain now?
What can waterlogging do to roots?
Compare with the explanation
Reduce air in soil and restrict root respiration
Water-filled pores can limit oxygen supply to roots.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Define leaching and explain why both excess water and water shortage can reduce crop performance.
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.