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A useful deficiency design compares matched plants supplied with a complete mineral solution and plants lacking one specified nutrient. Use the approved growth medium and solution formulation so the omitted nutrient is not supplied unintentionally by soil or water. Removing an entire mixed fertiliser changes several ions and does not isolate a single nutrient deficiency.
Video by Professor SNAB. Use the demonstration alongside this lesson’s specification reference and written explanations.
Viewing focus: Design a controlled mineral-deficiency comparison
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: What is the main purpose of a complete mineral-solution control?
To provide a comparison with all specified nutrients available. It helps separate deficiency treatment from general unsuitable growth conditions.
After watching 2: Why may a short trial fail to reveal a deficiency?
Stored nutrients can support early growth. Treatment duration and the starting biological material matter.
What you'll be able to do
A useful deficiency design compares matched plants supplied with a complete mineral solution and plants lacking one specified nutrient. Use the approved growth medium and solution formulation so the omitted nutrient is not supplied unintentionally by soil or water. Removing an entire mixed fertiliser changes several ions and does not isolate a single nutrient deficiency.
Control plant species, starting size or age, light, temperature, water availability and relevant growth conditions. Include independent plants or containers as appropriate to the design and randomise positions or rotate them using a predefined scheme. The complete-solution control checks whether the general growth conditions support the plants.
Record defined outcomes such as leaf number, shoot length, dry mass or a consistently scored symptom. Nitrate supply supports nitrogen-containing molecules, while magnesium has a role in chlorophyll; shortage can affect growth and appearance. Similar symptoms can have other causes, so a yellow leaf alone does not uniquely identify one missing ion.
A seed’s stored nutrients can delay a visible treatment response. Allow the planned appropriate duration rather than concluding immediately that an omitted mineral is unnecessary. Fresh mass includes variable water content; dry mass can support a biomass comparison if material is processed consistently to the specified stable endpoint. Destructive measurements need a suitable sampling plan.
Compare means and variation for the actual independent units, and retain the individual observations. Many plants sharing one treatment container can share its light, solution and preparation errors; they are not always fully independent treatment replicates. A single container per condition limits generalisation even if many leaves are measured.
Interpret the effect within the tested species, nutrient range and duration. Growth and visible deficiency support a response to the treatment, while the proposed molecular mechanism needs the controlled formulation and relevant biological knowledge. The linked SAPS fertiliser resource provides a related mineral-supply context; use your centre’s specified omission design when testing a particular deficiency.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: All ten plants in each treatment share one container. Why is n = 10 not automatically ten independent treatment replicates?
Report the actual experimental units and the shared-container limitation.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.