From R2102 Feb ‘17:

Q5a) State the range of pH values which indicate an alkaline soil  [2 marks]

b) Name ONE plant that can be grown in EACH of the following conditions:

i) alkaline         [1 mark]

ii) acid              [1 mark]

c) Describe TWO distinct horticultural practices which can be used to enable calcifuges (acid loving) plants to be grown well in alkaline soils under EACH of the following headings:

i) mulches        [2 marks]

ii) watering      [2 marks]

iii) fertilisers     [2 marks]

This question relates to several different parts of the syllabus, the main one being:

3.2 Explain the significance of soil pH to plant growth.

Others are also linked:

2.2 Describe the characteristics and uses of different types of organic matter added to soil.

2.3 Describe methods of composting and their use/application in horticultural practices.

3.1 Describe a range of nutrients required for healthy plant growth.

3.3 Describe how plant nutrients can be provided and maintained.

4.2 Describe a range of compost types.

This is an example of a question with lots of different parts. For parts a) and b) very short answers are required. Longer answers are required for part c) as it asks you to ‘describe’.

For part a) it is important to think about the pH likely to be found in soil, and not just the meaning of alkaline. The examiner’s comments state that ‘To gain full marks candidates were expected to state that a pH value greater than 7 would indicate an alkaline soil and that plants rarely grow in conditions above pH 8-9.

Candidates who stated the pH range of 7-14 could not be awarded any marks as it is very unlikely that soil would reach a pH level of 14’.

For part b) there are two important things to remember:

·        Full botanical names should be given for plant examples

·        Typical plant examples should be used that there can be no doubt about

The examiner’s comments stated that marks weren’t awarded for plant examples that could grow in all soil pH types.

Part c) has several parts to think about. It can help to underline or circle the key words in the question to help make it clearer. It is basically looking at what to do if you have an alkaline soil and want to grow acid loving plants.

For each part you need to suggest what to use and give detail about how to use it.

The examiner’s comments suggested the following:

i) Mulches – Composted pine needles, composted bracken, leaf mould or peat could be used as a mulch. These should be applied to the soil surface to a depth of 50 – 100mm and will need to be re-applied over time. Mulches are slow acting.

ii) Watering – Rain water should be used instead of tap water which will have a high alkaline content and be detrimental to calcifuge plants. Iron sequestrine or Miracid can be added to lower the pH of the water.

iii) Fertilisers – Flowers of sulphur or ammonium sulphate can be sprinkled over the root zone of the plant. Iron sequestrine can also be used as a foliar feed.