Questions on Soil are regularly found throughout the Agricultural Science Paper, but are particularly found in

Question 1 (General Question),

Question 2 (the Soil Question),

Question 4 (the Experiment Question),
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Question 9 (the Scientific Explanation/Reasoning Question)
Consider Question 1 of the past 2009 Higher Level paper, this question is typically broken into ten parts, two of which are from the soil section of the course. Remember that the examiner is looking for specific points of information.
For example in the 2009 HL Paper, Question 1 (General Knowledge), asked students to
(d) “Give three reasons for low earthworm populations in certain soil conditions”
Students are recommended to indicate any three valid reasons for this, some of the reasons suggested in the marking scheme include
 low pH / too dry / waterlogged / poor aeration / compaction / too cold / low or no organic matter / predators (e.g. New Zealand flatworm)
(4+3+3 marks)
(e) “Name three minerals present in igneous rocks”.

Mica / feldspar / quartz
(4+3+3 marks)
The main mistakes that students make in these particular types of questions is that they do not give the required number of points as asked for in the questions above.
In the 2008 HL Paper, Question 2 (Soil Question), asked students to
Q2 (a) “Explain how the weathering of rocks contributes to soil formation”
Four separate points are needed to answer this experiment question. One approach would be to answer in bullet point format or alternatively, using well labelled diagrams and a detailed paragraph e is required here. Marks will be rewarded for mentioning the following points:


Soil particles originate from rock (compulsory) (3 marks)

Sun or freezing water causes rock expansion or cracking

Wind carrying particles causes grinding

Rainwater causes chemical reactions etc.

(any correct examples of weathering)
(6 + 3 + 3 marks)
Sample Question and Answer
Describe how the parent material can influence soil formation.
Soil is a natural medium for the growth of land plants. It is derived from parent material by weathering and ageing processes. The nature of the parent material greatly influences the characteristics of a soil. It will determine where a soil is acidic or alkaline, frequently water logged or well aerated, has diffuse or poor root penetration, is well structured, fine and friable or structureless, plastic or blocky in nature. It is desirable that soils develop on calcareous
(limestone) rock. This is a soft permeable porous rock. It has a good reservoir of Calcium ions which maintains a desirable pH of between 6.5 and 7.5. As a result of the Calcium ions, the clay particles flocculate and provide a well aerated soil. This allows large populations of earth worms and bacteria to live here, which provide large levels of nutrients for rapid plant growth. However if a soil develops on weather Old Red Sandstone, it will be acidic in nature.
This is detrimental to micro and macro organisms. As a result of their absence, soils tend to be poorly aerated, they tend to have poor pore space and only grow plant species of poor agricultural importance. Sandstone and Quartz are very hard durable rocks and can take much longer that limestone to be weathered into a usable soil.