Question 1
The diagram below illustrates the components of a typical soil. Study it and answer the questions that follow.
(a) Name the soil components labelled III and IV. (2 marks)
(b) State the percentage composition of each of the parts labelled III and IV in a typical soil. (2 marks)
(c) Name three constituents of the part labelled III. (3 marks)
(d) Give four reasons each why the parts labelled II and IV are important to crops.
(8 marks)
Observation
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This question was adequately attempted by many candidates although some candidates
mixed up the positioning of organic matter and mineral matter as well as giving their
percentage composition in ranges; thus losing marks. Few candidates were not explicit
on the importance of soil water to crops but were writing generalized statements like
‘for crop growth’ instead of being specific.The expected answers include:
1. (a) Name of soil components
III - Mineral matter
IV - Organic matter
(b) Percentage composition of labelled parts in a typical soil
III (Mineral matter) - 45%
IV (Organic matter) - 5%
(c) Constituents of III (Mineral matter)
- Gravel
- Sand
- Silt
- Clay
(d) Reasons why II (Soil water) and IV (Organic matter) are important to cropsII (Soil water)
- Helps to dissolve plant nutrients
- Essential for photosynthesis
- Aids the turgidity of plant cells
- Promotes the activities of soil organisms
- Necessary for germination of seeds
- Provides medium for soil reactionsIV (Organic matter)
- Rich in plant nutrients
- Improves soil aeration
- Moderates soil temperature
- Improves water holding capacity of soils
- Improves soil structure
- Buffers soil pH
- Prevents leaching of nutrients
- Improves the activities of soil microbes