Back to: BIOLOGY NEW LOWER SECONDARY CURRICULUM BOOK 2
a) Colour. Have you noticed that different soils have different colours? Do you know the colour of loam soil? Why do you think it is that colour? The colour of soil is often determined by the mineral present and by the organic matter that covers the surface of the soil particles. Black soils are generally more fertile than lighter soils because they tend to have higher organic matter content.
b) Texture. This is how rough or how smooth a particular soil sample is. The texture of soil is determined by the relative proportions of sand, silt, clay and particle sizes present in the soil. Using the soil texture analysis chart as seen in figure 1.2, we see that sandy soils are coarse-textured and clay soils are fine-textured
Percent Sand
Figure 1.2: A key to soil types
(c) Particle size
Soil particles can be categorised into four the based on their size in terms of average diameter a the particle as seen in table 1.1.Different types of soil are made up of different soil particles, most soils have a combination of three or more particles.
| Table 1.1: Size of soil particles | |
| Particle size Average diameter | |
| Gravel | Greater than 2.0mm |
| Sand | 0.02 – 2.0mm |
| Silt | 0.002- 0.02mm |
| Clay | Less than 0.002mm |
1.2: Constituents of soil
Brainstorm on what you think makes up soil basing on their knowledge from the previous activity
Figure 1.3: Constituents of soil
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