Soil is the loose, upper layer of the earth’s surface in which plants grow. It is one of the most important resources in agriculture.
Soil Formation
Soil is formed by the weathering of rocks (the parent material) combined with the decay of organic matter. Weathering can be:
- Physical weathering: breaking of rocks by temperature changes, wind, water, ice (no chemical change).
- Chemical weathering: breakdown of rocks by chemical reactions (e.g. with water and acids).
- Biological weathering: breakdown by living organisms (roots, burrowing animals).
The Soil Profile
- O horizon: organic matter (humus) from decayed plants and animals.
- A horizon (topsoil): fertile layer rich in humus; where most roots and soil organisms are found.
- B horizon (subsoil): contains minerals leached from above; less fertile.
- C horizon: weathered parent rock.
- Bedrock: solid parent rock.
Types of Soil
| Soil type | Particle size | Properties |
|---|---|---|
| Sandy soil | Large | Drains easily, low water/nutrient holding, easy to cultivate (light soil) |
| Clay soil | Very small | Poor drainage, high water/nutrient holding, hard when dry (heavy soil) |
| Loamy soil | Mixture | Best for farming — balanced drainage and fertility |
Properties of Soil
- Physical: texture, structure, porosity, colour.
- Chemical: pH (acidity/alkalinity), nutrient content, cation exchange capacity.
Best soil for crops: Loamy soil, because it holds enough water and nutrients while still draining well and allowing air into the soil.
Summary
Soil forms from weathered rock plus organic matter. Its profile has horizons (O, A, B, C and bedrock). Sandy, clay and loamy soils differ in particle size, drainage and fertility — with loam being the most suitable for farming.
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