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In this lesson we are going to discuss about the introduction to soils

Answer Text:
Soil
- Uppermost layer of the earth’s crust on which plants grow.
Constituents/Composition of Soil
1. Inorganic Matter
- Weathered rock fragments made of minerals from parent rock.
- Forms skeleton or fabric of soil.
- Forms 45% of total volume.
2. Organic Matter
- Decomposed remains of plants and animals and their wastes.
- Forms 5% of total volume.
Significance of Organic Matter
a) Broken down by bacteria forming humus improving the soil fertility.
b) Soil with high organic matter is alkaline while one with low organic matter is acidic.
3. Soil Water
- Water contained in the soil.
- Forms 25% of total volume.
Types of Soil Water
Hygroscopic Water
- Water held as a thin film around soil particles.
Gravitation Water
- Excess water which moves downwards to the zone of ground water.
Importance
a) Solvent of minerals and nutrients essential for plant growth.
b) Causes leaching Carrying of minerals.
c) Causes water logging which blocks air circulation causing soil to lack oxygen and become acidic.
4. Soil Air
- Air contained within air/pore spaces of soil.
- Forms 25% of total volume.
Importance
a) For plant and soil organisms metabolism.
b) For oxidation which causes conversion of part of organic material into nitrogen.
c) For respiration of aerobic micro-organisms which break down organic matter to form humus e.g. bacteria.