These are the substances that make up soil. They include: soil living organisms, organic matter, water, air and mineral matter.
Soil living organisms
Living organisms found in the soil include micro-organisms like bacteria and macro-organisms like earthworms. These organisms have the following effects on agricultural production:
• Through burrowing, they help aerate the soil.
• They assist in the decomposition of organic matter.
• Some bacteria strains fix nitrogen in the soil.
• Some microorganisms may cause diseases in crops.
• Some living organisms may be involved in biological weathering processes.
Soil organic matter
Organic matter is made up of decayed animal and plant tissue. Soil organic matter has the following importance in agricultural production:
• Organic matter adds nutrients to the soil when it decays.
• It increases the cation-exchange capacity of the soil.
• It protects the soil against pH changes.
• It reduces the toxicity of chemicals or poisons in the soil.
• It improves soil structure.
• It improves the water holding capacity of the soil.
• It helps modify the temperatures of the soil.
Water
Soil naturally gets its water from precipitation. Irrigation is also used to supplement soil water during dry seasons. Soil water has the following importance in agricultural production:
• It is a solvent for plant nutrients.
• It is a raw material for photosynthesis.
• It brings a cooling effect on plants during transpiration. This is because latent heat of vaporization is lost during this process.
• It is an agent of weathering.
• It is necessary for the germination of seeds.
• It softens the soil for easier cultivation.
• It maintains the shape of plant cells by making them turgid.
Air
Soil contains air. Soil air has the following effects on agricultural production:
• Oxygen is used during germination of seeds and in aerobic decay of organic matter.
• Oxygen is used in root respiration. It is also used by soil organisms to respire.
• Nitrogen-fixing bacteria convert nitrogen into nitrates, a form in which it is used by plants as a nutrient.
Soil mineral matter
These are particles of inorganic compounds arising from weathered rock material. They include metallic mineral elements like copper, iron and zinc, and non-metallic elements like nitrogen, chlorine, sulfur and phosphorus. Soil mineral matter has the following effects on agriculture:
• It forms a framework for soil formation.
• Spaces between the mineral particles are filled with air which is used by plants during root respiration.
• It offers surface area for water adherence.
• The minerals are a source of nutrients for plants.
Clay soil
• Clay soil has a fine texture.
• It has a high capillarity.
• It is poorly drained.
• It has a high pH (alkaline).
• It is highly plastic, hence easily molded.
• It sticks when wet and cracks when dry.
• It has a high ion exchange capacity.
Sandy soil
• It has low capillarity.
• It has a coarse texture.
• It is slightly acidic.
• It is well drained.
• It is well aerated as it has large air spaces.
• It has a low water holding capacity.
Loamy soil
• Loamy soil has a moderate texture.
• It is well aerated.
• It is moderately drained.
• It has high capillarity.
• It has good water holding capacity.
• It contains good amounts of plant nutrients and organic matter, and is thus good for agricultural production.
