Soil Types, Composition and Properties

What is Soil?

Soil is the loose top layer of the earth's surface in which plants grow. It is formed over long periods through the weathering of rocks and the decomposition of organic matter, and it serves as the medium that anchors plant roots and supplies water and nutrients.

Composition of Soil

Soil is made up of four main components:

• Mineral particles (sand, silt, clay) — from weathered rock, forming the largest portion.
• Organic matter (humus) — decomposed plant and animal remains that enrich soil fertility.
• Water — held between soil particles, essential for plant growth.
• Air — found in spaces between soil particles, needed for root respiration.

Types of Soil

• Sandy soil: large particles, drains water quickly, does not hold nutrients well.
• Clay soil: very fine particles, holds water and nutrients well but drains poorly and can become waterlogged.
• Loamy soil: a balanced mixture of sand, silt and clay; considered the best soil for most crops because it drains well while retaining adequate moisture and nutrients.
• Silty soil: medium-sized particles, holds moisture well, fertile but can compact easily.

Properties of Soil

• Soil texture: refers to the proportion of sand, silt and clay particles, which determines how the soil feels and how well it drains.
• Soil structure: the way soil particles are arranged/clumped together, affecting root penetration and water movement.
• Soil pH: measures how acidic or alkaline the soil is; most crops grow best in slightly acidic to neutral soil (pH 6–7).
• Soil fertility: the soil's ability to supply essential nutrients for plant growth.

Importance of Soil in Agriculture

Soil anchors plants, stores water and nutrients, and hosts important microorganisms that aid decomposition and nutrient cycling. Understanding soil type and properties helps farmers choose suitable crops, apply the right amount of fertiliser, and manage irrigation effectively.