Soil Science Explained

Soil is far more than just "dirt." It is a living, breathing ecosystem — a complex mixture of minerals, organic matter, water, air, and trillions of living organisms. Soil is, quite literally, the foundation of almost all life on land.

The four components of soil

Healthy soil is made up of roughly equal parts of four key components:

• Minerals (45%) — fragments of weathered rock, including sand, silt, and clay particles
• Organic matter (5%) — decomposed plant and animal material, essential for fertility
• Water (25%) — held in tiny pore spaces between soil particles
• Air (25%) — oxygen and other gases that roots and organisms need to survive

How soil forms

Soil formation (pedogenesis) is an incredibly slow process — it can take up to 1,000 years to form just 1cm of topsoil. Rock is broken down by physical weathering (frost, temperature changes) and chemical weathering (water, acids). Plants colonise, die, and decompose, adding organic matter. Over thousands of years, distinct layers (horizons) develop.

A single teaspoon of healthy soil contains more living organisms than there are people on Earth. Soil is the most biodiverse habitat on the planet — teeming with bacteria, fungi, protozoa, nematodes, earthworms, beetles, and hundreds of other species.

Soil organisms drive the decomposition of organic matter, cycling nutrients back into forms plants can use. Without them, dead plant matter would accumulate and nutrients would be locked away permanently.

Soil contains more carbon than the atmosphere and all land vegetation combined — making it one of the most important carbon stores on Earth. This carbon is held in the form of organic matter (humus) and in the bodies of soil organisms.

When soils are disturbed — through ploughing, overgrazing, or deforestation — stored carbon is released as CO₂. Conversely, regenerative agriculture practices can rebuild soil carbon, helping to mitigate climate change.

Soil plays a dual role in climate change — it can be both a source and a sink of greenhouse gases, depending on how it's managed. Understanding this relationship is one of the most important areas of current environmental science.

How healthy soil helps the climate

• Stores carbon in organic matter and microbial biomass
• Regulates water cycling, reducing flood and drought extremes
• Supports plant growth, which absorbs CO₂ from the atmosphere
• Reduces surface runoff, preventing erosion and carbon loss

Almost everything we eat depends on soil. Whether it's the wheat in our bread, the vegetables on our plate, or the grass that feeds the animals we eat — the chain starts in the soil.

Healthy soil provides the nutrients plants need — nitrogen, phosphorus, potassium, and dozens of micronutrients. Soil degradation means less nutritious food, and ultimately less of it.

Soil acts as a natural water filter, sponge, and regulator. Healthy soil absorbs rainfall, filters contaminants, and slowly releases clean water into rivers and aquifers.

• Filtration: Soil particles and microbes remove pollutants, pathogens, and heavy metals from water as it passes through
• Storage: Topsoil acts like a sponge — absorbing and holding water that plants can use over weeks
• Flood prevention: Healthy soil absorbs rain quickly; compacted or degraded soil causes surface runoff and flooding
• Drought resilience: Carbon-rich soils retain more moisture, helping crops survive dry periods

Soil is the most biodiverse habitat on Earth, yet it remains the least understood. An estimated 25% of all species on Earth live in soil — and most haven't even been named or described by science yet.

The soil food web

Soil organisms form an intricate food web. Bacteria and fungi decompose organic matter; protozoa and nematodes eat the bacteria; larger invertebrates prey on smaller ones. This web drives nutrient cycling, soil structure, and plant growth.