The Soil Ecosystem

Soil, often called Earth’s skin, is more than just dirt.

It is a complex ecosystem made of abiotic factors, such as inorganic minerals, air, and water, and biotic factors, including microorganisms such as bacteria and fungi, as well as larger organisms such as plants, rodents, and earthworms.

Inorganic minerals make up 40 to 45% of soil volume. They enrich the ecosystem with nutrients such as nitrates, phosphates, and potassium.

Air and water together make up 50 to 55% of soil volume. Air enriches soil with gases such as oxygen, nitrogen, and carbon dioxide. Water helps dissolve nutrients and move them through the soil.

Organic matter, including living and dead organisms, makes up about 5% of soil. These organisms interact with each other and with abiotic factors to recycle nutrients.

Soil forms distinct layers called horizons. The O horizon is the top organic layer and is rich in decomposed plant and animal material.

Just below it lies the A horizon, also known as topsoil. This layer is especially important for plant growth because it contains minerals mixed with humus.

Humus forms when microbes break down dead plants and animals. It adds nutrients to the soil and improves water and air