What Is a Rich Organic Soil?

Organic Matter

• Organic matter consists of carbon-containing materials found in the soil, such as dead plant matter. Soil organic matter feeds the microbial life of your soil, and as these microorganisms break down organic compounds, they release nutrients for your plants to use. After the breakdown of organic matter, the microbes leave behind humus, organic material that continues decaying very slowly -- sometimes taking hundreds or even thousands of years -- and gives healthy soil its dark color and crumbly texture.

  High-quality garden soil contains at least 5 percent organic matter. Organic matter improves numerous soil properties, including soil structure.

Soil Life

• Although a handful of garden soil may seem merely nonliving dirt, healthy soil teems with life. Bacteria, actinomycetes, fungi and other microscopic critters work tirelessly at breaking down the organic matter found in your soil. This releases the nutrients tied up in the organic material, returning them to the soil in a form that plants can use. As populations of helpful microorganisms rise, they leave less room for harmful, disease-causing microorganisms to take hold, allowing for greater disease resistance. The microbe population in a teaspoon of healthy soil exceeds the Earth's human population.

  Once the microbes finish dining on the organic matter, it becomes a stabilized material known as humus. Humus improves the structure of your soil and its ability to hang onto water and nutrients, keeps the pH even, prevents toxic levels of minerals from developing and continues releasing small amounts of nutrients as its very slow breakdown continues.

Nutrients

• Your plants need 13 different mineral nutrients to survive. In conventional gardening, gardeners apply pure forms of these nutrients using synthetic fertilizers. In organic soils, microbes release nutrients as they break down organic matter. Healthy soils contain the right balance of nutrients; too much as well as too little of a particular mineral can cause damage to plants.

Water and Air

• Healthy soil contains about 50 percent water and air. Soil texture refers to the size of the soil particles. Large soil particles like gravel or sand contain large spaces between them for abundant amounts of air and water to collect. The tiny particles found in silt and clay soils allow for smaller spaces and less air and water.

  While you cannot change your soil texture, soils high in organic matter show improved soil structure. In soils with good structure, particles clump together to form aggregates, allowing just the right balance of air and water to fill the soil.