A microbe is any organism too small to see without a microscope: bacteria, archaea, fungi, protozoa, and some algae. A single teaspoon of healthy soil can hold billions of them, and their activities drive much of what farmers care about.

Soil microbes decompose organic matter, releasing nitrogen, phosphorus, and sulphur in forms plants can take up. Others fix nitrogen from the air, solubilise phosphate, or promote root growth. Some are pathogens. The balance matters. A soil rich in diverse microbial life tends to suppress disease better than one that has been fumigated or over-fertilised.

Where they matter most

• Decomposition and nutrient cycling
• Nitrogen fixation in legume nodules
• Mycorrhizal partnerships with roots
• Disease suppression and soil structure formation

Microbes respond quickly to management. Tillage, fumigation, and overuse of synthetic nitrogen all shift the community. Cover crops, compost, and reduced disturbance tend to rebuild it, though the science of exactly how is still developing.