A handful of good soil holds more living things than there are people on Earth.
Healthy soil isn't dirt. A single gram can contain up to billions of bacteria and thousands of species, plus kilometres of fungal threads. Scoop up a handful and you are holding more organisms than there are humans alive, working together to feed your plants.
To the eye, soil looks inert: crumbs of mineral and decayed matter. In fact it is one of the most biodiverse habitats on the planet. A gram of healthy topsoil can contain hundreds of millions to billions of bacteria belonging to thousands of different species, along with fungi, single-celled protists, microscopic nematode worms and tiny arthropods such as springtails and mites.
A handful of soil weighs perhaps a hundred grams or more, so it can easily hold more individual organisms than the roughly eight billion people alive. Fungal hyphae, the thread-like filaments fungi use to grow and feed, can run for many metres through a single gram of forest soil.
This underground community does essential work. Bacteria and fungi break down dead plants and animals, releasing nutrients plants need. Some bacteria fix nitrogen from the air. Fungal threads and bacterial secretions glue soil particles into crumbs, creating pores for air and water. Earthworms mix and aerate the soil; Charles Darwin was so fascinated that his last book, published in 1881, was about them.
For gardeners, this has a practical meaning. Adding compost and organic matter feeds the soil life that feeds your plants. Minimising digging and keeping the soil covered, with mulch or plants, helps preserve fungal networks and structure. Good gardening, in a sense, is good farming of creatures you will never see.
Source: Wikipedia — Soil biology · Text summarised from Wikipedia (CC BY-SA 4.0)
