Soil has an ecosystem all its own. It is very much alive and supports many life forms. From the tiny microscopic organisms we cannot see to the plants we grow, and of course to the bugs and insects we can see. Earthworms, insects, reptiles, nematodes, bacteria and fungus all reside in your soil. This ecosystem of life supports the soil composition helping with decay and nutrient cycles.
You have probably heard people say that earthworms in the garden soil is healthy. This is true. Earthworms tunnel through the soil. As they feed, organic matter passes through their bodies and is excreted as granular, dark castings. This enhances and adds to the soil structure as it mixes with the soil and breaks down. Earthworms also eat microorganisms that cause plant disease.
You will probably be surprised to find out what soil is made of. Beneath the ground surface the soil is full of living organisms that interact in a finely tuned living system but on a percentage basis, soil is mostly minerals weighing in at a whopping 45%, followed by air at 25% and water at 25%. The biological component (the balance of nutrients that is required to support healthy plant growth) is only 5%. But it is a very significant 5%.
When your soil is out of balance, you will see it through the plants. They will show signs of stress through discoloured leaves, wilting, blight, insect infestation, disease or fungus. You will definitely be able to see it if the soil is poor or seriously lacking something. Keeping in mind that factors in poor plant health can also be poor drainage or a lack of oxygen.