Constantly tunneling down with bits of organic matter, earthworms create a naturally aerated soil. These tunnels carry water throughout the soil, where it can be stored and used by roots, while providing good drainage to prevent rot. After eating the organic matter, they expel castings, which are extremely high in time release nitrogen, phosphorous, and potassium, as well as minerals and micronutrients. Aerated soil rich in nutrients and full of life is said to have good tilth. Chemical farming destroys tilth and worms which provide time released fertilizers eliminating the need for chemical fertilizers.
Healthy soil makes healthy roots.
Roots like aerated soil full of nutrients and water. Roots are better able to absorb simple, time-released nutrients provided in organic form than they are synthetic chemical fertilizers. Synthetic fertilizers only provide large molecules of a few basic nutrients, usually derived from petroleum, and actually kill earthworms. Soil that has been chemically treated has poor tilth. Healthy roots make healthy plants.