Living soil is the basis of food support for nearly every land creature, from plants to animals to humans to bacteria and fungi. It takes over 500 years to build an inch of topsoil through natural processes. This small percentage is called humus, and it is actually made of once-living matter that has decomposed beyond recognition. Its spongy quality helps the soil hold water and nutrients. Humus helps to support the life of plants and soil organisms.
Earthworms are another important component of good soil.
Like little tractors, they bore through the soil and aerate it, providing channels for water and roots. They digest microorganisms and decaying vegetable matter as they go, leaving fertile castings behind. Organic farming is the method used by people for thousands of years, before the advent of chemical fertilizers and pesticides. In the nineteenth century, German chemist Justus von Leibig burned a plant in his laboratory and found that the ashes contain a lot of nitrogen, phosphorus and potash. This was praised as a pioneering discovery in the new age of science, and factories began producing N, P, and K in powder form.