Why are soil layers important?

This question comes up a lot when trying we're trying to explain why we chisel plow and disc with a shallow rotavasion. Here's a short answer to why it's important to keep soil layers as intact as possible when preparing soil for planting.

A teaspoon of productive soil generally contains between 100 million and 1 billion bacteria.  The relationship between these bacteria and other microbes in the soil and the impact of the soil structure within these relationships are in their infant stages of exploration.

Within these relationships is complete interdependence among species that benefit the overall health of the soil. All of these microbes together are performing necessary chemical reactions to break down and release nutrients that are bound in form insoluble for plant uptake and for other microbes to use. Some bacteria fix nitrogen from the air into the soil, for example, which fertilizes or feeds the soil of this necessary nutrient that stimulates leaf growth. 

When a plant makes sugar through photosynthesis, that energy is used not only to grow the plant up, but also down through the roots.  The roots “exude” out amino acids, proteins and other compounds into the soil that attract different microbes.  These compounds are called exudates. One type of hormone exudate may attract one type of beneficial bacterial when released and another amino acid exudate may attract a different microbe, depending on the plant’s needs.

Much like our digestive tract, plants build a biological shied of immunity around their root stock with a dominating beneficial bacteria and a fungal held minority. In gardens it is bacteria that rule the top layers of soil, and in forests it is fungus that dominates the top layers. Tilling the soil and careless double-digging reverses the soil layers that plants create as a defense mechanism against pathogens.  This illustrates why blanket-spraying pesticides that destroy the biological shield of beneficial microbes weakens plant defense against biological attacks, creating more “need” for future poison-spraying and fertilizing.

Strong biological root defense systems also account for the higher antioxidant content in organic vegetables. When Forrest and I nurse together, he is receiving additional antibodies through the milk from that to which I was exposed. It is similar with plants. When exposed to pests and microbes the plant responds by producing more antibodies, which present as antioxidants, and essential oils that possess anti-microbial and anti-fungal properties. If fungicide is sprayed on a regular basis, the plant has little need to produce anti-fungal oils and anti-oxidants.  

This is the foundation of growing food organically. The symbiotic relationships that exist in nature are respected and revered for its innate intelligence and wisdom.