Healthy soil does not just occur by accident. When farming practices cause imbalance and destruction to soil biology and chemistry, the natural ability for the soil to heal and produce healthy plants is greatly decreased. The end result is soil that no longer can produce quality food without the use of expensive fertilizers, herbicides, pesticides and fungicides. Particular attention needs to be used to reduce the damage caused by current farming practices.
The aerobic zone is the layer of soil that is in contact with the atmosphere, where oxygen is able to penetrate between soil particles and atmospheric air makes up 25% of the overall soil composition.
This is the profile of the soil where plant feeder roots spread out and where water soluble nutrients are transported into the plant through diffusion and absorption. The aerobic zone is able to support millions of microscopic, air-breathing beneficial organisms that perform many vital roles in the growth of healthy crops.
A healthy aerobic zone is soft and mellow without crusting or lumps. Ideally, aerobic soil should be comprised of 6-10% humus content and therefore capable of holding half its weight in water. The soil should smell like fresh air; a soil with no aroma at all is a dead soil.
The depth of the aerobic zone varies from field to field and varies within fields as well. It is important that you become familiar with the depth of aerobic zone in your fields to ensure that your tillage practices do not result in lumps of anaerobic soil being turned up and deposited on the surface (see Anaerobic Soil).
Anaerobic soil is an environment that has no oxygen and is found horizontally below the aerobic layer. In areas that have had heavy chemical application or with high erosion, the anaerobic layer can be found very close to the surface. Any decaying plant material that is worked into this layer will not decay properly. Rather it will be preserved in formaldehydes and alcohols, the by-products of anaerobic organisms living in this layer of soil.
The anaerobic soil will smell musty, it may be sticky, slimy and or have a shiny appearance. Tap roots may penetrate this layer, but feeder roots are generally not found in the anaerobic zone.