There's so much more to healthy soil than what the eye can see.
Far from being merely a collection of minerals, healthy
soil is a working community whose business it is to recycle
most anything that passes by. Bacteria feed on pollutants
in the waste water. Viruses, in turn, seek out bacterial
hosts and live on their life fluids. Protozoa, the simplest
form of animal, prey on bacteria, and
nematodes — roundworms just visible to the
eye — consume organic matter of any kind.
Truly, there is no better cleanser and renovator than
living earth. A cleanser, because clay particles in the
soil act as electrostatic filters capable of adsorbing
virus pathogens before they can migrate; a renovator,
because microorganisms, as they work, transform harmful
microbes into carbon dioxide and soil nutrients, and
produce antibiotics in the bargain.
Oxygen is critical to the absorption field and the
creatures in it. Aerobic bacteria — those that thrive
in a well-aerated environment — are far better suited
to the chore of recycling effluent than are the anaerobic
varieties. Without sufficient oxygen, aerobic bacteria and
the protozoa that feed on them fall dormant or die. At this
point, anaerobic bacteria, fungi and yeasts will take over.
The anaerobic organisms work more slowly and give off less
heat. They also process waste material differently than the
aerobic variety, creating acids and methane rather than the
sugars and fixed nitrogen beneficial to the soil. Under
these conditions, ferrous sulfide forms and bonds with
algae and dead bacteria to make a layer of insoluble gum,
called the organic mat , that clogs soil pores and
restricts drainage. This clogging mat exists in limited
measure under aerobic conditions and is important to the
system as a natural filter. But when it spreads out of
control in unhealthy soil, the field will ultimately fail
to do its job.