Agriculture Reference
In-Depth Information
The Top Five Inches of Soil
A good soil is alive with microbial life. There are the protozoa, which
are the smallest forms of animal life. And there are the nematodes, little
eel-like animals that are more commonly thought of as parasites. The top
few inches of a soil system also hold bacteria, yeasts, fungi, actinomy-
cetes and algae. Researchers have calculated that a doublehandful of bio-
logically active soil will contain more units of life than there are people
on the face of the earth. Aerobic life must have its air. Anaerobic life —
below the top few inches — has to have an air-free environment. That is
one reason eco-farmers do not like the moldboard plow. That instrument
is unkind to the farmer's unpaid labor force. It puts aerobic life in airless
chambers, and moves anaerobic life up to where there is air.
The top five inches of almost any soil system contains 95% of the
soil's aerobic life. These bacteria, together with crop residue and organic
matter, need oxygen. Humus, as the end-line result of decayed organic
matter, is concentrated in the top two to five inches of soil. And humus is
the life of the soil, so to speak. Its tag reads physical, but it is really the
bridge between the biological and the chemical. Since most nutrient sys-
tems are prolific in the top five to seven inches of surface soil, and quite
the opposite in the subsoil, field samples of soil for laboratory analysis
must be taken at a uniform core depth. A separate subsoil sample directly
below the surface sample will reveal numerous differences.
— Charles Walters, in
Eco-Farm
