Soils form the earth’s surface skin occupied by an enormous
population of microorganisms, organic matter, water and minerals. Since early childhood, I have appreciated the soils of forests, fields
and gardens. I worked on a farm for several summers as a teenager and learned
about crop rotation methods of creating and preserving fertile soils. Cow
manure-fertilized fields grew crops that fed the cows. Fields that had produced crops were planted with clover and
alfalfa that fixed nitrogen in the soil and were plowed under in the fall to
increase the humus content of the solids. Expert plowing kept soils aerated and fluffy. These agricultural practices were sustainable over centuries.
The term “green” is applied to healthy environmental
practices. Developments in the media made "green" the slogan for action to limit
the adverse effects of air pollution. The media often suggested that this is a
relatively new consensus that there is an environmental crisis. Green, of
course, refers to the color of chlorophyll in plants. Human action destroys
plants and replaces healthy ecosystems with monocultures that are unsustainable.
Another slogan that emerged was "save planet earth." Humans will not save the
planet. The task for humans is to stop destroying the environments that sustain
their own kind. If we fail, the planet will do just fine without us. Perhaps the
green should be changed to brown in recognition that all plants grow in soils,
essential components of the Earth's ecosystem.
Soils are the second largest carbon reservoirs, reactive to human disturbance and climate
change. As the planet warms, soils will add carbon dioxide to the atmosphere . A
gram of soil can contain billions of organisms, belonging to thousands of species. Carbon in soils is returned to the atmosphere by organisms that feed on
organic material in the soil. Plants interact with soils in a complex manner through root systems. Fertile
soils hold water and are porous to growing roots.
Soil nutrients that are held by clay and humus. The pore network permits the infiltration and
movement of air and water. Compaction, a common problem with soils, reduces this
space, preventing air and water from reaching the plant roots and soil
Soil organic matter is made up of organic compounds and
includes plant, animal and microbial material, both living and dead. A typical
soil has a biomass composition of 70% microorganisms, 22% macrofauna, and 8%
roots. The living component of an acre of soil may include 900 lb of earthworms,
2400 lb of fungi, 1500 lb of bacteria, 133 lb of protozoa and 890 lb of
arthropods and algae. A small part of the organic matter consists of the living
cells such as bacteria, molds, and actinomycetes that break down the dead organic matter.
Most living things in soils, including plants, insects,
bacteria, and fungi, are dependent on organic matter for nutrients and/or
energy. Soils have organic compounds in varying degrees of decomposition; the rate is dependent on the temperature, soil moisture, and aeration.
Bacteria and fungi feed on the raw organic matter, which are fed upon by
amoebas, which in turn are fed upon by nematodes and arthropods. Organic matter
holds soils open, allowing the infiltration of air and water, and may hold as
much as twice its weight in water. Many soils, including desert and rocky-gravel
soils, have little or no organic matter. Soils that are all organic matter, such
as peat (histosols), are infertile. The final stage of organic decomposition is called humus.