Fertile Soil

Living on the Earth, May 9, 1997: Fertile Soil 

Fertile soil is one of the most essential elements for life on Earth. Its
destruction was responsible for the decline of the Mesopotamian, Persian and
Roman civilizations, and in more recent times, contributed to the Great

A report from the United Nations found that within the lifetimes of many of us,
11 percent of the Earth's vegetated soils have been significantly damaged.
Twenty-four billion tons of topsoil are lost worldwide each year, as the human
population grows.  For each new person to feed, we have 260 tons less topsoil.
To understand what we are losing, let's journey into the good organic soil in
our garden. Here is a whole ecosystem in which an incredible number of living
organisms use minerals, organic matter, sunlight, air and water to create an
environment which nourishes the plants which nourish us. 

Green and blue-green algae and some bacteria perform photosynthesis, using the
sun's energy to turn carbon dioxide into carbohydrates, adding organic matter to
the soil. Other bacteria and algae convert the most plentiful component of the
atmosphere, nitrogen, into the form plants use as a major nutrient.
Actinomycetes bacteria and many kinds of fungi consume organic matter and create
humus, that near magical substance that results from the healthy aerobic,
biological decomposition of organic matter. Rhizobia bacteria live in a
symbiotic relationship with the roots of legumes such as peas, beans or clover,
exchanging nitrogen they extract from the air for carbohydrates produced by the
legumes. Still other bacteria break down organic matter, or carry out key steps
in the nitrogen cycle.

The bacteria are so numerous that a half teaspoon of good soil can contain
billions of them, as well as millions of actinomycetes and fungi, and a hundred
thousand algae. There are also tiny animals, thousands of protozoa and rotifers,
and nematodes. All this in one gram of soil-about a half teaspoonful. 

Insects such as ants, beetles, centipedes,  springtails, spiders, sowbugs, mites
and millipedes aerate and mix the soil as they feed on organic matter and other
living things. Earthworms travel through the soil, aerating it while feeding and
leaving behind a trail of their very fertile castings.  The web of life is so
balanced and interdependent that it is very hard for any disease organism or
insect pest to become a problem.

Given enough organic matter, such as plant residues and roots, compost or
leaves, and minerals including calcium, this complex ecosystem is continously at
work collecting and storing solar energy, feasting on organic matter, cycling
minerals, creating humus, and exchanging gases and nutrients with plant roots. 

Humus, created by this ecosystem, acts like a sponge to hold water and creates a
crumb structure in the soil which allows air and plant roots to penetrate
easily. Humus helps a sandy soil hold water and a clay soil drain. It is a
reservoir of nutrition.

Plants send their roots through the soil, sometimes many feet down, opening up
additional passageways, bringing up fresh minerals from the deeper layers of
soil, and creating a zone of extraordinary biological activity, the rhizosphere,
around each root. Carbon dioxide and hydrogen given off by the roots increase
the acidity nearby and help release nutrients held by the humus and clay

A slightly acid soil, near neutral, will encourage soil organisims, and their
processing of organic matter helps maintain that condition.  Compaction by
machines or feet, and excessive rototilling can be as harmful to soil life as
tornadoes or earthquakes are to ours. Chemical fertilizers are harsh materials
which tend to make the soil more acid, and destroy organic matter. Toxic
pesticides wreck untold havoc on the microscopic life of the soil.

We can't begin to care for the world's soils if we don't each care for the soil
in our own yard. In the diversity, ecological complexity, and health of good
garden soil, we find an important model for our larger scale relationships to
the Earth.

This is Bill Duesing, Living on the Earth


organic vegetables) and Solar Farm Education (working on urban agriculture
November 1995 are available there.