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Soil Fundamentals

Soil chemistry basics.

By Will Newman II

What we choose to eat is often determined by family tradition, flavor, and convenience, occasionally with some concern for health thrown in the mix. Few of us think about what is – or should be – in what we eat.

Our food system

All domestic food regulations concern size, appearance, and contamination. None of address flavor or nutrition. This reflects our food system, which rewards growers for producing lots of food at low cost, and on time.

For conventional farmers this is achieved by treating the natural system of living things as if it were an industrial process. The by-product is injured and diseased farmworkers, dead and poisoned soils, polluted air and water, and food that has severely compromised nutrient value.

The energy cycle

Green leaved plants take carbon dioxide (CO2) and water (H2O) and, using the energy from the sun, build carbohydrate molecules. The formula looks like this:

6 CO2 + 6 H2O = 1 C6H12O6 + 6 O2

Six carbon dioxide molecules plus six water molecules yield one carbohydrate molecule with six O2 molecules left over. Plants take in carbon dioxide and water and breathe out oxygen. When we eat a carbohydrate we break it down like this:

1 C6H12O6 + 6 O2 = 6 CO2 + 6 H2O

One carbohydrate molecule combined with six O2 molecules yields six carbon dioxide molecules and six water molecules. People take in oxygen and breathe out carbon dioxide and water.

Seems like a lot of work for nothing, right? We started with carbon dioxide and water and ended up with carbon dioxide and water, so what’s the big deal? The net result of the process is that energy from the sun is now in our body. The plant has embedded energy in the molecule of carbohydrate, and we release it when we deconstruct the carbohydrate and re-form the carbon dioxide and water. We are unable to take energy directly from the sun, so we have a relationship with plants that allows us to tap the energy embedded in the plant’s cells.


The nutrient cycle

Each day we replace millions of cells in our bodies. To accomplish this ongoing regeneration, we use the substances we find in what we eat, breathe, and drink. While many of the nutrients we get come from breathing and drinking, we get most by eating plants, or by eating animals that eat plants.

Plants don’t only make simple carbohydrates. If the plant is healthy, and the nutrients are available, plants construct more and more complex molecules – complex carbohydrates, amino acids, proteins and a multiplicity of substances that we need to build healthy bodies and active immune systems.

The role of soil in nutrition

Plants get most of these critical nutrients from the soil, and from the living organisms in the soil. But only if the soil is healthy. Healthy soils have good tilth (structure), lots of micro- and macro-organisms (bacteria, fungi, protozoa, worms…), and food for them (living and dead organic matter.)

It is the structure of the soil that provides a steady supply of water and air to the roots of plants. The soil food web – the decomposing organic matter, and the decomposers – provides the nutrients that plants need to build complex molecules for its health and vitality.

Soil structure

Soil is a combination of mineral materials (sand, silt, clay), organic matter (living and dead), air and water. The bacteria hold together the smallest particles of soil by literally gluing them together. Fungus holds these basic structures together in larger aggregates. Worms and other macro-organisms keep paths open in and between the aggregates.

Water flow

In the narrowest spaces between aggregates, water is held by capillary action, moderating the flow of water both up and down in the soil, keeping water in the root zone for plant use. As the water is used by the plant, capillary action pulls water up from below to replenish the root zone. This is why plants in good soil can withstand prolonged drought without damage, while plants in poor soil wither and die.

These paths also allow water to move through the soil during rainfall, letting heavy rainfall pass down to replenish aquifers. It is this ability to absorb and transfer large amounts of water that minimizes runoff and erosion.

Air flow

The larger spaces between soil aggregates allow the flow of air and other gasses in and out of the soil. Air is primarily nitrogen, and air in soil makes nitrogen available to the soil food web, and thus to plants. Air in the air in the soil supports aerobic organisms and the succession of life, which in turn supplies plants with the nutrients they need, in the forms, and quantities they need, when they need them.

In turn, the plant uses these nutrients to build the carbohydrates, amino acids, proteins and other building blocks needed for the plant’s health and productivity. These healthy plants are the nutritious, tasty food human beings co-evolved with, and they keep us healthy and energetic.

Dirt first!

So it all comes back to the dirt: it is the soil that provides the building blocks to the plants, and the plants that provide the building blocks to us. Without good soil there are no healthy plants. Without healthy plants there is no healthful food. Without healthful food there are no healthy people.

Will Newman II is co-founder and Research and Education Director of OSALT (Oregon Sustainable Agriculture Land Trust). Will lives at Natural Harvest Farm near Canby, Oregon. He can be reached through the OSALT web site at

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