CompostFungiSoil BiologySoil Composition

Soil Science Basics for Beginners

by Aaron Jerad

It’s dark. You are surrounded by giant flesh eating amoebas. You can’t move very fast…. Welcome to the world of the bacteria, the smallest but most abundant member of the soil food web. Often feared but essential, whether directly or indirectly, for the survival of almost all other living organisms on earth.


Cover cropping, mulching and composting are three great ways to build soil. In this photo
Lance Swiggert explains his composting system. You can see many stages of the composting
process. In the far back is a rough pile of weeds and dead plants which have been removed
from the garden. In the foreground is a freshly made pile, with layers of old hay, manure and
other organic matter. To the left is a pile that has been turned. Lance is standing by a finished pile
of compost that he has run through a shredder. It is ready to go into the garden.

The Soil

Good soil is alive soil. It’s texture is a balanced mix of clay, silt and sand called loam. It has a high percent of organic material and humus. Not to be mistaken for hummus, the yummy middle eastern chick pea dish, humus is super-food for the soil. It is organic material that can not be broken down any further and can remain stable for many years. Humus is created by composting, the decomposition of organic matter. Good structure, humus, and other organic material allow a soil to soak up and hold moisture, flow oxygen to the roots of plants, and provide a continual and stable supply of nutrients and minerals.

Humus consists of very long, hard-to-break chains of carbon molecules with a large surface area; these surfaces carry electrical charges, which attract and hold mineral particles. — Teaming with Microbes, Jeff Lowenfels & Wayne Lewis, p. 31

All plants need several major nutrients and an array of micro nutrients. There are two significant groups of major nutrients, the first have a positive electrical charge: calcium, potassium, sodium, magnesium, iron, ammonium, and hydrogen. The second group has a negative electrical charge: chloride, nitrate, sulfate, and phosphate.

Electrical charges are significant because soil particles like clay and humus carry a negative charge and grab onto the first group of positively charged nutrients. When water floods through the soil the electrical bonds are like ‘life savers’ for some nutrients. The second group of nutrients with a negative charge, however, are actually repelled and left to helplessly wash away, unless… the soil is thriving with life.

In addition to bonding with certain nutrients, the inert mineral soil particles like clay and humus also create the ‘habitat’ for bacteria, fungi and other soil organisms. These organisms are the foundation of soil life (and all life in general). A spoonful of healthy soil can contain up to a billion hard-working soil microbes.

Soil organisms are a hungry bunch and they eat up available nutrients, each other and a whole lot of nitrogen (nitrates) which they need to form living tissue. Healthy soil is a giant frenzy of reproduction, ingestion and death. Nutrients that might be washed away are caught in this microscopic ‘nutrient juggling act’ that is taking place in the cycle of soil life: bacteria, fungi, protozoa, nematodes, insects and worms. This process forms an economy of soil nutrients in which plants are a major player.


Click for larger view

Most folks know that plants are important for photosynthesis and the cycling of oxygen. What we don’t see is that plants also exude a variety of carbohydrates (sugars) and proteins directly into the soil from their roots. These exudates fuel the feeding frenzy of bacteria and cultivate colonies that will specifically help the plant. Plants can even shift which exudates they produce in order to cultivate different bacteria and fungi, which in turn support the plant’s own life cycle and needs. The word cultivate is usually thought of as a human practice, but plants are also ‘farming’ the soil.

All the intricate connections, organisms and cycles that create healthy soil are sometimes collectively called “The Soil Food Web”. People depend on plants and plants depend on this interconnected living matrix. A creative approach to gardening is to work at cultivating soil life. If we get it right we will be throwing fuel on the fire that is life in the soil and our plants will reward us with abundance.

4 Comments

    1. Agreed DeepGreen. It does need one more paragraph to introduce and lavish praise upon mycorrhizal fungi, those fungi that form symbiotic relationships with living plants. They create huge networks of microscopic threads in the soil that connect with plant roots, transport nutrients, build soil structure and much more…

  1. Any chance of some links to more material by or about Lance Swiggert? So far as I can see he exists in cyberspace only in two articles by the current author. More exposure to this guy’s composting expertise would be welcome.

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