Biological Composition

Biological Life of the Soil and the Soil Food Web

It is essential to feed and promote the growth of biological soil life for the health of your plants. Soil micro and macro organisms are the link between soil nutrients and the plants. Microorganisms include bacteria, fungi, mycorrhizal fungi, nematodes, mites, actinomycetes, springtails, protozoas (amoebas, ciliates and flagellates). Macro organisms include insects, earthworms, crustaceans, sowbugs, arachnids, moles, gophers, prairie dogs, etc.

These are some of the organisms that make up the soil food web – the system that

  • Supports plant growth, protects air and water quality.
  • Ensures plant and human health by suppressing disease causing organisms.
  • Sustains biological activity, diversity and productivity.
  • Regulates the flow of soil water and dissolves nutrients in the soil.
  • Stores and cycles nutrients and other elements.
  • Filters, buffers, degrades, immobilizes and detoxifies organic and inorganic materials that are potential pollutants.

A complex soil food web will contain a diversity of organisms that competes with and prevents disease-causing organisms in many ways. The more complex the food web, the greater the biodiversity. The more biodiversity, the healthier your soil and plants will be. There are many species of the various micro and macro organisms, all with a specific job to perform. Some, but not nearly all, of their functions are photosynthesizing, decomposing, mycorrhizal associations, nitrogen fixing, and pathogen predators. (

Soil and Organic Principles

There are six organic principles, and three of the principles involve the soil. Those principles are:

  • Balance the Mineral Content of the Soil
  • Build and Maintain Soil Organic Content
  • Do No Harm to the Beneficial Soil Life

There are thousands of different kinds of beneficial soil life, all with different functions and interactions with soil particles, the plants and other components of the biological soil life. Soil with a healthy, thriving soil food web improves both the chemical and physical qualities of the soil. If it hadn't been for the German chemist, Prof. Justus von Liebig, the inventor of nitrogen fertilizer, the importance of the biology of soil and of beneficial biological soil life would have been stressed much sooner. Liebig's dismissal of the importance of humus and his promotion of nitrogen as the most essential plant nutrient has brought about the chemical intensive soil management practices that have increased soil erosion, pollution of surface and groundwater, loss of farm land production, soil compaction, loss of soil tilth in addition to the loss of biological soil fertility.

As mentioned, all the microorganisms have specific functions. Bacteria and fungi have large roles to play in a healthy soil. Bacteria are necessary for plant growth on new fresh sediments. Bacteria “fix atmospheric nitrogen and carbon, produce organic matter and immobilize enough nitrogen and other nutrients to initiate nitrogen cycling process in the soil.” (Soil Biology Primer, Soil and Water Conservation Society, USDA Natural Resources Conservation Service, 2000)

The use of fungicides can be particularly damaging to the soil food web. Fungi enhance soil quality by decomposing complex carbon compounds (organic matter), improves the accumulation of organic matter, retains nutrients in fungal hyphal strands which reduces the leaching of nutrients out of the root zone. Their hyphae physically binds soil particles together into aggregates, improves plant growth, is a food source for other microorganisms, competes with other plant pathogens and decomposes certain types of pollutants. (Soil Biology Primer)

Many of the organic and synthetic chemicals kill the beneficial soil life, as well as soil pathogens. Repeated use  of salt-based chemical fertilizers is responsible for an increasing build up of salts in the soil, which destroys the soil structure and decreases soil fertility.

Creating Sustainable Beds

The addition of organic matter and inorganic material (when your soil condition requires it) begins the process of creating a sustainable bed. The population of beneficial microorganisms may be low when you start out, but as you add their food to the soil, and create spaces in the soil for air and water, their numbers will increase. It’s not instantaneous, but good results begin within just a few months. Even just loosening up the soil improves their conditions. That’s why I recommend preparing your beds a few months in advance, in the planting “off season”.

If your soil is low in organic matter and beneficial soil organisms, inoculate the soil with composted manure, bat guano, worm castings, granular and liquid humus and other liquid microbial inoculants along with composted plant matter. Sir Albert Howard, British botanist and pioneer of organic farming believed it necessary to add both composted animal manures and plant products to the soil for a complete soil food web.

In subsequent years, the beneficial soil life will have increased dramatically, provided high nitrogen fertilizers, herbicides, fungicides and pesticides, etc, were not applied to knock the population back down. After a year or two, the ability of new plantings to establish faster is greatly increased. Existing plants are stronger and healthier. This means lower maintenance for the gardener. The beneficial microbes are working 24/7, so you the gardener doesn't have to.

Mulch your sustainable medium and high water-use beds with a few inches of high quality composted organic material in the fall as replenishment for your beds. Low water-use plants do not require as much replenishment. Always retain a mulch covering over the soil.

Herbicide Carryover and Killer Compost

Read here about herbicide carryover and killer compost.