Plants have existed on this planet for at least the last billion years. During that time there has been a very close co-evolution of plants with the microbes that inhabit the soil. You could say that the whole foundation on which the plant kingdom rests is made up of phenomenally large populations of bacteria, fungi, protozoa, nematodes, micro-arthropods, and larger organisms. This foundation has come to be known as the “Soil Food Web.”
All of these organisms interact to perform the functions needed by plants in the soil. Some of these essential processes are:
1) Suppression of disease organisms
2) Retention of nutrients that would otherwise leach away
3) Cycling and transport of nutrients to the root zone
4) Decomposition of waste to create optimal soil for root growth
All the nutrients that plants need are found in the soil. With the exception of sunlight and carbon dioxide (which combine on the leaf surface for photosynthesis), everything a plant needs to grow is found in the soil. The sand, silt, clay, and organic matter that surround the root system contain all the minerals in excess. When problems arise, and they do, it is because the minerals are not in a form that the plant can utilize.
It is the organisms in the soil that convert these minerals into a plant-available form that plants can use. When a plant shows signs of a deficiency, it is most often not a chemical problem, but a biological one. It is essential for the health of plants that the natural populations of soil organisms be preserved in adequate numbers to maintain the proper balance. A simplified version of how this works is as follows:
1) Bacteria and fungi consume detritus and minerals in the soil.
2) Bacteria are eaten by protozoa and some nematodes. Fungi are eaten by other nematodes and micro-arthropods.
3) The consumption of organisms and cycling of minerals between levels of the food chain releases a steady supply of nutrients to the root zone.
The use of chemical fertilizers and pesticides interferes with these natural processes. In fact, they decimate the native soil organisms and can cause sterilization of the soil. Consider these ill-effects when a gardener applies a nematicide to kill some root-eating nematodes that are bothering his plants:
1) The beneficial nematodes are killed along with the bad ones.*
2) The soil food web is impaired and nutrients are not available for the plants.
3) The bad nematodes recover faster than the beneficial nematodes.**
We have been taught to consider the soil to be a blank matrix whose sole purpose is to hold water and the fertilizer which it is incumbent on us to provide for the health of our plants. Nothing can be farther from the truth. The soil is alive and the soil will provide for the plants if the soils are allowed to return to a more natural state. In practical terms the most direct means of accomplishing the re-population of the soil after years of cultural mismanagement is through the use of compost and compost extracts.
Conventional horticulture does things differently than the way natural systems have evolved to perform. We need to understand the damage conventional practices cause. We need to learn how to maintain our gardens as naturally as possible, realizing that short term gain costs too much for the long term health and balance of the system.
*It is actually the beneficial nematodes that control the populations of bad nematodes.
**It is usually the case that the targeted organism will rebound first making the original problem worse.
-The preceding essay was borrowed and distilled from Life in Natural Agricultural Soil, Part 1 by Elaine Ingham, rodaleinstitute.org