Life in Natural Agriculture Soil, Part 1
By Dr. Elaine Ingham, Rodale Institute Chief Scientist
In March of 2011, just after starting as chief scientist at Rodale Institute, I toured the Shumei garden at the Institute and began to understand the principles that embody Natural Agriculture. It was wonderfully enlightening to find people who share a similar attitude that natural processes must be the basis for agriculture. My expertise is focused on the organisms that exist in soil, and the processes these organisms perform. Looking at what happens to these organisms in current “conventional” agricultural systems is extremely depressing. We need to understand what life is necessary in soil, how these organisms function, and what conditions must be present for soil organisms to perform their beneficial jobs. The more we maintain the proper conditions for the workers in the soil, the better we mimic nature and the higher the quality of our foods.
Conventional agriculture does things differently than the way things are done in natural systems. We need to understand how those differences influence and affect the soil, plants and the quality of plants. We need to understand the damage conventional practices cause. We need to learn how to maintain our plant production systems as naturally as possible, realizing that short term gain in yields costs too much to the long–term health and balance of the system. What are the constraints we impose? What are the sets of organisms that need to be there? How do these organisms behave in a natural system and how we can use them in our agricultural systems?
The Soil Food Web
The soil food web is comprised of the different organism groups in soil: bacteria, fungi (including mycorrhizal fungi), protozoa, nematodes, microarthropods, and larger organisms. These organisms interact to perform the functions needed by plants in the soil: disease suppression (around roots and around above-ground parts of plants), nutrient retention (so loss of nutrients through leaching does not occur), nutrient cycling (making nutrients available to plants in the root zone), decomposition of waste materials, and building of soil structure so roots can grow as deep as the plant requires.
Food web structure varies with season, climate, soil type, age of the ecosystem, etc. The existing food web will select for the growth of certain plants, and against the growth of others. Thus, defining health of the soil must be done relative to the desired plant. Is this food web healthy for this plant? To promote health, we need to understand soil as nature designed it. Plants have existed on this planet for at least the last billion years, meaning that the linkage between certain plants being selected by certain sets of organisms in the soil, and vice versa, has had plenty of time to develop.
To understand this system, then, we need to start at the beginning. The process of photosynthesis in plants uses sunlight energy to bond carbon molecules together and form sugars. Plants store sunlight energy by bonding one carbon, from one carbon dioxide molecule, with another carbon from a second carbon dioxide molecule. Depending on what the plant needs, and its physiology, additional carbons can be bonded to the chain, storing energy in that sugar for future use. The sugar formed can be used to grow the plant, or it can be sent to the root system to escort nitrogen, in the form of an amino acid, or protein, for example, to where the plant needs it. These sugars will bond with phosphorus, sulfur, magnesium, calcium, potassium, sodium, or any other nutrient in order to move those nutrients to where the plant needs that nutrient to continue growing.
All nutrients, except CO2 and sunlight, are provided to the plant through the soil. Soluble, inorganic forms of nutrients move into the plant by simple diffusion into the roots, but the inorganic nutrients have to be converted from the ionic form into carbon–bound forms once inside the root in order to prevent harm to the plant. Thus, once the soluble nutrient is inside the root, the plant uses enzymes to attach the nutrients to the carbon backbone of sugar from photosynthesis.