The Earth Beneath Our Feet

It is as enormous and fascinating as the sky above about which so much is known. The realm beneath our feet, the top layer of our planet's crust, the first few feet of earth is known as the rhizosphere.

The word literally means "root world" or "root domain". It is the environment that roots inhabit, and it is populated with a vast number of other life forms, herbivores and carnivores. This universe consists of a community of organisms living, working, eating, and dying together in close proximity to roots.

This hidden, almost secret population consists of multiple species of algae, fungi, bacteria, protozoa, millipedes, nematodes, mites, springtails, sowbugs, fly larvae, beetles, ants, centipedes, worms, land snails and slugs. The numbers per cubic inch are in the hundreds of millions. Each performs a vital function inadvertently embracing and nourishing the roots. The plants' roots, in return, release and supply sugars and carbohydrates as a food for their benefactors.

The surroundings for these unique, synergetic relationships is an indeterminate mix of sand, silt, clay and organic matter in varying stages of decomposition. Indeterminate, because the combinations are nearly infinite and, therefore, seldom uniform. The environment is constantly evolving with each inhabitant playing a role in decomposing the organic matter and the subsequent release of a nutrient stew we know as humus.

Humus helps stabilize the soil structure by acting like a glue to hold together soil particles. This soil then can absorb and retain adequate moisture for roots to penetrate and absorb, and still allow excess moisture to drain away. It is this mixture of water, humus, oxygen, nutrients and soil minerals that plants use for growth. And, they are necessary.

Sometimes, the organic matter becomes available from natural events, as in forests through leaf fall, the demise of trees and their parts, and wildlife, macro and micro. In the case of our gardens, we need to re-supply organic matter regularly as it's consumed and transformed. It's a delicate balance. If the rhizosphere population falls, so too will the plants' efficient uses of nutrients and their defenses against root attacking pathogens. If the plants fail, they will return to the earth and replenish some of the missing organic matter. The system evolves to correct itself. But, the system is fragile.

Disturbing this layer in any way is tantamount to assaulting the congregation that lives within it. Once the soil is disturbed, the structural characteristics are altered. Changed, also, are the complex relationships between soil organisms, chemicals, minerals, and soil particles. Another alteration is the exchange of atmospheric and soil gases: more oxygen is added to the soil, and more carbon dioxide is lost from the deep recesses of the soil.

And, what about the living community, the soil microorganisms? Many die from rapid drying out. Some are light intolerant and weaken and die. This is an inside glimpse into the life support system of a plant. Now we can conceive of what might happen as we turn and churn our top layers of earth.

Plants support all life on our planet. Important to remember that it is home. They may be food crops, grasslands, fruits, vegetables, trees, shrubs, herbs, etc..

By adding life to the soil in the forms of compost and organic matter, we feed the subterranean promoters of healthy plant life. This is by far the best way to prepare for planting.

Improving microbial health of your garden soil is one thing. Doing it without chemicals and fertilizers is another. These things interfere with the dynamic taking place in the rhizosphere. Both accelerate the decomposition of organic matter, kill countless beneficial microorganisms, and ultimately make the plant dependent on the reapplication of fertilizer at regular intervals. The new lush growth in no longer protected by the microbe conferring defense system, so the plant becomes dependent on chemical pesticides, which feeds into the negative cycle which is harmful to the rhizosphere.

The above are reasonable arguments against tilling, using chemical fertilizers, and using pesticides that are harmful to any forms of life. Pests are, after all, food for other animals. The old adage, "feed the soil and you feed the plants", has never been truer.

This kind of thinking goes hand in hand with the popularity of raised bed gardening. If your topsoil is gone or appears to be deficient of beneficial microbial life, and you wish to grow flowers or vegetables, build your garden beds with walls of stone, logs, cinder blocks, wood, water filled jugs to which a little anti-freeze has been added (painting them black will give the bed a head start at heating up), whatever works for you to hold soil and the various materials you will add.

These materials would include imported topsoil, peat moss, sawdust, shredded leaves, grass clippings, compost, aged manure, straw, and seasoned wood chips. Make the bed(s) small enough so that you never have to walk on it or do anything to compact the soil surface.

You won't believe how quickly your new rhizosphere takes on all the life giving creatures and characteristics for growing healthy, vigorous plants. There are mycorrhizal fungi, beneficial nematodes and rhizobium bacteria that can be purchased for addition, if desired. This is usually unnecessary. They'll all "come a runnin'" to this new habitat in no time flat.

A note about the compost: it should be understood that no diseased plant material was incorporated into it. Another note about the other materials: these should be free of pesticides and chemical fertilizers. This will assure your rhizosphere will be a welcome home to the new life support system of plants.

I advise a pH test to determine if limestone or sulfur are needed to either raise or lower the pH respectively. The vast majority of plants and vegetables flourish in soil with a pH range between 6.0 and 6.5. Cornell Cooperative Extension and several garden centers can perform this important test for a modest fee.

I would say we're on our way to a better appreciation of the earth beneath our feet, and an opportunity to either create a new rhizosphere for our use, or provide some measure of protection and nourishment of the ones we have. All hail the rhizosphere!


From The Garden of Ed. Submitted for publication in The Towne Crier on April 21, 2004

© 2004 Ed Mues. All Rights Reserved.