[Homestead] Soil 101, microbes

Gene GeRue genegerue at ruralize.com
Mon Sep 13 13:13:25 EDT 2004

To feed plants, we feed the soil. The soil community then converts the food 
we give it into a form the tiny plant root hairs can assimilate. To keep 
the process going, just keep feeding groceries to the gang underground. 
Lots of mulch does the trick.

There are sound reasons why informed gardeners do not plow or till, why 
they create and maintain garden paths, and shun chemical fertilizers. The 
living soil  is complex and well-ordered; everything is in its optimal 
place, and to till it is to turn things inside out, if not upside down. 
Imagine Zeus tilling a human subdivision with a hundred-foot RotoCruncher 
and you get the idea. Give the soil kids a break and sell the tiller.


The Secret Life of Microbes
By Barbara Damrosch
Special to The Washington Post
Thursday, July 8, 2004; Page H07
When I was in college, I marched into the woods one day to do a biology 
project on life in the soil. Brushing aside dead leaves and the leaf mold 
under them, I dug happily, encountering worms, ants, grubs, beetles -- 
sleeping pupae of insects that were airborne in summer.
Alas, much of that leaf layer was poison ivy. My professor hastily rerouted 
me into work on goldfish parasites in the campus pond. But had I stayed on 
track, I could have explored a world far more complex than what had first 
met my eyes.
The top six inches of the soil teem with microscopic organisms -- bacteria, 
fungi acetomycetes, algae, single-celled protozoa such as amoebas. Larger, 
but still unseen, are tiny animals such as nematodes and mites. The numbers 
are staggering -- millions of organisms per gram of soil, where conditions 
favor them. Their total weight, in a fertile acre of land, is as great as 
the total weight of the above-ground creatures that acre can support.
Counting soil microbes might seem like an odd corner of knowledge, a bit 
like those theological debates about how many angels can dance on the head 
of a pin. But these unseen workers quite literally make life on Earth 
possible. Of all the species, these -- the tiniest -- are the least 
expendable. Without them no plants would grow. Without plants no animals 
would exist.
Plants feed on organic wastes -- decomposed plant and animal matter -- but 
not directly. Soil microbes must break them down into compounds that plant 
roots can absorb, just as intestinal microbes break down our food for us.
The end result of decomposition in the soil is humus, which has other 
virtues besides plant nutrition. It gives the soil good structure and 
tilth, with plenty of air spaces between soil particles, so that plant 
roots can breathe, and a spongy texture that allows the soil to retain 
moisture and resist erosion. It helps moderate the temperature shifts that 
make up the soil's "weather." Certain soil fungi produce a gummy substance 
called glomalin that causes soil particles to clump up and produce the good 
crumb texture that gardeners prize.
In the wild, plant residues decay on the soil surface through the action of 
bacteria and fungi, and their remains are gradually worked down into the 
soil with the help of worms and other burrowers. Worms and plant roots also 
bring up minerals from below, so that a lot of trafficking in materials 
goes on. As long as the materials are there, microbial workers will show up 
to process them, so that the cycle of growth and decay can continue.
It's very busy down there. Entire civilizations are doing business, 
cooperating, battling, building structures, even herding one another. These 
populations are not only numerous but also varied, doing work under 
specific conditions and in different soil strata. In your compost pile, 
which seethes with life, heat-seeking bacteria work the center, while 
others perform best at the cooler edges. In alkaline soils you'll find 
mostly bacteria; in acid soils the fungi predominate.
If all these workers are so important, how can you make sure they're there 
-- and active -- in your garden? How do you become the guardian of a living 
First, it is very important to make sure that it contains plenty of organic 
matter in the form of compost, manure and other amendments. This will 
activate the microbes that are already there and cause them to multiply.
Then try hard not to disrupt the delicate structure beneath your feet. 
Stick to the paths and avoid walking on your beds. Dig and till as little 
as possible. Keep things growing. The principle "use it or lose it" applies 
to garden soil, because the absence of plants and their roots -- where 
microbes congregate -- means less soil life. Use cover crops, green manures 
and mulches.
I avoid chemical fertilizers because I fear these can kill soil organisms 
of any size. They may deliver the final product in a crude sense, but they 
bypass the process. You can deliver a molecule of nitrogen to a plant 
without microbial aid, but it will do nothing for the soil's texture and 
its resilience. You will have to keep your plants on life support, because 
a lifeless soil is not able to replenish what is used up.
Don't treat unseen microbes as hidden dangers. Though a few can be harmful 
to plants, animals and each other, poisoning them does more permanent harm 
to the helpful organisms that hold them in check. There is never anything 
to be gained from making your soil a sterile place.
Don't fear what seems dark, unknown or dirty. The sky may seem more bright 
and beautiful -- a perfect metaphor for infinite life, but the further you 
climb into it the less life you will find. The Earth's fragile skin is 
where the action is. If we keep it hospitable to life, it will support an 
infinity of helpers, all of them dancing.
© 2004 The Washington Post Company

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