By Donella Meadows
–November 16, 1989–
With a Thanksgiving feast spread before you, it’s easy to be thankful — for the food, for those who produced it from the farmers to the cooks, for all the blessings of life, including the unexplainable gift of life itself.
I bet it has never occurred to you, though, to be thankful for the most invisible contributors to the production of food and the continuance of life. They are the zillions of tiny creatures in the soil, about which most of us know nothing, and without which we could not exist.
So at this time of gratitude I’m here to put in a word for the soil bugs.
A heaping teaspoon of good garden soil may just look like dirt, but in fact it’s a teeming jungle. One teaspoonful could contain as many as 1 billion bacteria, 100 million actinomycetes, 1 million fungi, 100 thousand algae, 100 thousand protozoa, and 100 nematodes. Then there are the bigger creatures; in a square yard of soil there could be 10,000 mites, springtails, centipedes, slugs, beetles, and ants, and a couple hundred earthworms.
This is the team that performs the steady miracle of turning dead things — cornstalks, manure, old cabbage leaves, remnant alfalfa roots — back into life. They are recyclers of amazing efficiency. They glom onto a fallen leaf, shred it, break its big molecules into useful bits of nutrients, and pass those nutrients back up the chain of life into the grain that feeds the turkey that feeds you.
Scientists understand little about the exquisite interplay of this busy soil community, but what they do understand is mind-boggling. For example: fungi are needed for the first break-down steps. They have special enzymes that can break down lignin and cellulose in the cell walls of plants. (That is, they can dissolve wood.) But fungi are immobile. They can’t get themselves to where the pine needle or wheat stalk happens to be.
The mobility problem is solved by a crawling mite that looks much like Pac-man and gobbles up soil fungi in true Pac-man fashion. Out the back end of this mite come fungus spores, which it can’t digest. The spores emerge packaged by the mite in a tiny bag containing two special substances. One is a fertilizer that makes an ideal medium for the spores to grow into more fungi. The other is an antibiotic that prevents other kinds of fungi (which the mite doesn’t eat) from growing there.
The mite farms the fungus, plants it, fertilizes it, protects it with a pesticide, and distributes it everywhere, ready to recycle leaves or stubble or whole trees for that matter (and ready to feed more mites).
The mite/fungus interaction is just one of the million or so partnerships in a healthy soil ecosystem. Another one is the Rhizobium/legume trick, the association of a bacterium called Rhizobium with the roots of leguminous plants like clover, beans, peas, and locust trees. The Rhizobium grabs nitrogen out of the air and turns it into fertilizer for the plant, in exchange for a little food. We pull off the same chemical reaction in fertilizer factories, but we use up fossil fuels and generate heat and pollution in the process. The Rhizobia of the world create much more nitrogen fertilizer than we do, for free, quietly, with no pollution, right there at the root where the plant needs it.
Soil biologists, of which the world has too few, are discovering bacteria in the soil that actually suppress plant diseases, and others that inject growth-promoting substances into plant roots.
At the University of Nebraska researchers have been planting experimental plots side by side for over ten years — continuous corn with the full array of modern chemicals in one bunch of plots; corn grown organically, fertilized with manure and rotated with soybeans and other crops, in another bunch. Over ten years the no-chemical corn yields have increased so they now surpass the chemical corn yields. To understand why, the experimenters fumigated some of the plots and killed off all the soil life.
In the fumigated plots the chemical corn yields went up. Under a steady chemical rain the soil populations had shifted, some critters exploding in numbers, others being killed off. The ecosystem had evolved to be pathogenic to corn.
The organically farmed corn yields went down when the soil life was removed. That soil community had been actively helping the corn to grow.
So I make my pitch for the soil bugs, not only so we’ll accord them some much-earned thanks for recycling the nutrients that fed the pumpkin in our pumpkin pie, but so we’ll know enough about them to treat them with respect. Instead of, in ignorance, throwing their communities out of balance, we need to work with them, so that all people of the world can have beautiful meals spread before them for which to be thankful.
Copyright Sustainability Institute 1989