A GOLDEN RULE FOR GARDENING: DO NO HARM
By ROBERT KOURIK
1998 N.Y. Times News Service
What could be more natural than gardening? Most people who grow flowers
or their own food think they're ""healing the Earth'' in some small way.
Gardeners may be having fun, getting exercise and harvesting tasty
vegetables and fruits, but the best thing, as far as nature is
concerned, is probably no gardening at all. In fact, gardening can be
downright harmful: tillage releases carbon dioxide, contributing to
global warming; cultivation and compaction destroy beneficial soil
fungi, and excessive nitrogen fertilizers, even manure, can contaminate
water supplies.
While most gardeners assume that a plow, shovel or rototiller is
required for a good crop, the only comparable natural model is a
landslide. So why have most cultures used cultivation? Mostly to create
a zone where domesticated crops have little competition from native
plants.
Global Warming
The earth's soil contributes 10 times more carbon dioxide to the
atmosphere than all human activity, according to Dr. Tyler Volk, a
professor of biology at New York University and an expert on the carbon
cycle. It comes from the myriad life forms that inhabit the soil _
microbes, pill bugs, worms and fungi _ as they breathe, process food and
die.
Whereas in the past the increase in carbon dioxide gas produced by
small-scale tillage was absorbed by plants through photosynthesis, Dr.
Volk said, tillage has now become a large contributor to the surplus of
carbon dioxide. When soil is stripped of its living cover to grow crops,
up to one-fourth of its stored carbon, which contributes to fertility,
is lost as carbon dioxide.
Volk estimates that the rise of the average global temperature of one
degree Fahrenheit in this century has expelled an extra billion tons of
carbon into the atmosphere from the soil. Currently, he says, the global
carbon cycle may be able to absorb it, but carbon dioxide generated by
cultivation _ even in gardens _ may contribute to a warmer climate.
Gardeners can compensate for a loss of carbon, Volk says, by adding
compost and manure. And they can minimize the loss of carbon dioxide
from their plots by experimenting with ""no till'' gardening: growing
plants in deep mulch, up to a foot thick; sheet composting (thin layers
of a variety of compostable materials laid out over the soil like a
thick mulch), or by reserving portions of the garden for soil-improving
crops like fava beans or vetch.
In undisturbed soil under many trees, perennials and some vegetables
lurks a mostly unknown but beneficial fungus called vesicular-arbuscular
mycorrhizae _ VAM, for short _ which can sometimes be spotted because of
its above-ground fruiting bodies, including Boletus, Amanita, Lactarius
mushrooms and some types of puffballs.
VAM forms a remarkable symbiotic relationship with plants. Its
microscopic filaments either actually augment tree root hairs, or they
grow into the cells of the root hairs. The filaments provide nutrients
to the plant, mostly phosphorous, potash, zinc and copper, and they
receive carbohydrates for the fungus.
Many plants grow much more lushly with this association. For example,
according to studies at various universities, when VAM was present in
otherwise untreated or poor soils, oat plants were nearly twice as heavy
and strawberries five times as heavy than they would have been
otherwise. Citrus trees growing in soil inoculated with VAM were 16
times as heavy than trees in sterilized soil.
Most natural, undisturbed soils have plenty of VAM. But it can be
injured or destroyed by tillage, by removing the natural litter called
duff beneath trees, by stripping away topsoil for construction, by
compacting the soil (even by walking on it), by fumigation or by
overfertilization.
There are several ways of preventing compaction: keeping permanent
pathways away from trees, using deep mulches for little-used paths,
using some cover crops in your yard and rotating crops with root systems
of different depths to help keep untilled soil friable. Keep annual
crops away from trees (at least one-half to three times the width of the
canopy) so as not to disturb the VAM.
Some garden centers and catalogs are touting new VAM inoculants for all
gardens. They may not be required except in two cases: at a new house on
a bulldozed site or in sterile potting soil. But if you've spotted the
telltale mushrooms in a forest, you can just shovel up some duff there
and sprinkle it on your soil or add it to a sterile potting mixture.
Then let nature do the work, free.
Surplus Nitrogen
Most gardeners squander nitrogen, even manures. Because of its cost,
farmers tend not to waste fertilizer. To equal the amount a farmer
spreads on nitrogen-hungry crops like celery, cabbage and potatoes, a
home gardener need apply only a quarter to a third of an inch of compost
or steer or horse manure.
Kate Burroughs of Sebastopol, Calif., a certified crop adviser with the
American Society of Agronomy, a professional association, uses the same
guideline for home-grown sweet corn and lettuce. Broccoli and pear trees
need only a dusting. I often observe gardeners applying manure and
compost far heavier than this, wasting both money and nitrogen.
That excess nitrogen leaves the garden as a gas or leaches away with
rain or irrigation toward water supplies, and it can set back VAM
activity. Surplus nitrogen causes plants to grow more foliage, not
stems, tubers or other edible parts, and it stimulates weaker growth
more prone to pests and disease.
As it turns out, the ancient Greeks were right: all things in
moderation.
Steve Groff
-- "New Generation Cropping Systems": the cutting edge of sustainable agriculture http://www.cedarmeadowfarm.com Steve Groff Cedar Meadow Farm 679 Hilldale Rd Holtwood PA 17532 USA Ph. 717-284-5152
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