Lowenfels

[habitat_gardener]

I went to a talk by Jeff Lowenfels, author of Teaming with Microbes: A Gardener's Guide to the Soil Food Web, last week. If you haven't come
across this information on *why* organic gardeners say "feed the soil
not the plants," and why to avoid chemical fertilizers and pesticides
and rototilling, here's a very brief summary. For details, see the
book.

As Lowenfels described this elegant system, 60 to 70 percent of a
plant's energy goes to producing exudates that it drips out through
its roots to attract bacteria and fungi, who in turn attract
nematodes and protozoa to the root zone. To get carbon, the protozoa
eat bacteria, and the nematodes eat bacteria, fungi, and other
nematodes, and poop out the rest, which feeds the roots. The plant
can change the exudates it produces if it wants different foods!
That's because different exudates will attract different bacteria,
fungi, nematodes, and protozoa. The huge diversity of soil biota
helps the good guys keep the bad guys in check.

A common way to destroy the microbiology in the soil is to add salts
(nonorganic fertilizers). The salts kill the bacteria and fungi by
dehydrating them, with the result that the plant can no longer feed
itself and becomes dependent on its fert fix. In addition, without
bacteria and fungi, the other parts of the food chain start dying off
as well.

The soil food web is also responsible for soil structure. Bacteria
create slime that glues soil particles together, and fungi weave
threads to create larger soil aggregates. Larger fauna in the soil,
such as mites and earthworms, create pathways for air and water.
(Lowenfels called worms taxicabs for bacteria and fungal spores,
distributing them through the soil.) To destroy soil structure, the
most common methods are rototilling and using pesticides.

To bring soil back to life, you can do the following:
1. add a quarter inch of good quality compost
2. use appropriate mulches -- dry leaves for perennials, shrubs, and
trees (which prefer the form of nitrogen produced in soils where
fungi predominate), or straw/grass clippings for annuals (which
prefer the form of nitrogen produced in soils where bacteria
predominate)
3. use properly prepared aerated compost tea, made with good quality compost
4. apply mycorrhizal fungi, especially in a new garden that's been
rototilled or chemically fertilized.

(also, try to avoid walking on the root zone. Lowenfels said palm
trees were dying in Hawaii and redwoods were dying in Calif. because
tourists were walking all over the root zone, which kills fungi)

When asked about tomatoes, Lowenfels said tomatoes are perennials and prefer a fungal-dominated soil. He also said it's not a good idea to plant brassicas near tomatoes because brassicas are nonmycorrhizal.