In article
,
gardengal wrote:
Plants do not make soil acidic - acid soils occur
as a result of the mineral content and amount of rainfall.
AAAAAAAAAAh - wrong
All nitrogen is not the same
Ultimately, from the plant's perspective anyhow, the role of the soil
food web is to cycle down nutrients until they become temporarily
immobilized in the bodies of bacteria and fungi and then mineralized.
The most important of these nutrients is nitrogen‹the basic building
block of amino acids and, therefore, life. The biomass of fungi and
bacteria (that is, the total amount of each in the soil) determines, for
the most part, the amount of nitrogen that is readily available for
plant use.
It wasn't until the 1980s that soil scientists could accurately measure
the amount of bacteria and fungi in soils. Dr. Elaine Ingham at Oregon
State University along with others started publishing research that
showed the ratio of these two organisms in various types of soil. In
general, the least disturbed soils (those that supported old growth
timber) had far more fungi than bacteria, while disturbed soils
(rototilled soil, for example) had far more bacteria than fungi. These
and later studies show that agricultural soils have a fungal to
bacterial biomass (F:B ratio) of 1:1 or less, while forest soils have
ten times or more fungi than bacteria.
Ingham and some of her graduate students at OSU also noticed a correla-
tion between plants and their preference for soils that were fungally
dominated versus those that were bacterially dominated or neutral. Since
the path from bacterial to fungal domination in soils follows the
general course of plant succession, it became easy to predict what type
of soil particular plants preferred by noting where they came from. In
general, perennials, trees, and shrubs prefer fungally dominated soils,
while annuals, grasses, and vegetables prefer soils dominated by
bacteria.
One implication of these findings, for the gardener, has to do with the
nitrogen in bacteria and fungi. Remember, this is what the soil food web
means to a plant: when these organisms are eaten, some of the nitrogen
is retained by the eater, but much of it is released as waste in the
form of plant-available ammonium (NH^). Depending on the soil
environment, this can either remain as ammonium or be converted into
nitrate (NO,) by special bacteria. When does this conversion occur? When
ammonium is released in soils that are dominated by bacteria. This is
because such soils generally have an alkaline pH (thanks to bacterial
bioslime), which encourages the nitrogen-fixing bacteria to thrive. The
acids produced by fungi, as they begin to dominate, lower the pH and
greatly reduce the amount of these bacteria. In fungally dominated soils,
much of the nitrogen remains in ammonium form. Ah, here is the rub:
chemical fertilizers provide plants with nitrogen, but most do so in the
form of nitrates (NO,,). An understanding of the soil food web makes it
clear, however, that plants that prefer fungally dominated soils
ultimately won't flourish on a diet of nitrates. Knowing this can make a
great deal of difference in the way you manage your gardens and yard. If
you can cause either fungi or bacteria to dominate, or provide an equal
mix (and you can ‹ just how is explained in Part 2) , then plants can
get the kind of nitrogen they prefer, without chemicals, and thrive.
p 25 -26
Teaming with Microbes: A Gardener's Guide to the Soil Food Web
by Jeff Lowenfels, Wayne Lewis
€ Publisher: Timber Press, Incorporated (July 15, 2006)
€ ISBN-10: 0881927775
€ ISBN-13: 978-0881927771
--
- Billy
"For the first time in the history of the world, every human being is
now subjected to contact with dangerous chemicals, from the moment of
conception until death." - Rachel Carson
http://www.youtube.com/watch?v=WI29wVQN8Go
http://www.haaretz.com/hasen/spages/1072040.html