Soil should be dry before working it with machinery or by hand. You should
be able to squeeze a handful of it and it should just form a clump that
doesn't exude water. The clump should fall apart when disturbed or dropped.
If you work wet soil you will ruin the texture and will end up with big
clumps that dry into clod that will have to be delt with later.
In Nature, the earth is not tilled, and fertilizers (dead plants and
animals, fallen leaves, etc.) begin as mulches on the soil's surface.
Beneath this mulch layer, undisturbed soils develop two distinct
features central to the natural interactions between plants and soils.
One of these features consists of the soil "horizons" which result from
the tendency of the soil to separate into horizontal strata (i.e.,
mulch, topsoil, and subsoil). The other is a valuable, spongy condition
called "crumb structure." Tilling both mixes the soil's horizons and
destroys its crumb structure, interfering with the processes and
organisms which have evolved to depend upon these features.
The soil horizons include the mulch, topsoil, and subsoil layers. The
mulch layer consists of plant and animal remains, and is the primary
source of the soil's fertility. The topsoil consists of mineral soil,
huge numbers of soil organisms, dissolved nutrients, organic matter
brought down from the mulch layer, and humus (humus results from the
breakdown of organic matter and has an enormous capacity to absorb
moisture, hold nutrients, and buffer pH extremes). It is in the topsoil
that the majority of the soil's fertility is stored, in the form of soil
life and as nutrients held in solution by the soil's humus and clay. The
subsoil consists mostly of mineral particles, leached nutrients, and the
deeper water- and mineral-seeking plant roots.
Crumb structure is a spongy state developed and maintained by the
movement of earthworms and plants' roots through the soil. The crumb
structure is held together by soil colloids (gel-like substances created
by decay organisms), and by earthworms' secretions, used to aid their
movement through the soil. Natural crumb structures are quite stable and
remain largely intact after rains. The sponginess of the crumb structure
is extremely conducive to soil aeration, and to infiltration of water
and dissolved nutrients into the soil.
Using Rock Powders to Increase Fertility
Since no-till gardening relies on earthworms to do all the digging
(which includes mixing mineral powders into the soil), prior to each
mulching a rock-powder mix is applied at the rate of about 4 to 5 pounds
per 100 square feet. A good mix consists of roughly equal parts of soft
rock phosphate (for slow-release phosphorous), gypsum (for a
non-alkaline source of calcium - use lime if your soil is acidic),
hardwood ashes (potassium and trace minerals), and bone meal (more
phosphorous and calcium). These rock powders will then be slowly and
evenly dug in by the worms and the rain as the mulch is consumed.
Tilling and Soil Structure
Tilling mixes organic matter from the mulch layer into the topsoil where
is decomposes too quickly for plants to completely utilize (creating a
feast-or-famine nutrient cycle) and also mixes mulch materials into the
subsoil where they are attacked by anaerobic bacteria (which excrete
metabolic byproducts toxic to plant life and soil organisms). Tilling
exposes the topsoil's extremely valuable and slowly-forming humus to the
air where it can be oxidized and lost, and destroys the soil's existing
crumb structure. Tilling decimates the earthworm population, thereby
slowing reestablishment of a new crumb structure, and can cause the
formation foa hardpan by dislocating fine soil particles and allowing
them to be washed downward toward the subsoil where they collect and
form a dense sedimentary layer. In short, naturally occurring soil
horizons and crumb structures serve vital functions which are
interrupted, not aided, by tilling. And since natural patterns always
begin to reestablish themselves immediately once disturbed, the gardener
who tries to circumvent or override them has to work constantly to
prevent their return.
Mulch and Soil Tilth
From these facts it is clear that tilling is an ineffective and at best
temporary approach to increasing soil tilth and fertility. Rather than
attempting to enforce our own idea of soil tilth on our gardens, we are
better advised to cooperate with and use the soil's own natural method
for improving fertility - a thick, rich mulch of organic materials to
feed soil organisms and plants, which then work toghether to establish
natural soil tilth.
The most important single strategy in a no-till garden, then, is keeping
a thick mulch on the beds at all times to feed the earthworms and the
soil. The right proportions are as important for mulches as they would
be for compost. The mulch must contain enough grass clippings or other
sources of nitrogen to suppoly decomposition microorganisms, or it will
temporarily rob the soil of nitrogen (thereby starving plants). Also
needed are high-carbon materials like tree leaves, which create humus
and keep nitrogenous materials from packing into a mucky layer which
would exclude rainwater and air from the soil. By spreading mulches
directly on the soil, instead of first converting them to compost,
organic materials do double duty - serving as mulch, and as a
slow-release organic fertilizer, soil coniditioner, and worm food.
Furthermore, the fertilizing value of the materials is more fully
utilized, since in a compost pile much of the nitrogen, humus, and
minerals are lost through conversion to gases and by rainwater leaching.
Gary and Karen Manning wrote:
Celestial Habitats by J. Kolenovsky
2003 Honorable Mention Award, Keep Houston Beautiful
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