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  • From: "TradingPostPaul" <tradingpost@riseup.net>
  • To: livingontheland@lists.ibiblio.org
  • Subject: [Livingontheland] 21st Century Homesteading: Build Better Garden Soil
  • Date: Sat, 26 May 2007 21:20:32 -0600


For those who may have missed it, here's Harvey's previous piece on
building soil, in Mother's April/May 2007.
http://www.motherearthnews.com/Homesteading-and-Self-Reliance/2007-04-01/Bet
ter-Garden-Soil.aspx

paul tradingpost@lobo.net
------------------------------------------

21st Century Homesteading: Build Better Garden Soil
By Harvey Ussery

Caring for the soil is the key to growing more of our own food

Soil is the key to health, both for ourselves and for the animals and
plants we depend on. But soil “in good heart,” as farmers used to say,
is not something we can take for granted. For gardeners and farmers, caring
for the soil must always be our first priority, and the process of building
soil fertility is vast and complex.

The best question to ask is not “What is the best soil care?” but
“What is the best soil care for this particular piece of ground?” Over
the seasons, the soil itself becomes our teacher and shows us which
practices lead to beneficial changes.

Let’s begin with this intriguing question: Why is it that in natural soil
ecologies, soil fertility tends to accumulate spontaneously over time,
while human agriculture often leads to drastic declines in soil quality?
Whether we look at prairies, bogs or forests, we find that topsoil tends to
deepen and become more fertile over time. Why are humans more likely to
destroy than to build soil quality, when natural systems operating on their
own produce the opposite result?

One implication is obvious: The key to soil management is imitating natural
systems. But perhaps the best answer to this riddle is that topsoil is
alive, and any approach to agriculture that treats it as an inert substance
is almost certain to be destructive.

WHAT IS TOPSOIL?

Topsoil is formed from tiny particles weathered or worn from their parent
materials (rock, of various types). Both the chemical composition of the
parent material and the average particle size help determine fundamental
characteristics of soil — whether it is acid, alkaline or neutral; and
whether it is sand (large particle size) or clay (extremely small particle
size). But a layer of small rock particles is not “soil,” and it is not
capable of growing a crop.

Healthy topsoil also consists of a complex community of living creatures,
and each class of organisms has its own strategies for feeding itself,
adapting to environmental conditions and coexisting with its neighbors. Any
practice that destroys some or all of those classes of organisms is likely
to reduce soil fertility.

The number of living organisms in healthy topsoil is enormous: It has been
estimated, for example, that the total biomass of organisms in a prairie
soil exceeds 15 tons per acre, with the weight of the bacteria alone —
invisible to the eye—totaling 13 tons! A single teaspoon of that soil may
contain 600 to 800 million individual bacteria from a possible 10,000
species; several miles of fungal hyphae; 10,000 individual protozoa; and 20
to 30 beneficial nematodes from a possible 100 species.

Living organisms in the soil include bacteria, fungi, protozoa (single-cell
animals), nematodes (minuscule non-segmented worms), arthropods (insects,
spiders, mites and centipedes — from microscopic to several inches long),
earthworms, and larger organisms such as moles, voles and even gophers,
which have their role to play in recycling nutrients and maintaining good
soil structure.

THE ROLE OF ORGANIC MATTER

Organic matter is constantly being produced in and over the topsoil —
fallen leaves, dead plants and animals, roots shed by living plants, and
droppings of passing animals. Different classes of soil organisms
“specialize” in breaking down different sorts of organic matter in
accordance with the natural principle that every creature’s “waste”
is a priceless resource for another, and they pass their own wastes on to
other members of the soil community.

The energy represented by the original organic material is passed from one
level of the soil food web to another, rather than being lost from the
system. The energy of sunlight is constantly being added at the other end
of the equation through photosynthesis, so if all nutrients are re-captured
by soil organisms, the result has to be added fertility.

For example, when fresh green material is added — say in the form of crop
residues, or green cover crops cut and used as mulch — it is bacteria
that take the lead in breaking them down. Nematodes, protozoa and tiny
arthropods feed on the bacteria, and are fed on in turn by larger
arthropods and nematodes. Earthworms feed on the bacteria, as well as
leaves and other organic matter, converting it all to castings rich in
minerals and other nutrients in forms easy for plant roots to take up, and
conducive to good soil structure. In the meantime, soil fungi colonize and
feed on the denser plant tissues such as stems and leaf veins, as well as
other more carbon-dense organic materials such as leaf mulches.

Dead organic material is not the only source of food for soil-dwelling
species. Roots of living plants form cooperative, mutually beneficial
associations with various soil organisms. Some plants, including beets and
spinach, form such associations with bacteria; others, including tomatoes,
potatoes and corn, with mychorrhizal fungi. In both cases, the plant
creates complex sugars and other nutrients in its leaves, then releases
them through its roots to feed its “buddies” in the soil. In exchange,
the mychorrizae or bacteria provide nitrogen, enzymes, minerals and other
nutrients to the roots in forms easy for them to absorb.

These are simple sketches of complex relationships and food exchange. The
end result of the process is humus, the final residue of the parent organic
materials, now visible only as a darkening of the soil. The microscopic
humus particles are no longer a source of food for soil organisms, but they
help with water retention, bond with nutrients in the soil and pass them on
to plant roots, and bind carbon into the soil. Many soil organisms also
help “glue” soil particles together into larger aggregate particles,
increasing the size of pore spaces between particles, bringing more air to
the soil (most soil organisms need oxygen to thrive) and increasing water
flow down into the soil (reducing chance of runoff and erosion in heavy
rains).

Some soil organisms are pathogens, but with a diverse mix of species, they
are usually controlled by other organisms in the system, which feed on the
disease-causing organisms, out-compete them, or otherwise inhibit them.
Simply put: Diversity of soil organisms is key to plant health.

STRATEGIES FOR MANAGING SOIL

Most of us have grown up thinking that soil fertility revolves around the
question of what we need to buy and add to soil. We sometimes use soil
tests to guide us in making the proper purchases. When we begin working
with a piece of ground, especially if it has been abused, there may be
additions we need to make. Be cautious about soil tests, however, because
different laboratories use different procedures, report results differently
and adopt different approaches to interpreting the results.

For example, I remember how confused I was by test results I used to get
from my local extension service: They always noted that both phosphorus and
potassium were “very high” — and then went on to recommend
application of chemical fertilizers containing 10 percent of each. Later, I
worked with a soil consultant (a student of pioneering soil scientist
William Albrecht), who also noted the high levels of phosphorus and
potassium, but recommended no fertilizer application.

Indeed, he pointed out that it would be easy for my soil to rise to
dangerously excessive levels of phosphorus if I wasn’t careful with
certain organic matter applications, such as manures. Since most soil
analyses focus so much on crop needs for nitrogen, imagine my surprise when
he also recommended no added nitrogen. When I asked about that, he replied
dismissively, “Oh, with organic matter at the level you have, you don’t
need any added nitrogen, except maybe a little for really heavy feeders
like corn.”

By all means, find and work with a competent soil consultant if you feel
your soil has serious deficiencies or special needs. But your main focus
should not be what purchased inputs you need to add to your soil, but on
strategies to maximize the diversity, health and population densities of
soil organisms.

Three agricultural practices in particular are injurious to soil life:

Monoculture. The growing of a single species on vast tracts reduces
diversity of soil life.

Use of harsh chemicals. Many chemicals — whether intended to fertilize
crops, suppress disease, or kill insects and weeds — also destroy
populations of soil organisms.

Excessive tillage. Frequent tillage of soil disrupts soil life and robs it
of its carbon (organic matter) reserves.

The alternative to such destructive practices is to imitate natural soil
ecologies, which will:

Take advantage of the diversity and population densities of soil organisms.
While homesteaders are unlikely to practice monoculture — to grow nothing
but carrots, for example — we should constantly find ways to “mix it
up” in how we manage our soil. Crops of different families should rotate
over the available ground in succeeding seasons. Diverse sources of organic
matter should be used — composts, mulches, cover crops, etc.

Feed the soil using sources of fertility grown on the homestead or close
by. Deep-rooted cover and fertility crops can “mine” minerals from the
deep subsoil and make them available to more shallow-rooted plants.
Nitrogen-fixing legumes (clovers, alfalfa, beans and peas) can boost
nitrogen for heavier-feeding crops. Recycle autumn leaves and crop residues
by composting or using them as mulches. Manures and mulching materials may
be available from nearby farms. If a soil test does indicate the need to
add minerals, use slow-release rock powders, such as greensand or colloidal
rock phosphate, rather than highly soluble chemical fertilizers, which
quickly leach into groundwater.

Protect and improve soil structure. Plant in wide beds and don’t compact
the soil by walking in the growing spaces. Keep the soil constantly
covered—by closely-planted crop plants, cover crops or mulches. Addition
of lime to most clay soils can help “flocculate” the almost microscopic
soil particles into aggregate clumps, resulting in a looser, more open soil
structure with better air and water penetration. When tight soil must be
loosened, do it with a broadfork rather than a power tiller or even a
spading fork to avoid inverting soil layers.

THE LONG-TERM EFFECTS OF TILLAGE

Many farmers, gardeners and homesteaders avoid monoculture and harsh
synthetic chemicals. However, many people committed to sustainable
agriculture unknowingly till the soil in ways that inhibit long-term soil
improvement.

Tillage of soil releases a flush of nutrients, which can give an impressive
initial boost to crop growth. But this surge of available nutrients results
mostly from the death of large numbers of soil organisms, whose biomass
decomposes rapidly into the soil. These nutrients tend to be in soluble and
volatile forms, and if not taken up immediately by plant roots, are leached
to groundwater or outgassed to the atmosphere. In the meantime, life cycles
of many soil species are disrupted — fungal threads are broken, and
earthworm burrows are destroyed — and it can be some time before their
populations recover. If the next tillage occurs before they have done so,
we have started a cycle which degrades the health and diversity of the soil
food web.

One of the worst effects of excess tillage is the loss of carbon bound in
the soil in the form of humus. Oxygen is necessary to soil life, which is a
major reason we work to improve aeration in soil through creation of
looser, more open “pore structure.” Excessive exposure of the soil to
oxygen, however, as occurs in heavy tillage, leads to oxidation of the
carbon content and its loss to the atmosphere as carbon dioxide (CO²).
Not only is fertility — which is so dependent on humus content —
impaired, but high-tillage agriculture is a major, and growing, cause of
accumulation of CO², a greenhouse gas, in the atmosphere.

The amounts of carbon involved are not trivial: Every 1 percent increase of
carbon sequestered in a garden’s soil is estimated to be equivalent to
the weight of all the carbon in the atmosphere above that garden, right out
to the vacuum of space. By reducing tillage while adding all the organic
matter we can, we reverse CO² emission: Carbon is bound up in soil in the
form of humus. The solution to climate change begins in your back yard.

— In the next issue, Harvey Ussery will discuss how to get started with
these three soil management techniques.







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