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In light or sandy soils, the particles are relatively large and boulder shaped creating an open structure with an abundance of air spaces. Sandy soils have sharp drainage and do a poor job of holding moisture and nutrients.
Heavy or clay soils have small, flat particles that stack together for a closed structure containing very little space for air. Clay soils resist wetting but once wet become very water retentive. Clay soils are more subject to damage as a result of compaction.
A good loam soil has chemical and structural properties that
are somewhere in between the extremes of a sandy soil and
clay. This sub-section is about the physical structure and
content of soil. See sub-section B.02.*
regarding the physical properties.
Soil particles are classified by size and shape. Clay
particles are the smallest and flat. Sand particles are the
largest and boulder shaped. Silt particles are intermediate.
The physical performance of soils is mostly a function of
particle size and shape. "Soil Texture" is a term that is used
to discuss the physical properties of soils based on the
relative percentages of these different particles.
Sandy soils have an open soil structure. The particle size is
large and there is a lot of open space between and around the
particles. They take up water readily and are sharp draining.
They are often short on nutrients but easy to work. Soils
should contain at least 70 percent by volume sand particles to
be classified as "sand".
Clay soils have a very dense soil structure. The particle size
is extremely small and there is very little open space between
and around the particles. Water enters and drains from clay
slowly. Clay soils can be very fertile but hard to work. Soils
should have at least 35 percent by volume clay particles to be
classified as "clay".
Silt is the soil particle that is intermediate in size between
the smaller clay particle and the larger sand particle. Silt,
in combination with clay and sand, are the building blocks of
loam.
Loam has a mixture of sand, silt, and clay particles. Typically, loam soils contain approximately 40% by volume sand, 40% by volume silt, and 20% by volume clay. Loam is ideal for most plants and is easy to work.
There are a number of intermediates in the classification of
soil texture such as loamy sand or sandy loam but they are
still the result of the relative percentages of sand, silt and
clay.
One of the most popular home tests for measuring the percentage of sand, silt, and clay involves nothing more sophisticated than a quart or liter glass jar with lid and a ruler. It is based on the rate these different particle types settle in water. The large, boulder shaped sand particles settle the fastest, followed by the smaller particles of silt, and then followed by the very small and flattened particles of clay.
Collect about 2 cups (500 ml) of soil to be tested and pick out the bulk of the organic matter. Let the sample dry in the sun and break up any clumps by tapping with a hammer. Put about 3/4 cup (200 ml) of the soil sample into the glass jar, fill almost to the top with water, cap the jar and shake vigorously for five minutes.
Let the jar sit undisturbed for 24 hours and measure the depth of the settled soil with the ruler. This is the total amount of soil particles. Shake the jar again for an additional 5 minutes and allow it to stand for 40 seconds. Measure the settled soil. This is the amount of sand in the sample.
Keep the jar undisturbed and measure the settled soil at the end of 30 minutes. This is the amount of sand and silt together. Subtract the amount of sand from that total for the amount of silt.
Subtract the amount of sand and silt together from the total amount of soil particles to obtain the amount of clay.
Percentage of sand = (depth of sand/total depth) * 100
Percentage of silt = (depth of silt/total depth) * 100
Percentage of clay = (depth of clay/total depth) * 100
Soil structure is the way in which the sand, silt, and clay
particles are grouped together. The drainage capacity of the
soils and the ability of the soils to make nutrients available
to the plant are functions of soil structure. See B.03.03 on the role of humus in forming
and maintaining soil aggregates.
The National Gardening Association's "Gardening for Dummies" has a simple test for approximating soil texture. They call it, "The Ribbons and Bows" test. Take a handful of moist soil and squeeze it into a ball. Work the soil into the shape of a ribbon by pressing and rolling it between thumb and forefinger. Stand the ribbon straight up.
If you can't make a ribbon without it falling apart, the soil
is at least 50% by volume sand with very little clay. If the
ribbon is much less than 2" (5 cm) in length before it breaks,
the soil has about 25% by volume clay. If the ribbon is between
2" (5 cm) and 3 1/2" (9 cm) long, it has about 40% by volume
clay. If it is still together at much longer than 3 1/2" (9
cm), it is at least 50% by volume clay.
Soil aggregates are clusters of soil particles. They are the
bodies that give the soil structure. Soils develop different
structures as a result of the way they are treated. Top soils
rich in organic content will often develop a granular or crumb
structure which is ideal for most gardens. The soil aggregates
in such soils are bound together with humus adding to the
soil's nutritional value.
Soil aggregates help to build and to sustain soil porosity. A porous soil structure helps in several ways:
The pores or cavities between the soil particles or aggregates are called micropores or macropores depending on their relative size. The macropores are large enough to give free movement of water and air into and through the soil. Macropores are essential to good drainage and giving soil organisms and root hairs ready access to air. They also give roots and root hairs easy channels for growth.
Micropores are much smaller. Air and water pass through these
restricted cavities but slowly. They seem to be of importance
because they help the soil to retain water. They do not seem to
help with the movement of air into or through the soil.
The roots of most plants and all of the soil organisms need oxygen to survive. Life in the soil is dependent on both air and water. Topsoil differs from subsoil primarily because topsoil has a more open structure that contains sufficient oxygen to support both root growth and soil organisms.
Topsoil is usually a darker color because of it's higher
organic content. The thickness of the topsoil layer tends to
be thin in arid or semi-arid regions. The thickness can be
increased by mixing subsoil with the topsoil and adding
additional organic material. The mix becomes topsoil once the
blend establishes it's new ecosystem and begins to support new
communities of soil micro and macro-organisms.
Subsoil is the soil that's left after valuable topsoil has been
lost to erosion. The thickness of the subsoil layer is seldom
more than a few feet.
Hardpan is a dense, hard, crust-like soil layer that occurs in some subsoils. It is usually formed by an accumulation of mineral salts and it is virtually impervious to water. Hardpan can also be formed by severe mechanical compaction. The end result is that hardpan blocks drainage. In some situations, it is considered as a structure of value in that it holds water. In most gardens, however, it is considered a major problem.
If the hardpan layer is relatively thin and close to the
surface, it can be broken up by deep digging. In some
situations, it is possible to correct the bulk of the problems
by simply poking a series of drainage holes through the hardpan
layer using steel rods. Apparently, earth worms present in the
subsoil can also penetrate some hardpan layers. If the hardpan
can't be resolved mechanically and the earth worms can't get
through, the remaining option is to use raised beds.
Compacted soil is soil with most of the air squeezed out. A good top soil should contain as much as 25% by volume air which is needed to support plant growth and the soil organisms. Tramping around in moist beds is a sure way to compact the soil and is something that is best to avoid.
The passage of soil macro-organisms, and particularly earth
worms, going back and forth through the soil repair compacted
soils. Compacted soils can also be corrected by digging in
additional organic material.
Organic material has a number of important functions in the soil:
Most garden soils would benefit by the addition of more organic
material but it can be overdone. Soils with too much organic
material can be excessively soft and fail to give plants,
particularly trees, a sufficient foothold or anchor.
Excessively high levels of organic material could also keep the
soil excessively moist. 15% by volume organic material is about
right for most gardens. Native soils frequently run as low as
3% by volume organic.
Organic soils contain large amounts of organic material. They are relatively light but can hold up to four times their weight in water. They are soils that were originally formed in shallow lake bottoms, swampy areas or bogs. They tend to be very rich in terms of the major nutrients but they are often shy in terms of the micro-nutrients and particularly zinc, copper, and manganese. Organic soils are almost black when moist.
Organic soils contain more than 20 percent organic material
which is more than enough for general garden use. Take it easy
in terms of adding manures and composts to organic soils except
to improve drainage. Feeding with something like fish emulsion
supplemented with materials containing trace micro-nutrients
would be appropriate for organic soils.
Organic material is consumed by the various soil micro and macro organisms throughout the year. The quantity of organic material that needs to be added to maintain a reasonable and appropriate level of organic material depends on the soil type and the length of the growing season. In areas with Mediterranean climates which have greatly extended growing seasons, some soils will use as much as 4 inches (10 cm) of organic material per year. A figure of 2 inches (5 cm) of organic material per year would probably be more realistic for areas with a more seasonal climate and shorter growing seasons.
Rake to smooth and to clean the soil surface of unwanted
debris. Apply half of the needed organic material at the start
of the growing season and the balance at the start of Summer.
Be sure that the organic material is well composted. Lay down
the layer of organic material over the entire soil surface and
rake smooth. It is generally best to leave the layer
undisturbed rather than digging it into the soil. The soil
seems to do better without the digging and the organic material
also serves as a functional mulch. Earth worms travel from the
top soil layer into the organic mulch layer to feed and return
to the top soil where they eliminate organic matter back into
the soil. This back and forth movement through the top soil
also gives the soil increased porosity. Leave some air space
between the existing plants and the organic layer to minimize
rotting.
Bog is soil that is permanently saturated with water and fails
to drain. Soils that don't drain fail to draw air into the soil
pores. Bog soils are frequently very acidic. It takes
specialized plants to grow in bog conditions.
A foul smell indicates anaerobic decomposition. The soil
doesn't have enough air. It can be corrected by adding
additional organic material and turning it into the
soil.
Potting soils are soil-less mixes used as the medium for growing plants in pots. They are soil-less to make them lighter in weight and they are close to lifeless in terms of soil microorganisms as houseplants are prone to soil rot. Some potting soils are also steam sterilized. Potting soils usually don't contain significant quantities of nutrients. Their primary function is to hold air, water and any added fertilizer.
A good mix must stand up to repeated watering without losing structure and still be quick draining. A good do-it-yourself recipe for potting soil: 4 parts by volume peat moss, 2 parts by volume well composted plant material, 1 part by volume vermiculite, perlite, or sponge rock, and 1 part by volume sharp sand or grit.
Peat comes from those regions that are characterized by: cool, wet climates; acid, bog soils; and an abundance of decaying plant material with a high carbon content. Peat forms when the organic content in the soil accumulates faster than the soil microorganisms are able to bio-degrade. Apparently nature's production of peat in the commercial bog fields in Canada is keeping up with the demands of the market but in most other parts of the world, demand has exceeded capacity and the bog fields are becoming or have become deplete. Peat moss is a material in high demand and it is a prime candidate to become a non-renewable product of nature.
Coco-peat is a renewable material with properties similar to
those of peat moss. It should be considered as an
environmentally friendly substitute or as an extender. A 1:1
mix of peat moss and coco-peat would seem realistic for most
applications.
Planter mixes are primarily soil amendments based on composted
materials frequently with added balanced fertilizers. These
products are not closely regulated and may contain materials
you don't want in your garden. Some planter mixes contain
composted municipal sewer sludge which may contain high levels
of heavy metals. Soil is better amended with compost from known
sources.
Propagating mix is a soil-less mix used strictly for propagation. It contains no nutrients. A typical recipe for a propagating mix for green stemmed perennials might be 1/3 by volume sponge rock, 1/3 by volume peat moss, and 1/3 by volume grit. A typical recipe for a propagating mix for woody stemmed perennials like roses might be 1/3 by volume white peat moss and 2/3 by volume regular peat moss.
See Section F.08.*
for comments on plant propagation. See
Section B.01.24 for comments on the use
of peat moss.
Soils used in containers and planters need to be both water
retentive and well draining. In practice, this means the need
for a high organic content. The soils should also be free of any
pathogens. A good loam with about 1/4 by volume clean compost
would seem about right in most applications.
There are billions of microorganisms in a handful of soil and almost all of them are both garden and gardener friendly. A few, however, are clearly pathogens that can cause problems and wearing gloves while working in the garden is a good idea. It is also a good idea to keep current on tetanus vaccination. Working directly in the soil with any kind of an open wound or when pregnant is asking for trouble. Dog and cat feces and fresh manures can also introduce problem pathogens into the soil.
One never knows just what kind of sharp things might be
encountered when working in the soil.
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This sub-section is about amending the physical properties of soil
to build better tilth.
Some of the chemical fertilizer manufacturers objected to packaged manures or composted plant materials being labeled and sold as "fertilizers". They argued that these materials were primarily of value as soil amendments and were too low in terms of their nutritional content to warrant the title of "fertilizers." They presented their case to legislators asking for legislation to be established making it illegal to market manures and composted plant materials as fertilizers. In some cases, they were successful and in those jurisdictions it became the "law of the land".
Consequently, the distinction between organic soil amendments
and fertilizers is mostly one of political semantics. Both
manures and composted plant materials are of value as soil
amendments and as fertilizers. While they may be low in terms
of nutrient concentration, they are used in greater
quantities. See
Section D.02.* on the nutritional content of
fertilizers and soil amendments.
The OCIA's International Certification Standard restricts the use of raw manures on Certified Organic Crops. See Appendix A. Their comment: Raw manures "can be harmful to soil life and cause unhealthy levels of nitrates in produce and salt build-up in soils. Can also contain pesticide residues depending on what animal has been eating. Composted strongly recommended since it can stabilize the nitrogen content, kill weed seeds, and help neutralize pesticide residues."
Some of the riding stables treat their manure with
disinfectants and/or deodorants which are also toxic to
plants. Most of these materials are bio-degraded during the
hot composting process.
The soil microorganisms responsible for converting organic material into plant nutrients consume nitrogen as they go about their work. Most plant materials contain enough nitrogen to meet this need. Raw sawdust and raw ground bark, however, contain very little nitrogen forcing the microorganisms to take nitrogen from the soil to meet their nutritional needs. Eventually the nitrogen is returned back to the soil but the overall effect is that the use of raw sawdust or raw ground bark causes a temporary drop in the available soil nitrogen.
If raw sawdust or raw ground bark is to be used as a soil
amendment, it should be supplemented with a nitrogen rich
fertilizer such as fish meal or blood meal.
Technically, pH is a measurement of the concentration of
hydrogen ions. Common language, pH is a measurement of acidity
or alkalinity. The pH of totally pure water is 7.0. The lower
the numbers away from 7.0, the greater the acidity. The higher
the numbers away from 7.0, the higher the alkalinity. It uses a
logarithmic scale so a material with a pH of 4.0 is ten times as
acidic as a material with a pH of 5.0 and a hundred times as
acidic as a material with a pH of 6.0.
Most plants will tolerate a range of soils extending from decidedly acid to moderately alkaline. Most, however, prefer a soil that is just slightly acidic. A pH range between 6.3 to 6.8 would be about right for most gardens. A soil containing a significant amount of organic matter will often have a pH in that range as a result of the organic acids produced in the composting process.
The "acid-loving" plants seem to do best when the pH is closer
to 5.5. Generous quantities of peat moss or oak leaf mold will
help the soil to become that acidic. Some of the plants that
are native to arid regions tolerate or even prefer soils that
are mildly alkaline. See Section
B.01.24 regarding use of peat moss.
Soils that are marginally too acidic or too alkaline can be
corrected by simply adding extra organic material. Soils that
are decidedly too acidic or "sour" are usually corrected by
adding ground limestone. Soils that are decidedly too alkaline
or "sweet" are usually corrected by adding agricultural sulfur.
A soil test would tell the extent of the excess acidity or
alkalinity and it would also tell the quantities of material
needed to correct the problem. If the soil is more or less
reasonable, it would be better to use extra organic material. It
does the job and it would also be safer. Both ground limestone
and agricultural sulfur can burn plant roots when used in
excess.
It would certainly be a better environmental practice to select plants that would do well in the specifics of the garden. Picking the right plants is one of the first steps in the making of a successful garden. Acid loving plants, for example, simply do better in acid soils than they do in alkaline soils. Plants that do well are resistant to both pests and disease. It is just a poor practice to try to grow something like an English cottage garden in a desert environment. A good part of the reason is that most of the "English cottage garden" plants like soils that are relatively acidic. Desert soils are usually alkaline. Adding lots of oak leaf mold and/or peat moss as a way of transforming an alkaline desert soil into a soil like that of an English cottage garden is only a partial solution. The relative cool, moist and humid conditions of the English cottage garden aren't duplicated by oak leaf mold or peat moss. In terms of design, an English cottage garden also looks out of place in a desert environment.
There are some situations, however, in which the pH of the
soil needs to be corrected if there is to be any kind of a
garden. For example, there are many communities in Southern
California that might not get any rain for as long as 8 or 9
months. Many of the soils are also sharp draining accompanied
by low humidity and drying winds. Added water is needed to
sustain a garden and most of the water sources are alkaline. A
pH of from 7.5 to 8.0 would be typical and alkaline salt
build-up is common. Adding lots of organic material to the
soil to neutralize the alkalinity and to hold the needed
moisture is a practical and effective answer.
difference.
Climate and mineral content are the ultimate causes of soil pH.
Soils in hot and dry areas tend to be alkaline because with
little rainfall, there is little plant growth and with little
plant growth, there is little acid producing organic material in
the soil. Also, little rainfall allows for the accumulation of
alkaline salts. Soils in areas with plentiful rainfall tend to
be acidic for the opposite reasons.
"Depleted" soils is a term that is used for soils with
diminished levels of plant nutrients. Depleted soils often have
a diminished community of soil micro and macro-organisms as
well. Soils can become depleted by erosion or simple over use.
"Degraded" soils is a term that is used for soils that have been
corrupted or injured. A soil soaked with a residual toxic
material would be an example of a degraded soil. The soil micro
and macro-organisms in a degraded soil are frequently either
destroyed or seriously impaired.
Depleted soils should be tested by analysis for mineral content and for organic content. Specifically, which minerals are deficient and by how much? Assume that you will be gardening to a depth of approximately of 12 inches (30 cm). Calculate how much organic material should be added to bring the total organic content in that gardening layer up to 15% by volume. The process of restoring the soil is as follows:
Rake the soil clean and smooth. Apply the needed amount of well composted organic material along with the needed amount of the mineral nutrients and fork this material into the soil. Repeat the raking to clean and smooth. Throughly water the cleaned soil, allow what ever weed seeds present to germinate, hand weed and then plant. Add an additional generous layer of well composted organic material as a mulch. Most soils recovering from depletion need twice a year feedings of composted organic material to rebuild their communities of soil micro and macro-organisms. Allowing the soil to lay fallow for a season seems to help the soil to recover faster.
Another alternative is consider growing a "green manure crop". These are plants that are chopped and tilled or spaded into the soil when they are still green (before they blossom and produce seed). Green manures are grown and used primarily for their organic content and for the texture they give to the soil. Some of the deeper rooted green manures such as alfalfa are said to contain higher levels of mineral nutrients while those based on legumes (such as peas, beans, clovers, & vetches) are used because they are particularly rich in terms of nitrogen.
These crops are usually grown during the main growing season,
between crops, or just after harvesting a crop. A combination
of oats, red clover, field peas and mustard is one of the
stand-by favorites. Vetch is another favorite as well. In
order to become well established, they should be sown at least
6 weeks before the first Fall frost.
The best way to know the extent of damage to the soil is to have
the soil tested. The best way to tell when the damage has been
corrected is to have the soil tested again. Soil organisms have
the capacity to clean up just about everything including toxic
waste. (See B.03.04 on Bio-remediation.)
They do, however, work by their own schedule and clean-up
of seriously corrupted soils may take several years. In those
situations where the damage is limited to a relatively small
area and there is no good way to garden around it, it may be
more realistic to simply dig out the problem soil and to replace
it with a good garden loam. In most cases however, the problem
soil can be cleansed by simply digging in an abundance of well
composted organic material, keeping the site well watered and
giving the soil organisms the time to do the job. The extra
organic material and the extra water are to help build stronger
populations of the soil organisms.
Field tiles are mechanical structures designed to help soil
areas that are chronically too wet to drain. Their use may or
may not qualify as a "do-it-yourself" project. The top layer of
the wet soil area is removed to a depth of at least four feet
(125 cm). The area is then raked smooth and covered with a foot
(30 cm) layer of gravel, rubble, or rock. The field tile is
then laid on top of this layer of gravel, rubble, or rock and
aimed to direct the flow to some remote low spot. The field tile
is then buried under an additional foot (30 cm) layer of gravel,
rubble, or rock. The entire field drain system is then buried
with soil back up to grade. Wrapping the field drain with a single layer of
landscape fabric or drain filter cloth helps to keep
materials from sifting into the drains interior to
prevent clogging. A single layer of landscape fabric
added to the top of the gravel layer just below the
soil can also prevent soil from sifting through and
clogging the system although it does cause some slow
down in drainage.
Erosion is the gnawing away of the soil surface by moving water,
wind, or other geological agents. The word, erosion, has the
same Latin root as the word, rodent . . . both noted for their
gnawing ways.
There are a number of things that can be done to minimize
topsoil from being washed away. Probably, the best way would
mean the use of several ways used in combination. Things that
can be done include:
Selecting plant material that works and that is also
appropriate to the specifics of the garden is not easy.
Probably the best way of finding the best plant material
to use is to look at other slopes in your particular area
and to see what really works with your conditions. Pay
particular attention to the directions the sloping face
and shade cover. Slopes with similar soils, facing in the
same direction, and with the same shade cover should give
similar growing conditions. In addition to being
functional, they should also be relatively easy to
maintain and they should be appropriate for the specifics
of your garden. If your initial selection doesn't work
out, try something else. The main thing is to protect the
soil.
Just as in B.02.15, keeping soil from
being washed away by moving water, probably the best way to
minimize soil from being blown away by strong winds is to use
several of the preventive steps in combination. They
are:
Raised beds, as used in this FAQ, can be either free standing
mounds of soil sitting on top of grade or elevated beds
contained within supporting structures. Generally speaking, they
both work in the same way and they both offer the gardener the
same advantages. Raised beds give good drainage and they can be
a good answer when drainage is a problem. It is also easier to
garden in a raised bed because they are at a better height. They
can also be a good design feature as they clearly define the
planting area. Raised beds can be used as steps on terraced land
to minimize erosion. They can be as handsome as they are
functional.
The main problem with raised beds is that they can be difficult to design and to construct. Beds that seemed the right size at the time of installation can end up being too small, making them too limiting, or too big and wasting needed space. There can also be problems relative to location. Beds that seemed well placed can end up being in the way or an eye sore when viewing the garden as a whole.
The selection of materials used to construct the enclosures for raised beds can also be a problem. Structures made from pressure treated wood or wood treated with preservatives are usually toxic to the soil. Structures made from wood that isn't treated fail to stand up for more than a couple of seasons. Structures made of cinder block often clash with the design or look of the garden and using field stone or rock is more than many can handle.
The flip side of raised beds giving good drainage is that this also means the need for more frequent watering. This is particularly true if the supporting structure of the raised bed is relatively open.
All things considered, raised beds can make for better and
easier gardening, but it's not easy to bring it all
together.
Generally speaking, if there are to be multiple raised beds, there should be at least a 3' (1 meter) clearance between them for free passage of wheel barrows or garden carts. Beds used to grow edible crops work best when there is access from both sides and when they are no wider than 3' (1 meter). Beds for ornamentals don't need as much access and they can be as wide as design will allow.
Outline the proposed bed with stakes and string after the decision has been made as to size, shape, and location. Then walk away and look at the outline from various points in the garden. Does it really look right? Is this the best location? Is this the best size and shape?
If so, clear the site of debris and put in any required
edging. Add a 2" (5 cm) layer of native soil followed by an
inch (2.5 cm) layer of compost and scratch in until uniform.
Add successive 2" (5 cm) layers of native soil followed inch
(2.5 cm) layers of compost until the desired height is
achieved. Scratch in until uniform. Water thoroughly, allow
whatever weeds present to germinate, hand weed, rake smooth
and the bed is finished.
Soil testing is controversial. It is easy to assume that the generous use of manures and composts will provide the garden with all of the essential nutrients and that soil testing isn't necessary. In practice, however, manures and composts can be deficient relative to some of the essential nutrients, and particularly relative to some of the trace elements, and the organic gardener is not exempt from problems with mineral deficiencies.
Many soils around old buildings also contain high levels of
materials like lead and copper. Soil tests help to identify
these kinds of problems. It's probably a good idea to have the
soil tested every couple of years and especially if the soil
is used to grow edible crops.
Soil probes are devices used to obtain core samples from the soil. They measure the depth at which the soil turns from moist to dry. Deeply rooted trees do best with deep but infrequent watering. Annuals and perennials with the roots closer to the surface do better with more even watering. In addition, some spots in the garden drain faster or slower than others. A soil probe can tract these things and tell the gardener where there is too much or too little water throughout the garden. Soil probes are usually tough, life-time tools but they are also rather pricey. They may not be totally necessary but generally speaking, they are probably worth every penny. Its hard to give really good tree care without a soil probe.
Peaceful Valley Farm Supply has a quality "18 inch soil sampler"
that sells for about $35 (U.S.). Their address is P.O. Box 2209,
Grass Valley, Ca., 95945 or
http://www.groworganic.com
The simplest way to test for drainage is to simply dig a
hole about a foot deep (30 cm) in the test soil.Cover the
hole with a plastic sheet to let it really dry out and then
fill it with water. If all of the water drains out in less
than 10 minutes, it's draining too rapidly. If it takes more
than 4 hours to drain, it is draining too slowly. Adding
additional organic material improves drainage for both soils
that drain too rapidly or too slowly. Hard pan shows up as
very slow drainage. See B.01.14
Soil that has a suitably crumbly structure, sufficient humus,
and is well drained is said to be "in good tilth". To help
secure good tilth, grow a green-manure crop or use composted
plant material or composted manure.
Common-sense points gardeners to work their soil about as deeply as their backs will allow. Digging in generous quantities of manures and composts, burying cover crops, or just plain turning the soil improves the feel and look of the soil almost immediately. Increasing the organic content "is a good thing". One of the benefits of tillage is that it loosens the soil by incorporating large quantities of air. The problem, however, is that it often incorporates too much which accelerates the breakdown of the organic material over and above the needs of the garden.
In practice, simply covering the soil surface with a layer of
organic material and letting nature do the job seems to work
just as well, if not better, and it is considerably easier.
One exception is heavy clay soil that has been undisturbed for
an extended period of time. The best way of dealing with that
challenge is to simply dig in a lot of organic material and to
repeat the process a couple of times per year. Eventually, it
will become really good soil.
Soils with too much salt can usually be flushed out with water.
Sandy soils with sharp drainage are easier to flush than are
clay soils that drain more slowly. The best way to deal with
salt is work at keeping salt out of the soil. It can be a real
problem.
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The work of these soil microorganisms is exceedingly complex
and extends into nearly every section of this FAQ. The ways
the soil bacteria and fungi break down plant and animals
residues and wastes are addressed in
Section C, "Composting &
Use of Compost". The ways the soil bacteria and fungi
breakdown and then convert materials into plant nutrients as
well as the ways the soil bacteria, fungi, and amoeba hold
these nutrients in place and then make them available to the
plants are addressed in
Section D, "Plant
Nutrition".
The ways some of the soil microorganisms assist the plants in
their physiology are addressed in
Section F, "Botany for the
Home Gardener".
The ways some of the soil bacteria and SOME of the fungi both
cause and control plant disease are addressed in
Section G, "Plant & Soil
Disease; Treatment and Prevention"
and the ways some of the nematodes, some of the soil insects,
and some of the various micro-arthropods such as mites attack
and/or protect plants are addressed in
Section H, "Plant & Soil
Pests; Prevention and Treatment". This sub-section is
limited to the ways the soil microorganisms impact on the
physical, chemical, and bio-chemical properties of
soil.
In addition to producing humus, the soil microorganisms
breakdown and/or bind a variety of organic and inorganic
materials to clean up corrupted or polluted soils - petroleum
products, synthetic pesticides, and heavy metals included. See
B.03.10 regarding soil cleanup using
bio-remediation.
"Detritus" is the proper term for the
recognizable debris from dead plants and animals. Humus is the
dark colored, sweet smelling, goo. Humus is often called,
"Black Gold" because of its great value to plants,
soil, and the soil microorganisms.
"Humic, Fulvic, and Microbial Balance: Organic Soil Conditioning" by William R. Jackson says, "During humification, all cellular makeup undergoes a pattern of transformations, modifications, and structural re-arrangements, resulting in highly complex polymeric humic compounds. Although some of these modifications are chemical, most are bio-chemical and develop through the enormous numbers of enzymes released by the microorganism population".
The relatively small and simple polymers, specifically those
humic substances with a small molecular weight, are known as
fulvic acids. The relatively large and complex polymers,
specifically those humic materials with a high molecular
weight, are known as humic acids. It is believed that fulvic
acids become humic acids with more polymerization and that
humic acids become humin with even more polymerization. Humic
substances include fulvic acids, humic acids, the salts of
both fulvic and humic acids, and humin.
Fulvic acid working in concert with the soil microorganism can
bio-degrade most problem materials. Adding an abundance of
organic material to the soil will elevate the levels of fulvic
acid and it will also build larger and more active populations
of soil microorganisms. In time, the combination will clean up
most problem materials. Because, it is seldom self-evident as
to when the problem materials have been degraded, it would be
a good idea to have the soil tested before counting it as
safe.
Problem areas in the garden where things just don't grow well may be the result of pH or toxic levels of metals. Soil testing, if done properly, should identify these problems as well.
One of the problems with soil testing is that the results are usually given strictly in terms mineral content and the recommended corrections assume the sole use of synthetic materials. The organic content, including the humic substance content, is critical to the fertility and function of the soil and this is largely ignored.
Dr. Elaine Ingham, Department of Botany and Plant
Pathology, at Oregon State University tests soils for soil
micro-organism populations. She measures the bio-diversity and
the vigor of the microbe communities which is probably even
more important. Her address is Cordley Hall 2082, Oregon State
University, Corvallis, OR 97331-2902. The costs for this
testing is said to be just a few dollars.
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