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The
Soul of Soil --
By Countryside Staff
Growing good crops that will bring health to man and beast
requires fertile soil. This does not mean chemicals from a bag, especially when
spread without understanding
There are two ways to farm or garden: You can rely on
technology and buy a bag of fertilizer and spread it on your land and hope for
the best - or you can learn what soils and plants really are and how they
function. The first is certainly the easiest, but the second is part of The
Simple Life, and by far the best. (And incidentally, if we're living in the
Information Age, just what is it that we supposedly know so much about, and how
important is it?)
Some people like to point out that the sum total of human
knowledge is now doubling every 18 months. This "information
explosion" suggests that we know far more than our grandparents, and their
grandparents.
Yet, what do we "know" about even the most basic,
the most important elements of the world we live in. . . such as the soil that
feeds us? Probably much less than our ancestors!
Most people who rely on supermarkets and restaurants for
their food regard soil as dirt. . . something filthy, to be avoided, and
certainly of no great importance. To them, it's all the same, and it doesn't
matter.
But if you grow your own food you are very aware that all
soil is not the same, and it certainly does matter, even to those who have no
personal contact with it beyond the food they purchase.
And that lack of knowledge - basic, life-giving essential
knowledge - allows the modern sophisticate to ignore the source of food and its
production techniques. Much worse, that ignorance allows the technological and
industrial society to make poor decisions regarding everything from land use in
housing and commercial developments, to policies regarding agriculture, to the
choice of foods that keep them alive.
Here are some facts about soil taken from a textbook
published in 1909. These facts were common knowledge 90 years ago, but have been
overshadowed by and largely forgotten during the "Green Revolution"
and information explosion.
Some people will say this is old and outdated information,
and we should concentrate instead on all the wonderful new scientific advances
and the latest data - such as gene splicing and cloning and terminator
technology.
I say it's time, and past time, that we take another look
at the basics so we can use, or reject, the modern science with not only
knowledge but with wisdom.
This is an edited and abridged chapter from a high
school textbook,
Elements
of Agriculture, by G. F. Warren.
Most people see soil as "dirt." They almost
invariably think of it as a dead thing. But in reality, soil is teeming with
life, and it's full of activities of the most complex and interesting kinds.
Rock particles
Rock particles are 65 to 95 percent of the weight in
most soils. (One exception is muck soils, where nearly all the solid matter is
made up of organic materials. These are some of the most fertile soils on the
planet.) Organic matter usually constitutes 2 to 5 percent. (This was in 1909:
many farm soils today are much lower.) Most of the remaining weight is water.
The mineral matter furnishes the solid food, and acts as a reservoir for holding
the water. Both functions are dependent on the size of the soil particles, which
in turn has much to do with the value of the land. (This, of course, is in
reference to food production. Today, much real estate is evaluated by location,
location, and location, regardless of its food production capabilities, meaning
that even prime farmland is often destroyed when someone can make more money by
using it for a housing or commercial development.)
If a soil is thoroughly shaken up with water and then
allowed to settle for a few minutes, the larger particles will be separated out.
The riley water can then be poured off and allowed to settle for a longer
period, and the next larger particles will have settled to the bottom. If the
riley water is again poured off, the soil is separated into three sizes of
particles. Any number of divisions can be made in this manner.
(That knowledge was exploding beyond the needs, and
perhaps even the understanding, of the common man, even in 1909, is demonstrated
by this footnote: "The common method of making the separation is to put the
samples of soil in bottles of water, and shake for a day in a shaking machine.
This separates the particles that are stuck together. A centrifugal machine is
used to aid in making the separations, as it is more rapid than waiting for the
particles to settle. The material is usually separated into three grades by
means of water. The sands are further separated by means of sieves.")
The finest soil particles are called clay, the next
smallest silt. The larger particles are different grades of sand and gravel. The
following table shows the mechanical analyses of three important soil types as
separated by the Bureau of Soils:
The Norfolk sand is one of theeading truck soils of
the Atlantic coast. A large part of the vegetables for eastern cities are grown
on this soil. The Miami silt loam is one of the leading types of soil in the
corn belt of the Central West. The Wabash clay occurs along many river bottoms.
It is used for corn, oats, cotton and hay.
How soils are named
The soils that contain a large proportion of the
finest particles are called clay. At the other extreme we have sands and
gravels. Soils that are intermediate in texture are called loams. Those with a
large proportion of silt particles and not too much clay are called silt-loams.
Then these words are joined together to describe
intermediate types. There are gravelly loams, sandy loams, fine sandy loams,
clay loams, etc.
Since many soils as thus named are very different in
other respects, the Bureau of Soils prefixes another name to distinguish them.
These are usually names of towns near which the soils were first mapped. (Today,
Miami silt loam might make one think of Florida; think Ohio instead.)
Local names used in any community are often
misleading. In a region where nearly all the soils are sandy, a loam soil is
usually called a clay; while in regions where most of the soils are heavy clays
the same loam is likely to be called sandy.
Soils are also named in many other ways. Glacial
soils are those formed as a result of glaciation. Arid soils are those that do
not receive enough rain to produce regular crops without irrigation. Humid soils
are those that receive sufficient rainfall to produce crops.
The importance of the size of soil particles
The size of the soil particles influences the
water-holding power of the soil, the amount of food that can be dissolved for
plant use, the ease of movement of water and air, the growth of organisms in the
soil, and the crop-producing power.
The rock particles of the soil can hold water on
their surfaces only. Therefore the water-holding power of the soil increases
when the surface area of the particles is decreased.
Dip a pebble in water and a film of water will remain
on it when it is removed. Wipe the pebble and the water will be gone, because no
water has soaked into it. If such a pebble is broken in two it will have more
surface area. The finer the material is broken, the more surface there will be,
and the more water it will hold.
The finest soil particles are extremely small - less
than four hundred-thousandths of an inch in diameter. The total surface area in
a cubic foot of such material would be very great. Such fine particles do not
always act as individuals in holding water: some of the particles usually stick
together.
A cubic foot of soil grains having a diameter of
one-thousandth of an inch (coarse silt) would have a surface area of 37,700
square feet. A column of such soil one foot square and four feet deep would have
a water-holding surface of not less than 3.4 acres.
The water capacity of a soil is the amount of water it will
hold when all the free water is allowed to drain out. Some clay soils will
retain about 40 percent of water. That is, 100 pounds of soil may retain 40
pounds of water. A cubic foot of clay weighs about 80 pounds and could,
therefore, hold about 32 pounds of water. Sandy soils might have a water
capacity as low as five percent.
Which one would you rather garden in? The answer might not
be as apparent as it seems.
Plants cannot remove all the water from a soil. They die
for lack of water long before the soil is absolutely dry. They can use a larger
proportion of the water from a sandy soil than from a clay. In one study, in a
sandy soil with a capacity of 18 percent, corn was able to reduce the water to
4.17 percent. In a clay soil whose capacity was 26 percent, corn used the water
down to 11.79 percent. In this case, the sandy soil actually furnished more
water for the growth of the corn than had the clay.
Water
The rock particles are very slowly soluble. Soil
water can act on the surface of the particles only. Since smaller particles have
more surface area for a given volume of soil, they are able to furnish plant
food more rapidly. Finer soils are usually more fertile, but are less easily
managed.
Air
About half the volume of a dry soil is air; that is,
a cubic foot of such soil contains about half a cubic foot of air. The small
particles of which a clay soil is composed do not pack so closely as do the
larger sand particles, because they are lighter. Therefore, there is more pore
space in clay than in sand.
But the spaces in a sandy soil are larger, so the air moves
more freely, making such a soil better aerated.
Temperature
The temperature of a soil is influenced by its color,
topography, humus content, and several other factors. But the chief factor is
water capacity.
•Early truck 1,955,000,000
•Truck and small fruit 3,955,000,000
•Tobacco 6,786,000,000
•Wheat 10,228,000,000
•Grass and wheat 14,735,000,000
Warren said, "No person can comprehend such
figures as these, but the comparison is the valuable point. The table shows how
much coarser the truck soils are than the wheat soils."
But even if the clay soils would produce good truck
(garden) crops, they have another drawback: they are difficult to work.
Vegetables already require more labor than crops such as hay or wheat, and using
soils that are hard to work only adds to the labor cost.
Sandy and other well-drained soils are not only
easier to till, but the number of days on which they can be worked is much
greater. They can be tilled earlier in the spring, and more quickly after rains.
Flocculation
When a silt or clay soil is in good condition, many
of the particles are united into compound particles. Such a soil is
"flocculated." Good management of such a soil consists very largely in
maintaining this granulated condition. If such a soil is worked while wet, and
if it then dries, it will be greatly injured, sometimes so much as to damage the
crop for several years. Working a clay soil when wet makes "bricks" of
it. The crust that forms on the surface of a soil after it rains is due to this
breaking down of compound particles.
Soil water
Amount of water
Too much water is as bad as too little. Optimum water
content is 50 to 60 percent of the soil's capacity. In many areas the soil is
saturated with water during the early part of the growing season, and too dry
later on, injuring the crop at both extremes. However, a good soil, rich in
humus, modifies both extremes.
The most serious result of too much water in the soil
is the exclusion of air, which is essential for plant growth and for the
activities of soil organisms. It also prevents roots from growing deeply into
the soil, makes the soil cold, and delays farm or garden work. When the work
cannot be done at the proper time, weeds are more likely to gain a foothold. Wet
land is nearly always weedy land.
One of the first effects of too-wet soil is yellowing
of leaves. This is due to the lack of nitrogen. The fixation of atmospheric
nitrogen ceases when air is excluded from the soil by an overabundance of water.
When air is excluded from the soil, beneficial soil organisms become inactive.
It is from the air in the soil that these organisms and leguminous plants secure
free nitrogen for the use of crops. Not only does the fixation of nitrogen cease
when air is excluded from the soil, but under these conditions the organisms
that break down nitrogen compounds are very active, so that the nitrogen that
was fixed previously is being lost.
For optimum plant productivity, we want just the
right balance of air and water in the soil.
Organic matter
All productive soils contain decaying roots, leaves
and animal life. This partly decayed organic matter is called humus. It is humus
that gives soils their dark color.
Humus has many functions. It increases the
water-holding power of soils, which is particularly important on sandy land. It
loosens heavy soil and promotes aeration, which are of special importance on
clay soils. It furnishes food for bacteria. These, acting on the humus, change
nitrogen to nitric acid so that it is ready for plant food.
As humus decays, it also liberates carbon dioxide.
This acts on the minerals of the soil, making them soluble and ready for plant
use.
Another extremely important function of humus is that
it encourages the growth of bacteria that fix free nitrogen from the soil air,
making it available as plant food.
The more air in the soil, the more rapidly the humus
is decomposed. If a soil is saturated with water, the oxidation practically
stops and organic matter accumulates. This is the way that peat and muck are
formed. For crop production, a moderate rate of decomposition is preferred. If
too rapid, the supply is exhausted; if too slow, the plant does not receive
enough food.
Life in the soil
As we have seen, soil is not a dead thing. It is much
more than a collection of rock particles. It is teeming with life. If all the
living things in the soil should die, the soil would soon fail to produce crops.
(Note: This "common knowledge" of a century
ago was debunked by the so-called Green Revolution, which held that the only
function of soil was to hold the plant roots while they were being fed
artificial fertilizers. Organic farmers never lost, or in some cases
rediscovered, the old knowledge. But today, even some high-tech agriculturists
have sorted out the information overload and are returning to the old wisdom.)
The 1909 high school students who studied Elements of
Agriculture learned pretty much what today's so-called "conventional"
farmers who are turning towards organic or sustainable farming are learning only
now.
Keeping the soil productive, Warren wrote almost a
century ago, is very largely a matter of keeping these organisms thrifty. The
roots and stems of plants furnish food for bacteria and molds. The waste
products furnish food for other bacteria. Eventually, the food is in a form
available for crops to use again. Any break in the link will affect all of the
chain. If the organisms do not decompose the roots and stems properly, the new
crops will suffer. If there is not enough humus in the soil, the bacteria suffer
and the crops are immediately affected.
Earthworms serve a useful purpose in the soil by
helping to break down the organic matter. They also do much good by making the
soil porous. A soil that is full of earthworms is nearly always fertile.
The molds help in breaking down the organic matter,
particularly the woody matter. But the most important forms of life in the soil
are the microscopic organisms, yeasts and bacteria.
Soil bacteria
On an average, it takes about 25,000 bacteria placed
end to end to measure one inch. Of the very smallest ones, it takes about
150,000 to measure an inch.
The small size of the bacteria is more than made up
by their immense numbers and by the rapidity with which they multiply. They
reproduce by simple division: one individual divides into two. Under favorable
conditions this can take place every 15-30 minutes. If each one divides into two
every quarter of an hour, there will be an immense number of them at the end of
a day, even if there was only one in the morning.
A turn-of-the-century New Jersey Agricultural Bulletin put
it this way:
We can start by going back even further, and seeing how
soils were formed.
How soils become
productive
Thus soils were formed, over many thousands of years,
and became ever more fertile.
How rich virgin soils become less productive
There are people, still living, who can tell about
wonderfully productive crops grown on virgin soils. And they can also tell how,
after a few years of such crops, the soil became "worn out." Humans
didn't have time to replicate nature's method of creating soils, so for a time,
they simply wore out the land and moved on.
Then there was no more virgin land to exploit.
Humans (as a species) weren't smart enough to follow
nature's methods. To make things worse, they thought they were smarter than
nature: they could do the job much faster and more easily by using their
technical knowledge. But that's getting ahead of our story.
The first farming of a virgin soil has nearly always
been grain farming. (In the United States, this was due largely to economics;
i.e., the industrial system. It was much easier and cheaper to ship grain from
the frontier to the population centers than it was to ship meat, eggs or dairy
products.) Grain is grown every year, with no provision for keeping up the humus
supply, either by means of barnyard manure or by plowing under the crop
residues, even straw often being burned. Little barnyard manure is produced, and
that which is is either thrown away or allowed to lose most of its value before
being put on the land.
G. F. Warren noted in 1909 that "Very few
farmers in any part of America have yet learned to handle manure without losing
one-half of its value." (In some regions this hasn't changed. . . and the
availability of chemical fertilizers has made it even worse.)
The virgin soils, Warren continued, are so productive
that farmers nearly always make the mistake of thinking that they will always
remain so. "But the constant tillage exhausts the humus supply, and the
virgin soils become less and less productive. The change is so gradual and is so
obscured by the weather variations from year to year that the real state of
affairs is often not realized until the soil is so poor that it does not pay to
farm it."
Even in the early 1900s, according to Warren,
sometimes commercial fertilizers were resorted to. But he points out that while
these might pay for a few years, sooner or later some provision for renewing the
humus supply must be made, or the field must be temporarily abandoned to allow
nature to renew the supply by growing weeds. "Many fields in the older
sections of the United States are thus abandoned for a few years to recuperate
to such an extent that a small crop may be grown. A wiser way of farming would
be to begin to raise animals for manure production before the soils become so
exhausted."
The causes of
decreased productivity
Warren said even more soil fertility was lost by wind
and water erosion than by cropping. In spite of a much wider recognition of
this, soil erosion remains a serious problem even as we enter the 21st century.
In fact, there are places where windbreaks planted after the Dust Bowl years are
now being torn out to accommodate ever-larger fields and equipment, and by
running after short-term profits rather than long-term interests.
Warren suggested keeping the soil in sod, keeping
cover crops during the winter, and terracing.
Productivity can be decreased when the soil no longer
holds enough moisture. This can be remedied by adding humus, Warren said.
The soil may cease to be favorable for the
development of soil organisms. Again, Warren suggests adding humus. . . and
lime.
Constant cropping can exhaust the available supply of
a specific plant food. Each crop removes a certain amount of nitrogen,
phosphorus and potash (as well as others). If any one is lacking, the crop will
suffer no matter how much of the others is available. Usually it is not a
shortage of the absolute amount in the soil, but a shortage of that which the
plant can secure in usable form. Again, the addition of humus. . . to feed the
soil, so the soil can feed the plant. . . is called for.
The exhaustion of the humus supply is usually the
fundamental cause for decrease in crop yields, Warren said. If that was a
problem in 1900, it has become ten-fold worse. This affects crops in many ways.
It may result in an unfavorable physical condition of the soil that will limit
the crop even when there is no shortage of plant food. The soil may bake, or
lose its water-holding power. Since the humus furnishes nitrogen by its
decomposition and encourages the fixation of free nitrogen, the exhaustion of
humus will be accompanied by a shortage of nitrogen. Or because of the lack of
humus, the mineral elements may not be rapidly enough dissolved, although
present in abundance. In such a case, the addition of phosphoric acid or potash
might increase the crop, Warren said, but it would usually be wiser to supply
humus so as to render available the food that is already in the soil. Once
again: "Many soils are losing their fertility in all of the waysmentioned
above". . . and that was nearly 100 years ago. It's much worse now.
Materials used as
fertilizers
It's easy to see how early farmers could have learned
to follow that natural method, even if they didn't think about it. Perhaps
someone noticed that the grass was greener or the grain yield better around
animal droppings. The same effect could be seen around old campfires, or even
after grass or forest fires. Barnyard manure and wood ashes are among the oldest
fertilizers used by humans to maintain or restore natural fertility.
The Indians taught European settlers in America how
to grow corn and use fish as fertilizer. One account says, "According to
the manner of the Indians, we manured our ground with herrings, or rather shads,
which we have in great abundance and take with ease at our doors. You may see in
one township a hundred acres together set with these fish, every acre taking a
thousand of them, and an acre thus dressed will produce and yield as much corn
as three acres without fish."
Nitrogen
All nitrogen comes from the air. There is no nitrogen
in stone. Nearly four-fifths of the air is nitrogen. Warren said there are over
35,000 tons of this gas over every acre of land. And yet, plants swimming in
this sea of nitrogen can be nitrogen starved, yellow and sickly. That's because
no plants except legumes are able to use atmospheric nitrogen.
Note that the legumes themselves do not fix nitrogen.
This is done by the nitrogen-fixing bacteria that live in the root nodules of
the plants. If the right kind of bacteria are not in the soil, a legume cannot
produce nitrogen, for itself or for subsequent crops.
But other bacteria also increase nitrogen under the
proper conditions. Warren cites one early study from the New Jersey Experiment
Station where millet (not a legume) was grown in boxes without fertilizer, with
one gram of nitrogen added in the form of nitrate of soda, and one gram of
nitrogen added in the form of barnyard manure. A fourth box got no fertilizer,
no crop was grown, and the soil was kept bare.
The soil that was bare contained a gram more nitrogen
in the fall than it did in spring. There was a slight gain when millet was
grown. When one gram of nitrate of soda was added, the crop and soil contained
3.73 grams more than was present at the beginning. But when the manure was used,
the gain soared to 10.48 grams.
These gains came from the air. The nitrogen was fixed
by organisms acting independently of legumes. The striking results with the
barnyard manure, Warren speculated, were probably due to the humus it contains,
and perhaps partly due to the organisms it brings with it. "This partly
explains why fertilizers alone cannot take the place of manure."
Grasses don't have the power to obtain nitrogen from
the air, but when land is left in sod there is usually a considerable gain in
nitrogen. Every farmer knows (or at least used to know) that a field that has
been in sod for a few years produces much better crops. This is partly due to
the humus added by the decaying roots, Warren said, and is undoubtedly partly
due to the fixation of nitrogen. Probably the humus has much to do with the
nitrogen fixation.
"In the regions where soils have been so farmed
as to become unproductive, the fields are commonly abandoned for one or more
years, then they will produce crops again. Where the soils are not quite so far
exhausted, one or two tilled crops are grown and are then followed by hay a few
years, after which small crops can once more be raised. The same principle
should be applied in regular farming. Under most conditions, the land should be
in sod one to three years out of every five. The poorer the land, the more time
it should be in sod. If legumes can be combined with this sod, so much the
better. The same results may be accomplished in other ways, as by plowing down
green manure crops."
There are other organisms in the soil which
accomplish the opposite results. They act on nitrogen compounds and break them
up so that the nitrogen escapes into the air as free nitrogen. This is called
denitrification. When manure is left in loose piles, or simply spread on the
land without being worked in, much of the nitrogen is lost by denitrification.
Composting manure is the best way to retain the nitrogen in it.
Nitrogen may also be lost by being made too soluble
too rapidly, in which case it may leach out of the soil. The humus in a sandy
soil is likely to be burned out so rapidly that the nitrogen may be lost in this
way.
Dried blood or blood meal is usually about 12 percent
nitrogen, and is commonly used by organic gardeners.
Another organic fertilizer, bone meal, also contains
nitrogen: about 4 percent. (At least it did in Warren's day: the package we have
makes no mention of this, so it probably doesn't contain any.) But bone meal is
used for its phosphorus.
For potash, Warrens (and many present-day organic
gardeners) recommends wood ashes. . . and barnyard manure.
Lime is usually spoken of as a soil amendment rather
than a plant food or fertilizer, but again, Warren recognizes the
interdependence of nature, including soil fertility. Lime helps to improve the
physical condition of some soils, it corrects acidity, and it helps liberate
other plant foods, but perhaps its most important effect is its influence on
soil organisms. If there isot sufficient lime in the soil, the fixation of
atmospheric nitrogen cannot go on properly, nor can the liberation of nitrogen
from the humus.
"The addition of lime to the soil so favors the
preparation of nitrogen food that its effect is often the same as nitrogen. If a
soil is deficient in lime it is unwise to go on farming it until this deficiency
has been corrected. The other fertilizers or barnyard manure cannot be used most
economically if there is not sufficient lime. On the other hand, lime does not
take the place of these fertilizing materials."
All of this provides a mere glimpse into a book
written nearly one hundred years ago, to explain to high school students facts
known to few college graduates today. . . probably including some with degrees
in agriculture. And yet, to those exploring organic methods, it's all
"up-to-the-minute news in depth."
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