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
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
Some people will say this is old and outdated information, and we should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
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
This is an edited and abridged chapter from a high school textbook,
Elements of Agriculture, by G. F. Warren. – Jd
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.
The almost universal idea is that soil consists of small particles of
rock that have been made fine by the process of weathering. But no crop
could grow on a soil composed entirely of rock particles. An
agricultural soil also needs soil water, soil air, decaying organic
matter, and living organisms in order to be productive. (Organic matter
is defined as any material that is, or once was, an organism or living
thing, such as wood, straw, manure, etc.)
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.
The mineral components of a soil are of course dependent upon the type
and origin of the rock it was derived from.
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
Then these words are joined together to describe intermediate types.
There are gravelly loams, sandy loams, fine sandy loams, clay loams,
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.
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.
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
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.
The temperature of a soil is influenced by its color, topography, humus
content, and several other factors. But the chief factor is water
It requires about 20 heat units to raise the temperature of 100 pounds
of dry soil 1 degree F. To raise the temperature of the same weight of water
1 degree requires 100 heat units. This is why gardeners often speak of “wet”
and “cold” soils in the same breath.
But the effect of water is most striking when it evaporates. To
evaporate 100 pounds of water requires 966.6 heat units. This explains
why wet soils are always cold soils. Clay soils are cold chiefly because
of the large amount of water that evaporates from them.
Few crops begin growth until the soil is 45-50 degrees. The best growth
usually doesn’t take place until the soil is 70 degrees. It’s easy to see why
gardeners want sandy soils for early truck crops.
However. . . another caution. No single soil is “best” for all crops. One
early soils researcher (Whitney) gives the following as the number of
soil particles per gram of soil adapted to different crops:
- 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.
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.
This became a more serious problem when farmers started using bigger and
bigger equipment, and worked more and more land. . . and forgot (or never
learned) what their forefathers knew about soil. With so much area to
work, waiting until the soil was ready was more often neglected, and if
a powerful tractor could work even wet soil, this was considered
progress. But such progress has ruined many soils.
If such a soil is too finely pulverized – which often happens when eager
but uninformed gardeners think they’re “improving” their soil by getting
out the rototiller every time they see a weed – it “runs together” and
bakes because the granules have been broken up.
The relative fineness of the soil is called its texture, just as the
word is used when speaking of the texture of cloth. If the soil is
composed of very small particles that are flocculated, it can still be
of a coarse texture.
Structure refers to the arrangement of soil particles. If small
particles are united, it is possible to have a soil of fine texture and
In an agricultural sense, Warren wrote in 1909, the most important use
of soil is to act as a storehouse for water. The productiveness of soil
is limited by the amount of water that the soil can hold, and by the
extent to which growing crops are able to remove the water. The soil
water is important not only because it is the chief plant food, but
because it acts as a carrier of all the other plant foods that come from
Soil water is very different from rain water. It contains all the plant
foods in solution. The solution is very dilute, but plants use a large
amount of it.
The chief ways water exists in the soil are as film water and free
water. The particles can hold a certain amount of water on their
surfaces, just as one’s hand remains wet when removed from water. Only a
limited amount can be held in this way. If too much water is present, it
will drop off.
If more water is present in the soil than can be held as film moisture,
it will fill the pore spaces between the particles. If there is an
outlet, this free water will drain away and leave the film or capillary
Free water moves downward by gravity. Capillary water can move in any
direction, because the force of adhesion between the soil particles and
the water is strong enough to lift the water, just as oil is lifted in a
After a heavy rain the soil may be filled with water. Gradually the free
water drains away and leaves capillary water only. The surface soil
loses some of the water by evaporation. This leaves it drier than the
soil below. Some of the water of the lower layer is then drawn up by
capillary action. In this way water may be removed from the soil very
rapidly, particularly when the weather is dry, warm and windy.
Water also evaporates within the soil, into the soil air. There is a
constant movement of this air in and out of the soil, and this aids in
drying a soil.
If there is not an abundance of rainfall, it is desirable to stop this
movement of water to the surface where it evaporates. Any loose mulch,
like straw, on the surface of the soil will accomplish this purpose.
Capillary water moves very slowly through dry soil, so one of the best
methods for preventing evaporation is to form a dust mulch on the
surface. When possible, the soil should be cultivated after every rain
as soon as it is in the proper condition for working. This cultivation
will break up the crust, break the capillary connection, and prevent
much of the evaporation. At the same time, it leaves the soil in a loose
condition, ready to absorb the next rain.
(Note, however, that this means shallow cultivation, not deep digging
with a rototiller.)
When seeds are planted it is often desirable to increase evaporation, so
that the seeds, which are near the surface, will be kept moist by the
water as it rises. This is the reason for packing seeds. Corn planters
pack over the rows of seed only. Rollers are often used to pack new
plantings of grasses and small grains such as oats and wheat. In the
garden, the same effect can be achieved by patting down the soil over
the seeds with the hand, or by placing a board over a row of seeds and
standing on it. Lightly. We’re not talking about stomping down the
rows, causing compaction.
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.
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
(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
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
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.
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.
Warren noted that the limit of food supply and other conditions prevent
this rapid multiplication from continuing. He could not have foreseen
his students, and much more so their sons, not only adopting farming
methods that would knowingly limit that food supply, but also killing
those microorganisms by the application of chemical fertilizers and
He continued by saying that bacteria are present in all soils, ranging
from less than 28,000,000 per ounce of soil (and far fewer than that in
many soils today) to many times that number. In fertile soils like
gardens there are many billions per ounce. There is usually a
relationship between the number and kinds of soil bacteria and
Bacteria may seem to be too small to be of much consequence, but they
are far from unimportant. We know how many contagious diseases are
caused by bacteria, so we must recognize their power. But while certain
ones cause disease, others are useful to us.
Bacteria are microscopic plants. We should look on them as we do other
plants. Some plants, such as corn and cotton, are useful. Others, like
poison ivy, are to be avoided.
We could not live were it not for the activities of the useful bacteria
and yeast plants.
A turn-of-the-century New Jersey Agricultural Bulletin put it this way:
“The different chemical changes produced by soil bacteria are quite
numerous. Some kinds are specialized for one series of changes, others
for changes of a different sort. Some will attack by preference
carbohydrates like starch or sugar, some will decompose woody tissue,
some will cause the decay of proteins, some of fats, etc. This division
of labor allows an effective decomposition of humus. Various gases and
acids are produced in the course of decay, and help to decompose the
rock particles in the soil and to render the mineral plant food
contained in them available. The insoluble protein compounds in the
roots and stubble are broken down and their nitrogen changed partly to
ammonia. The particles of ammonia, as they are thus generated by
bacteria of many kinds, are at once pounced upon by a special class of
germs whose function it is to change the ammonia into nitrate. Thanks,
therefore, to the activities of many species of bacteria, the nitrogen
locked up in the humus and green manure is transformed gradually into
nitrate, and is then quite suitable for the building of roots, stems,
leaves and fruit.”
If we accept all of this, and prefer it to the modern high-tech chemical
company ag college explanations and solutions, the next question is, how
can we maintain the fertility of the land? People who think they have so
much more information than these primitives of a hundred years ago will
simply buy a bag of fertilizer – probably without even knowing how to
read the label – and scatter it around without the foggiest notion of
what they’re doing, and consider themselves progressive and educated.
But what can those of us who think do to improve our soils, and our
We can start by going back even further, and seeing how soils were
How soils become productive
It has required untold ages for the soils of the world to be formed and
to become productive. At first the particles of rock were capable of
supporting only lichens and mosses. After generations of these plants
died and added their material to the soil, it became possible for other
plants to grow. For tens of thousands of years grasses grew, died, and
decayed, enriching the barren soil with humus. Trees shed their leaves,
and eventually fell back to the Earth themselves. Tiny root hairs probed
into cracks and crevices formed by freezing and thawing, and along with
acids, broke the rocks into ever-smaller particles. Birds and animals
added to and accelerated the process.
Thus soils were formed, over many thousands of years, and became ever
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
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
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
Materials used as fertilizers
Naturally fertile soils were made that way over thousands, and sometimes
tens of thousands of years, by a combination of the basic rock, plant
growth and the return to the Earth of the plants, as well as the animals
that fed on them, and their waste products, all worked upon by the
activity of soil biology.
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
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.”
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.
A small amount of nitrogenous compounds are brought down with rain and
snow. This can amount to 2-3 pounds per acre per year. But about 40
pounds is required for a fair wheat crop.
Nitrogen from the air can be “fixed” by bacteria on legumes. Some of the
old writings on farming note that pea-like plants have some effect on
the soil that benefits following crops. Only in the last 150 years has
this been explained. Until then, the Chinese saying that “beans are good
for the soil” was as good as any.
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
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.”
The information explosion might have made us smarter. But now it’s time
to become wiser.