The Soul of Soil: Facts for the Modern Homesteader

15 Facts About Soil for More Productive Gardens and Effective Land Management


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 plant and soil facts and how they function together. 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?)

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.

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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 soil facts taken from a textbook published in 1909. These soil facts were common knowledge 90 years ago, but have been overshadowed by and largely forgotten during the “Green Revolution” and information explosion.

It’s 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. — Jd


This shows a profile of soil under poor land treatment (left), and one resulting from an excellent cropping system. Note the difference in structure and organic matter. — USDA photo.

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.)

Soil Fact #1: 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 two to five percent. (This was in 1909: many the soil facts today suggest farm soils 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.)

Here’s an interesting soil fact: 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 soil fact table shows the mechanical analyses of three important soil types as separated by the Bureau of Soils:

The Norfolk sand is one of the leading truck soils of the Atlantic coast. A large part of the vegetables for eastern cities are grown on this soil. Fact is, 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 growing 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.


Soil Chart

Soil Fact #2: 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.

Soil Fact #3: 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 increased.

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.

Here’s an interesting soil fact: 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 managed.


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 capacity.

It requires about 20 heat units to raise the temperature of 100 pounds of dry soil 1°F. To raise the temperature of the same weight of water 1° 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°F. The best growth usually doesn’t take place until the soil is 70°. It’s easy to see why gardeners want sandy soils for early truck crops.

However… another caution and soil fact you should know. 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.

Soil Fact #4: 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.

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 coarse structure.

Soil Fact #5: Soil as Storehouse for Water

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 the soil.

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 water.

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 lamp wick.

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.

Soil Fact #6: 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.

Soil Fact #7: 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.

Soil Fact #8: 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 Fact #9: 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.

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 pesticides!

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 fertility.

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 world?

We can start by going back even further, and seeing how soils were formed.

Soil Fact #10: 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 more fertile.

Soil Fact #11: 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.”

Soil Fact #12: 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 ways mentioned above”…and that was nearly 100 years ago. It’s much worse now.


Two samples of soil. The one on the left shows deterioration due to 40 years of soil depleting cropping, contrasted with a soil sample (right) taken where a good grass rotation has been practiced. Note color and structure of the samples. (USDA photo by John McConnell)

Soil Fact #13: 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 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.”

Soil Fact #14: 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.

A small amount of nitrogenous compounds are brought down with rain and snow. This can amount to two or three pounds per acre per year. But about 40 pounds are 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.”

Soil Fact #15: Manure Management

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 four 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) suggest the best manure for gardens and fields is 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 is not 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 100 years ago, to explain to high school students soil 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. I hope you enjoyed learning these soil facts. What soil facts would you add to this list? 

Originally published in the Sept./Oct. 1999 issue of Countryside and regularly vetted for accuracy.


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The Soul of Soil: Facts for the Modern Homesteader