IN a very important sense, soil is not eroded, for the more or less pure mineral substances that are left after all the organic matter has disappeared from the land are not, properly speaking, soil at all. They are merely the raw materials of the kind from which soil was originally made and from which it can be made again. Erosion begins only after the soil surface has become virtually non-absorbent —a condition induced by the compactness resulting from the loss of highly absorbent, cellular organic matter present in nearly all undisturbed soils.

In native meadow or forest, rainfall — even the most torrential—strikes the spongy mass of humus and is held, with little or no run-off. Wherever there is run-off, the movement is retarded and ultimately halted by the successive areas of absorbent organic matter over which the water moves. In a tight soil, free from organic matter, erosion is almost inescapable because the very tightness of the soil defeats the gravitational movement of water.

Equally, a soil surface nicely charged with organic matter - decayed vegetable growth, plant tops, and dead and still living roots of all kinds—is poor field for the forces of wind erosion which have been so destructive in certain western States. But a soil which has been impoverished of organic matter is all too often gone with the wind.

Human generations are too short for us actually to have witnessed the complete cycle from virgin to eroded soil. William Byrd, ⁽¹⁾, the Virginia landsman of the eighteenth century, described the portion of this cycle that most people to-day have never seen. The following account of corn planting by a farmer of the early days is quoted from Ben Ames Williams's 'Come Spring':

He early cleared a patch of land and planted corn as soon as he had done his burning. The green wood was not consumed by the fire, and charred carcasses of trees lay everywhere; but he did his planting among them, poking a hole in the ground with a sharpened stick, dropping in two or three kernels, brushing earth into the hole with his foot. ⁽²⁾

Such highly productive land was not eroded. It could not be. There was no clean, smooth surface such as we now know. The entire depth of soil, perhaps ten to fifteen inches of it, was filled with visible organic fragments or was stained with the fine black smudge which represents the final stages of organic decay in the soil. This material was highly absorbent to the last black stain. Such a substance would scarcely permit a single drop of an ordinary rainfall to escape over the surface. There was too much empty space to be filled within the organic matter itself. Indeed, little water drained down through this material until it had taken in all it could hold. The depth of the black zone and the amount of water it already held determined how much additional water could be absorbed. In periods of very heavy rainfall most of the water would go on through this mass, of course. There could be no run-off water, except in long-extended wet periods. Even then the run-off water would not be stained with clay. It would be as clear as crystal quite different from anything we see to-day. The surface drainage from cultivated lands in our time is always the colour of the land.

It will perhaps be objected that when this mass becomes frozen solid no more water can get into it than can penetrate any other solid mass. This is true—if the mass becomes frozen solid. But it is difficult to freeze such a mass so solid that water cannot penetrate it. There are two very good reasons for this: (1) The water retained by fragments of organic matter is held within the fragments, leaving open spaces between them. Examine a saturated straw pile. There is no water between the straws, though the straws themselves will be full. Even when this water is frozen, there is still plenty of open space throughout the mass. (2) Such a mass of organic matter is so perishable that decay processes are continually in progress, except when there is too little heat or too little moisture. To some extent these fermentation processes provide their own necessary heat. (Remember in this connection that gardeners depend upon the heat of fermenting manure to keep up the temperature of their hot beds.) This ability to maintain higher temperatures, even in winter-time, shortens the period during which a highly organic soil can be frozen.

There are other influences that conspire to prevent tight freezing of a soil that is chiefly organic matter. A covering of snow is the best kind of insulation against the much colder upper air. Soil will often remain unfrozen through a long, cold winter in temperate latitudes, provided it is covered by enough snow. It is well known that snow falling on weeds or any other kind of organic matter is more apt to remain snow than it would if it fell on moist, unfrozen mineral soil. When snow falls on the latter, it immediately melts, much as it would if it fell into water; yet at the same time, that which falls on grass, boards, rail fences, roofs, or any other dry substance may accumulate rapidly and remain unmelted. Soil which is highly organic in character, similarly, accumulates snow more readily, because it always presents a drier surface. It is reasonable to believe that through-out the winter it retains a thicker blanket of snow than the pure mineral soil; and with the coming of spring the heat of fermentation within the soil will more quickly thaw out any frozen layer that might exist near the surface. This improves internal conditions for water penetration.

It has long been known that relatively little water escapes from a forest floor as run-off. Just why this is true has been a matter for conjecture, though part of the explanation at least was advanced earlier in this chapter. A commonly held theory is that the organic matter hinders the progress of the water over the surface of the minerals in the soil, thus allowing more time for the minerals to soak it in. Doubtless there is some such effect. It may be more important than I think. It certainly is true that much of the water soaks directly into the leaves and other plant residues which are found on the ground. And we know that the entry of moisture into leaf tissue is much easier than into mineral soil.

It may not be generally known that when water penetrates mineral masses it does so by finding its way between the particles. The tiny particles of clay, silt, or sand are almost completely exclusive. Water cannot enter them. It can only cling to their outer surfaces. This is extremely important information to keep in mind in a study of soils, for organic matter, by contrast, literally pulls liquids into itself. Volume for volume, then, organic matter can hold many times as much water as can any kind of soil mineral; for organic matter is chiefly open space internally, while mineral substances are dense and solid; a fateful distinction where water relations are concerned.

The idea is abroad that man is the lord of creation—that he dominates the earth. In certain minor respects this may be true, but in the main it is the purest propaganda; as ineffectual, when we examine the facts, as whistling in the dark. Consider the single example of erosion. The alarm of thinking men to-day, when they consider the plight of coming generations starving on eroded soil, borders on panic. What would they think if there were immediate prospects of a renewal of the world-wide erosion which originally sculptured the present features of the earth's surface ? That was erosion with a vengeance—millions on millions of years of it. Mountains were buried in the sea by the tearing down of the original fire-formed stone of which they were composed, and the removal of the debris by the unhindered waters and winds which shuttled back and forth across such continents as then existed. Geologists still puzzle over the wreckage trying to piece out the story.

That original large-scale erosion was finally curbed. But it was not done by that self-advertising animal called man. It was done by vegetation—plants. Plants, the conquerors, had to start from nothing but powdered rock. Some structural materials they extracted from the minerals themselves, some from the air and the rays of the sun, and the rest from water. The porous architecture they were able to create from these materials is still the wonder of existence, though so common-place as seldom to be even an object of curiosity. A casual glance at a bit of onion skin, or a few strands of alga, under a microscope is a revelation to the uninitiated, even though no further thought is given to it. If it is considered that this delicate fabric of cells could not have arisen but for the presence, in infinitesimal amounts, of such chemicals as phosphorus, iron, sulphur, calcium, potassium and magnesium, the miracle of life becomes apparent. To know, then, that world-wide erosion was curbed in the beginning by stuff similar to that on the microscope slide ought to give us a healthy respect for all plants and for their disintegrating remains; for, down to the last black colloidal remnant of the dead plant or animal tissue, organic nature continues to fight erosion by the trick of absorption. By eternally coaxing water to enter, organic tissues keep it under control. Hence the importance of having the organic tissues where the water can reach them the instant it hits the earth as rain.

Plants are the real masters of the earth. Independent of human management, since they antedated the race, plants came spontaneously from the sea and threw a restraining influence over the unstable surface of the land, quieting its restlessness. Botanists explain the process in detail and with plausible reasoning, allowing eons for the lapse of time from the original appearance of the first single cells to the days of giant sequoias, and other eons for suitably equipped plants to complete the vegetative mantle over the earth. Moses offers a different story, of course, but be that as it may, we can be sure that man will master the rest of creation only as he comes to terms with plants, the real masters. They hold the key to his food supply.

Admittedly, we have serious erosion to contend with now. Much of our land is again in almost precisely the condition all land was in before plants arrived. It is bare, and it is in movement. Yet the present situation is immeasurably more favourable than the earlier one. The same destructive forces of wind and water are at work now as then, but the forces of plant opposition are now fully organized and mobilized. Alone, unless interfered with by man, plants can reclaim wayward land in an infinitesimal fraction of the time that was required eons ago, before they had adapted themselves to such work. Even so, such a reclamation period, when measured in terms of human lifetimes, may be excessively long. We are likely to get hungry waiting for natural forces alone to stop erosion and restore soil to the denuded mineral surface. Men must lend a helping hand.

The processes by which vegetation accomplishes a new cover where the previous cover has been destroyed are neither secret nor mysterious. All botany text-books and a variety of other scientific treatises discuss the influences that determine the development of plant communities. These factors have been so ably discussed elsewhere that there is no necessity for my doing so here. It may be pertinent, however, to introduce some of the underlying principles which determine the nature of plant successions as they occur.

Important among the life factors that occasion the growth of one plant as against another in a given location are the requirements of the species for water and for heat. Although the temperature of the air is influenced to a certain extent by the soil, we may pass it over, because it is not of major concern. Water, being literally managed by the surface upon which it falls, becomes the key factor to be discussed. Moreover, the manner in which the supply of water available for future plants is increased or decreased from year to year as a result of changes wrought by successive generations of plants on the site is an important consideration for us.

The earliest plants to occupy an area are composed of a more or less spongy tissue capable of absorbing and holding water for future need, in addition to that being used currently. This reserve water is supplied to the active plant tissues as required, and saves the plant from extinction when its roots have exhausted the supply of water in the soil. Such are the lichens and mosses. Their remains, unless whisked away by the wind, accumulate from year to year. In a few years the soil itself will necessarily have become intermixed with these spongy remains, so that many times more water will be retained in the soil than could be held by the pure minerals in the beginning. This additional water makes the living lichens thrive, which in turn further increase year by year the accumulated sponginess in the soil itself. If there were no other kinds of plants in the world, it is easy to conjecture that these pioneer plants might develop to giant sizes, like the cacti of the desert.

Miles away from this hypothetical spot where the lichen-moss drama has attracted a better water supply, another spot is covered by plants that could not possibly have endured the conditions through which lichens and mosses lived and prospered. As if by magic, seeds of these less hardy plants arrive by wind, bird, or animal. Presently the new plants annihilate the pioneers by the simple procedure of growing taller and robbing them of their essential sunshine. So the plants that prepared the way for these interlopers have to find another bare spot on which to make a new start. Later, the newcomers in their turn are driven away by other kinds even less hardy for which they have paved the way. In this evolution of plant populations on a given spot, the indispensable condition to a thriving community is increasing ability of the soil to retain rainfall.

The availability of water, while a prime consideration, is no more important than other requirements of plant growth; but it may prove the key factor in determining the degree to which a given species is provided with or exposed to other needed conditions. Thus water availability, by developing more expansive tissues, necessarily creates light limitations for low-growing plants, so that water, not the unavailability of light, becomes the primary factor in crowding out a species which fails because of lack of light. It would not be surprising to find that the presence or absence of water is the real key to situations supposedly created by other factors.

In any case, each successive stage in the laying down of an absorbent mat on the earth's surface removes one step further the possibility of run-off and erosion. It is not for nothing that writers have referred in literary contexts to " the earth's carpet," for in a very practical sense it is the carpet which covers and protects the landscape. Consider the fallen autumn leaves: snow will billow high upon them in the winter months, melt in the sunshine of spring, and yet the leaves in the centre of a heap will be dry. It is the humus below which has profited, as the winter moisture has filtered slowly down, to be caught and held by the sponge of true earth.

Conventional thinking about erosion so far has centred about the idea of securing greater infiltration into the mineral soil, since that is about all that is left on many farms. We have given almost no thought to the idea of providing volumetric space in and on top of the soil into which the rainfall would be helplessly snatched as soon as it fell, thus halting erosion at its source. Two reasons have favoured such thinking:

(1) It has never been thought possible for planting and cultivation to be done except on a smooth surface. Hence, nobody thought to try or suggest the possibility of growing cultivated crops without first disposing of whatever rubbish littered the surface. Such rubbish was always disposed of by ploughing.

(2) Farmers and scientists have long known that the chief need of soils is organic matter, but that need was supposed to be met by ploughing the organic matter into the soil to a depth of six to eight inches. Nobody seemed to realize that this procedure actually robbed the following crop of virtually all the substance of this buried organic matter.

By such hapless reasoning we have preserved for generations a system of soil management which should long ago have been revised to conform to the known facts. Planting can be done in a plant-strewn surface. It had to be done so when the land was first cleared. Doubtless, it is easier to manage land which has nothing on the surface to be caught and dragged along by the sliding equipment we use for planting and cultivating. But, if the crop planted in such smooth land must necessarily produce a smaller yield because of the purity of the mineral substances (freedom from decaying organic matter), it seems logical to suggest the wisdom of trying to devise implements which will negotiate the surface rubbish. Equally, if crop yield is greater from a surface full of plant debris, as has been proved by official tests at the Nebraska Experiment Station, the desirability of the necessary equipment is beyond question.

We emerge with two highly important objectives well within our grasp: improved crop yield, which is immediate, and arrested erosion, which is long range but closely related to our ultimate welfare. Both are attainable by the simple procedure of abandoning the ancient practice of ploughing organic matter under and substituting instead the effective practice of leaving the matter on the surface or working it in from the top. The organic sponge on top precludes erosion and provides the substance for maximum plant growth. That which has been ploughed under leaves a denuded and tight surface ideally suited to the processes of erosion, while the nutriment for plants lies six to eight inches below their incipient roots, out of reach and therefore ineffectual for the principal purpose at hand.

It can be said with considerable truth that the use of the plough has actually destroyed the productiveness of our soils. Fortunately, however, this result may be said to be temporary. With surprising suddenness the soil which is supposedly ruined will respond with bumper crops, providing it is supplied plentifully with organic matter properly incorporated into the surface. This generous response by soil thought to be " worn out " shows that our farmland has not been exhausted by cropping but has been rendered impotent by inept management.

Our faults are oftentimes excused on grounds of necessity. Ploughing, however, can summon no such defence: there is simply no need for ploughing in the first instance. And most of the operations that customarily follow the ploughing are entirely unnecessary, if the land has not been ploughed. It is possible to farm land without a smoothing harrow, without a cultipacker, without a drag, without a roller, without a single implement which is ordinarily used after ploughing - in preparing the seed bed. The single exception to this is the disc-harrow, which is used to incorporate the rubbish into the surface as fully as possible. If the land has been disced without previous ploughing, there are no clods whatever; consequently there is no need to use the customary smoothing equipment.

" Soil conservation " is a phrase which has been widely used but little understood. There is undoubtedly an important sense in which we must save soil losses, must prevent dissolved plant food from escaping down our streams; but that is only a minor part of the task ahead. The main job is to activate and to put into biological circulation mineral substances that, since the beginning of time, have been locked in the structures of the rocks of the earth's crust. Our failure to solve that problem generations ago resulted in our adding commercial fertilizer to land, not because the land held none of the minerals contained in the fertilizer, but because we had not found a way to dissolve those minerals so that crops could use them. We now know how to perform this trick; so the future of soil conservation work is destined to be concerned more with releasing additional minerals from the soil rock than with saving losses which by comparison are relatively light.

Fortunately, however, the same practices which result in prying more minerals out of the rock result also in maximum saving of the previously dissolved minerals. Whether we call the method " conservation " or " proper soil management " is immaterial; but it is important that we consciously imitate the natural soil profile which always and everywhere leaves all the organic matter on or mixed into the surface.

Since ploughing cannot leave organic matter on or in the surface except under such conditions as the pioneers found when they first cleared the land (when the entire soil mass was often black with intermixed organic and inorganic materials to a depth of a foot or more), ploughing, as it is now done, is definitely out as a means of breaking the land surface.

When ploughing is stopped, erosion will stop with it, for the organic matter mixed into the soil surface will cause that surface to appropriate the rain as it falls, thus removing the flow of water which is essential to the processes of erosion. Therefore, the cure for erosion is automatic when soil is again created, for real soil—the complete soil—is not liable to erosion.

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