Chapter VIII: The Soil (2)

In the mangrove marshes the tree which gives the areas their name covers all the field which is visited by the tide. This tree grows with its crown supported on stiltlike roots, at a level above high tide. From its horizontal branches there grow off roots, which reach downward into the water, and thence to the bottom. The seeds of the mangrove are admirably devised so as to enable the plant to obtain a foothold on the mud flats, even where they are covered at low tide with a depth of two or three feet of water. They are several inches in length, and arranged with booklets at their lower ends; floating near the bottom, they thus catch upon it, and in a few weeks' growth push the shoot to the level of the water, thus affording a foundation for a new plantation. In this manner, extending the old forests out into the shallow water of the bays, and forming new colonies wherever the water is not too deep, these plants rapidly occupy all the region which elsewhere would appear in the form of savannas.

The tidal marshes of North America, which may be in time converted to the uses of man, probably occupy an area exceeding twenty thousand square miles. If the work of reclaiming such lands from the sea ever attains the advance in this country that it has done in Holland, the area added to the dry land by engineering devices may amount to as much as fifty thousand square miles--a territory rather greater than the surface of Kentucky, and with a food-yielding power at least five times as great as is afforded by that fertile State. In fact, these conquests from the sea are hereafter to be among the great works which will attract the energies of mankind. In the arid region of the Cordilleras, as well as in many other countries, the soil, though destitute of those qualities which make it fit for the uses of man, because of the absence of water in sufficient amount, is, as regards its structure and depth, as well as its mineral contents, admirably suited to the needs of agriculture. The development of soils in desert regions is in almost all cases to be accounted for by the former existence in the realms they occupy of a much greater rainfall than now exists. Thus in the Rocky Mountain country, when the deep soils of the ample valleys were formed, the lakes, as we have before noted, were no longer dead seas, as is at present so generally the case, but poured forth great streams to the sea. Here, as elsewhere, we find evidence that certain portions of the earth which recently had an abundant rainfall have now become starved for the lack of that supply. All the soils of arid regions where the trial has been made have proved very fertile when subjected to irrigation, which can often be accomplished by storing the waters of the brief rainy season or by diverting those of rivers which enter the deserts from well-watered mountain fields. In fact, the soil of these arid realms yields peculiarly ample returns to the husbandman, because of certain conditions due to the exceeding dryness of the air. This leads to an absence of cloudy weather, so that from the time the seed is planted the growth is stimulated by uninterrupted and intense sunshine. The same dryness of the air leads, as we have seen, to a rapid evaporation from the surface, by which, in a manner before noted, the dissolved mineral matter is brought near the top of the soil, where it can best serve the greater part of our crop plants. On these accounts an acre of irrigated soil can be made to yield a far greater return than can be obtained from land of like chemical composition in humid regions.

In many parts of the world, particularly in the northern and western portions of the Mississippi Valley, there are widespread areas, which, though moderately well watered, were in their virgin state almost without forests. In the prairie region the early settlers found the country unwooded, except along the margins of the streams. On the borders of the true prairies, however, they found considerable areas of a prevailingly forested land, with here and there a tract of prairie. There were several of these open fields south of the Ohio, though the country there is in general forested; one of these prairie areas, in the Green River district of Kentucky, was several thousand square miles in extent. At first it was supposed that the absence of trees in the open country of the Mississippi Valley was due to some peculiarity of the soil, but experience shows that plantations luxuriantly develop, and that the timber will spread rapidly in the natural way. In fact, if the seeds of the trees which have been planted since the settlement of the country were allowed to develop as they seek to do, it would only be a few centuries before the region would be forest-clad as far west as the rainfall would permit the plants to develop. Probably the woods would attain to near the hundredth meridian.

In the opinion of the writer, the treeless character of the Western plains is mainly to be accounted for by the habit which our Indians had of burning the herbage of a lowly sort each year, so that the large game might obtain better pasturage. It is a well-known fact to all those who have had to deal with cattle on fields which are in the natural state that fire betters the pasturage. Beginning this method of burning in the arid regions to the west of the original forests, the natural action of the fire has been gradually to destroy these woods. Although the older and larger trees, on account of their thick bark and the height of their foliage above the ground, escaped destruction, all the smaller and younger members of the species were constantly swept away. Thus when the old trees died they left no succession, and the country assumed its prairie character. That the prairies were formed in this manner seems to be proved by the testimony which we have concerning the open area before mentioned as having existed in western Kentucky. It is said that around the timberless fields there was a wide fringe of old fire-scarred trees, with no undergrowth beneath their branches, and that as they died no kind of large vegetation took their place. When the Indians who set these fires were driven away, as was the case in the last decade of the last century, the country at once began to resume its timbered condition. From the margin and from every interior point where the trees survived, their seeds spread so that before the open land was all subjugated to the plough it was necessary in many places to clear away a thick growth of the young forest-building trees.

The soils which develop on the lavas and ashes about an active volcano afford interesting subjects for study, for the reason that they show how far the development of the layer which supports vegetation may depend upon the character of the rocks from which it is derived. Where the materials ejected from a volcano lie in a rainy district, the process of decay which converts the rock into soil is commonly very rapid, a few years of exposure to the weather being sufficient to bring about the formation of a fertile soil. This is due to the fact that most lavas, as well as the so-called volcanic ashes, which are of the same material as the lavas, only blown to pieces, are composed of varied minerals, the most of which are readily attacked by the agents of decay. Now and then, however, we find the materials ejected from a particular volcano, or even the lavas and ashes of a single eruption, in such a chemical state that soils form upon them with exceeding slowness.

* * * * *

The foregoing incomplete considerations make it plain that the soil-covering of the earth is the result of very delicate adjustments, which determine the rate at which the broken-down rocks find their path from their original bed places to the sea. The admirable way in which this movement is controlled is indicated by the fact that almost everywhere we find a soil-covering deep enough for the use of a varied vegetation, but rarely averaging more than a dozen feet in depth. Only here and there are the rocks bare or the earth swathed in a profound mass of detritus. This indicates how steadfast and measured is the march of the rock waste from the hills to the sea. Unhappily, man, when by his needs he is forced to till the soil, is compelled to break up this ancient and perfect order. He has to strip the living mantle from the earth, replacing it with growth of those species which serve his needs. Those plants which are most serviceable--which are, indeed, indispensable in the higher civilization, the grains--require for their cultivation that the earth be stripped bare and deeply stirred during the rainy season, and thus subjected to the most destructive effect of the rainfall. The result is, that in almost all grain fields the rate of soil destruction vastly surpasses that at which the accumulation is being made. We may say, indeed, that, except in alluvial plains, where the soil grows by flood-made additions to its upper surface, no field tilled in grain can without exceeding care remain usable for a century. Even though the agriculturist returns to the earth all the chemical substances which he takes away in his crops, the loss of the soil by the washing away of its substance to the stream will inevitably reduce the region to sterility.

It is not fanciful to say that the greatest misfortune which in a large way man has had to meet in his agriculture arises from this peculiar stress which grain crops put upon the soil. If these grains grew upon perennial plants, in the manner of our larger fruits, the problem of man's relation to the soil would be much simpler than it is at present. He might then manage to till the earth without bringing upon it the inevitable destruction which he now inflicts. As it is, he should recognise that his needs imperil this ancient and precious element in the earth's structure, and he should endeavour in every possible way to minimize the damage which he brings about. This result he may accomplish in certain simple ways.

First, as regards the fertility of the soil, as distinguished from the thickness of the coating, it may be said that modern discoveries enable us to see the ways whereby we may for an indefinite period avoid the debasement of our great heritage, the food-giving earth. We now know in various parts of the world extensive and practically inexhaustible deposits, whence may be obtained the phosphates, potash, soda, etc., which we take from the soil in our crops. We also have learned ways in which the materials contained in our sewage may be kept from the sea and restored to the fields. In fact, the recent developments of agriculture have made it not only easy, but in most cases profitable, to avoid this waste of materials which has reduced so many regions to poverty. We may fairly look forward to the time, not long distant, when the old progressive degradation in the fertility of the soil coating will no longer occur. It is otherwise with the mass of the soil, that body of commingled decayed rock and vegetable matter which must possess a certain thickness in order to serve its needs. As yet no considerable arrest has been made in the processes which lead to the destruction of this earthy mass. In all countries where tillage is general the rivers are flowing charged with all they can bear away of soil material. Thus in the valley of the Po, a region where, if the soil were forest-clad, the down-wearing of the surface would probably be at no greater rate than one foot in five thousand years, the river bears away the soil detritus so rapidly that at the present time the downgoing is at the rate of one foot in eight hundred years, and each decade sees the soil disappear from hillsides which were once fertile, but are now reduced to bare rocks. All about the Mediterranean the traveller notes extensive regions which were once covered with luxuriant forests, and were afterward the seats of prosperous agriculture, where the soil has utterly disappeared, leaving only the bare rocks, which could not recover its natural covering in thousands of years of the enforced fallow.

Within the limits of the United States the degradation of the soil, owing to the peculiar conditions of the country, is in many districts going forward with startling rapidity. It has been the habit of our people--a habit favoured by the wide extent of fertile and easily acquired frontier ground--recklessly to till their farms until the fields were exhausted, and then to abandon them for new ground. By shallow ploughing on steep hillsides, by neglect in the beginning of those gulches which form in such places, it is easy in the hill country of the eastern United States to have the soil washed away within twenty years after the protecting forests have been destroyed. The writer has estimated that in the States south of the Ohio and James Rivers more than eight thousand square miles of originally fertile ground have by neglect been brought into a condition where it will no longer bear crops of any kind, and over fifteen hundred miles of the area have been so worn down to the subsoil or the bed rock that it may never be profitable to win it again to agricultural uses.

Hitherto, in our American agriculture, our people have been to a great extent pioneers; they have been compelled to win what they could in the cheapest possible way and with the rudest implements, and without much regard to the future of those who were in subsequent generations to occupy the fields which they were conquering from the wilderness and the savages. The danger is now that this reckless tillage, in a way justified of old, may be continued and become habitual with our people. It is, indeed, already a fixed habit in many parts of the country, particularly in the South, where a small farmer expects to wear out two or three plantations in the course of his natural life. Many of them manage to ruin from one to two hundred acres of land in the course of half a century of uninterrupted labour. This system deserves the reprobation of all good citizens; it would be well, indeed, if it were possible to do so, to stamp it out by the law. The same principle which makes it illegal for a man to burn his own dwelling house may fairly be applied in restraining him from destroying the land which he tills.

There are a few simple principles which, if properly applied, may serve to correct this misuse of our American soil. The careful tiller should note that all soils whatever which lie on declivities having a slope of more than one foot in thirty inevitably and rapidly waste when subject to plough tillage. This instrument tends to smear and consolidate the layer of earth over which its heel runs, so that at a depth of a few inches below the surface a layer tolerably impervious to water is formed. The result is that the porous portion of the deposit becomes excessively charged with water in times of heavy rain, and moves down the hillside in a rapid manner. All such steep slopes should be left in their wooded state, or, if brought into use, should be retained as pasture lands.

Where, as is often the case with the farms in hilly countries, all the fields are steeply inclined, it is an excellent precaution to leave the upper part of the slope with a forest covering. In this condition not only is the excessive flow of surface water diminished, but the moisture which creeps down the slope from the wooded area tends to keep the lower-lying fields in a better state for tillage, and promotes the decay of the underlying rocks, and thus adds to the body and richness of the earth.

On those soils which must be tilled, even where they tend to wash away, the aim should be to keep the detritus open to such a depth that it may take in as much as possible of the rainfall, yielding the water to the streams through the springs. This end can generally be accomplished by deep ploughing; it can, in almost all cases, be attained by under-drainage. The effect of allowing the water to penetrate is not only to diminish the superficial wearing, but to maintain the process of subsoil and bed-rock decay by which the detrital covering is naturally renewed. Where, as in many parts of the country, the washing away of the soil can not otherwise be arrested, the progress of the destruction can be delayed by forming with the skilful use of the plough ditches of slight declivity leading along the hillsides to the natural waterways. One of the most satisfactory marks of the improvement which is now taking place in the agriculture of the cotton-yielding States of this country is to be found in the rapid increase in the use of the ditch system here mentioned. This system, combined with ploughing in the manner where the earth is with each overturning thrown uphill, will greatly reduce the destructive effect of rainfall on steep-lying fields. But the only effective protection, however, is accomplished by carefully terracing the slopes, so that the tilled ground lies in level benches. This system is extensively followed in the thickly settled portions of Europe, but it may be a century before it will be much used in this country.

The duty of the soil-tiller by the earth with which he deals may be briefly summed up: He should look upon himself as an agent necessarily interfering with the operations which naturally form and preserve the soil. He should see that his work brings two risks; he may impoverish the accumulation of detrital material by taking out the plant food more rapidly than it is prepared for use. This injurious result may be at any time reparable by a proper use of manures. Not so, however, with the other form of destruction, which results in the actual removal of the soil materials. Where neglect has brought about this disaster, it can only be repaired by leaving the area to recover beneath the slowly formed forest coating. This process in almost all cases requires many thousands of years for its accomplishment. The man who has wrought such destruction has harmed the inheritance of life.