The Problem of Soil Conservation

Forest and Bird, Issue 58, 1 November 1940, Page 14

The Problem of Soil Conservation

Condensed and adapted from an article by Dr. G. V. Jacks, Rothamsted, England, in “Trees,” July-September, 1940.

IT has been said that “Nature treats the Earth kindly, man treats her harshly.” The truth of this statement becomes apparent when we realise that the necessities of life all come from the soil, and that Nature takes care that every member of the community of life, whether animal or plant, plays its part in keeping the soil healthy, but that man often destroys the soil by means of over-grazing or overcultivating grassland and burning or overcutting the forest. As a result of any or all of these activities of man, there are large areas of the world in which the soil has lost its stability and has become liable to be washed or blown away by rain or wind, or, in other words, is eroded. This type of erosion is not to be confused with the natural process of denudation also called “soil erosion.” This natural process is an extremely slow one and has always, throughout the ages, taken place; its effect is to enrich, not to destroy, the soil.

Destructive soil erosion has reached immense proportions in many parts of the world during the last 20 years. Untold millions of acres have been destroyed. Once started it rapidly, very rapidly, spreads. Usually “sheet erosion” is the first state; that is, after every rain thin layers of soil are washed away. Soon, the whole fabric of the land is so weakened that gullies begin to form; “gully erosion,” as it is called, has started. These gullies spread fanwise with great rapidity and unless the erosive process is checked these gullies will ultimately meet and the land will then be entirely useless. Also, as there is by this time little soil or vegetative covering to absorb rainfall, uncontrollable floods are caused in the rivers fed by this land. Well-known examples of recurrent disastrous floods caused by soil erosion over vast areas are those of the Mississippi and Yellow Rivers. Huge dykes built to enclose the channels of these rivers often burst with disastrous results, and it is a fact that often the beds of such rivers are in places so filled with eroded soil that they are raised above the level of the surrounding plain.

Where the land is level and treeless the effects of wind can be as destructive as those of water if the plant covering has been removed and the soil pulverized by cultivation. Everyone has heard stories of American farms in the “Dust Bowl” having all their soil blown away in a single dust storm. It is more than possible that the disappearance of many former civilisations has been due to mismanagement of the soil, or as Dr. Jacks expresses it “to the cumulative effects of human greed which caused men to pay too much attention to the satisfaction of their desires and too little to the maintenance of their defences against the forces of nature.” The sands of many a desert cover the remains of numerous ancient cities, many of which must have been thriving and luxurious; but in our own time American farmers in the “Dust Bowl” are being driven off once prosperous farms which, in a few months or even weeks, are converted into sandy deserts. Dr. Jacks entirely disagrees with the oft expressed view that man is a harmful parasite on the earth, upsetting the smiling face of nature, and considers that no other form of life can, or does, raise the productivity of the earth higher than does civilised man. He cites the case of scientific agriculture in Britain in support of his statement. In Europe the demands of closely populated towns raised the productivity of the land to a high level and when these demands were such that they exceeded the limit of productivity of the land, supplies of food from abroad were made available by the opening up of virgin land. These virgin soils were in no condition to stand an increased and, for them, unnatural production. In Europe the productivity of the soil was increased before extra production was attempted; in these virgin soils productivity was not increased and they were soon exhausted and then eroded. Soil exhaustion appears to be the real cause of soil erosion of cultivated land. It has been shown experimentally that a crumb structure enables a soil to resist erosion

best. A healthy soil consists of particles aggregated into crumbs of various shapes and sizes according to the condition of its formation, and this structure is formed chiefly by the action of the roots of vegetation and of humus. Forest gives more protection, by itself, against erosion than grass; but compensating for this the crumb structure is most highly developed under grass. Chiefly for this reason grassland can often be intensely cultivated for some years before erosion becomes manifest, whereas cleared forest land may begin to be eroded long before the soil is exhausted. To prevent erosion on cultivated land, care must be taken that no deficiencies, especially in humus and nitrogen, develop; and the utilizers of the land must enter into such a relationship with the land that the stability of the soil is preserved and its fertility increased. It will become apparent that erosion prevention and control is largely a social question as well as a scientific one. In the United States, where a soil conservation technique is well established, there is a definite trend away from extreme individualism towards co-operation, not only between individuals but also between states. Amongst primitive peoples, however, the problem is different. Erosion is usually caused among them by overgrazing and wasteful cultivation, and it is exceedingly difficult to persuade or even to force them to adopt a system of agriculture which means changes, often drastic changes, in their agricultural habits. And when a change in agricultural habits will often mean revising and re-ordering the local system of land tenure and ownership (in parts of Africa such a change may even involve inter-tribal relationships), the control of erosion passes from the soil chemist to the sociologist. So the problem is more than merely that of the structure and composition of any particular soil and its covering; it is a problem deeply concerned with the attitude of mind of the users of the land respecting the function and purpose of the land. Given the correct mental attitude towards the land plus a sound scientific knowledge of the soil much of the now waste or wasting exhausted land may be reclaimed, but scientific knowledge alone can accomplish very little. Sad to relate, this aspect of the problem is not restricted to primitive peoples.