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Page:Popular Science Monthly Volume 73.djvu/14

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THE POPULAR SCIENCE MONTHLY

lands, to choke the reservoirs, to waste the water-power, and to bar up the navigable rivers. The highest solution of the problem for the tiller of the soil essentially solves the whole train of problems.

How is this control to be effected? All the known and tried methods of preventing wash and turning the rainfall into the soil should be duly employed. It is obvious that all methods of culture and all crops that increase the granularity and porosity of the soil contribute to the end sought. Deep tilth to promote soil granulation and deep-rooting plants to form root-tubes are specific modes of great value. Artificial underdrainage by preventing water-logging and promoting granulation aids the end sought. Contour cultivation by arresting and distributing the surface wash may also assist. Alternate strips of protected and cultivated land, reservoirs for catching and distributing concentrated rainfall, and other devices, serve to limit the wash of the slopes and give the surface waters the right direction.

It is possible that some of the more radical and permanent remedies will be found by a closer study of nature's methods. Nature has been working at this complex problem of balance between soil formation, soil waste, surface slope, plant growth and stream development, for millions of years. Looking closely at her methods, we note that she uses a much larger variety of plants to cover and protect the soil than we do, and that these plants have a wider range of adaptation to the special situations where protection is needed. We may, therefore, inquire whether we should not follow this precedent farther by developing more kinds of profitable plants and by using the protective varieties more freely on slopes especially subject to wash. Forest trees are a resource of this kind and should be employed as fully as practicable, as will, no doubt, be urged with great cogency by those who discuss the problem of forestry. We also have many shrubs, vines and fruit trees, whose employment to the maximum in covering areas subject to wash is likewise urged, either alone or in conjunction with trees. We are forced to recognize, however, that for the greater part the berries and fruits which render these profitable are perishable and have limitations of preservation, transportation, market, etc. But if shrubs and vines could be evolved by modern selective methods, whose nut-meats or dry seeds should be available for food in place of the watery pulp, and which could be treated much as cereals are, and have similar wide year-round markets, there would be a larger choice of crops to grow in soils subject to wash, and we might secure soil-protection with less crop-limitation. There would then be less need to press the culture of the cereals so far as we do now, and they could be limited more largely to surfaces less subject to harmful soil-loss.

Another of nature's marked methods is the formation of plantsocieties, or, from our point of view, combination-crops. No doubt