The Economic Environment

soil, nitrogen, plant, food, mountain, elements and air

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1 It is an interesting fact that the soils of the states north of the Ohio and Missouri rivers are glacial.

Chemically, neither clay, nor sand, nor cal cium contributes much, if anything, to plant growth ; but they determine the physical char acter of the soil, and the productivity of land depends quite as much on its physical as on its chemical properties. The presence of clay tends to make the soil moist and tenacious, obstructing the circulation of air in the soil and rendering cultivation difficult. Sand, on the contrary, makes the soil dry, loose, and easy of cultivation.' Only an extremely small portion of the culti vated soil is actually made use of as plant food. From soil of which one foot in depth will weigh three to four million pounds to the acre, an ordinary crop will take of plant food about two hundred On the other hand, the por tion thus utilized constitutes only about one per cent of the weight of the plant The rest has come from the air. The principal ele v. d. Goltz in SchUnberg's Handbuch, Vol. I., p. 29.

2 American Encyclopedia, Art. Agricultural Chemistry.

3 In the case of grass two per cent. Atwater, " The Food Sup ply of the Future," in November (1891) Century Magazine. In ScWnberg's Handbuch, v. d. Goltz estimates it at from two to seven per cent.

ments of the soil suitable for plant food are : Iron, lime, magnesia, silica, sulphuric acid, potash, phosphoric acid, and nitrogen. In un cultivated lands these elements are returned to the soil by the decay of the plants which have taken them. When the products of the soil are removed, whether in the form of vegetables, fruit and grain, or in the form of animal flesh, certain of the elements become exhausted. Potash, phosphorus, and nitrogen are the ele ments that are likely to disappear in this man ner. Methods are found of supplying phos phates and potash compounds, but the case of nitrogen has been more difficult. Plants do not ordinarily have the power of using nitrogen in its pure form, otherwise there would be no pos sibility of exhausting the abundant supply fur nished by the free nitrogen of the atmosphere.

Ammonia and nitric acid, both a result of the decay of organic matter, are the forms best suited for plant food. The former is a com pound of nitrogen with hydrogen, and is always present in small quantities in the air. The lat ter, uniting with various minerals to form ni trates or mineral salts, furnishes the chief supply that is obtained from the soil.' A special science, agricultural chemistry, is occupied largely with an investigation of the methods by which these necessary elements may be supplied, in order that the fertility of soils may be systematically restored or increased.

Next in order after climate and soil, belongs a consideration of the geographical configura tion. The insular position of England has probably been a more important factor in determining the nature and development of her industry than either her soil or her cli mate, and in nearly all countries the geograph ical position has been of marked influence. We have already referred to the effects upon climate which may be traced to elevation and to position in relation to ocean and mountain ranges. Furthermore, the outline of the coast, the direction of navigable river courses, the presence of mountain passes, and, in general, all those features of the local geography which determine the difficulty or ease of communica tion and migration, are to be considered essen 1 The recent discovery of the bacteria called " nitrifying or ganisms" explains the method by which nitrogen is supplied to plants. Consult any recent work on bacteria.

tial features of the environment of any given region. North America is less fortunate than Europe in the character of her coast-line, since it is less indented, furnishing fewer harbors and bringing a smaller portion of the entire area into direct contact with the ocean, the highway to other continents. But this is fully compensated by the extraordinary opportunities provided for access to the interior by the great river systems, and by the absence of serious mountain barriers between the various parts of the continent.

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