Page:Popular Science Monthly Volume 60.djvu/552

544 general in making them more soluble in the ground waters, and thus more available to plant nutrition.

It will thus be seen that it is possible to control, in a measure, the soil. In another way much has been done in controlling soil and soil conditions, and that is in controlling the climate above the soil. This climate, or condition of the atmosphere above the soil and in contact with it, is also a most important factor in the growth and development of plants, and any way in which this can be controlled, correspondingly can the development of the plants be controlled. This is familiar to every one in the use of frames, hot-houses and conservatories, and, in some of the modern structures of this kind, it can hardly be said that the method is one adapted to a small scale only. In illustration, attention might be called to an establishment in Rhode Island which has upwards of fourteen acres under glass for the cultivation of one crop alone. And this can hardly be regarded as an isolated instance. Many others as extensive, or perhaps even more extensive, might be cited. In the last few years an even more striking illustration, because much greater in extent, of this control of climate has been developed in this country. For this purpose as well as for some other reasons, enormous areas in Florida are covered with either slats or cloth tent-like arrangements. These are erected for the purpose of protecting the plants and developing abnormal or unusual growth in certain varieties of tobacco, and have proved immensely successful in prolonging the growing season, through a modification of the climate about the plant, keeping it moist and warm, not cutting off the light entirely, but partially, and preventing the great evaporation from the surface which would dry the soil, and hasten the ripening of the plant. The experiment has been repeated in Connecticut under the auspices of the Bureau of Soils, U. S. Department of Agriculture, in cooperation with the Connecticut Experiment Station, over a very considerable area, sometimes single fields of as much as eight acres in extent being now protected by these cloth coverings for the production of a high-grade wrapper leaf tobacco. The shading of one crop by another with a taller, umbrageous growth, is a similar procedure. And this is practiced quite extensively in some places, as in the shading of coffee trees by larger tree growths, or the more familiar nurse crops, common in some parts of the United States. Modifications of the climate in other ways, by planting of trees, erection of wind brakes, and devices of a similar nature, have been used with greater or less success in certain regions, and are all more or less well known.

It is thus possible to greatly modify the soil and the soil conditions. Nevertheless the fact remains that it is impossible to make one soil just like any other soil. Consequently characteristic differences do exist in them, and it follows that some soils are adapted to some purposes for