Like all popular sayings, this one contains much truth. But it is sometimes untrue or at least misleading. For whether or not the soil be poor will depend entirely upon the point of view, and that there may be at least more than one point of view for any given soil will, it is believed, become evident from the following pages. Soils which are seemingly poor, and supporting but a poor population, may be in fact, or at least potentially, quite rich. But in order to make plain what is meant, it will be well to point out briefly some of the facts that are now known, and some of the views that are held by those who are making an especial study of soils. It will not be necessary to go into very much detail, for it will be sufficient to present the leading ideas in a general way in order to show that the work of the physical scientist touches, as a necessary consequence, both the field of economics and sociology. From these points of contact the effort will be made to indicate a few at least of the social and economic possibilities which a study of the soil presents, and to submit a plea that those to whom we look as leaders in these latter directions will find this subject of such importance and of so much interest that they will be impelled to do something towards the development of this side of it for the benefit of our country and possibly mankind at large. It would seem, as indicated above, that an almost virgin field for investigation is offered here, which can hardly fail to yield rich rewards to the student.
The soil is a very complex, heterogeneous mixture, or as one may say technically, material system. It is composed of three distinct parts or phases: First, the mineral and organic matters in a solid condition; second, the water, or water solution, which all soils contain; and third, the gaseous part, which fills the interstitial spaces between the solid components of the soil not occupied by the ground solutions. Furthermore, the soil is in contact with the atmosphere above it. It is probably from the ground solutions alone, or almost entirely alone, that the plants take their nutriment as far as the soil itself is concerned. Of course it is perfectly well known that the carbon and oxygen, which form so large a part of the plant tissues, are obtained mainly from the atmosphere above the soil and in contact with it. But the plant can derive its mineral foods from the soil solution only, and it is upon the concentration and composition of the solution that the well-being of the plant is primarily dependent. The nature of this soil solution is in turn dependent both upon the nature of the solid and of the gaseous components of the soil. Furthermore, it is intimately connected with the physical conditions of the soil—that is to say, with its texture, or the size of the solid particles, and the structure, or the arrangement of the particles, mainly because upon these factors depends the amount of water which the soil will hold under any given conditions of temperature, climate, etc. And upon the amount of water which it will hold