Page:Popular Science Monthly Volume 67.djvu/629

Rh fertilizers as applied to the growing of crops as to any other single thing that farmers have been so hostile to 'scientific' farming and to scientific agricultural institutions.

The physical conditions of the soil in regard to fertility are as important perhaps to the farmer as all the others put together, because they are more directly under his control. Yet this has never been fully understood by the farmer, nor has it been developed with agricultural students as it should have been. Air and moisture are the two most important substances in the soil. The conservation of these and the bringing of them to the roots of the plants is, therefore, one of the chief problems. It is merely the management of these two substances, for they are always present, that the farmer should concern himself with. Timely and suitable cultivation, then, for the development of crops is of the highest importance. Indeed, manuring of soil resolves itself largely into a question of supplying moisture and placing soil in such a condition that the air and moisture are in the best situation for use by the plant. In fact, when a farmer plows under a crop of rye he does not add any material to the soil excepting what the plant obtained from the air, and this is always available from the air. The other substances contained in the rye are simply restored to the soil. There is no addition. The rye is, therefore, not a manure in the proper sense, but a means by which the farmer improves the physical conditions.

It is not difficult to see, therefore, that the artificial manures in powder form can not contribute to any very great extent to fertility, if fertility is so largely a physical question. There are conditions of soil, such as size, shape and arrangement of particles, which have to do directly with the air and the water content. The arrangement of the particles can be controlled largely by the farmer.

There is one other force called physical affinity, which is of the highest importance because it is largely through the interaction of this force among the various substances in the soil that plants are capable of extracting solids in solution from it. This physical affinity is exercised among the various soil constituents, each one exerting an influence over the others. Now, if some substance (not in the soil) be added to it, the whole equilibrium may be disturbed by the affinity this may have for the substances already there. A chemical analysis can not determine this. The soil yields up to chemical analysis all that it contains, no matter what the relationship may be among the constituents. To the plant, however, which depends upon a form of physical affinity for its soil food, all the soluble substances will probably not be given up. Therefore, it is a question of physics, as well as one of chemistry, which will determine soil fertility.

When the farmer summer-fallows a field he does not add anything directly by the way of a fertilizer to the field, yet it is much more fertile the year after the summer-fallowing has been done. One benefit of