Page:Popular Science Monthly Volume 84.djvu/57

Rh applied in liberal quantities, but in low-pricecl forms, and then made available on the farm by economic natural methods.

Nearly 150 years ago Sénébier, of Switzerland, found that the carbon of plants is derived from the carbon dioxid of the air, and it is more than a century since DeSaussure, of France, first gave to the world a correct and almost complete statement concerning the essential mineral food of plants. Later, Lawes and Gilbert, of England, established the fact that for most plants the soil must furnish the nitrogen as well as the mineral elements; and more than a quarter-century has passed since Hellriegel, of Germany, discovered that bacteria living in symbiotic relationship with legume plants have power to gather nitrogen from the inexhaustible atmospheric supply.

These are the four great fundamental facts upon which the science of plant growth and permanent fertility must be based, and they were all discovered before the Illinois Experiment Station was established.

There remained, however, two very important general problems, and in the solution of these Illinois has made some contributions. One of these relates to the amount of nitrogen taken from the air by legumes under normal field conditions; and the other concerns the liberation of mineral plant food from insoluble materials.

It is not enough to know that clover has power to secure nitrogen from the air; we should know how much nitrogen is thus secured in order that we may plan intelligently to provide nitrogen for the production of corn, oats, wheat and other non-legumes, instead of using clover merely as a soil stimulant in systems of ultimate land ruin, as is still the most common practise.

It is also a matter of the greatest economic importance that definite information should be secured in regard to the practical means of utilizing mineral plant food from the abundant natural supplies nearest at hand, such as Tennessee phosphate rock, natural limestone, and the potassium minerals already present in our normal soils.

In brief, there are ten elementary substances which bear the same relation to the making of crops as brick and mortar bear to a wall of masonry. If any one of these ten elements is entirely lacking, it is impossible to produce a grain of corn or wheat, a spear of grass, or a leaf of clover.

Two elements, carbon and oxygen, are taken into the plant from the air through the leaves; hydrogen is secured from water absorbed by the roots, and iron and sulphur are also supplied by nature in abundance.