PERMANENT FERTILITY 53 



applied in liberal quantities, but in low-pricecl forms, and then made 

 available on the farm by economic natural methods. 



Four Fundamental Facts 



Nearly 150 years ago Senebier, of Switzerland, found that the car- 

 bon 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 re- 

 lationship 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. 



Illinois Contributions 



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 produc- 

 tion 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 utiliz- 

 ing 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. 



Plant-food Elements 



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 im- 

 possible 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. 



