THE QUEST OF NITROGEN III 



soluble organic matter influenced crops' growth. This 

 view was held by some investigators De Saussure par- 

 ticularly advocating it. It was overthrown, however, 

 when Liebig proposed his mineral theory. 



Liebig's theory: so-called "mineral theory." The 

 author of this theory was the real beginner in chemistry, 

 as applied to things agricultural. He worked with soils ; 

 he studied many agricultural plants; he devoted a great 

 part of his useful life to many problems of plant nutrition. 

 His theory held that only the ash or mineral substance 

 used by plants is obtained from the soil ; that the carbon, 

 as well as the nitrogen, is secured by the plant from the 

 atmosphere the great storehouse of these materials. 

 Liebig contended that when mineral substances are abun- 

 dant, either through nature or through other supply, 

 maximum yields will result, other things being provided, 

 regardless of the quantity of potential nitrogen in the 

 soil. He further claimed that if an abundance of the 

 necessary minerals is present, the plant will be well able 

 to take care of itself, and by its own efforts secure just 

 as much nitrogen as is required from the nitrogen com- 

 pounds of the air that are washed down in rain, snow and 

 hail, as is required for every need of the plant. For did 

 not the leguminous plants show this? He thought so. If 

 the cereals failed to do likewise in soils apparently no 

 worse, it was solely because minerals were present in- 

 sufficiently to supply the plant with its requirements ; and, 

 because of this fact, these cereal plants were rendered 

 somewhat impotent in their ability to get what nitrogen 

 they needed. This mineral theory simply meant this : 

 put minerals into the soil, and the plant will be strong and 

 vigorous, and quite able to secure its nitrogen, irrespect- 

 ive of the supply of the soil. 



The theory of non-fixation : no plants "fix" atmospheric 



