4 SOILS AND FERTILIZERS 



humus as a factor of soil fertility from being recog- 

 nized. The writings of Thaer were of a most prac- 

 tical nature, and they did much to stimulate later 

 investigations. 



About 1830 there was renewed interest in scientific 

 investigations relating to agriculture. At this time 

 Boussingault, a French investigator, became actively 

 engaged in agricultural research. He was the first to 

 have a chemical laboratory upon a farm and to make 

 practical investigations in connection with agriculture. 

 This marks the establishment of the first agricultural 

 experiment station. Boussingault's work upon the as- 

 similation of the free nitrogen of the air is reviewed in 

 Chapter IV. His study of the rotation of crops was 

 a valuable contribution to agricultural science. He dis- 

 covered many important facts relating to the chemical 

 characteristics of foods, and was the first to make a 

 comparison as to the amount of nitrogen in differ- 

 ent kinds of foods and to determine their value on the 

 basis of the nitrogen content. His study of the pro- 

 duction of saltpeter did much to prepare the way for 

 later work on nitrification. The investigations of Bous- 

 singault covered a variety of subjects relating to plant 

 growth. He repeated and verified much of the earlier 

 work of De Saussure, and also secured many additional 

 facts regarding the chemistry of growth. As to the 

 source of nitrogen in crops, he states : " The soil fur- 

 nishes the crops with mineral alkaline substances, pro- 

 vides them with nitrogen, by ammonia and by nitrates, 



