238 Report of the Department of Chemistry of the 



What is the relation of soil composition and the solubility of 

 soil constituents to fertility? 



Minor related questions also arose as the work advanced. 



It had been the intention of the writer not to publish some of 

 these data because they are practically a repetition of emphatic re- 

 sults previously reached, but in view of the newer phases of the 

 discussions of soil fertility it is deemed wise to make these data 

 public. 



This bulletin is, therefore, the first of a series in which are set 

 forth the results of experiments in the field of plant nutrition that 

 have been carried on during the past ten or twelve years. The 

 publication of these results has been long delayed partly because 

 of the large amount of chemical work involved. 



Those of my associates who have aided in carrying on these 

 experiments are C. G. Jenter, F. D. Fuller, W. E. Tottingham, 

 E. B. Hart and E. L. Baker; and due acknowledgment is hereby 

 made of the execution by these gentlemen of the details of the 

 experiments and the necessary chemical work. 



THE AVAILABILITY TO CERTAIN SPECIES OF 



PLANTS OF PHOSPHORIC ACID FROM 



VARIOUS SOURCES. 



general considerations. 



Considered merely from the standpoint of quantity phosphoric 

 acid is the most important ingredient of commercial fertilizers. 

 It is probably true also that no other ingredient is used with 

 greater profit. On the average, the various brands of fertilizers 

 contain larger proportions of it than of either nitrogen or potash. 

 Indeed, the material bearing phosphoric acid may properly be 

 considered the basis of practically all compounded brands. 



The main sources of phosphoric acid are the deposits of mineral 

 phosphates found in various parts of the United States and in other 

 countries. These natural forms are used in comparatively small 

 quantities in crop production. Phosphoric acid comes to the farm 

 mostly in combinations that have been produced by the chemical 



