FERTILIZER CONTROL STATION. 297 



treated alike is taken as representing the jield from the method of 

 manuring used on those plots. 



The Comparative Production from Different Forms of Phos- 

 phoric Acid. 



A very large part of the phosphoric acid that is applied to the soil 

 in commercial fertilizers does not exist in the fertilizers in the forms 

 in which it is found in nature. 



The larger portion of the bone, and about all the phosphatic guanos 

 and mineral phosphates used, are treated with sulphuric acid before 

 going to the farm. This is done in order to make the phosphoric 

 acid available to plants, and the cost of this ingredient of fertilizers 

 is thus greatl}' increased. 



The question is now raised whether the increased cost caused by 

 the use of sulphuric acid is profitable in all cases. It is well known that 

 a soluble phosphate does not remain in solution in the soil, but that 

 immediately after the application of a fertilizer to moist earth the sol- 

 uble phosphoric acid becomes combined in insoluble phosphates, which 

 are deposited in minute particles. The particles are so finel}' divided 

 that the roots of plants easily secure plant food from them. It seems 

 from the knowledge at present available, therefore, that the ultimate 

 and valuable result of treating a phosphate with sulphuric acid is its 

 distribution through the soil in a mechanical condition so fine that it 

 is readily available to plants. 



The query ver^^ naturally follows whether practically the same re- 

 sult cannot be reached by the use of very finel}' ground undissolved 

 phosphates, and thus lessen the expense of crop production, especially 

 of grain and grass. This is one of the points involved in the field 

 experiments undertaken by the Station. 



Three forms of phosphatic material are being used in this experi- 

 ment, viz. : Dissolved bone black, in which the phosphoric acid has 

 been rendered largely soluble b}' the action of sulphuric acid ; finely 

 ground bone, undissolved ; and finely ground South Carolina rock, 

 undissolved. 



In ever}' case other necessary' ingredients of plant food besides 

 phosphoric acid are supplied so abundantU' bj* the use of muriate of 

 potash and sulphate of ammonia that a failure of the crop to grow 

 could only be ascribed to a lack of available phosphoric acid. 



The quantity of phosphatic material applied is sufficient in every 

 case to furnish the same amount of phosphoric acid per acre 



