144 BOARD OF AGRICULTURE. [Pub. Doc. 



least in connection with grasses, may be wonderfully in- 

 creased by liming, so that it ranks close behind, if not quite 

 equal to, the superphosphates.* It is probable that this 

 experiment will throw some light upon some of the con- 

 flicting data and opinions now on record regarding this 

 phosphate. 



Superphosphates. — A superphosphate is essentially bone 

 or mineral phosphate, treated with sufficient acid to com- 

 bine with about two-thirds of the lime, leaving the other 

 third in combination with phosphoric acid in a condition so 

 that it is soluble in water. In this form it is customarily 

 called soluble phosphoric acid. So far as concerns all of 

 these dissolved phosphates, the data at hand indicate that, 

 when properly manufactured, the phosphoric acid dissolved 

 from the superphosphate by water is equally valuable, no 

 matter from what it is derived. In case an excess of sul- 

 furic acid is used in the manufacture, the acidity may be so 

 great as to injure plants to some extent for a time, at least, 

 and hence the phosphoric acid would be prevented from per- 

 forming its function normally. Such a result should be laid 

 at the door of the sulfuric acid, and not to the inefficiency 

 of the soluble phosphoric acid (monocalcic phosphate). 

 Barring sandy and gravelly soils, particularly when they 

 lack carbonate of lime and exert an acid reaction upon blue 

 litmus paper, and barring soils of even other character which 

 may be acid, superphosphates may be considered as being 

 the quickest-acting and surest form of phosphoric acid to 

 employ, wherever crops must be pushed to maturity rapidly ; 

 or where the natural period of growth is limited, and the 

 soil has not been well stocked for several years previously 

 with dressings of floats, basic slag undissolved bone or min- 

 eral phosphate of similar character. 



Enough must have been said in this discussion to bring 

 out in the strongest light the influence of the physical and 

 particularly of the chemical character of soils upon the 

 action of various phosphates. It must be obvious, in view 

 of the probability that large quantities of ignited alumina 



* Andouard (Annales Agron. 21 (1895), pp. 171-181), who experimented with a 

 soil containing carbonates of lime and magnesia, obtained good results with this 

 phosphate in the case of several liinds of plants. 



