COMMERCIAL FERTILIZER MATERIALS 459 



equal money values. If rock phosphate could be made to 

 equal or nearly equal the availability of acid phosphate, ob- 

 vious advantages would accrue, since raw rock costs much less 

 than acid phosphate and carries about twice as much phos- 

 phoric acid. 



The availability of the phosphorus of raw rock phosphate 

 varies considerably with conditions. At least four major in- 

 fluences have been recognized: (1) the character of the crop 

 grown, (2) reaction of the soil, (3) the character of accom- 

 panying salts, and (4) the decomposition of organic matter. 

 It is to be expected that the various kinds of plants should 

 not be equally influenced by the phosphorus of tri-ealcium 

 phosphate. Prianischnikov ^ found that lupines, mustard, 

 peas, buckwheat, and vetch responded to fertilization with 

 raw rock phosphate in the order named, while the cereals 

 did not respond at all. He did not include maize in his ex- 

 periments, but that crop is said to respond well to diffictdtly 

 soluble phosphates. It is generally considered that those 

 plants which have a long growing season are better able to 

 utilize tri-calcium phosphate than are more rapidly growing 

 plants. 



A number of investigators have stated, as a result of their 

 experimentation, that the availability of raw rock phosphate 

 is greater in acid soils than in those strongly basic. If acidity 

 of the soil is due to the presence of an actual acid, it is con- 

 ceivable that the availability may be due to the solvent action 

 of the soil acid on the calcium of the tri-calcium phosphate, 

 producing the di-ealcium salt which appears to be fairly read- 

 ily available to plants. When, however, soil acidity is due 

 to a lack of certain active bases, the case is different. Gedroiz ^ 



* Prianisclinikov, D., BerieM uber VerseUedene Versuche mit Bohphos- 

 pTiaten unter Beduction; Moscow, 1910. 



* Gedroiz, K. K., Soils to which Bocb Fhosphates May Be Applied 

 with Advantage; Jour. Exp. Agron. (Bussian), Vol 12, pp. 529-539, 

 811-816, 1911. The autliors are indebted to Dr. J. Davidson for tlie 

 translation. 



