COMMERCIAL FERTILIZER MATERIALS 461 



indicate that the availability is increased by decay. A large 

 number of experiments have been conducted with raw rock 

 phosphate composted with stable manure, among which may 

 be mentioned those by Hartwell and Pember * and also by 

 Tottingham and Hoffman, 2 who, in carefully conducted experi- 

 ments, failed to find that the availability of the raw phos- 

 phate, as indicated by chemical methods, was increased by 

 fermentation with stable manure. Opposing results have also 

 been obtained, however, and the evidence is somewhat con- 

 flicting. 



With so many factors active in varying the results, espe- 

 cially those from raw rock phosphate, it is not surprising that 

 satisfactory field data where acid phosphate and raw rock 

 are compared are difficult to obtain. Thorne, 3 after a critical 

 review of the field experiments where acid phosphate and raw 

 rock were used, comes to the conclusion that, while raw rock 

 phosphate is an excellent fertilizer, acid phosphate is gener- 

 ally superior. He finds that, while raw rock may be used 

 with profit on land materially deficient in phosphorus, acid 

 phosphate has generally proven to be the more effective and 

 the more economical carrier of phosphoric acid for crops. 



These conclusions, which are corroborated by other in- 

 vestigators, 4 do not imply that raw rock phosphate is never 

 equal or superior to acid phosphate, nor that raw rock does 

 not have a place as a fertilizer on the average farm. On a 



1 Hartwell, B. L., and Pember, F. E., The Effect of Cow Dung on the 

 Availability of Rock Phosphate; K. I. Agr. Exp. Sta., Bui. 151, 1912. 



"Tottingham, W. E., and Hoffman, C, The Nature of the Changes in 

 Solubility and Availability of Phosphorus in Fermenting Mixtures; Wis. 

 Agr. Exp. Sta., Res. Bui. 29, 1913. 



3 Thorne, C. E., Raw Phosphate Rock as a Fertilizer; Ohio Agr. Exp. 

 Sta., Bui. 305, 1916. 



4 Wiancko, A. T., and Conner, S. D., Acid Phosphate versus Raw Rock 

 Phosphate as Fertilizer; Purdue Univ. Agr. Exp. Sta., Bull. 187, 1916. 



Brooks, W. P., Phosphates in Massachusetts Agriculture ; Mass. Agr. 

 Exp. Sta., Bull. 162, 1915. 



Waggaman, W. H., and Wagner, C. R., Analysis of Experimental 

 Work with Ground Raw Rock Phosphate as a Fertilizer; U. S. Dept. 

 Agr., Bui. 699, 1918. 



