118 BULLETIN 699, IT. S. DEPARTMENT OF AGMCULTUKE. 



conducted on fields showing little or no response to phosphate 

 treatment. 



In 21 experiments the applications of raw rock phosphate were 

 relatively light (250 pounds or less per acre), yet 15 of these ex- 

 periments or 71.4 per cent showed distinctly favorable increases in 

 yields on the plots treated with this material. 



In 16 experiments where the raw rock phosphate applications were 

 more liberal, 13 or 81.3 per cent resulted favorably to raw-rock 

 phosphate, and the remaining 3 experiments were conducted on soils 

 showing little or no response to phosphate treatment. 



Eaw rock phosphate was applied in connection with organic matter 

 in 23 experiments. Out of this number 18 or 78.3 per cent gave dis- 

 tinctly favorable results, and of the 5 remaining experiments 3 were 

 conducted on fields unresponsive to other forms of phosphoric acid. 



In regard to the cumulative effect of ground raw rock phosphate 

 it may be said that in 17 instances (46 per cent of the entire number 

 of experiments) there was evidence of greater availability after raw 

 rock had been applied for a number of years. In 13 out of the re- 

 maining 20 experiments the data are not sufficient to give evidence 

 on this point, and in 4 out of the 7 cases where no cumulative effect 

 was shown the soils were not responsive to phosphate treatments. 



In order to determine the sentiment toward ground raw rock phos- 

 phate as a fertilizer a letter and set of questions were sent to each of 

 1,000 progressive farmers who had used the material for one or more 

 years. Out of 315 replies, 219 farmers or 69.6 per cent were favor- 

 able to its use, 55 or 17.5 per cent were doubtful concerning its value, 

 and 41 or 13 per cent regarded the material unfavorably. 



CONCLUSIONS. 



The data presented in this paper were gathered in order that those 

 interested in the use of raw rock phosphate might draw their own 

 conclusions. The classification of the experimental work according 

 to states was made so that the experience with this material in each 

 particular locality might be studied in the least possible time. Some 

 of the experiments, however, undoubtedly conflict and in others, re- 

 sults Avhich on close analysis agree fairly well, appear on the surface 

 contradictory. It is hoped, however, that by carefully considering 

 the factors influencing crop yields as outlined in page 18 to page 28, 

 and applying them to the individual experiments much confusion 

 can be avoided and the reader be able to obtain a fairly clear idea 

 of the value of the results. 



While the writers do not wish to influence the judgment of anyone 

 reading this paper, they feel, after carefully weighing the data con- 

 tained therein, that certain general conclusions are justified. 



