118 BULLETIN 699, U. S. DEPARTMENT OF AGRICULTURE. 
conducted on fields shoe 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 i 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. | 
Raw ook 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 138 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 18 per cent regarded the material nampa ot | 
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 which 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. 
