EXPERIMENTAL WOEK WITH EAW ROCK PHOSPHATE. 107 



latter material after lying in the soil for some time (two years), and 

 becoming thoroughly distributed through tillage and cultivation. 



On bringing up the applications of slag, bone, and acid phosphate 

 to the point where equal amounts of phosphoric acid were added to 

 all plots except the checks, the latter forms were on the whole some- 

 what more effective than raw rock phosphate, particularly on the 

 limed plots. This, however, is what might be expected in view of the 

 greater solubility of bone, slag, and the acidulated phosphates and 

 the greater ease with which they are distributed in the soil. Indeed, 

 it seems rather surprising that raw rock phosphate should have given 

 such continued increases in yield when the total quantity added in 

 20 years (provided none was removed by the crop grown) was 

 sufficient to add less than 0.03 per cent of phosphoric acid to the 

 upper 9 inches of a soil of medium texture. When using a phos- 

 phatic fertilizer, the effectiveness of which depends upon heavy ap- 

 plications, the use of 2,000 or 2,500 pounds per acre in 20 years seems 

 a very light application. 



A pot experiment with the soil taken from the 20 plots of the ex- 

 periment field just described was undertaken by the Rhode Island 

 station in 1905,^ just three years after the phosphoric acid applica- 

 tions had been equalized on all the phosphate plots. Limed soil was 

 taken from the odd numbered plots and unlimed soil from the even 

 numbered plots. 



The results obtained in the growing of wheat for two weeks were 

 fairly well in accord with the field results obtained on the same soil 

 when equal applications of phosphoric acid were employed. In 

 both cases the beneficial effect of lime was very marked. The short 

 duration of this experiment, however, renders detailed discussion un- 

 warranted. 



The results of the Ehode Island station's work, in the opinion of 

 the writers, point strongly to the value of raw rock phosphate as a 

 fertilizer. Even when applied under such adverse conditions as in 

 the station's 20-year experiment the raw rock phosphate plots gave 

 very marked increases over the no-fertilizer plots, and in many in- 

 stances surpassed those treated with more soluble phosphates. The 

 writers feel, however, that the data afforded by this experiment are 

 insufficient to warrant a strict comparison of the relative merits of 

 the various forms of phosphoric acid. 



SOUTH CAROLINA. 



While the South Carolina Experiment Station has reported 23 ex- 

 periments with raw rock phosphate, 20 ^ of these have been conducted 

 for one year only and 2 ^ for a period of three years. 



»R. I. Expt. Sta., Bui. No. 109 (1905). 



«S. C. Agr. Expt. sta., Bui. No. 5 (1889) ; Bui. No. 12 (new series) (1893) ; Bui. No. 

 14 (new series), p. 4 (1893) ; Bui. No. 18 (new series) (1894). 

 » S. C. Agr. Expt. Sta., Bui. No. 2 (new series) pp. 80-82 (1891). 



