108 BULLETIN' 699, IT. S. DEPARTMENT OF AGRICULTURE. 



A raoi-e valuable experiment with raw rock phosphate is that re- 

 ported by Keitt ^ in 1914. While the results of four years' work in 

 the growing of com and cotton on plots treated with various phos- 

 phates alone, and in combination with other fertilizer materials have i 

 been reported, this work is said to be only preliminary and is there- I 

 fore not discussed here. : 



None of the experiments of the South Carolina station have been ! 

 continued long enough to warrant discussion and therefore no con- ' 

 elusions may be drawn concerning the value of raw rock phosphate j 

 as a fertilizer. 



TENNESSEE. \ 



} 



The Tennessee station has published the results of 10^ field ex- i 



periments with raw rock phosphate. Seven of these experiments ' 



cover periods of only one to two years. | 



The average results obtained in three experiments covering periods \ 



of from three to four years and conducted by, or under the direction ] 



of the State station, were published by Mooers ^ in 1912. A rotation ' 



of cowpeas and wheat was practiced in these experiments and four i 



different types of phosphate fertilizers were tested both on limed and ; 



unlimed plots. i 



The beneficial effect of liming on these three forms was quite ] 



marked except in the case of the raw rock phosphate and basic slag ' 



plots. The latter material appears to have been the most effective of | 

 all the phosphates, owing in part no doubt to the free lime which it 

 contained. 



If the average yields of all three forms are considered, the raw rock 



plots (unlimed) compare very favorably with the acid phosphate j 



(unlimed) plots, but where lime was applied the average yields i 



were considerably more favorable to acid phosphate. i 



If, however, the average yields obtained on the station farm only : 



are considered (the experiment at this place having been conducted < 



the longest) the raw rock phosphate plots compare favorably with ; 



those receiving acid phosphate and bone both on limed and unlimed ■ 

 land. 



These three experiments have not been running long enough to 



give conclusive evidence on the relative values of the four forms of ' 



phosphoric acid used and therefore are not repeated in detail, but the : 



indications are that applications of raw rock phosphate were effec- ] 



tive in increasing the yield of various crops. j 



»S. C. Agr. Bxpt. Sta., Bui. No. 178 (1914). 



• Tenn. Agr. Expt. Sta., Ann. Rept. 1885-1886, pp. 100-112 (1886) ; Bui. No. 2, vol. 

 13, pp. 11-14 (1900) ; Bui. No. 1, vol. 16, pp. 14-16 (1903) ; Bui. No. 86 (1909) ; Bui. 

 No. 90 (1910) ; Bui. No. 92 (1911) ; Bui. No. 96 (1912). 



•Tenn. Agr. Expt. Sta,, Bui. No. 96, pp. 16-24 (1912). I 



