EXPERIMENTAL WORK WITH RAW ROCK PHOSPHATE. 73 



By studying the detailed yields obtained during the 18 years of 

 this experiment it will be seen that the method of computing fer- 

 tilizer values used by Brooks, namely, comparison of the treat- 

 ments with the nearest check plots, is distinctly favorable to the 

 plots receiving soluble and so-called available phosphates, since 

 these plots lie closer to the check giving lower yields. As far as the 

 figures are complete in detail, the plots treated with South Carolina 

 and Tennessee phosphate exceeded in yield those treated with acid 

 phosphate in eight out of nine and six out of nine cases, respectively. 



In view of the fact that the difference between the yields of the 

 check plots in this experiment are in many instances much greater 

 than the differences between the yields of the treated plots, the 

 drawing of rigid conclusions concerning the value of the different 

 types of phosphates hardly seems warranted. Neither of the two 

 long-time field experiments coixducted by the Massachusetts Station 

 appear to warrant a definite conclusion concerning the relative 

 merits of raw rock and acid phosphate. Under the conditions of the 

 first experiment (where equal money values of the two forms of 

 phosphoric acid were applied) the results indicate that raw rock 

 was more effective than acid phosphate. In the second experiment 

 (where phosphoric acid was applied in various forms at the same 

 rate) the results may be interpreted as favorable or unfavorable to 

 raw rock phosphate depending on the method employed in compar- 

 ing the yields with those of the check plots. 



MISSISSIPPI. 



The first field work with raw rock phosphate conducted by the 

 Mississippi station was described by Ferris ^ in 1906. Owing to the 

 short duration (one year) ,2 this experiment as well as six others^ 

 which were conducted for periods of from one to four years are not 

 considered in detail in this bulletin. 



In 1911 Ferris* reported the results of six years' work with fer- 

 tilizers on cotton at the McNeill branch station, and early in 1912 ** 

 gave the results obtained during six years of field work on corn and 

 cotton. 



The fields on which these experiments were conducted are de- 

 scribed as nearly level and as uniform as possible. The soil, it is 

 said, was typical of the pine lands in south Mississippi. The plots 

 were one-twentieth acre in size, and the treatments on each crop were 



iMiss. Agr. Expt. Sta., Bui. No. 94 (1906). 



* It is stated that this experiment was continued for four years hut details ai-e given 

 for one year only. 



»Miss. Agr. Expt. Sta., Buls. Nos. 110 (1908) ; 122 (1909) ; 155 (1911) ; 158 (1912) ; 

 161 (1913) ; 160 (1914). 



*Miss. Agr. Expt. Sta., Bui. No. 155 (1911). 



*Miss. Agr. Expt. Sta., Bui. No. 158 (1912). 



