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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 le 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 coi.ducted 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),? 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 19125 
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 
1Miss. Agr. Expt. Sta., Bul. No. 94 (1906). 
21t is stated that this experiment was continued for four years but details are given 
for one year only. 
8 Miss. Agr. Expt. Sta., Buls. Nos. 110 (1908); 122 (1909) ; 155 (1911) ; 158 (1912) ; 
161 (1913) ; 169 (1914). 
Miss. Agr. Expt. Sta., Bul. No. 155 (1911). 
5 Miss. Agr. Expt. Sta., Bul. No. 158 (1912). 
