EXPERIMENTAL WORK WITH RAW ROCK PHOSPHATE. 59 



members of which — ^barley, corn, and oats — yielded nearly double 

 the amount produced by either the floats or Redonda phosphate. 



The fact that the same quantity of phosphoric acid was applied 

 in all forms and that this application was light for the relatively 

 insoluble phosphates is distinctly unfavorable to these phosphates. 

 Moreover, it is stated that the sand used in this experiment was 

 nearly free from organic matter, which fact would also be unfavor- 

 able to the raw rock phosphate. It is not surprising, therefore, that 

 greater yields were obtained from the use of the soluble phosphate 

 in these experiments. 



The results of both the field and greenhouse experiments conducted 

 by the Maine Station indicate strongly that applications of raw rock 

 phosphate increase the yields of many crops and that this material 

 is more effective when applied liberally. The data, however, are 

 insufficient to be conclusive as to the relative merits of raw rock and 

 acid phosphate. 



MARYLAND. 



The first work conducted by the Maryland station to test the fer- 

 tilizer value of the relatively insoluble phosphates consisted of sev- 

 eral experiments^ on corn, wheat, sweet potatoes, and tomatoes, but 

 in all these experiments the natural phosphates employed were 

 guanos from islands in the Caribbean Sea. According to the analy- 

 ses of these guanos they contained a certain amount of available 

 (so called) phosphoric acid, and in some instances a small percent- 

 age of nitrogen, so it is hardly fair to place them in the same class 

 with the amorphous phosphates of Florida, South Carolina, and 

 Tennessee. For this reason the results of these experiments are not 

 included in this paper. 



The results of five years' work in testing the relative values of 

 various carriers of lime were published by the station in 1906.^ 

 While finely ground South Carolina rock was used on one of the 

 plots, no comparison can be made of its value with that of acid 

 phosphate in this experiment since all the plots, with the exception 

 of the checks received in addition to the lime carriers applications 

 of a complete fertilizer. Under these conditions lime in the form of 

 oxide, hydrate or carbonate produced yields as great as that obtained 

 from lime combined with phosphoric acid in ground rock phos- 

 phate. It is worthy of note, however, that the plot receiving ground 

 rock phosphate in addition to a complete fertilizer produced greater 

 yields than the plot treated with complete fertilizer alone. 



The results of work carried on for 12 consecutive years with vari- 

 ous kinds of phosphate were published by the Maryland station in 



iMd. Agr. Expt. Sta., Bui. No. 5 (1889) ; Special Bui. (Fair edition) fl889) ; Buls. 

 Nos. 10 (1890) ; 14 (1891). 



»Md. Agr. Expt. Sta., Bui. No. 110 (1906). 



