EXPERIMEISTTAL WORK WITH RAW ROCK PHOSPHATE. 43 



Table XIX. — Average yields of corn, wheat, legumes, and oats. Cutler field. 



Treatment. 



Average yield per acre (1904-1915). 



Com, 4 

 crops. 



Wheat, 3 

 crops. 



Legumes, 1 

 crop. 



Oats, 2 

 crops. 



Residues, lime, bone, potash 



Residues, lime, potash 



Lime, potash 



Residues, lime, acid phosphate, potash. 



Lime, acid phosphate, potash 



Residues, lime, phosphate rock, potash 

 Lime, phosphate rock, potash 



Bushds. 

 34.9 

 38.4 

 36.9 

 36.0 

 37.1 

 42.2 

 37.3 



Bushels. 

 25.1 

 16.9 

 16.3 

 28.7 

 26.6 

 25.8 

 18.5 



Tom. 

 2.74 

 2.11 

 1.80 

 2.52 

 2.40 

 2.51 

 2.06 



BusTiels. ' 

 27.1 

 3L6 

 25.5 

 28.8 

 31.8 

 . 24.6 

 29.3 



In almost every instance plots treated with ground raw rock 

 phosphate gave noticeable increases in yield over the check plots, 

 and at Odin and Mascoutah showed to better advantage than the 

 acid phosphate plots. At Cutler the acid phosphate plots appeared 

 to greater advantage. However, none of the phosphate treatments 

 gave very large increases, and, as Hopkins says, " These investiga- 

 tions have shown that phosphorus is not the factor which first limits 

 the crop yields on these southern Illinois soils, both limestone and 

 organic matter being of greater initial importance." Owing to the 

 adverse climatic conditions during the latter part of the experiment 

 it is impossible to tell whether or not any cumulative effect can be 

 attributed to the use of raw rock. 



The data presented in the 12 field experiments with raw rock 

 phosphate conducted by the Illinois station and considered here in 

 detail point pretty strongly to the conclusion that this phosphate 

 carrier increases crop yields very materially when applied liberally. 

 Since raw rock was compared with other phosphates in only 3 

 of the 12 experiments, and on fields where phosphoric acid appar- 

 ently was not the limiting factor, the work hardly appears to justify 

 a comparison of the relative merits of the different phosphate 

 carriers. 



ESTDIANA- 



The first mention of the use of raw rock phosphate as a fertilizer 

 made by the Indiana Experiment Station was in 1896,^ when phos- 

 phatic marl containing from 10 to 12 per cent of phosphoric acid 

 was tried on two series of wheat plots of one-twentieth acre each. 

 The short duration of this experiment (one year), however, and the 

 little data presented make the results relatively unimportant. 



Two experiments with raw rock phosphate were described by 

 Goss^ in 1907 and several others by Abbott and Conner^ in 1912, 



ilnd. Agr. Expt. Sta., BuL No. 61, p. 64 (1896). 



«Ind. Agr. Expt. Sta., Circular No. 10, pp. 9-11 (1907). 



»Ind. Agr. Expt Sta., Bui. No. 155 (1912). 



