PHOSPHATES IN MASSACHUSETTS AGRICULTURE. 165 



13. The phosphoric acid capital in our soils is certainly not too large; 

 doubtless it should in many cases be increased. Phosphates should be 

 used in our agriculture, and the question whether the natural rock phos- 

 phates should be employed is an important one. 



14. In experiments which have continued eighteen years, in which 

 various fine-ground mineral phosphates, bone meals (raw, steamed and 

 dissolved), slag meal, dissolved bone black and acid phosphate have been 

 compared on the basis of equal annual liberal appUcation of phosphoric 

 acid, the results have been highly unfavorable to the natural mineral phos- 

 phates with all important crops. 



15. The percentage increases (of all crops, 1899 to 1914, inclusive) show 

 the following averages: — 



Per Cent. 

 Natural mineral phosphates, . . . . . . . .9.13 



Slag and bone meals, . . . . . . . . . .42.24 



" Dissolved " phosphates, ......... 44.85 



16. The "dissolved" phosphates are much more favorable to rapid 

 early growth than the natural mineral phosphates. 



17. The "dissolved" phosphates favor ripening, as shown by the smaller 

 proportions of immature product, especially with corn, onions and cab- 

 bages. 



18. The increases in crops produced by the slag, bone meals and "dis- 

 solved" phosphates exceed cost of the materials in much greater degree 

 than is the case with the natural mineral phosphates. The average figures 

 are, per acre : — 



For natural mineral phosphates, annually, . . . . . . $6 21 



For slag and bone meals, annually, . . . . . . . 36 23 



For "dissolved" phosphates, annually, . . . . . . . 34 57 



19. The natural mineral phosphates gave yields after eighteen years' 

 continuous use, yet more inferior as compared with the dissolved phos- 

 phates than in the earher years. The increases for the corn crop are, per 

 acre : — 



20. It is clear that the natural agencies active in the soil in these ex- 

 periments act upon the mineral phosphates with extreme slowness, in 

 spite of the fact that large amounts of organic matter have been incor- 

 porated with it by the growth and turning under of green crops. 



