Phosphatic Fertilizers 285 



phosphate rock, the supply of cheap phosphoric acid is 

 assured. Under such conditions it would be possible to 

 add much larger quantities of phosphoric acid to the 

 soil for the same money expended, and thus provide, 

 not only for large harvests in the near future, but, also, < 

 for large harvests in the more distant future. The value 

 of soil-humus, well appreciated by practical men every- 

 where, becomes more definite when considered from this 

 point of view, as well as in its other relations. A clearer 

 insight into the process of plant-production is gained 

 as an understanding of the manifold reactions in the 

 busy laboratory of the soil is developed. Soil-humus 

 stands revealed to us, then, not alone as the storehouse 

 of nitrogen, but as a medium wherein countless species 

 of microscopic life achieve a great work, as a key that 

 unlocks the abundant treasures of the inert rock masses. 



Ground bone. — The rate at which ground bone be- 

 comes available is determined, as in case of floats, by the 

 amount and character of the soil-humus and the bac- 

 terial activities occurring in it. The fineness of division 

 plays an important part here in so far as it concerns 

 these activities. It is quite evident that the finer the 

 particles, the more intimate their contact with the bac- 

 teria and their products. The phosphoric acid of fine 

 bone becomes more quickly available than that of coarse 

 bone because it presents a greater surface for the attack 

 of the microorganisms. Lime seems to decrease the 

 availability of the phosphoric acid in ground bone. 



A number of experiments in which smaller returns 

 were secured from bone on the limed portions of the 

 field are on record. The decrease is accounted for on 



