SOILS HI 



cient in phosphorus, and the results of many experiments in 

 the United States and in England have shown that the 

 application of phosphorus in good systems of farming pro- 

 duces marked and profitable increases in crop yields. 



The important question is what form of phosphorus we 

 shall apply. There are many kinds of fertilizing materials 

 containing phosphorus, and one may cost many times as much 

 as another. For example, 280 pounds of phosphorus in a 

 ton of finely ground natural rock phosphate may be pur- 

 chased at the mines in Tennessee and delivered at the farm- 

 er's railroad station in the central states for about $12. 

 Or, the ton of raw phosphate may be mixed with a ton of 

 sulphuric acid in the factory, and the two tons of acid phos- 

 phate may be sold to the farmer for $60. Again, the fer- 

 tilizer manufacturer may mix two tons of acid phosphate 

 with two tons of filler containing a little nitrogen and potas- 

 sium, and then sell the four tons of complete fertilizer for 

 $160. And the farmer gets only as much phosphorus in the 

 complete fertilizer for $160 as he would get in the one ton 

 of natural phosphate for $12. 



Common sources of phosphorus are raw bone, steamed bone, 

 raw rock phosphate, acid phosphate, and basic slag. The next 

 important question for consideration is the problem of mak- 

 ing the phosphorus available as it appears in these various 

 sources. 



When the natural rock is used, it should be ground so 

 that at least 90 per cent will pass through a sieve with ten 

 thousand meshes to the square inch, and a content of from 

 12 to 15 per cent of phosphorus should also be guaranteed. 



