COMMERCIAL FERTILIZERS 



527 



They then call attention to the quantities of sulfur 

 trioxide contained in average soils which, as shown by 

 Hilgard, are less than the quantities of phosphorus pen- 

 toxide. 



To ascertain whether the supply of sulfur in the soil 

 is really depleted by cropping, the same authors made 

 parallel determinations of sulfur in five virgin soils and 

 in five soils of the same respective types that had been 

 cropped for sixty years. In each type the cropped soil 

 contained less sulfur than the virgin soil, the average for 

 the cropped soils being .053 per cent SO 3 and for the 

 virgin soils .085 per cent SO 3 . 



There is no doubt that the quantity of sulfur carried 

 down by rain and snow is much less than that removed 

 in drainage water. There can be no question therefore 

 that most soils, and especially cultivated soils, are losing 

 more sulfur than they receive by natural processes. 



It has been customary to add to soils manures of one 

 kind or another that contain more or less sulfur. Among 

 these are farm manure and other animal or bird excre- 

 ments, residues of crops, animal offal, gypsum or land 

 plaster, superphosphate, ammonium sulfate, potassium 

 sulfate, kainit, and the like, all of which contain conse- 

 quential quantities of sulfur. It seems probable that 



