80 Fertilizers 



European vegetation and field experiments show pretty 

 clearly that two parts of phosphoric acid from the Thomas 

 phosphate powder are approximately equivalent to one 

 part from soluble phosphoric acid, and that this phosphate 

 is especially useful on wet, marshy soils and those poor in 

 lime. Experiments conducted in this country practically 

 confirm these conclusions. 



The relative availability of the phosphates in the 

 natural guanos has also been shown to be somewhat 

 higher than in other insoluble phosphates. These latter 

 substances for this reason possess a distinct value over 

 others for certain classes of crops, as, for example, cran- 

 berries, where the soluble phosphates would be liable to 

 be washed out, and where the organic phosphates would 

 be liable to float on the surface of the water, and also 

 where lands are cold and sour, and not readily fermentable. 



The practical point, however, to the farmer is the 

 amount of increase that he may obtain from a certain 

 definite expenditure, a matter which will be discussed 

 later, in the discussion of the use of fertilizers for the 

 various crops. 



