FERTILIZERS AND PLANT FOOD. 233 



It might be true, and doubtless is in some, perhaps many, localities 

 that the soils yearly liberate more potash than phosphoric acid, and 

 there are cases where phosphoric acid alone will give bountiful crops, 

 thus showing that in such soils there is enough available potash, but in 

 many cases it has been assumed that phosphoric acid is the regula- 

 ting substance, when experiments carefully conducted have proven 

 that it is potash. This leads us to inquire whether there is any 

 method by which we may satisfy ourselves of the requirements of 

 our particular soil. 



The answer must be, field experiments ! and the method must be 

 based upon the use of fertilizing materials which contain the three 

 forms of deficient jjlant food in separate substances, so that we 

 may test them singly and in a variety of combinations, having nitro- 

 gen, phosphoric acid and potash in varying proportions. These 

 tests when well conducted and when properly duplicated and made 

 by the side of plots having no fertilizer, are capable of giving a great 

 deal of practical information. 



