228 THE FARMER OF TO-MORROW 



analyze the supernatant liquid. Set down in 

 black and white how much potash and phos- 

 phorus the water contains. 



Next, take another sample of the same soil, 

 and "dress" it with commercial fertilizers in 

 their most soluble form. Mix them thoroughly 

 with the soil, and let the mixture stand for 

 some time to insure the soil moisture acting on 

 the chemicals added. 



Then treat this "fertilized" soil in exactly 

 the same way you treated the first sample. 

 Extract all the soluble "plant food" possible 

 with distilled water for the same number of 

 hours. Then analyze that water. The result 

 is surprising. 



The two analyses will be practically the 

 same. There is no more potash or phosphorus 

 in the second solution than the first, in spite 

 of the fact that you have "fed" this soil with 

 these elements in their most soluble form. 

 You cannot recover these salts by solution. 

 The soil has seized upon them and retained 

 them as its own, and will liberate them only 

 at a definite rate. 



It may be asked in this connection what 

 element of fertility does the farmer add to his 

 soil when he applies mineral salts? Has he 



