22 



X. H. AGR. EXPERIMENT STATION. 



[Bulletin 170 



Table XVI 



of experiments with calcium sulfate indicate that small amounts 

 of potassium are made soluble. These determinations have been 

 made colorimetrically. 



It has been shown in a preceding table how the soil behaves 

 toward potassium salts when applied as soluble fertilizer constit- 

 uents. The amount of water-soluble potassium in many dif- 

 ferent samples of soil has been determined to show, if possible, 

 whether there is any definite relation between the total potas- 

 sium content of the soil and the amount of water-soluble 

 potassium in the same soil. Such a relation has not been 

 established with satisfactory assurance because it has not been 

 possible to secure soils which differ only as regards the total 

 potassium content. 



The amount of potassium is usually in proportion to the 

 amount of clay in the soil. The amount of clay has consider- 

 able effect on the nature of the organic matter. The amount 

 and nature of organic matter apparently affects the solubility 

 of potassium and other mineral constituents; also, some soils 

 carry a large portion of their potassium in the form of minerals. 

 This is particularly true of the sandy soils. The solubility of 

 potassium in mineral form must be different from that in the form 

 of clay. This must be true because of the influence of the clay 

 itself. Also, the past treatment of the soil may influence the 

 solubility of potassium, depending upon cultivation, and whether 

 or not commercial fertilizers have been used. 



The solubility of potassium in pure ground feldspar, for in- 

 stance, is very different, depending on whether the solvent con- 



