ACTIVE PLANT FOOD, ETC. 



189 



acid dissolved from these plots and the crop production. All 

 these materials would give up their phosphoric acid equally well 

 to the solvent used. 



A soil containing less than 50 parts per million of active potash 

 probably contains all its potash in the form of highly insoluble 

 silicates, such as the felspars. A soil containing over 50 parts per 

 million of active potash contains some of more easily dissolved 

 potash minerals or compounds. Since the solvent does not 



Fig. 40. Corn grown with and without phosphoric acid on four soils con- 

 taining 60 to 100 parts per million of active phosphoric acid, Te^as Station. 



decompose such minerals fully, and some fixation also occurs, the 

 quantity of potash extracted is less than the quantity present in 

 easily soluble compounds. 



Relation of Active Phosphoric Acid to Growth in Pot Experi- 

 ments. At the Texas Experiment Station, studies were made of 

 the relation between the active phosphoric acid present in the soil 

 and the crop produced in pot experiments. The comparison was 

 made between the crops grown with phosphoric acid, nitrogen, and 

 potash, and those grown with nitrogen and potash only. The 



