PLANT FOOD MUST BE AVAILABLE TO BE USEFUL. 25 



while the second two pots of each soil were given the regu- 

 lar potash application. While the clayey soil without 

 potash fertilizer produced a heavier growth than the sandy 

 soil under the same conditions, the application of potash in 

 both cases showed a material gain from its use, notwith- 

 standing the fact that, in all the pots, the soil contained 

 enormous quantities of potash naturally Of the two soils 



FIG. 9. THE POTASH IN SOILS IS OF NO VALUE, UNLESS AVAILABLE 



used, the amount of potash in the top twelve inches of one 

 acre, was as follows: 



Clayey soil 8249 Ibs. 



Sandy soil 2110 u 



The amount of potash applied to the soil was about 

 100 pounds per acre, whereas the crop removed only about 

 70 pounds. This small fertilizer application of available 

 potash made all the difference between success and failure 



