AVAILABILITY OF POTASH IN GROUND ROCK. 11 



THE AVAILABILITY OF POTASH IN GROUND ROCK. 



The attention of the writer was first turned to the availability of 

 potash in ground rock by a study of the decomposition which takes 

 place when various rocks are used to form the surface of macadam 

 roads. The binding power of rock dust depends upon the decom- 

 position of the particles under the action of water and other sub- 

 stances. It has always been believed heretofore that only the potash 

 that could be leached or dissolved out of a finely ground nuiterial 

 with water was available for plant growth. As a nuitter of fact 

 even the most finely ground feldspar which it is possible to obtain 

 yields extremely minute (pumtities of 2)otash to actual solution in 

 Avater. Feldspar which contained about 10 per cent of potash and 

 was ground to a very fine powder yielded only 0.025 per cent to 

 solution in Avater, and only 0.03(5 per cent to the action of a dilute 

 acid. A large number of similar observations has led to the confi- 

 dent belief, almost universalh' held for many years, that although 

 rocks which were disintegrated by natural processes served as the 

 original source of potash, the action was so slow that it would be use- 

 less to grind rocks and attempt" to use them as fertilizers. In the 

 writer's investigations, however, evidence has been obtained which 

 seems to show that decomposition of fine-ground feldspar goes much 

 farther than was indicated by the simple solution tests with water 

 and dilute acids. B}- the use of laboratory methods it has been 

 shown that almost complete decomposition can be made to take place 

 in comparatively short periods of time under the action of water 

 alone. In order to accomplish this result it has been necessary to 

 use a method by which the potash is continually removed as fast as 

 it is set free from its combinations in the rock. Now, as the roots of 

 plaukts are continually performing this function, it is possible that in 

 nature the decomposition of the feldspathic particles in the soil must 

 be continually going on as long as the product is being used, and 

 slowing down to the stopping point when no removal is effected by 

 plant growth. For further information on the scientific discussion 

 of the decomposition of the feldspars the original papers should be 

 consulted." 



The fact, frequentlj^ cited and familiar to almost every person, 

 that rocky hillsides with little or no soil can support growths of tim- 

 ber, would appear to demonstrate that rock potash is available. 

 When it is remembered that wood ashes contain anywhere from 5 to 

 12 per cent of potash, it will be seen that a large tree represents, as it 

 stands, a considerable quantity of this substance. However, trees 



a Bui. 92, Bureau of Chemistry, U. S. Dept. of Agriculture ; Cir. 38 and Bui. 28, 

 Office of Public Roads. 



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