POTASH SULPHUR. 1 15 



POTASH. 



The relation of potash in the soil is almost exactly the same as 

 that of phosphorus. It comes primarily from the rocks where it 

 exists largely in the form of silicate of potassium. This is an insoluble 

 salt, and soils may contain it in large quantity and still suffer from 

 lack of available potash. It is rendered available in very much the 

 same way as in the case of phosphorus, largely through the action 

 of the decomposition produced by the soil bacteria. 



SULPHUR. 



Sulphur is one of the ingredients of protein, and, therefore, 

 is necessary to plant life. Ordinary plants obtain it only in the form 

 of sulphate, which they absorb from the soil. But microorganisms 

 are concerned in the transformations by which the soil is properly 

 stocked with the sulphates. The transformations show at least two 

 different steps: 



i. Sulphur is set free from its combinations. 2. Sulphur is 

 re combined into sulphuric acid that unites with mineral matter to 

 form sulphates. 



Liberation of Sulphur as H 2 S. All proteid matter contains 

 sulphur, and when its decomposition takes place through the agency 

 of bacteria the sulphur is liberated in the form of hydrogen bi- 

 sulphid (H 2 S) which vile-smelling gas may usually be detected 

 around decomposing proteid. This same gas is liberated from the 

 decomposition of sulphate of lime that is carried in drainage waters 

 to the ocean. Several kinds of bacteria have been found capable 

 of liberating H 2 S from such deposits. In certain parts of the world 

 large deposits of such sulphites (gypsum) have accumulated and 

 are constantly acted on by bacteria which liberate H 2 S, producing 

 the "curative muds" of the Black Sea and other localities. Such 

 muds are saturated with hydrogen bisulphid gas. This reduction 

 of sulphates is, in a way, comparable to denitrification since it is 

 the result of deoxidation and since it also destroys substances that are 

 already plant foods. Some species of bacteria appear able to attack 

 pure sulphur, causing it to combine with hydrogen as H 2 S. From 



