EXPERIMENT STATION BULLETINS. 151 



CHANGES IN POTASH COMPOUNDS. 



Potash is quite insoluble .in water in the form in which it is usually found in 

 the soil. One of the end products of the decay of humus in the soil is carbon 

 dioxide gas, which, dissolved in the soil water, has a certain amount of solvent 

 action upon the insoluble potash salts producing carbonates, which, in turn, act 

 upon the silicates in the soil, forming an important class of bodies known as 

 potash zeolites (Chester). In this form the potash is less stable and although not 

 strictly soluble in water, it is readily so in dilute organic acids such as result 

 from the decomposition of organic matter. 



STTLPHUR BACTERIA. 



The formation of sulphates in the soil may also be carried on through the 

 agency of micro-organisms. In the dissolution of proteid matter, hydrogen sul- 

 phide gas is set free. The sulphur bacteria in the soil and soil water seize upon 

 the hydrogen sulphide, using it as a source of energy, oxidizing the gas and 

 setting the sulphur free. The same bacteria, as well as others, oxidize the free 

 sulphur to sulphuric acid, which unites in the soil to form sulphates. Hence the 

 cycle is complete, the total result of the action being that the sulphur is reduced 

 to soil sulphates in which form it may be utilized by the plant. 



IRON BACTERIA. 



Iron compounds in the soil are also changed by the activity of micro-organisms, 

 certain bacteria making use of these compounds as sources of energy just as the 

 last group makes use of the sulphur compounds. The iron is found originally in 

 the soil, and is also formed in the destruction of organic matter, the liberated 

 iron combining with carbon dioxide gas present to form carbonates. The car- 

 bonates are oxidized by the bacteria, forming iron hydroxide, which is an active 

 chemical agent, and readily unites with phosphorus or silica which may be in 

 the soil, to form phosphates or silicates of iron. These salts are important soil 

 ingredients and contribute to the mineral food of plants. 



In discussing the biological changes of the soil we have to consider the relative 

 influence of one process upon another. We may isolate a single species of micro- 

 organism from the soil and study it when growing alone, supplying the same 

 conditions, so far as possible, as are met with in its natural habitat. We find 

 that it produces certain changes. Now, if we isolate another species, and combine 

 It with the first, different products may result. One organism may delay or 

 hasten the growth of another, as is sometimes the case in milk, where it is known 

 that the different kinds of bacteria present exert more or less influence over each 

 other. Further, one organism may precede and pave the way for another, as in 

 vinegar making, where yeasts first change the sugar of the cider to alcohol, 

 making "hard cider," the fermentation being carried on from this point by bac- 

 teria which convert the alcohol into acetic acid. So In the soil, the different 

 species undoubtedly are influenced in their products by this associative action, 

 one species, perhaps, by the changes It produces, preparing food for another 

 species or otherwise establishing favorable conditions for its growth; one species 

 in the ascendency at one time, another at another time, the whole result being 

 the maintenance of suitable conditions for the growth and development of plants. 



In closing, the author wishes to express his appreciation to Professor Marshall 

 for valuable suggestions, and to Professor Jeffery, of the department of soil 

 physics, Vho kindly consented to review and criticise the manuscript from the 

 practical standpoint. 



