Kinds of Bacteria and the Phosphates 289 



which the phosphoric acid of manure and of other 

 organic materials must pass before it becomes available 

 as plant-food are, is still to be learned. We know that in 

 its action the phosphoric acid of manure compares 

 favorably with that of superphosphate, the results 

 being modified by the physical and chemical nature of 

 the soil. 



In different soils there are probably different species 

 of decay bacteria that come to the foreground as far as 

 the phosphoric acid is concerned. Whether any of the 

 species of decay bacteria are particularly prominent in 

 the processes of transformation to which the phosphoric 

 acid of organic manures is subject, is still to be learned. 

 However, interesting differences in this direction must 

 exist since, in the process of evolution, species have 

 been developed that differ in their relations to phosphoric 

 acid, just as the soil bacteria differ in their relations to 

 nitrogen. In one instance, at least, it is known that the 

 nitrogen-fixing bacteria of the azotobacter group are 

 sensitive as to the supply of phosphoric acid in the media 

 in which they grow; also, that, with conditions otherwise 

 favorable, their growth is but meager in soils deficient 

 in available phosphoric acid. 



ACTIVITIES OF SOIL BACTERIA IN RELATION TO POTASH 



Most of the potash in the soil exists there in the rock 

 particles. A small proportion is found in combination 

 with the humus. Clay soils derived from the weathering 

 of feldspar and of oth^r minerals rich in potash, naturally 

 contain a large amount of the latter. Sandy soils formed 



