SOIL ORGANISMS 441 



attention to certain significant facts. In the first place, the 

 soil fauna and flora, especially the latter, are exceedingly 

 complex. The number of plant forms are so numerous that 

 the discussion already presented serves as little more than an 

 introduction. In the second place, the transformations facili- 

 tated by soil organisms involve all of the normal constituents 

 of the soil, both organic and inorganic. Moreover, biological 

 activities determine to a large degree the efficacy of every 

 addition, natural or artificial, made to the land. While the 

 cycles generally recognized are apparently clear cut, the 

 transformations themselves are actually involved in intrica- 

 cies, which man will probably never entirely unravel. 



A third phase of outstanding importance is the relationship 

 of the biological activities of the soil to the nitrogen prob- 

 lem. Not only are the complex nitrogenous compounds of the 

 soil readily made available to higher plants by soil organisms, 

 but means are provided whereby considerable nitrogen, in- 

 ert as it is, may be wrested from the atmosphere and forced 

 into activity within the soil. It is not impossible that in cer- 

 tain favored cases 150 pounds of nitrogen to the acre may 

 be yearly added to the soil by such processes. This phase 

 alone is worthy o£ the most careful practical study. Obvi- 

 ously uo.system of soil management can be wholly successful 

 unless full advantage is taken of this and other biological 

 possibilities of the land. 



