BUREAU OF SOILS. 503 



Studies on these latter are in progress, not only as they are affected 

 by mechanical agencies but as they are affected by all cultural 

 operations, especially fertilization. Substantial progress has been 

 made in showing that profound physical effects are produced in soils 

 of quite as great signification for crop production as are the chemical 

 changes and that methods are now available for studying these 

 physical changes. It has been shoAvn that certain properties of the 

 water, such as its density, which influences its movement in soils, is 

 greatly changed by the addition of salts. The optimum \vater content 

 is also altered by such additions, and in fact all the relations between 

 the solid soil particles and the soil water. 



Finally, these studies have led to the formulation of the soil prop- 

 erties affecting crop production as a dynamic system involving 

 dependent factors only. The chief importance of this formulation 

 is that it points out the way for more systematic studies of the soil 

 than have been possible hitherto, indicates the relationships of the 

 numerous factors determining crop production, and brings clearly to 

 mind that it is the changes these factors undergo and the control of 

 these changes by cultural operations that are of importance, rather 

 than a static inventory of the soil materials. 



SOIL-FERTILITY INVESTIGATIONS. 



During the last year considerable progress has been made in the 

 lines of work pursued in connection with soil-fertility investigations. 

 The new point of view which has been brought to bear on the prob- 

 lems connected with the fertility of soils has opened up avenues of 

 profitable investigation and alread}' forecast results of great eco- 

 nomic importance. 



The biological relationships existing in soils have received special 

 attention, as the importance of such relationships can hardly be over- 

 estimated. It has been found that the soil can not be considered as 

 the dead, inert remains of rocks and previous vegetation, but must 

 be considered as the accumulation of such material in which the 

 processes of formation, alteration, and transposition are still at work. 

 The soil in its entirety is not dead or inert, but endowed with func- 

 tions analogous to life itself. In the soil there take place the same 

 processes of solution and deposition that have taken place in past 

 ages and are taking place to-day in the geologic processes connected 

 with the action of water on the rocks and minerals of the earth's crust. 

 Tliere take place in the soil the same ph^^sical and chemical inter- 

 action as take place in .the movement of surface waters generally, 

 resulting in ore formations or depositions. These researches have 

 shown that in the soil there take place likewise the same })rocesses of 

 fermentation, digestion, or decay of organic materials as take place 

 in animals and plants or in the j)roduction of industrial products, 

 such as cheeses, wines, beers, etc., brought about in the soil as in 

 these other processes by means of ferments, enzymes, bacteria, fungi, 

 or molds. These biochemical studies have likewise shown that in 

 the soil there take place the same processes of oxidation and reduc- 

 tion whicli play so vital a part in all life processes and that tiie nature 

 of compounds in the soil organic matter are the same as those derived 

 from such life j^rocesses or h'om similar laboratory processes of diges- 

 tion, oxidation, or reduction. 



