6 ORGANIC CONSTITUENTS OF SOILS. 



the higher plants, such as oxidation, reduction, enzymotic and 

 catalytic, producing and destroying in the soil the organic constitu- 

 ents of which I shall speak presently. 



The soil is not simple, but complex. The soil properties and 

 functions are likewise complex, not simple. All of the investigators 

 preceding me in this symposium have emphasized to you by their 

 papers how complex the subject is and how much remains to be done 

 before a clear insight is obtained, buf they have also shown to you 

 clearly that a well-trained army of scientists is at work on the prob- 

 lems connected with soil fertility, applying thereto all the principles 

 of modern science. The old view was simplicity itself; the soil was 

 a mere trough in which the plant found its nourishment. But I can 

 do no better than to let Liebig speak for himself. I quote from 

 Letter XII of his "Familiar Letters on Chemistry": 



A field in which we cultivate the same plant for several successive years becomes 

 barren for that plant in a period varying with the nature of the soil; in one field it 

 will be three, in another seven, in a third twenty, in a fourth a hundred years. One 

 field bears wheat and no peas; another beans and turnips but no tobacco; a third 

 gives a plentiful crop of turnips but will not bear clover. What is the reason that a 

 field loses its fertility for one plant, the same which at first flourished there? What 

 is the reason one kind of plant succeeds in a field where another fails? 



Liebig answered these questions by saying: 



Wheat, clover, turnips, for example, each require certain elements from the soil; 

 they will not flourish where the appropriate elements are absent. Science teaches 

 us what elements are essential to every species of plant by an analysis of their ashes. 

 If, therefore, a soil is found wanting in any of these elements, we discover at once the 

 cause of its barrenness, and its removal may now be readily accomplished. 



But has science removed the causes of the barrenness of a soil 

 by the analysis of the soil or of the ashes of the plants ? In this 

 connection it might be well to quote a statement from an article by 

 Coleman, which was awarded the prize of the Royal Agricultural 

 Society of England in 1855. The author says: 



The causes which operate in producing the fertility or barrenness of soils have 

 hitherto to a great extent been shrouded in mystery, not from any want of study, but 

 owing to the difficulties which meet the inquirer at every step and the fact that most 

 important results frequently depend upon causes which have eluded the search of 

 the experimenter. The science of chemistry it was hoped would afford the key 

 wherewith to unlock the mysteries of nature, but though its discoveries have con- 

 ferred much practical benefit on the agriculturist, it has up to a very recent period 

 effected comparatively little toward settling the cause of fertility or sterility. The 

 theories of scientific men led us to expect that fertility depended upon the presence 

 of certain mineral substances which were found invariably present in the ashes of 

 plants, and the analysis of the soil it was believed would confirm the practical experi- 

 ence of the farmer; these hopes have been falsified except in the few cases of almost 

 simple soils, such as pure clays and sands. In all other cases the analysis presented 

 the existence in varying proportions of those substances supposed to induce fertility 

 in the barren as well as in the fertile soil. The proportion of the various ingredients 



