622 POPULAR SCIENCE MONTHLY. 



SOIL FERTILITY. 



BY J. B. DANDENO, 



MICHIGAN AGRICULTURAL COLLEGE. 



~T)ROBABLY the most important single problem which confronts 

 -■- the farmer to-day is that of the conservation of the fertility of 

 the soil. Fertility may be defined as that condition of the soil which 

 yields the maximum of that material which the plant is capable of 

 using for the best development of those qualities which the farmer 

 desires. Strange as it may seem, just wherein this fertility consists 

 is not yet fully known. Some years ago it was well known, that is to 

 say, it was thought, that all that could be said had been said about it. 

 At the present time, the more thoughtful and cautious among those 

 studying the question of plant growth from a scientific standpoint are 

 by no means settled upon the point. They recognize that there is 

 yet much to be cleared up in regard to it, especially from the physical 

 and the bacteriological sides. The question may be examined from 

 the chemical, physical, bacteriological and ecological standpoints. 



Much has been done in the chemical laboratory — too much, in fact, 

 judging by the results obtained. It was thought that a knowledge 

 of the chemical composition of the soil was the key to the solution 

 of the problem. But it has never been decided just what the chemical 

 composition should be to produce the best results, for the simple reason 

 that it is not known exactly what the requirements of the plants are. 

 Nor does a chemical analysis of the plant itself answer the question. 

 There are certain elements which are no doubt necessary for proper 

 growth, but the analysis of the content of the plant and of the soil does 

 not give a very complete notion of the proper conditions under which 

 certain substances should exist when in the soil. The chemical analysis 

 of soils and fertilizers, though not without considerable importance, 

 is now being relegated to the background in comparison with the phys- 

 ical and the bacteriological conditions. The so-called perfect fertil- 

 izers, as sold on the market to the farmer, have been looked upon with 

 some distrust, mainly because they have not produced the results in 

 the production of crops which might be expected from the chemical 

 standpoint. The farmer becomes skeptical and again and again sends 

 samples to the chemist to see if the materials have the proper chemical 

 constituents. The chemist finds it all right, and it is all right from 

 his point of view, but to the farmer the results are still unsatisfactory. 

 It is as much to the futile results of the chemical analyses of soils and 



