PART III 



SOIL INVESTIGATION BY CULTURE 

 EXPERIMENTS 



IN the preceding pages we have considered the subject of soil 

 fertility in large part from the chemical and mathematical stand- 

 point (the last chapter being disregarded). Thus, we have dis- 

 cussed briefly the chemical composition of earth, air, water, plants, 

 and animals; the essential plant-food elements and their relative 

 abundance in plants and in plant and animal products and resi- 

 dues, also in normal and abnormal soils; and the sources and forms 

 of materials whose use is necessary for the adoption of systems of 

 permanent agriculture on ordinary lands under general farming. 



We have thus far referred to field or pot-culture experiments 

 mainly to cite the existing evidence concerning the possibility and 

 practicability of using methods or materials regarding which the 

 scientific, agricultural, and commercial interests are not agreed. 



Before taking up a study of various factors that influence crop 

 production, including the use of special fertilizers for special soils 

 and crops, it seems wise to consider in detail the results of some of 

 the long-continued field experiments with general farm crops on 

 ordinary normal soils; and, after wandering through the wilder- 

 ness of the last chapter, the seeker after truth will welcome the 

 positive data from thoroughly scientific cultural investigations, not 

 from 20-day cultures in pound pots or water extracts or even from 

 single-year tests, but the definite yields of mature crops year after 

 year for twenty, thirty, and even for sixty years. 



At the same time the author begs some consideration for the 

 question if we need prepare to avoid in America a repetition of 

 the Dark Ages that followed the high civilization of the Mediter- 

 ranean countries, until relieved by the discovery of the New World, 

 and that still exist for the masses in Russia, India, and China. 



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