22 MISC. PUBLICATION 3 6 9, U. S. DEPT. OF AGRICULTUKE 



The presence of undesirable or toxic elements in the soils and their 

 relation to disease has nowhere been studied in the systematic and 

 comprehensive manner in which the selenium survey was conducted 

 by the United States Department of Agriculture and some of the 

 State experiment stations. That selenium poisoning is related to soils 

 and their characteristics through the vegetation growing on them 

 seems to have been demonstrated beyond doubt, while a nutritional 

 disturbance in a certain area of England has been ascribed to the pres- 

 ence of excessive quantities of molybdenum in the herbage. 



There are probably more contradictory data relating to the effect 

 of soils on the occurrence of goiter troubles than to the occurrence of 

 any other nutritional disturbance. A careful survey of the facts indi- 

 cates, however, that the iodine in soils, either because of deficiencies 

 or because of its low availability when present, must play some part 

 in animal and human nutritional disorders. 



Actually contradictory data are found in studies of all of these 

 diseases considered in this review. The solutions of problems of this 

 nature are difficult because of the large number of variables, and it 

 may be necessary in the future to undertake studies statistical in 

 nature, because the minute quantities and the catalytic character of 

 the mineral elements involved often make it difficult to determine by 

 chemical or physical means the role these elements play. Furthermore, 

 modern techniques for soil examination and classification must be 

 employed if the part played by soils is to be properly evaluated. 



FACTORS AFFECTING THE MINERAL COMPOSITION OF 

 I PLANTS 



Effect of Soil Composition on Mineral Composition of Plants 



The complex relationships between the composition of the plant and 

 that of the soil have never been fully understood by man, although 

 investigations of those relationships have been conducted for more 

 than 300 years. Many problems confronting the agriculturist of the 

 seventeenth century were not unlike those of today; and for this 

 reason, and because of the remarkable ingenuity of the early workers, 

 a few references to these investigations will be quoted from the 

 unpublished portion of a manuscript prepared by C. A. Browne 4 for 

 the Yearbook of Agriculture, 1938, Soils and Men. 



Nehemiah Grew was the first who attempted to make quantitative determina- 

 tions and analyses of plant ashes. In his "Anatomy of Plants," 1682 [(228)], he 

 recognized three classes of salts in vegetable materials: (1) The mineral or marine 

 salts, such as common salt, (2) the essential salts, which occur in plants, such as 

 tartar, and (3) the lixivial salts or water-soluble ash of plants and plant products. 

 The influence of soil upon the yield of lixivial salts is shown in the experiments 

 with scurvy grass, which in a garden soil yielded 1.69 percent of lixivial salt and in 

 a soil near the seashore 7.29 percent. In his studies of plant composition and 

 growth Grew recognized the important relationships of soils, which he classified 

 into mellow, sandy, clayey, chalky, etc., and mixtures of the same. He recom- 

 mended that experiments upon the growth of plants be conducted on single soils 

 of types, "that it may appear how far any of these may contribute to the growth 

 of a plant, or to one above another." 



John Clayton's remarks [(114)], in 1688, upon the relationship of the quality 

 of tobacco to the soils upon which it is grown is the earliest correlation of this 

 character in the history of American agriculture. "The same sort of seed in differ- 

 ent earth," writes Clayton, "will produce tobacco much different as to goodness." 



4 Supervisor of chemical research, Bureau of Chemistry and Soils, U. S. Department of Agriculture. 



