MINERAL COMPOSITION OF CROPS 37 



the soil. Thus, the calcium content of this grass growing in red soil 

 averaged 0.38 percent as compared with an average of 0.67 percent 

 for that grown in calcareous soils and 0.54 percent for that grown in 

 the dark-brown soils. 



Depardon {152) in 1938 reported on the effect of soil, climate, and 

 geology of three regions in France on the composition and quality of 

 wheat, forage beets, and potatoes. He concluded that the pre- 

 dominant factor in the production of plants was distinctly the soil. 

 Thus in every case studied, the phosphorus content of plants grown in 

 Perche was lower than that in plants from either of two other localities. 



A few studies have been made that were concerned with the more 

 unusual minor elements in the soil. The most comprehensive study 

 of this nature is that conducted by the Department of Agriculture and 

 some of the State experiment stations on selenium. The importance 

 of selenium in relation to the health of the animal has already been 

 noted, and a brief discussion will be presented concerning the relation 

 between selenium in soils and its occurrence in plants growing in the 

 soils. 



Byers and Knight (108) reported in 1935 on the selenium content 

 of soils and two species of grass. All of the soils and grasses contained 

 selenium, and variations occurred in the amounts, but the greatest 

 variations by far were between the different species of grasses. 



Beath and coworkers (48) published the selenium contents of a 

 number of crops grown in certain shales in Montana. Their data 

 seem to indicate that certain species, such as alfalfa, do not absorb 

 selenium, and that crops grown in soils developed from the Niobrara 

 shales contain less selenium than do those grown in soils from Steele 

 shales. 



Byers, in a series of reports on the occurrence of selenium-bearing 

 soils in South Dakota, Colorado, Kansas, and Montana (100, 101, 

 104), states: 



The distribution of selenium in soils appears to be general. No true soils 

 containing colloids in any significant quantity have been found in which the 

 presence of selenium cannot be demonstrated. The source of the selenium is 

 believed to be the residual selenium derived from the soil parent material, sup- 

 plemented by that derived from direct absorption from the air by rain. It has 

 been demonstrated that selenium may exist in soils as the element; as a substit- 

 uent in sulfide minerals, particularly pyrites; as selenite, particularly basic ferric 

 selenite; as selenate, particularly as calcium selenate; and as organic selenium 

 compounds of undemonstrated composition. Of these forms apparently those 

 most available to the soil solution are the organic and selenate forms. 



The distribution of selenium within the soil profile is extremely variable, and 

 definite general statements are not possible concerning these variations. 



When plants grow in seleniferous soil they seemingly absorb selenium to some 

 degree in all cases, though under many circumstances the quantity so absorbed is 

 vanishingly small. For a given species [of plant] the quantity found by analysis 

 appears to depend upon a number of variables. These include at least the follow- 

 ing: The quantity and character of the selenium in the soil [{282)] and its distribu- 

 tion in the soil; the portion of the plant examined, whether seed, blossom, leaves, 

 stem or root; the stage of maturity of the plant; and seasonable variations which 

 might be attributed to rainfall. It is also certain that variations in selenium 

 absorption are brought about by variation of available sulfur [(285)]. 



In a later publication (331), Lakin, Williams, and Byers state: "A 

 lack of quantitative correlation between the selenium content of the 

 soil and the vegetation has been evident throughout the entire investi- 

 gation of seleniferous areas." They reported, for example, that the 

 Yunes silt loam of Hawaii contains from 2 to 10 p. p. m. of selenium 



