MINERAL COM POSITION 0(P CROPS 41 



Conclusive evidence is to be found in the literature to prove that 

 significant differences occur in the minor or trace element content of 

 the plant or its part, that these differences may be directly attributed 

 to differences in soils, and that they are responsible for nutritional 

 disorders. Thus, the selenium content of a plant may be related to 

 the amount of selenium occurring in a soil; but enormous differences 

 are also observed that are the result of (1) differences of distribution 

 of the selenium in the profile, (2) differences of availability of the 

 selenium compounds that occur in the soil, (3) the presence of inhibi- 

 tory agents such as certain compounds of sulfur, or (4) the water rela- 

 tionships in the soil. Information of such complete nature is available 

 for no other element except selenium, but the sporadic deficiencies or 

 occurrence of other trace elements such as boron, iodine, chromium, 

 and even gold, may be taken as an indication that similar relationships 

 would be found for all elements. This and other investigations em- 

 phasize moreover that there is probably no direct relationship between 

 any single characteristic of the soil and any characteristic of the plant 

 or of plant production. 



The influence of soils on the botanical composition of flora of pas- 

 tures has long been known. This is also an important factor in soil 

 genesis, for the character of a soil will vary tremendously, depending 

 upon whether it is developed under a high-calcium grass, a high-sodium 

 grass, or under forests, for example, of beech-maple or of conifers. 



Difference of species of pasture herbage should also affect the health 

 of the animal, for, as will be shown in the appendix, these different 

 species vary markedly in their chemical composition. 



That a relationship should obtain between the soil taken as a whole 

 and the composition of the plant grown therein is a reasonable assump- 

 tion, for soils, being the products of their environments, show marked 

 variations because of differences in climate, vegetation, parent mate- 

 rial, and relief. Thus, the Podzolic and Lateritic soils are well-leached 

 acid soils generally quite low in bases and phosphorus, while the 

 Chernozem and Chestnut soils are not leached, are high in base con- 

 stituents, and are nearly neutral in reaction. 



Within any soil group, however, there will be variations in fertility 

 and reaction because of differences in parent material or relief. Thus, 

 in the Chernozem soils we may find deficiencies in potash and phos- 

 phorus where the parent materials were very low in these elements, 

 and in Kentucky and Tennessee bluegrass regions we find variations 

 from the well-leached acid soils common to the gray-brown Podzolic 

 group. In the rolling or hilly sections of these States, erosion removes 

 the acid and leached materials as rapidly as they are formed. The 

 soil that remains is young and relatively immature, and calcareous 

 soil lies within the reach of the plant roots. These soils often have the 

 additional advantage of being formed from parent materials relatively 

 high in phosphorus, and a very evident result of an abundance of 

 these bone-forming materials is the excellent type of horse developed 

 in those localities. 



Effect of Fertilizers on Plant Composition 



Fertilizer experiments have, for the most part, been concerned with 

 the study of yields, and, in comparison with the number of investiga- 

 tions of this nature, very few have included the probelem of modifying 

 the composition of the plant. That the composition of the plant is 



