52 MISC. PUBLICATION 3 69, U. S. DEPT. OF AGRICULTURE 



variance in results by most investigators would tend to prove that 

 this is a problem that can be solved only by study of the characteristics 

 of each soil type. 



In general it can be stated that in many instances known deficiencies 

 of some particular element can be remedied by adding that element 

 to the soil. Deficiencies of phosphorus and iodine are good examples 

 of such a situation that seems to be easily remedied. 



The use of soil amendments to prevent injury to plants by certain 

 elements seems to be a promising field of investigation, although the 

 experience of Franke and Painter (196) with selenium emphasizes the 

 necessity for knowing in what form the toxic element may exist in the 

 soil, or, as in the case of the inhibition of aluminum injury by phos- 

 phorus, whether or not the phosphorus may become "fixed" by the 

 soil before it reacts with the aluminum. 



Liming of soils has varied effects on the composition of the plant, 

 but in most cases it exerts a depressing effect on iron and manganese. 

 Depending upon the soil, for example, the phosphorus in the plant 

 may be depressed, unchanged, or increased by liming. The same 

 observations apply to the effect of liming on magnesium and other 

 elements. The Virginia work (108) cited in this report shows clearly 

 how indirect effects of soil treatment may result in conclusions being 

 made in one place that are directly opposed to those in some other 

 locality. 



The effect of the applications of minor elements to the soil has been 

 studied mainly from the viewpoint of increasing that element in the 

 plant, and not from the viewpoint of modifying the general plant 

 composition. The latter type of investigations would seem to be of 

 paramount importance. 



The influence of the fluorine in phosphatic fertilizers on the fluorine 

 content of the plant has been determined in a very limited area. What 

 the effect is on plants grown in soils of different types than those 

 studied is entirely unknown. 



Some observations of the effect of fertilizers on the quality and the 

 technological uses of crops have been made. 



Miscellaneous Factors Influencing the Mineral Composition of 



Plants 



age of plant 



It has already been noted that changes in the mineral composition 

 of the plant as it matured were observed in the early part of the nine- 

 teenth century, and many investigations since that time have em- 

 phasized the importance of this factor in relation to animal nutrition 

 problems. A few of these investigations are cited here in order to 

 demonstrate the necessity of making observations on the age of the 

 plant in interpreting soil and fertilizer studies. 



Hills (270) in 1893 noted that both the phosphorus and potassium 

 contents in corn decreased rapidly with the age of the plant, until, in 

 some cases, less than half of the amounts present in the plant at tassel- 

 ing stage were found in the mature plant. 



Recent investigations include those of the sunflower by Neidig and 

 Snyder (431) in 1925 and of the alfalfa plant by Sotola (532) in 1927. 

 So tola determined the chemical composition, digestibility, and 

 protein utilization of the first, second, and third cuttings of alfalfa 



