74 Journal of Agricultural Research voi. xvni. No. 2 



supplementary studies later, have shown very clearly that the soil 

 solution is never in a state of final equilibrium but on the contrary 

 fluctuates daily and seasonally and is profoundly modified as a result 

 of absorption by the plant in such manner that during certain periods 

 the concentration of the soil solution may be reduced to a very low level. 

 Further work by Bouyoucos and McCool (4) recently has confirmed these 

 absolutely essential principles. 



Along with the concentration and composition of the soil solution, 

 the reaction, or hydrogen-ion concentration, is a definite chemical 

 factor, which under certain circumstances may become of importance 

 through its modifying influence on the soil solution and on absorption 

 by the plant. Previous work by Gillespie (zj) and by Sharp and the 

 author {38) has demonstrated the common existence of soils of distinctly 

 acid reaction as shown by hydrogen electrode measurements. More 

 recent studies by Gillespie and Hurst (14), Plummer (jj), and Gainey (11) 

 indicate that various important deductions relative to the soil solution 

 may be drawn from the data obtained by these methods of investigations. 



It has been deemed essential to present the foregoing introduction, 

 since the experiments to be described in this paper have their basis in 

 the theoretical considerations, experimental data, and methods resulting 

 from the researches mentioned above, or others concerned with similar 

 underlying principles. However small the beginning, it is hoped that 

 the present studies in plant nutrition may have a special interest due to 

 the use of the more recent methods of investigation and to the attempt 

 made to correlate the results with such knowledge as we now have regard- 

 ing the soil solution. 



GENERAL METHODS OF EXPERIMENTATION 



Since it is impossible to govern the exact concentration, reaction, and 

 composition of the soil solution, any rigid control of nutrient solutions 

 requires the use of water and sand cultures. These methods have been 

 employed since the beginnings of the scientific study of agriculture, yet 

 it is only recently that any systematic attempt has been made to elucidate 

 by their use the fundamental problems of plant nutrition aside from the 

 determination of the elements essential for growth long since established 

 in the literature of plant physiology. Even at the present time the con- 

 trol of conditions is very incomplete. Somewhat surprising is the general 

 absence of chemical control as exercised in the analyses of nutrient solu- 

 tions or of the plants produced. The actual absorption under varying 

 conditions has seldom been studied on any sufficient scale with plants 

 grown for an extended period, although there may be a few exceptions 

 to this statement, as in the recent work by Waynick (52) on antagonism 

 and of Schreiner and Skinner {37), who have made a large number of 

 analyses of solutions in which wheat seedlings had grown. The question 



