RELATION OF THE CONCENTRATION AND REACTION 

 OF THE NUTRIENT MEDIUM TO THE GROWTH AND 

 ABSORPTION OF THE PLANT 



By D. R. HOAGLAND 1 

 Division of Agricultural Chemistry, California Agricultural Experiment Station 



INTRODUCTION 



The investigation of the growth of plants from the standpoint of the 

 agricultural chemist involves the study of both the soil and the plant. 

 Until recently far greater attention has been given to the chemistry of 

 the soil than to the nutrition of the plant, yet it is obvious that any 

 satisfactory understanding of crop production is concerned as indis- 

 pensably with the metabolism of the plant as with the chemical reactions 

 of the soil. It is essential to learn what the plant absorbs and metabo- 

 lizes as well as what the soil solution contains. Of fundamental impor- 

 tance to either phase of the problem is the recognition of the dynamic 

 nature of both the plant and soil systems. Nearly all the studies of 

 the past in soil chemistry have been concerned with the soil as a static 

 system, and thus we have recorded countless experiments dealing with 

 the total composition, hydrochloric acid extracts, lime requirements, 

 and other gross characteristics of the soil. C. B. Lipman {zsY has pointed 

 out the great servdce performed by Cameron in introducing certain 

 physico-chemical considerations into soil studies, even though the 

 neglect of some of the modifying factors led to conclusions at variance 

 with the true state of affairs. 



Recent researches recognize the paramount importance of the soil 

 solution as the medium from which plants derive their inorganic nutri- 

 ment. As a result various attempts have been made to obtain some 

 definite conception of the concentration and composition of the actual 

 soil solution by such methods as those proposed by Morgan (jj) and C. B. 

 Lipman {22). A very great advance in this direction has been made by 

 Bouyoucos and McCool (j) in their application of the freezing-point 

 method to the study of soil phenomena. 



About four years ago this laboratory became engaged in an extensive 

 research on the water extracts of soils held under conditions of excep- 

 tional control {42). The freezing-point method just mentioned was 

 used also in determining actual osmotic pressures in the soil solution (77). 

 The results from both methods of investigation, reinforced by many 



' With the cooperation of F. W. Weitz. Acknowledgment is jnadc also of the careful analytical work 

 performed by J. C. Martin and A. W. Christie of this laboratory. 



2 Reference is made by number (italic) to literature cited, p. 114-117. 



Journal of Agricultural Research, Vol. XVIII, No. 2 



Washington, D. C. Oct. 15, 1919 



sn Key No. Calif .-022 



(73) 



