THE FREEZING-POINT METHOD AS AN INDEX OF 



VARIATIONS IN THE SOIL SOLUTION DUE TO 



SEASON AND CROP GROWTH ^ 



By D. R. HOAGLAND, 



Assistant Professor of Agricultural Chemistry, College of Agriculture of the University 



of California 



INTRODUCTION 



In the preceding article by Stewart (8)^ it has been conclusively shown 

 that water extracts of different soils may have widely varying concen- 

 trations of important nutrient elements, and that the water-soluble 

 substances in the 13 cropped soils were strikingly diminished in quantity 

 when the barley crop had reached its maximum power of absorption. 

 In the uncropped soils significant seasonal variations were also noted. 

 These studies suggested the importance of correlating the water extracts 

 with the actual soil solution, the immediate source of nutrients for the 

 plant. 



Various attempts have been made to separate the soil solution, but in no 

 case has any appreciable quantity of solution been obtained when a soil 

 contained only the optimum percentage of moisture. Recently Bouyou- 

 cos and McCool (2) have proposed a method which seems capable of 

 giving direct experimental evidence concerning the concentration of the 

 soil solution. The procedure consists in determining the depression of 

 the freezing point in the soil itself under varying moisture conditions. 

 The soils used in the investigation described by Stewart seemed uniquely 

 adapted for further study by the freezing-point method. Accordingly 

 such determinations were made on the various soils under controlled 

 conditions, and the present paper deals with observations made on the 

 depressions of the freezing point in soils as affected by season, cropping, 

 moisture content, and other factors of significance in plant growth. 



GENERAL METHOD OF PROCEDURE 



The technic employed was essentially that described by Bouyoucos 

 and McCool (2) . The experience of the Agricultural Chemistry Laboratory 

 confirms their statements with regard to the possibility of obtaining 

 closely agreeing duplicates and general consistency of results. The 

 freezing-point blank with distilled water, however, was not found to 

 maintain a constant value from day to day, and to obviate any possible 



1 Approved for publication in the Journal of Agricultural Research by the Director of the Agricultural 

 Experiment Station of the University of California. 



2 Reference is made by number (italic) to " Literature dted," p. 394-395. 



Journal of Agricultural Research, Vol. XII, No. 6 



Washington, D. C Feb. 11, 1918 



ly Key No. Cal.— 17 



(369) 



