124 



SOIL CONDITIONS AND PLANT GROWTH 



The clay also contained 32-6 parts of magnesium in the 

 dried soil and I32'3 in the solution. 



A more rapid, but less accurate method of obtaining a soil 

 solution has been adopted by the United States Bureau of 

 Soils, The soil is stirred up with water and filtered under 

 pressure through a Chamberland filter. The results are taken 

 to indicate the following average composition of the soil 

 water : — 



7-64 



NO3 



5-47 



Ca 



11-67 



K 



2274 per million of dry soil.^ 



A centrifugal method was used by Whitney and Cameron 

 (305^) with the results given in Table XXXV. : — 



Table XXXV.— Composition of Soil Solution (Centrifugal Method). 

 Whitney and Cameron (305a). 



The method, however, is difficult in application and has not 

 come into general use. 



Pressure methods have been adopted by several investi- 

 gators. In Ramann's {211c) laboratory 3 kilos of soil were 

 subjected to a pressure of 300 kilos per sq. cm. The amounts 

 of calcium and of potassium were found to vary considerably 

 in different extracts obtained from the surface soil, the pro- 

 portions relative to the other constituents increasing as the 

 solution became concentrated by dry weather and falling as 

 the solution became diluted by rain. In extracts prepared 



1 The Bureau of Soils prefers to express the compositions in terms of dry soil 

 rather than of solution. 



