64 



SOIL CONDITIONS AND PLANT GROWTH 



Instead of using this method the United States Bureau of Soils 

 investigates the solution obtained by stirring up soil with water, and 

 filtering under pressure through a Chamberland filter. The results 

 (304) are taken to indicate the following as the average composition of 

 the soil water : — 



PO, NO3 Ca K 



7-64 5-47 11-67 2274 per million of dry soil. ^ 



The numerous analyses of land drainage water that have been 

 made in this country and on the Continent throw some light on 

 the composition of the soil solution. As might be expected from 

 the known absorptive properties of clay and of humus, drainage water 

 contains mere traces of NH^ and PO^, and only little K ; it contains 

 chiefly carbonic acid, SiO^, CI, SO4, NO3, Ca with some Fe, Mg and 

 Na. Typical analyses are given in Table XXIX. : — 



Table XXIX. — Analyses of Drainage Waters from Cultivated Fields ; 

 Per Million of Solution. 



Parts 



It will be observed that the total concentration of the Rothamsted 

 drainage water varies from -02 to -05 per cent. 



'The Bureau of Soils prefer to express the composition in terms of dry soil, rather than 

 in terms of the solution. 



2 A. Voelcker's analyses of five samples collected between 1866 and 1869 (289). 



^Von Seelhorst's analyses of samples collected weekly, or fortnightly, from a field 

 between August, 1899, and August, 1900 (261). 



