CHEMICAL ANALYSIS OF SOILS 



321 



The water extract method generally followed in this country 

 is that established by the Bureau of Soils. One hundred 

 grams of soil are mixed with 500 cubic centimeters of water 

 and stirred for three minutes. After standing twenty minutes 

 the supernatant liquid is filtered through a Pasteur-Chamber- 

 land filter under pressure. It is then ready for analysis. 

 Colometric and turbidity methods are usually employed in de- 

 termining the amounts of the constituents removed. 1 The 

 method is of greatest use in estimating the nitrate content of 

 soils. 



The quantity of extracted material depends on the absorp- 

 tive properties of the soil, on the amount of water used in the 

 extraction, and on the number of extractions. Analyses of 

 the aqueous extract of a clay and of a sandy soil from the 

 Cornell University farm serve to illustrate the greater reten- 

 tive power of the former for nitrates. Sodium nitrate was 

 applied to a clay soil and to a sandy loam soil at the rate of 

 640 pounds to the acre. Analyses of aqueous extracts some 

 ninety days later showed the following : 



Table LXXI 



There was apparently a much greater retention of nitrate 

 by the clay soil, as shown by a comparison of the fertilized 

 and unfertilized plats on both soils. 



1 Schreiner, O., and Failyer, G. H., Colorimetric, Turbidity and Titra- 

 tion Methods Used in Soil Investigations; U. S. Dept. Agr., Bur. Soils, 

 Bui. 31, 1906. 



