CHEMICAL ANALYSIS OF SOILS 323 



are a good comparative measure of the concentration and 

 composition of the soil solution (see par. 145). They also con- 

 sider water extractions as criteria of the crop-producing power 

 of a soil so studied. The practical value of such a method as 

 a means of estimating fertility is, however, somewhat ques- 

 tionable, since much time and labor are required to make the 

 necessary extractions and analyses before conclusions at all 

 reliable may be drawn. 



171. Fertility evaluation by means of chemical analyses. 

 — The important part that chemistry plays in soil investiga- 

 tion and research should not be overlooked. Nor can a satis- 

 factory presentation of soil phenomena, whether with a tech- 

 nical or an applied bearing, be made without the use of some 

 chemistry. Chemistry, in fact, is the fundamental science 

 that is most utilized in soil study. 



In spite of these relationships, the value of chemistry in the 

 direct solution of practical fertility problems is neither abso- 

 lute nor ja.nal. The objections already raised to the digestion 

 of the soil, either with concentrated or dilute acids, shows the 

 inadequacy of these methods so far as practical problems are 

 concerned. 



Of all the chemical analyses discussed those that have to do 

 with the determination of organic carbon, total nitrogen, total 

 calcium and phosphoric acid are of outstanding value. Or- 

 ganic matter is such an important soil constituent that a 

 knowledge of its amount cannot fail to throw much light on 

 the physical and chemical condition of the soil. Much of the 

 soil nitrogen is carried by the organic matter and becomes 

 available in much larger proportion than do the mineral 

 nutrients. An analysis for total nitrogen is, therefore, a 



Produdnff Power; Jour. Agr. Ees., Vol. XII, No. 6, pp. 297-309, 1918. 



Stewart, Gr. R., Effect of Season and Crop Growth m Modifying the 

 Soil Extract; Jour. Agr. Res., Vol. XII, No. 6, pp. 311-368, 1918. 



Hoagland, B. R., The Freezing Point Method as an Index of Varia- 

 tions in the Soil Solution Due to Season and Crop; Jour. Agr. Res., 

 Vol. XII, No. 6, pp. 369-395, 1918. 



