326 NATURE AND PROPERTIES OP SOILS 



some good, some poor, by several different methods. Repre- 

 sentative figures are given below : 



Table LXXIV 

 chemical. composition of a good and a poor soil as 



INDICATED BY SEVERAL DIFFERENT METHODS 



rimer TiinnTmsT q 



Percentage of 





K^O 



CaO 



MgO 



P.O5 



Bulk analysis 



Productive silt loam 



1.98 

 1.85 



1.05 



,89 



.039 

 .039 



p.p.ni. 

 57 

 52 



1.48 

 1.50 



1.43 

 1.48 



.452 



.422 



pp.m. 



127 



45 



2.66 

 3.57 



2.46 

 3.32 



.220 



.144 



p.p.m. 



40 



23 



.23 



Unproductive silt loam 



Concentrated HCl digestion 



Productive silt loam 



Unproductive silt loam 



One per cent, citric acid 



Productive silt loam 



.21 



.22 

 .20 



.101 



Unproductive silt loam 



Water extract 



Productive silt loam 



Unproductive silt loam 



.072 



p.p.m. 



12 



5 



A comparison of the figures from the good and poor soil 

 seems to indicate no differences large enough to warrant opin- 

 ions regarding their relative fertility, except in the case of the 

 water extracts. These latter figures, however, are seasonal 

 averages and required as long a time to procure as was neces- 

 sary to grow a crop. Such fertility measurement is not as 

 practicable as actually using the crop as an indicator. 



172. Resume. — The conclusion that chemical analyses are 

 of but little direct practical value as a guide to soil prod- 

 uctivity is unavoidable. In spite of the great importance of 

 chemistry in research and teaching, it fails to indicate either 

 the permanent or the immediate fertility of the land. No 

 chemical method is capable of showing substantial and con- 

 stant differences between soils producing within 20 per cent. 



