CHEMICAL COMPOSITION OF THE) SOIL 



Relation of Composition to Fertility. The relation of the com- 

 position to the fertility of the soil is studied by comparing the 

 chemical analysis with the productiveness of known soils. 



Soils containing comparatively high quantities of plant food 

 are generally very productive and durable, under favorable 

 physical conditions. The following table shows the composition 

 of some very productive soils. 1 These soils are all well known 

 for their fertility and wearing qualities. 



PERCENTAGE COMPOSITION OF FERTILE SOILS. 



The Arroyo Grande Valley soil is considered one of the richest 

 soils in the world. The other soils mentioned in the table are all 

 productive and durable. The analyses were made by Hilgard's 

 method. Soils containing about I per cent, lime, 0.15 per cent, 

 phosphoric acid, and I per cent, potash, by Hilgard's method, may 

 be regarded as highly fertile. The same standards apply to the 

 Association method, excepting it is possible that 0.50 per cent, 

 potash is sufficient for a fertile soil. This, however, remains to be 

 demonstrated. 



When soils contain only small quantities of plant food, they 

 will usually be found deficient in plant food for crops, or become 

 so in a comparatively short time after being placed in cultivation. 

 It appears probable that the plant food which can be taken up by 



1 Hilgard, The Soil, p. 343. 



