68 



DRY-FARMING 



two regions must differ greatly in their fertility or 

 power to produce and sustain plant life. It cannot 

 be believed that the water-washed soils of the East 

 retain as much fertility as the dry soils of the West. 

 Hilgard has made a long and elaborate stud}" of this 

 somewhat difficult question and has constructed a 

 table showing the composition of typical soils of 

 representative states in the arid and humid regions. 

 The following table shows a few of the average results 

 obtained bv him : — 



Source op 

 Soil 



Samples 

 Analyzed 



Humid region 696 



Arid region 573 



Partial Percentage Composition 



Insoluble Soluble 

 Residue ] Silica 



S4.17 4.04 

 69.16 6.71 



AluniinalLime 



3.66 

 7.61 



0.13 

 1.43 



Phos- 



Potuslilphoric Humus 



acid 



0.21 

 0.07 



0.12 

 0.16 



1.22 

 1.13 



Soil chemists have generall}' attemjjted to arrive 

 at a determinati(.)n of the fertilit}^ of soil by treating 

 a carefull}' selectetl and prej^ared sample with a 

 certain amount of acid of definite strength. The 

 portion which dissolves under the influence of acids 

 has been looked upon as a rough measure of the pos- 

 silile fertility of the soil. 



The column headed "Insoluble Residue" shows 

 the average proportions of arid and humid soils 

 which remain undissolved by acids. It is evident 

 at once that the humid soils are much less soluble 



