SOIL FORMATION 27 



Table 7. — Percentage Composition of Loess 



All of the important plant-food materials, particularly 

 lime, are abundant in these soils. They rarely need liming, 

 and up to the present time commercial fertilizers have been 

 used but little on them. 



Adobe is the name applied to another seolian soil similar 

 to loess in its physical qualities, but differing somewhat 

 in its mode of formation. It is supposed to be a mixture 

 of loess with debris from the mountain slopes and has been 

 formed under arid conditions. The soils thus formed are 

 extremely fertile when placed under irrigation, which is 

 usually necessary for their cultivation, because they are 

 found in Colorado, Utah, southern California, Arizona, New 

 Mexico and arid portions of Texas. The composition of two 

 typical soils is given below : 



Table 8. — Percentage Composition of Two Adobe Soils 



Constituents 



Phosphoric acid . . 



Potash 



Lime 



Magnesia .... 



Iron ...... 



Silica 



0.94 

 1.71 



13.91 

 2.96 

 5.12 



44.64 



