CEREAL CULTIVATION WESTERN AREA 379 



Humus is black or brown and gives the same color to 

 the soil, though occasionally a soil may be black from some 

 other cause, and not have a large percentage of humus. 

 When solutions of caustic alkali and sodium carbonate are 

 present they dissolve portions of the humus, giving rise 

 to the name " black alkali " (465). 



408. Deficiency of humus. The Western area is 

 partly distinguished from the Great Plains by a general 

 deficiency of humus. In the surface soil there is even less 

 humus in this region than in the Eastern or Humid area. 

 In soils of the latter area there is an average of 2.73 per 

 cent of humus or 109,200 pounds to the acre, in the first 

 foot ; while in the soils of California, for example, the aver- 

 age is 1.35 per cent. But the sharply defined change from 

 the black hurnus color to gray or yellow, in soils of the 

 Eastern area, occurs usually at a depth of 6 to 9 inches, 

 while in western soils, humus occurs to a depth of 12 feet 

 or more. 



In the upper 3 feet of California soils, which is the chief feed- 

 ing range for the roots of cereal plants, the total humus is 3. 17 per cent 

 or 126,800 pounds to the acre. Adding to this the humus occurring 

 still lower down within 12 feet, the total humus to the acre is found 

 to be 236,000 pounds. In the soils of the San Joaquin Valley, 

 the humus is 2.91 per cent of the soil in the upper 3 feet, but only 

 .8 per cent in the first foot. The nitrogen content of the humus is 

 6.27 per cent in the upper 3 feet, and .04 per cent of the soil. In 

 the Sacramento Valley, the soil is not only richer in humus in the 

 first foot than that of the San Joaquin Valley, but in every foot to 

 a depth of 12 feet. The nitrogen content of the humus in the upper 

 3 feet is 5.79 per cent and .04 per cent of the soil. 



While, therefore, humus is lacking in the surface soil 

 in this area, it is so well distributed downward that west- 

 ern soils are well adapted for deep-rooted plants such as 

 alfalfa and other perennials. Stewart (1910) also found 



