1914:] Loughridge: Humus and Nitrogen in Calif ornia Soil Columns 191 



Table 8. — Averages op Humus ix Soil Types, Sacramento Valley 



Black adobe Stream alluvial Clay loam Red mesa and 



Composite columns clay loam of plains bedrock 



4 columns 4 columns 7 columns 3 columns 



Humus in first foot 1.16 1.47 .99 .47 



Sum of, in upper 3 feet 2.41 3.54 2.40 .90 



Sum of, in entire column 3.88 7.50 4.91 1.25 



Nitrogen in humus — 



In first foot 5.56 5.51 4.68 8.58 



Average in upper 3 feet.... 5.45 5.78 5.53 7.32 



Average in entire column 4.96 6.46 5.03 6.29 



Nitrogen in soil — 



In first foot 06 .06 .05 .04 



Average in upjier 3 feet.... .04 .07 .05 .02 



Average in entire column .02 .04 .02 .01 



The figures speak for themselves, and show that the alluvial lands 

 of the streams are richest in humus throughout and that the clay 

 loams of the plains are next, while the black clay, in spite of its 

 color, contains le.ss humus in the upper three feet and in the 

 entire column than the lighter colored plains soil. As a rule, the 

 alluvial lands do not need green-manuring crops, but the others, 

 and especially the red lands, would be greatly benefited thereby. 



Nitrogen in Humus and Soil. — There is but little difference 

 in the percentage of nitrogen in the humus of the upper three 

 feet of each group, except that in the red soils the figures are 

 highest ; but for the entire column the alluvial lands stand at 

 the head, with an average of 6.46 per cent. 



For the soil itself the nitrogen is greatest in the stream 

 alluvial, the average in the upper three feet being 0.07 per cent, 

 or approximately 2800 pounds per acre-foot : this is but little 

 more than the minimum amount (0.05 per cent) that is regarded 

 as essential to fertility. Other groups contain less than the 

 alluvial throughout. 



SOIL COLUMNS OF THE SAN JOAQUIN VALLEY 

 San Joaquin Valley, with an area of eleven thousand square 

 miles. po.ssesses seven or more large and distinct soil types or 

 regions, each of which is represented in our soil collection. 



Twenty- four localities in eight counties were selected from 

 which to secure columns of soil as nearly typical as possible of 

 each region, and fifteen of the columns were taken to depths of 



