1914] Loughridge: Sumus and Nitrogen in California Soil Columns 205 



Table 17. — Percentages op Humus and Nitrogen According to Soil Types, 



San Joaquin Valley 



Tule stream Black Red Delta Valley Alkali Lake 



marsh alluvial clays lands lands loams lands bed 



1 col. 1 col. 4 col. 4 col. 3 col. 7 col. 3 col. 1 col. 

 Humus — 



Per cent in first foot 14.10 1.29 1.09 .95 .81 .75 .34 .18 



Sum of, in upper 3 feet 50.05 2.50 2.32 2.15 1.49 1.68 .91 .42 



Sum of, in entire column 81.75 3.67 2.93 3.51 2.63 3.13 1.58 1.20 



Average per foot in upper 



3 feet 16.68 .83 .82 .72 .49 .56 .30 .14 



Average per foot in entire 



column 6.81 .30 .25 .32 .22 .27 .12 .10 



Nitrogen in Humus — 



Average in first foot 5.85 4.25 5.46 5.52 6.38 6.56 7.09 3.33 



Average in upper 3 feet 5.30 4.40 6.09 6.72 6.93 6.09 5.30 1.68 



Average in entire column 5.10 4.16 7.10 7.06 6.85 6.10 5.33 1.46 



Nitrogen in Soil — 



Average in first foot 83 .06 .06 .06 .04 .05 .03 .01 



Average in upper 3 feet .88 .04 .04 .05 .03 .04 ,02 .01 



Average in entire column .35 .02 .03 .03 .02 .02 .01 .01 



There are large differences in the amount of humus in the 

 several groups, as is to be expected from soils of such extremely 

 different characters, the highest percentage being in the Stockton 

 tule marshes and the lowest in the strong alkali lands and in the 

 Tulare Lake bed. 



The surface soils of the valley are not rich in humus as a rule, 

 and this is well shown in these tables. Even the black clays and 

 loams, which because of their color would be supposed to contain 

 high percentages, were found to have but little more than 1 per 

 cent, and in some instances less than that. Similarly the alluvial 

 and delta soils of Kings and Kern counties are very low in 

 humus. The tule marshes in the region of Stockton are naturally 

 rich, because of the great amount of vegetable matter such as 

 roots and leaves that have accumulated in them, and we find as 

 much as 14 per cent of humus in the first foot and 19 per cent 

 in the second. 



Humus and Nitrogen in the First Foot. — The general average 

 of humus in the surface soils of the state is 1.25 per cent, and it 

 thus appears that the soils of the San Joaquin Valley fall much 

 below that. In but eight of the columns (omitting the Stockton 

 tule) is there as much as 1 per cent in the surface foot, the 



