1914] Loughridge: Humus and Nitrogen in California Soil Columns 237 



isolated levels as often occurs in other soils, but throughout the 

 entire column, the general average being 0.15 per cent, or 

 approximately 6000 pounds of nitrogen per acre-foot through the 

 entire depth. No other column from the entire collection has 

 a similar record. Bacterial activity to render this humus-nitrogen 

 available to plants should make unnecessary the use of nitrogen 

 fertilizers. 



The Santa Ana Alluvial Plain is represented by two columns 

 taken by Mr. F. E. Johnson. One of these from two miles south 

 of Santa Ana, represents a considerable area of heavy black 

 adobe ; the other, from Irvine Station six miles southeast of 

 Santa Ana, represents a lighter clay loam soil. Both of these 

 columns are from the south side of Santa Ana River. 



Table 36. — Humus in Soil Columns 



Plain, Orange 



Santa Ana 



Humus- 

 Soil Nitrogen in 



Clay 25.01 , -^^- ^ 



Ft. Humus Humus Soil 



1 Black clay .... 2.42 3.71 .09 



2 Black clay .... 1.44 3.51 .05 



3 Black clay .... 1.02 4.80 .05 



4 Light clay 83 5.90 .05 



5 Light clay 76 2.22 .02 



6 Light clay 46 2.75 .01 



7 Light clay 31 2.72 .01 



8 Light clay 22 2.55 .01 



9 Sandy 12 2.34 tr. 



10 Sandy 14 3.01 .... 



11 Sandy 14 3.01 .... 



12 Sandy 20 4.18 .... 



Sum of per cents 8.06 



Average per foot .67 3.40 .03 



Upper 3 feet :* 



Sum of per cents 4.88 



Average per foot 1.63 4.00 .06 



* Range of most annual plant roots. 



OF Santa Ana Eiver Alluvial 

 County 



Ievine 



Humus- 

 Soil Nitrogen in 



Clay 18.31 , -^- ^ 



Humus Humus Soil 



Clay loam 70 5.86 .04 



Clay loam 50 8.40 .04 



Clay loam 44 4.09 .02 



Clay loam 38 3.42 .01 



Clay loam 34 1.76 .01 



Sand 22 1.82 .01 



Sand 19 .63 .01 



Sand 20 1.50 .01 



The adobe clay of Santa Ana contains a fair amount of 

 humus, but the humus is very poor in nitrogen throughout the 

 entire column. In spite of the latter fact, however, the per- 



