1914] Loitghridge: Humus and Nitrogen in Calif ornia Soil Columns 273 



3. The humus in California soils is usually distributed 

 through depths of twelve or more feet, the highest percentage 

 being in the upper three feet and diminishing downward as 

 shown in each of the 109 soil columns taken from the seven 

 agricultural regions; as much as 41 per cent was found in the 

 fifteenth foot of the Ft. Romie column, and 0.74 per cent in the 

 thirteenth foot of that of Davis and Hayward ; water was reached 

 in each case. 



4. The surface soils of California have an average of 1.28 per 

 cent of humus as shown in the analysis of several hundred 

 samples taken from the many agricultural regions of the state. 

 This is not sufficient to maintain good tilth in the soil ; but as 

 supplemented by that of many feet below often affords a fair 

 supply of nitrogen. The upper three feet of soil proper has an 

 average of 1.06 per cent per foot, or a sum of 3.17 per cent. 



5. The tule swamps have the highest percentage of humus 

 because of the mass of decaying roots and other vegetable matter, 

 while the desert plains have the least. 



6. Humification is retarded in close compact adobe clays and 

 the amount of humus is less than in lighter loam and sandy soils. 



7. The valleys of the Coast Range in the western part of the 

 state have higher percentages of humus in their soils than have 

 any of the other agricultural regions of California, probably 

 because of the greater humidity of the climate of that region 

 and a denser vegetation. 



8. The humus of the soils of this state is very generally 

 derived from plant roots instead of from accumulations of 

 vegetable material at various depths as the soil was being built 

 up, thus showing that the native vegetation has for ages been 

 deep-rooted. 



• 9. The black color of a soil is not always due to a high 

 humus content; many black soils have a smaller percentage of 

 humus than soils of a gray color. In one instance a very black 

 clay soil from the Santa Clara Valley contained no humus, its 

 color being due to the presence of a black rock powder. 



10. Humus contains nitrogen in combination, the amount 

 depending largely on the source of the humus. The average 

 percentage in the humus of the first foot of the soil columns is 



