1914] Loughridge: Humus and Nitrogen in California Soil Columns 271 



foot of the 109 soil columns including the marsh lands the 

 average is 1.35 per cent. 



But the depth of soil in which most of the plant roots are 

 held in the arid region, and in which the humus color is most 

 pronounced is three feet, and taking this as the true soil of 

 California we find that there is a sum of 3.17 per cent, or an 

 average of 1.06 for each foot ; this is equivalent to about 127,000 

 pounds per acre. To this should be added the percentages of 

 humus found at lower levels of the soil, as shown in the averages 

 of the 109 columns gi/en in the accompanying table, which would 

 bring the total humus to 233,000 pounds in twelve feet. 



The amount of humus then in the average of California soils 

 (three feet deep) is greater than in those of the humid region; 

 and for the depth of twelve feet it is more than twice as great. 



The determinations of humus-nitrogen in the soils of the 

 humid region have been so few and miscellaneous that it is not 

 advisable to deduce from them an average to represent the whole 

 region. 



