1914] Loughridge: Humus and Nitrogen in Calif ornia Soil Columns 259 



The humus itself then is the most reliable source of nitrogen, 

 keeping it in reserve to be given to the roots of plants by degrees 

 by ammonifying and nitrifying bacteria and at the time when 

 most needed, namely, in the growing season. The fertilizing 

 value of humus depends, as has already been remarked, upon 

 the amount of nitrogen that it contains and which may be 

 changed to ammonia and nitrates through the agency of bacteria 

 and given to the soil and plant. The nitrogen content naturally 

 varies according to the nature of the materials from which the 

 humus was formed and to any diminution that may have occurred 

 from bacterial action or other causes, and we therefore find 

 great differences in one and the same column of soil. Sometimes 

 the difference is very great between one foot and the next, for 

 which it is difficult to account. 



Nitrogen in Humus. — ]\Iore than one thousand of these 

 nitrogen determinations in the humus of the soil columns have 

 been made and the results were found to vary from 1 per cent 

 to 24 per cent, but the greater number were from 4 per cent to 

 6 per cent. 



The highest percentage of nitrogen in humus was 24.10 per 

 cent, found in the eighth foot of the Berkeley adobe column, and 

 in this were three other levels with more than 10 per cent, all 

 of which were below the sixth foot. The column from Kenwood, 

 Sonoma County, had in its sixth foot 23.2 per cent, while two 

 others of its series had above 10 per cent. The sixth foot of 

 the Santa Paula soil had 20.5 per cent and in the fifth and 

 ninth foot there was more than 10 per cent. The humus of the 

 entire soil column from Fullerton, from the place of Dr. S. S. 

 Twombly, has the credit of being richer in nitrogen than any 

 soil thus far examined, the fifth foot having 20.5 per cent, the 

 eighth and tenth having more than 19 per cent each, the third 

 18.4, and the others above 10 per cent, excepting the second 

 foot which has 7.8 per cent ; the general average of the column 

 is 15 per cent. The amount of humus is, however, quite small 

 throughout the column, and hence the amount of humus-nitrogen 

 given to the soil is but 0.05 per cent. The humus of the 

 Kearney Park soil is another notable example of rather high 

 percentages of nitrogen, as in each of the seven feet below the 



