1914] Loughridge: Humus and Nitrogen in California Soil Colu^nns 225 



The humus of the upper three feet of the Fort Romie soil 

 is richest in nitrogen, 7.50 per cent, while that of the Santa Clara 

 adobe has only an average of 1.74 per cent. The general average 

 of all of this portion of the columns is 5.00 per cent, although 

 fourteen of the twenty-four have a higher percentage. 



The humus-nitrogen in this portion of the column varies from 

 0.13 per cent in the Berkeley adobe, 0.11 per cent in the soils 

 from Gilroy and Arroyo Grande, to more than 0.05 per cent in 

 all others except four. 



Humus in the Entire Column. — Nine of the twenty-four 

 columns have greater amounts of humus in their depths of ten 

 or twelve feet than has been found in any of the columns 

 representing other parts of the state. The two columns from the 

 Arroyo Grande, with sums of 16.74 per cent and 15.56 per cent, 

 have the highest amounts and are followed in the order of highest 

 by Gilroy, Santa Clara, and Lompoc, each with more than 13.00 

 per cent, and Berkeley, Russian River Valley, Yountville, Santa 

 Rosa, and El Verano, each with more than 11.00 per cent. 



The humus of the entire soil columns of the Coast Range 

 valleys is about as rich in organic nitrogen as that of other soils 

 of the state, the highest average percentage being in the Santa 

 Maria soil and the Berkeley adobe, 10.40 and 10.21 per cent 

 respectively; the Kenwood and Lompos soils are the next in 

 amount, with 7.79 and 6.50 per cent respectively. The Walnut 

 Creek column has an average of 6.04 per cent, but all other 

 averages are below 6 per cent for the entire column. The 

 organic nitrogen of the soil itself varies from 0.08 per cent in 

 the Arroyo Grande, Berkeley, and Kenwood columns, 0.07 per 

 cent in the Arroyo Grande seed-farm to 0.05 per cent in Santa 

 Rosa, Walnut Creek, San Ramon, and Lompoc; but all others 

 have less. 



SOIL COLUMNS OF SOUTHERN CALIFORNIA 



The region known as Southern California embraces that part 

 of the state lying south of the Sierra Madre and Santa Ynez 

 mountains and includes a number of large and fertile valleys 

 and jslains. 



