1914] Loughridge : Humus and Nitrogen in California Soil Columns 211 



part is higher and comprises better lands. A black adobe clay 

 seems to be the prevailing soil and a column of this was taken 

 near the village of El Verano. 



Napa Valley. — The soil is chiefly loamy in nature, interspersed 

 with some adobe belts on either side. A column of the former 

 was obtained near Yountville, Napa County, to a depth of twelve 

 feet. 



Vaca Valley. — This valley is situated among the foothills on 

 the west side of the Sacramento Valley, into which it opens, and 

 is noted for its early fruits. The soil is chiefly a reddish loam, 

 as shown in the column obtained southeast of Vacaville. 



These valleys are characterized by having a high humus per- 

 centage in the upper foot and also in the four feet which is the 

 usual range of plant roots. The soil from Yountville, Napa 

 Valley, is the richest of the group, and contains nearly 6 per cent 

 of humus in the upper three feet. The Kenwood and El Verano 

 soils are the next in humus content, each containing more than 

 2 per cent in the first foot and more than 5 per cent in the upper 

 three feet, the range of most plant roots. A notable feature in 

 four of the columns — Russian River, Santa Rosa, El Verano, and 

 Yountville — is that there is more than 1 per cent in each of the 

 upper four feet ; in the Santa Rosa column that percentage is 

 found in six feet and almost in the seventh foot. The distribution 

 of humus downward through the entire column of twelve feet is 

 good, the average for the Russian River alluvial being more than 

 1 per cent for each foot, while the Santa Rosa and Yountville 

 averages very nearly equal it. This is a splendid record and 

 places these soils among the best in the state. 



The humus of the Kenwood soil is richer in nitrogen than 

 that of any other column, the average being 10.61 per cent for 

 the seven feet. That of the Santa Rosa has an average of 5.87 

 in its twelve feet. The richness of the Kenwood soil is chiefly 

 in its lower fourth, fifth, and sixth feet. The humus of the 

 El Verano adobe is for some reason or other weaker in nitrogen 

 than any other (except in its first foot), the general average 

 being but 2.67 per cent in each foot. 



The most important consideration, however, is the amount of 

 humus nitrogen occurring in the soil, and we find it to be highest 



