1914] Lougliridge: Rumus and Nitrogen in Calif ornia Soil Columns 221 



These soils are very different in texture, that of Fort Romie 

 being of a sandy nature throughout eighteen feet or more, while 

 that from King City is a stiff clay for a depth of three feet, 

 changing to sand and then a clay loam. The effect of the 

 presence of the sand is shown in the sudden diminution of 

 humus in the fourth foot, and the same change is noted in the 

 tenth foot. 



The deep rooting of plants is more marked in the Fort Romie 

 soil by the higher percentages of humus in the lower half of 

 the column. The humus and the soil are each also richer in 

 nitrogen than that of the King City clay, which clearly would 

 be greatly benefited in texture and richness by systematic green- 

 manuring with legumes. 



The column of soil from Fort Romie was continued to water 

 at fifteen feet and humus found in fair amount in the last foot. 



Arroyo Grande Valley. — The soil of this narrow but important 

 valley is of a dark and heavy clay loam nature to the depth of 



Table 25. — Humus in Soil Columns of Abroyo Grande Valley, 

 San Luis Obispo County 



Range of most annual plant roots. 



