1914] Loughridge: Humus and Nitrogen in Calif ornia Soil Columns 183 



There is but little doubt that the humus in both the Cotton- 

 wood and Chico soils reaches much deeper than the twelve feet 

 in which the percentage is quite large, for the soil texture is 

 especially favorable for deep development of tree and plant roots, 

 from the decay of which the humus was doubtless derived. In 

 the Chico column there is a sudden increase of humus in the 

 twelfth foot (0.52 per cent), which would indicate former strong 

 development of roots at that point, probably just above a water 

 stratum. 



The humus of the Cottonwood column is richest in nitrogen 

 in the upper three feet and shows remarkable and a sudden 

 increased percentage in the tenth foot. 



The Chico humus is interesting because of its richness in 

 nitrogen in the lower half of the column. 



The Cottonwood and Chico columns alone of the four have 

 humus in sufficient amount and richness to give general averages 

 of more than 0.05 per cent of nitrogen in the entire soil column, 

 and are the only ones having as much as 0.10 per cent of nitrogen 

 in the upper three feet of soil. 



Clay Loams of the Valley. — These reach south from near Red 

 Bluff and occupy the central part of the Sacramento Valley. As 

 typical of this class of soils, seven columns were obtained from 

 the following localities: three miles west of Tehama, Tehama 

 County; Willows, Glenn County; J. W. Walton's place a few 

 miles south of Yuba City, Sutter County ; Woodland, Yolo 

 County ; the University Farm, Davis, Yolo County ; Live Oak, 

 Sutter County, and from near Elmira, Solano County. In each 

 case a depth of twelve feet was reached, except at Live Oak, 

 where at nine feet the presence of water prevented a deeper 

 sampling. 



The clay loams of the Sacramento Valley are generally 

 deficient in humus, as shown by the first foot in each of these 

 seven typical columns and by the results of previous examination 

 of soils from many localities, the average being below 1 per cent. 

 The cause is chiefly continuous grain-growing with shallow 

 cultivation on these lands for thirty or forty years, which has 

 depleted them. This is prominently shown in the soil from the 

 University Farm at Davis which, before purchase by the Univer- 



