254 University of California Puhlications in Agricultural Sciences [Vol. 1 



the examination been made. In fact, the column of Fort Romie 

 was carried through fifteen feet, and 0.41 per cent of humus 

 with 6.83 per cent of nitrogen was found in the lowest foot. 



The next point of interest is the small amount of humus in 

 the first foot of each of the columns excepting those of the 

 meadowlands and the tule marshes. This is especially noticeable 

 in the composite of the San Joaquin Valley and in that of the 

 "desert" plains. The general average of the surface foot for all 

 of the columns, excluding the marshes, is 1.16 per cent. 



Another point of special interest is the gradual diminution 

 of humus percentage downward in each of the composite columns 

 with an occasional slight increase, as is seen in the eleventh foot 

 of the Sacramento Valley and in the twelfth foot of the Coast 

 Range valleys. This decrease indicates smaller amounts of 

 humus-forming vegetable material, presumably the roots of 

 plants, in each successive foot downwards, the main mass of the 

 root systems being in the upper three or four feet. 



Averages of Three Upper Feet. — A depth of one foot in Cali- 

 fornia does not in reality represent the soil which is at least three 

 feet deep, and it would not be correct or fair to the cultural 

 possibilities of the land to draw conclusions from the humus of 

 the first foot alone. It is very true that its presence to the 

 extent of several per cent near the surface is of special import- 

 ance in maintaining proper physical textural conditions for 

 aeration, avoidance of crusts and easy penetration of water, but 

 it is of as great importance that there should be several per cent 

 of humus in each of the upper several feet ; for in arid regions 

 it is below the first foot and away from hot and dry soil that 

 the feeding roots of plants prefer to carry on their activities, 

 and it is in the upper three feet that the main mass of fine 

 feeding roots are usually located, and where they must secure 

 the needed plant food supplied by the humus. This not only 

 protects the roots but gives to them a far greater feeding area 

 which is enlarged with the extension of the humus downward. 

 The summations for three feet are given at the foot of the table. 

 Sacramento Valley. — This valley, represented in the above 

 table by a composite column of eighteen individual columns, is 

 not only richer than the San Joaquin Valley in the first foot in 



