194 



University of California Publications in Agricultural Sciences [Vol. 1 



Table 10. — Humus in Columns of Gray Clay Loams, 



San Joaquin Valley 



FRESNO COUNTY 



Near Mendota 



Humus- 

 Soil Nitrogen in 



Clay 24.91 ,. -^ p, 



Humus Humus Soil 



Clay loam 55 7.10 .04 



Clay loam 42 6.19 .03 



Clay loam 38 7.10 .03 



Clay loam 22 7.27 .02 



Clay loam 17 7.65 .01 



Clay loam 12 6.66 .01 



Clay loam 22 4.09 .02 



Clay loam 25 2.40 .01 



Clay loam 40 2.00 .01 



Clay loam 30 10.33 .03 



Clay loam 23 2.60 .01 



Clay loam 19 3.15 .01 



3.45 



.29 5.55 .02 



1.35 

 .45 6.79 .03 



* Range of most annual plant roots. 



The Tracy soil is tlie only one of the above group which eon- 

 tains a fair amount of humus in the first foot and in the three 

 upper feet. But in its lower depths it is much poorer than 

 either that from Los Baiios or Mendota. It is interesting to note 

 the distribution downward in the two latter columns, which in 

 the twelfth foot contain one-third of what is in the first foot. 

 The lower six feet of the Los Baiios column contains about one- 

 half as much as the upper six feet, while in the Mendota column 

 the upper and lower half are nearly equal in their percentages. 

 The upper half of each column is much richer in nitrogen than 

 the lower, as is the case with all California soils; but there are 

 only traces in the lower six feet of the Tracy column. Deep 

 rooting of plants is thus more favored in the Los Baiios and 

 ]\Iendota soils and, with an increased supply of humus in the 

 surface and abundant water, these soils should prove to be fully 

 as productive as that from Tracy. 



