206 University of California Publications in Agricultural Sciences [Vol. 1 



highest being found in the brownish lands of Farmington, and the 

 lowest of 0.18 per cent in the soil of Tulare Lake bed. The 

 general average of all is 0.80 per cent, which is much below the 

 requirements for good texture and productiveness. 



The humus of the surface foot contains for the most part a 

 fair percentage of nitrogen, the general average being 5.98 per 

 cent, but there are several soils in which the humus is very poor, 

 and a high amount of such humus is necessary to give to the soil 

 an amount adequate for fertility. It is thought that a fertile 

 soil should not have less than 0.05 per cent of organic or humus 

 nitrogen in the surface foot, and from the tables it is seen that 

 because of the small amount of humus, many of the soils have 

 much less than 0.05 per cent. 



The soil richest in nitrogen in the above group is that from 

 Farmington which, because of the abundance and richness of its 

 humus, has 0.14 per cent of nitrogen, equivalent to more than 

 5000 pounds per acre-foot. The sandy soils of the sandy and 

 black loam plains west of Tulare and the black clay southeast 

 of Stockton each contains from 3000 to 3500 pounds of humus 

 nitrogen per acre-foot. 



The humus of the Stockton tule soil contains a fair amount 

 of nitrogen, and the very high percentage of the former gives 

 to the soil the enormous amount of 0.83 per cent of nitrogen, 

 or approximately 32,000 pounds of humus nitrogen per acre-foot. 

 The second foot is even richer. 



Humus in the Upper Three Feet. — The range of annual plant 

 roots in California soils is in the upper three feet, and this 

 may be considered as the true soil. This combination of three 

 feet more than doubles the amount of humus and its nitrogen 

 that is to be regarded as directly influencing fertility, though 

 the average per foot is lessened. The distribution through the 

 three feet is of greater advantage than if concentrated in the 

 upper foot, for the roots thus secure their nitrogen in a moister 

 soil and away from the heated surface. The general average 

 summation of humus in this depth of three feet for all of the 

 columns, omitting the Stockton tule, is 1.78, or 0.66 per cent per 

 foot, and this is about one-third less than for the state at large. 

 The humus is however fairly rich in nitrogen (6.22 per cent) 



