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



of the northeastern part of the state have in the composite of 

 eight columns a high percentage of hnmns. not only in the first 

 foot but in the second. This is natural as the soils are moist 

 from underlying water and there is a strong vegetation whose 

 roots penetrate deeply. The total sum of humus percentages in 

 the twelve feet is 4.25 per cent, the upper three feet holding more 

 than one-half of it. The humus is poorer in nitrogen than in any 

 of the regions except the desert, the average in the upper three 

 feet being 3.79 per cent, or 0.05 per cent in the soil. 



Tule Marshes. — The tule marshes near Stockton and Klamath 

 and the Pomona cienega have extremely high humus percentages 

 in each of the four upper feet, and the humus is also quite high 

 through the column of seven feet, all derived from the large 

 amount of decaying tule roots. The humus-nitrogen of the 

 upper three feet is, however, only 5.75 per cent in the humus or 

 0.44 per cent in the soil; the latter is much higher than found 

 in any of the colunuis. 



Nitrogen in the Humus and in the Soil 



Nitrogen exists in the soil partly in the free .state in the air 

 that permeates the soil ; partly in the vegetable and animal 

 material that has not undergone humification ; partly in the 

 humified vegetable and animal matter ; and partly as nitrates 

 soluble in water, and hence very variable in amount from day 

 to day and liable to be lost by drainage. That the unlmmified 

 material in the soil does not yield its nitrogen to the plants until 

 after complete humification has been shown by the experiments 

 of Professor Hilgard, whose conclusions are as follows : 



"It thus appears that although the nitrogen of the un- 

 humified organic matter constituted about 40 per cent of the 

 total in the original soil, it would during the entire year have 

 contributed only to an insignificant extent to the available 

 nitrate supply ; while the fully humified ' matiere noire ' con- 

 tributed fourteen times as much. During the growing-season of 

 four or five months the unhumified organic matter would have 

 yielded practically nothing to the crop."® 



9 Soils (Macmillan & Co., 1906), p. 360. 



