1914] Loughridge: Humus and Nitrogen in California Soil Columns 255 



humus, but in every foot of the entire column to a depth of 

 twelve feet. One half of the total amount is held in the upper 

 three feet. Its first foot contains a little less than that of the 

 Southern California column, but in the upper three feet and in 

 the entire column there is more. The percentage in the first foot 

 is too small and clearly shows the need of being increased by a 

 system of growing and turning under of green crops. With this 

 to encourage the growth of the young grain and trees, the 

 lower portion of the column will afford humus-nitrogen and other 

 plant food for the roots that find their way downward to twelve 

 or more feet as was the case with wheat and barley roots on the 

 University Farm at Davis. In the latter soil the humus of the 

 first foot was only 0.85 per cent and that of the second foot 

 1.49 per cent, and the ordinary yield had been but from twelve 

 to fourteen bushels of wheat per acre before the University 

 bought the property. By proper methods of treatment and 

 without irrigation or fertilization the agronomist in charge. 

 Professor G. W. Shaw, secured a yield of 40.4 bushels of wheat 

 per acre as an average of three years, during which time the 

 average for the state was but 14.5 bushels." 



The humus-nitrogen content of the upper three feet of the 

 Sacramento composite column is 5.79 per cent of the humus which 

 thus gives 0.04 per cent to the soil. This is approximately 1600 

 pounds of nitrogen per acre for each foot in depth. 



San Joaquin Valley. — The composite of twenty-three columns 

 from the San Joaquin Valley shows humus percentages much 

 below those of other regions, both in the surface foot (0.80 per 

 cent) and in each foot of the entire column. The sum of 3.11 

 per cent, if contained in the upper foot of the three feet, would 

 be a fair amount, though much below that of other regions. The 

 low percentages may be due in part to the presence of alkali 

 salts in some of the soils examined, also to a more arid climate 

 of far less rainfall than in other regions, and to a less luxuriant 

 vegetation upon the decay of whose roots the amount of humus 

 is dependent. 



Although this humus percentage is so low in the upper part 

 of the soil, yet a proper system of deep plowing to break up any 



7 Bull. no. 211, Cal. Agr. Expt. Sta. 



