396 



University of California Publications in Agricultural Sciences [Vol.3 



B and C horizons of the Diablo. The average amount of nitrogen is 

 higher in the A horizon of the Altamont than in the Diablo, contrary 

 to what one would expect from the color of the soils, since the Alta- 

 mont is typically a brown soil and the Diablo a dark gray to black soil. 

 San Joaquin sandy loam. — The nitrogen content of these soils is 

 uniformly low (table 14 and fig. 13) , from 0.03% to 0.05%, and is but a 

 third to a half of what Hilgard believed adequate for crop production. 



N 



P2O5 



7 Soils 



Fig. 12. Graph showing the percentages of nitrogen and of phosphorus in 

 the three samples of Altamont clay loam. 



P205 



10 



11 



12 



13 



17 



18 



21 



20 Soils 



Fig. 13. Graph showing the percentages of nitrogen and of phosphorus in 

 the eight samples of San Joaquin sandy loam. 



The nitrogen content is seen to vary more or less directly with the 

 amount of the finer sediments present in the soil — nos. 11 and 12 

 being heavy members of the type, with 0.05% and 0.047% respec- 

 tively, and nos. 17 and 18 light members of the type with 0.029% and 

 0.027% respectively. It may be noted that the nitrogen content of 

 tbe various horizons are not as far apart as in the other tj^pes. The 

 averages for the three horizons are: A — 0.037%, B — 0.027%, and 

 C — 0.026%. It must be borne in mind that the San Joaquin sandy 

 loam horizons are not full 12-inch samples, and that the total depth 

 of the sampling is less. 



