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



The results of these soil examinations have brought out the 

 fact that, while the supply of potash is as a rule very large and 

 should not need replenishment by fertilizers for decades of years 

 and that phosphoric acid is generally fair in amount, except in 

 lands that have been in wheat culture for many years, the per- 

 centage of humus in all surface soils except tule swamps is quite 

 low and has required a system of green manuring to bring the 

 land back into the best condition. 



Regular Analyses. — Since the establishment of the station, 

 nearly six hundred complete analyses have been made of soils 

 chosen to represent the different agricultural regions and con- 

 ditions in the state, and among the determinations was that of 

 the exact amount of humus in 331 surface soils. The method of 

 analysis used was what is known as the Grandeau Method as 

 modified by Professor Hilgard. The results, therefore, more 

 nearly represent actual average conditions in the soils of the 

 state. The following table shows the average percentages of 

 humus in the soils of the several regions : 



Table 3. — Percentages of Humus in Surface Soils; Regular Method 



No. of soils 

 examined for 

 Regions humus 



Tules and meadows 14 



Coast Range valleys 91 



Sierra Foothills 46 



Sacramento A'alley 29 



Southern California 61 



San Joaquin Valley 67 



Desert plains and lava bed valleys 23 



General average for state 331 1.2.5 40 



The general average of humus in the 331 surface soils taken 

 from different parts of California and supposed to represent 

 fairly all of the agricultural regions is 1.25 per cent. If, how- 

 ever, the tule marshes and the meadow lands are omitted from 

 the calculation, then we find that the general humus percentage 

 is 1.15. 



