FERTILIZERS 63 



99. The mechanical analysis of soils is always 

 important. Most California soils are sedimentary 

 and composed of irregular strata varying in thick- 

 ness from a few inches to many feet. They may be 

 impenetratable and poorly drained, or too open and 

 coarse to hold the requisite moisture. The subsoil 

 conditions should be known. (20-21-22). 



100. The following table is compiled mainly from 

 the records of the California State Experiment Sta- 

 tion and from Dr. Hilgard's book, "Soil," which 

 state quite positively that when the chemical deter- 

 mination of certain elements in soils run below a 

 certain amount that soil is quite sure to be unpro- 

 ductive. These figures are the result of a large num- 

 ber of analyses representing years of work. 



ADEQUATE PLANT FOOD. 



RICH ADEQUATE INADEQUATE 

 PER CENT. PER CENT. PER CENT. 



Humus in soil 2.00 1.00 0.85 



Nitrogen in humus 9.00 4.00 2.00 



Lime 1.50 1.00 0.40 



Phosphoric acid 0.20 0.10 0.05 



Potash (K 2 O) 1.00 0.45 0.25 



These figures will vary for different crops. Ade- 

 quacy for one kind of crop might be inadequate for 

 another. But they are averages for a large number 

 of determinations and very suggestive. It has been 

 well established also that when the per cent, of lime 

 is high, much smaller amounts of the other plant 

 foods will suffice. 



