472 University of California Publications in Agricultural Sciences [Vol.3 



Altamont samples show much variation. Therefore with reference to 

 the amount of phosphorus, and the types studied, the separation into 

 types may or may not be of significance. 



If the results of the potassium (K 2 0) determinations are com- 

 pared, it is very evident that but one conclusion can be drawn, and 

 that is that the variations in the amount of potassium within each 

 type are great enough so that any differences between the averages 

 of the several types have no significance whatsoever. Therefore, with 

 regard to total potassium the field separation of soils as represented 

 by these twenty-four samples of four types means nothing. 



Comparison of Bacteriological Data 



The wealth of the data obtained from over nine hundred bacteri- 

 ological tumbler cultures is hardly of sufficient significance to com- 

 pensate for the effort involved. There is one outstanding conclusion 

 from all this work, namely, the lack of any very definite, distinct, and 

 constant bacteriological activity of the samples of one type that is not 

 to a considerable extent shared by the samples of the other types. 

 There are tendencies in certain types with regard to bacteriological 

 activity which show that some of the types as a whole are more or less 

 distinct from one or more of the others. 



Ammonification. — The amount of ammonia produced from dried 

 blood varies to a great extent. The Altamont samples gave between 

 10 and 33 mg. nitrogen as ammonia; the Diablo samples gave between 

 7 and 26 mg., and the Hanford samples gave between 35 and 72 mg. 

 The Altamont and Diablo types are thus seen to be about alike in their 

 low ammonifying power, as compared with the higher ability of the 

 San Joaquin types and still greater ability of the Hanford types. 

 And since there are somewhat greater variations between the types 

 than between the samples of a given type, the ammonifying power 

 may be significant. 



Nitrogen fixation.— -The two heavy types, Diablo clay adobe and 

 Altamont clay loam, show no characteristic differences, while the two 

 lighter types show considerable differences. As a whole the types are 

 different one from another, yet the variations within the type are 

 sufficient to prevent any statement that the rate of nitrogen fixation 

 is a function of the type as determined in the field, or vice versa. 



Nitrification. — The nitrification data are the most puzzling. The 

 figures are extremely variable within a given type ; the erratic way 



