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University of California Publications in Agricultural Sciences [Vol. 3 



closely from sample to sample (table 28 and fig. 19a). This may be 

 due to the textures, which are quite similar throughout the soil column. 

 The averages for the three horizons were : A, 18.6 mg. ; B, 12.6 mg. ; 

 and C, 8.9 mg. 



A 



B 



3 4 7 Soils 



Mg N. as NH3 Produced 



Fig. 20a. Graph showing ammonification in the three horizons of the three 

 samples of Altamont clay loam. 



10. 



7.5 

 B 



2.5 



3 4 7 Soils 



Mg N. Fixed 



Fig. 20b. Graph showing nitrogen fixation in milligrams in the three horizons 

 of the three samples of Altamont clay loam. 



Altamont clay loam. — As regards horizon A the amount of am- 

 monia produced in one soil is three times that in the lowest, 10 mg. 

 nitrogen and 33 mg. nitrogen as ammonia, with 8.9 mg. as the average 

 (table 30 and fig. 20a). The amount of nitrogen as ammonia pro- 

 duced in the B horizon averaged 12.6 mg., in the C horizon 8.9 mg. 





