1919] 



Pendleton: A Study of Soil Types 



417 



San Joaquin sandy loam-. — The amount of ammonia produced in 

 the A horizon varied between 30.4 rag. of nitrogen and 57.1 mg., the 

 average was 40.2 mg. (table 31 and fig. 21a). The production of 

 ammonia, in milligrams of nitrogen, by the B samples varied between 

 4.5 mg. and 38.1 mg.. with 20 mg. as the average. In the C samples 

 the variation was nearly as great, between ">.7 mg. and 32 mg., with 

 the average of 20.9 mg. Thus there are notable variations among the 



Ml 



50 



40 



30 



20 



10 



O 



A 



10 



11 



21 



C 



26 Soils 



12 13 17 18 



Mg N. as NHj produced 



Fig. 21a. Graph showing ammonification in the three horizons of the eight 

 samples of San Joaquin sandy loam. 



samples of this type, the proportional variation being very great, con- 

 sidering the three horizons. Possibly the reason that the B and C 

 horizons are so divergent from the surface is that there is a very 

 marked variation in the texture between the surface horizon and 

 those below the surface. 



Han ford fine sandy loam. — The variation is large here also (table 

 32, fig. 22a), the largest quantity of ammonia produced in the surface 

 soil is twice that of the smallest production, 72 mg. and 35 mg. The 

 subsoil variations, in a general way, parallel those of the surface. 

 The average production of ammonia in the three horizons is as fol- 



