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University of California Publications in Agricultural Sciences [Vol. 3 



stant throughout all the samples (except no. 14) and cannot well 

 be supposed to affect the results greatly. No. 14 has a low nitrifying 

 power throughout, but it is not representative of the type, for it is 

 heavier in texture than the rest. Moreover, it had been submerged 

 by river overflows shortly before the collection of the sample. One 

 would expect these factors to influence the numbers and the activity 

 of the bacterial flora. There is but little similarity in the way the 

 different samples of the A or B horizons behave toward any given 



10 



A Soil Nitrogen 



11 



11 



A S. N.+ (NHO2SO4 



S. N. +Cottonseed Meal 

 26 Soils 



13 17 18 



Percentages of N. Nitrified 



Fig. 25. Graph showing the percentages of nitrogen in various nitrogen 

 containing materials nitrified in the eight samples of the San Joaquin sandy 

 loam. 



nitrogen containing material. Variations from 1% to 50%, from 

 0% to 14%, from 4.5% to 8%, or from 15% to 15.5% from soil to 

 soil, without regularity, give slight basis for generalizations. The 

 average effect of the A horizon samples of the Hanford fine sandy 

 loam as regards the several nitrogenous materials is as follows : dried 

 blood, 5.62%; cottonseed meal, 13.72%; ammonium sulfate, 3.29%; 

 incubated control, 1.55%. In a general way there is a similarity 

 between the effects of a given nitrogen containing material on the 

 surface sample, and on the B horizon. This should be so, since these 

 soils are very deep and uniform in texture. However, in the C 

 horizon there were still greater decreases in the bacterial activity. 



