12 University of California Publications in Agricultural Sciences [Vol. 1 



these soils, not only for those plants which are able to absorb 

 ammonia nitrogen, but also for that larger class of normal 

 plants which absorb their nitrogen in the nitrate form. It must 

 be said here, however, that nitrate formation proceeded always 

 more rapidly in soils from the first foot than in cultures pre- 

 pared from the other depths. This may indicate a smaller num- 

 ber of nitrifying organisms in the lower layers of the soil or 

 perhaps a less vigorous flora, but their activities are uniform 

 from the second foot down to the last depth in which they 

 show no activity as indicated in table II. In soil No. 6, which 

 we find on analysis contained merely a trace of humus, that cir- 

 cumstance seems to have made the soil unfit for the develop- 

 ment of the vigorous bacterial flora and is supported by the 

 data in tables II and III. As to the nitrate formation in 

 culture solutions by the inoculation with this Hanford soil, 

 nitrates were produced only after a month's incubation and only 

 in small quantities in the culture prepared from the upper foot 

 of soil, whereas all other surface soils, when inoculated into solu- 

 tions with the exception of those which show no nitrification at 

 all, showed nitrate formation before the end of two weeks. In 

 culture solutions from soil No. 6, kept about three months and 

 prepared from the lower layers of soil, no nitrates were ever to 

 be found. The depressing effect of alkali on the bacterial flora, 

 as well as the inhibiting effect of a lack of humus, moisture, 

 and the proper physical condition, are again exemplified in 

 tal)le II in soils 8, 9, and 10, as they were for the same soils in 

 table I referring to ammonifieation. Even after one month's 

 incubation, not one of these soil-samples showed any nitrate 

 formation, whether the culture was prepared with the soil from 

 the upper layers or from the lower. There seems to be a total 

 absence of nitrifying bacteria of one kind or another. 



The best example of the penetration of nitrifying bacteria 

 to great depths was obtained in soil No. 11, a fine alluvial loam 

 from Hayward, where nitrate formation was obtained down to 

 the ninth foot in the soil. In this case also there was, besides 

 a mere formation of nitrates, as shown by a qualitative test, an 

 actually vigorous nitrate formation in the lower layers as well 

 as in the upper layers of the soil. It would seem again here 



