1912] Lipman: Bacteria in Soils of Arid Regions 9 



to the tenth foot and therefore an indication that in these soils 

 there is constantly being made available nitrogen, if organic 

 nitrogen be present from humus and other sources, for the needs 

 of plants with deep root systems. 



In soil No. 3, which is more sandy than the other alluvial 

 soil described and which rapidly becomes coarser in texture as 

 we descend into the lower layers, we find vigorous ammonifica- 

 tion to obtain down to the fourth foot, below which we find a 

 considerable decrease in ammonifying power, owing to the fact 

 that in that coarse soil neither water nor humus, nor soluble 

 minerals, are present in sufficient quantity to encourage bacterial 

 development. Here, however, we find the general tendency for 

 ammonifying organisms to penetrate to the greater depth quite 

 plainly visible. The remarks made for soils 2 and 3 are just 

 as truly applicable to the other alluvial soils from the same 

 district represented by Nos. 4, 5, and 7. The marked produc- 

 tion of ammonia, even in the twelfth foot of No. 7, is in accord 

 with the fine physical and chemical condition of that soil to 

 that depth and therefore deserves additional mention here. 



As to other types of soils, the data in the table show plainly 

 enough what a profound effect strong alkali salts (both black 

 and w^hite alkali salts among them) may exert on the ammoni- 

 fying flora and their vigor. Here ammonification is indeed very 

 feeble in the surface soil, becoming feebler as we go down until 

 the eighth foot is reached, at which depth, as w^ell as in the ninth 

 foot, we find quite a marked increase in ammonia production. 

 This is doubtless due to the fact that the total salt-content is 

 at that depth much lower and therefore not so seriously affecting 

 the activities of the organisms there contained. As for the 

 desert soils, which never have contained much humus and very 

 frequently contain too much alkali, it is natural to expect a 

 rather feeble ammonifying power on the part of the soils. Table 

 I shows that in this case the expected happens. In soil No. 9. 

 for example, not only the lack of humus and moisture, but the 

 very unfavorable physical condition, above referred to under 

 the description of that soil, along with its salt-content, have so 

 far affected the ammonifying power of that soil as to reduce it 

 to a little over one-third of what the normal vallev soils de- 



