Oct. 9, 1916 
Nitrifying Powers of Humid and Arid Soils 
57 
in the Bay area containing less than 0.05 per cent of total nitrogen, the 
last-named group of soils is not unlike the foreign group. The soils of 
the latter contain 14 per cent of such soils as against 16 per cent for the 
Bay area. No soil in the Bay area contains less than 0.023 per cent of 
total nitrogen. 
After a study of one form of nitrogen at a time and in the same 
order as before, a striking difference is found between the absolute quanti¬ 
ties of nitrates produced by the soils of the Bay area out of their own 
nitrogen and those produced by the foreign soils under similar circum¬ 
stances. Thus, for example, only 1 soil out of 30 in the Bay area pro¬ 
duces a little more than 5 mgm. of nitrate nitrogen, and all other soils 
produce less. If this observation is compared with the corresponding one 
for the foreign soils of the humid region, the feeble nature of the nitri¬ 
fying power of the soils of the Bay area for their own nitrogen is very 
noticeable, as is the very vigorous power in that direction possessed by 
the foreign soils. In the latter only 2 soils out of a total of 47 produced 
less than 5 mgm. of nitrate nitrogen, while in the former only 1 soil pro¬ 
duced more than 5 mgm. of nitrate nitrogen. The absolute magnitude 
of nitrate production in soils of the Bay area varies from 0.1 mgm. to 
5.50 mgm., thus making a very small range. Again, there is evidence 
in Table III that the magnitude of nitrifying power for soil nitrogen is 
independent of the total amount of nitrogen present. Thus, for exam¬ 
ple, the largest production of nitrate occurs in the soil with the highest 
total nitrogen content in the whole series. On the other hand, the 
lowest nitrate production occurs in the soil with the third highest quan¬ 
tity of total nitrogen. 
It follows from what has been said in the preceding paragraph that 
only small percentages of the nitrogen present in the soils of the Bay 
area could have been transformed into nitrate. The best record made 
consists in a conversion by the Pleasanton soil of over 6 per cent of the 
total nitrogen present into nitrates. In three other soils 5 per cent of 
the nitrogen was thus converted, and in the other 26 soils the records are 
much poorer. Comparing the relative data of Table III with those set 
forth in Table I, section 1, one can not help being struck by the remarka¬ 
bly high nitrifying efficiency of the foreign soils as compared with that 
of the Bay area soils. 
The use of sulphate of ammonia as a nitrifiable material with the Bay 
area soils shows also the relatively low nitrifying power of the latter. 
Nevertheless Table III, Group II, brings out a very important fact— 
that is, that in the case of the absolute amounts of nitrate produced 
the Bay area soils gave increases over the amount of nitrate produced 
from the soil alone in all but 5 out of a total of 30 soils. This is a dia¬ 
metrically opposite effect to that induced by sulphate of ammonia in the 
foreign soils. On a relative basis the results in the sulphate-of-ammonia 
